s/AvLEN/AvMAX/ in perlguts

[perl5.git] / pod / perlguts.pod

diff --git a/pod/perlguts.pod b/pod/perlguts.pod
index 8ccdde8..124712c 100644 (file)
--- a/pod/perlguts.pod
+++ b/pod/perlguts.pod
@@ -5,7 +5,7 @@ perlguts - Introduction to the Perl API
 =head1 DESCRIPTION
 
 This document attempts to describe how to use the Perl API, as well as
 =head1 DESCRIPTION
 
 This document attempts to describe how to use the Perl API, as well as

-containing some info on the basic workings of the Perl core. It is far
+to provide some info on the basic workings of the Perl core. It is far

 from complete and probably contains many errors. Please refer any
 questions or comments to the author below.
 
 from complete and probably contains many errors. Please refer any
 questions or comments to the author below.
 


@@ -29,32 +29,47 @@ Additionally, there is the UV, which is simply an unsigned IV.
 
 Perl also uses two special typedefs, I32 and I16, which will always be at
 least 32-bits and 16-bits long, respectively. (Again, there are U32 and U16,
 
 Perl also uses two special typedefs, I32 and I16, which will always be at
 least 32-bits and 16-bits long, respectively. (Again, there are U32 and U16,

-as well.)
+as well.)  They will usually be exactly 32 and 16 bits long, but on Crays
+they will both be 64 bits.

 
 =head2 Working with SVs
 
 
 =head2 Working with SVs
 

-An SV can be created and loaded with one command.  There are four types of
-values that can be loaded: an integer value (IV), a double (NV),
-a string (PV), and another scalar (SV).
+An SV can be created and loaded with one command.  There are five types of
+values that can be loaded: an integer value (IV), an unsigned integer
+value (UV), a double (NV), a string (PV), and another scalar (SV).

 
 

-The six routines are:
+The seven routines are:

 
     SV*  newSViv(IV);
 
     SV*  newSViv(IV);

+    SV*  newSVuv(UV);

     SV*  newSVnv(double);
     SV*  newSVnv(double);

-    SV*  newSVpv(const char*, int);
-    SV*  newSVpvn(const char*, int);
+    SV*  newSVpv(const char*, STRLEN);
+    SV*  newSVpvn(const char*, STRLEN);

     SV*  newSVpvf(const char*, ...);
     SV*  newSVsv(SV*);
 
     SV*  newSVpvf(const char*, ...);
     SV*  newSVsv(SV*);
 

-To change the value of an *already-existing* SV, there are seven routines:
+C<STRLEN> is an integer type (Size_t, usually defined as size_t in
+F<config.h>) guaranteed to be large enough to represent the size of
+any string that perl can handle.
+
+In the unlikely case of a SV requiring more complex initialisation, you
+can create an empty SV with newSV(len).  If C<len> is 0 an empty SV of
+type NULL is returned, else an SV of type PV is returned with len + 1 (for
+the NUL) bytes of storage allocated, accessible via SvPVX.  In both cases
+the SV has value undef.
+
+    SV *sv = newSV(0);   /* no storage allocated  */
+    SV *sv = newSV(10);  /* 10 (+1) bytes of uninitialised storage allocated  */
+
+To change the value of an I<already-existing> SV, there are eight routines:

 
     void  sv_setiv(SV*, IV);
     void  sv_setuv(SV*, UV);
     void  sv_setnv(SV*, double);
     void  sv_setpv(SV*, const char*);
 
     void  sv_setiv(SV*, IV);
     void  sv_setuv(SV*, UV);
     void  sv_setnv(SV*, double);
     void  sv_setpv(SV*, const char*);

-    void  sv_setpvn(SV*, const char*, int)
+    void  sv_setpvn(SV*, const char*, STRLEN)

     void  sv_setpvf(SV*, const char*, ...);
     void  sv_setpvf(SV*, const char*, ...);

-    void  sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
+    void  sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool *);

     void  sv_setsv(SV*, SV*);
 
 Notice that you can choose to specify the length of the string to be
     void  sv_setsv(SV*, SV*);
 
 Notice that you can choose to specify the length of the string to be


@@ -76,10 +91,6 @@ L<perlsec>).  This pointer may be NULL if that information is not
 important.  Note that this function requires you to specify the length of
 the format.
 
 important.  Note that this function requires you to specify the length of
 the format.
 

-STRLEN is an integer type (Size_t, usually defined as size_t in
-config.h) guaranteed to be large enough to represent the size of
-any string that perl can handle.
-

 The C<sv_set*()> functions are not generic enough to operate on values
 that have "magic".  See L<Magic Virtual Tables> later in this document.
 
 The C<sv_set*()> functions are not generic enough to operate on values
 that have "magic".  See L<Magic Virtual Tables> later in this document.
 


@@ -115,11 +126,11 @@ Also remember that C doesn't allow you to safely say C<foo(SvPV(s, len),
 len);>. It might work with your compiler, but it won't work for everyone.
 Break this sort of statement up into separate assignments:
 
 len);>. It might work with your compiler, but it won't work for everyone.
 Break this sort of statement up into separate assignments:
 

-       SV *s;
-       STRLEN len;
-       char * ptr;
-       ptr = SvPV(s, len);
-       foo(ptr, len);
+    SV *s;
+    STRLEN len;
+    char * ptr;
+    ptr = SvPV(s, len);
+    foo(ptr, len);

 
 If you want to know if the scalar value is TRUE, you can use:
 
 
 If you want to know if the scalar value is TRUE, you can use:
 


@@ -180,7 +191,7 @@ have "magic".  See L<Magic Virtual Tables> later in this document.
 If you know the name of a scalar variable, you can get a pointer to its SV
 by using the following:
 
 If you know the name of a scalar variable, you can get a pointer to its SV
 by using the following:
 

-    SV*  get_sv("package::varname", FALSE);
+    SV*  get_sv("package::varname", 0);

 
 This returns NULL if the variable does not exist.
 
 
 This returns NULL if the variable does not exist.
 


@@ -189,12 +200,27 @@ you can call:
 
     SvOK(SV*)
 
 
     SvOK(SV*)
 

-The scalar C<undef> value is stored in an SV instance called C<PL_sv_undef>.  Its
-address can be used whenever an C<SV*> is needed.
+The scalar C<undef> value is stored in an SV instance called C<PL_sv_undef>.
+
+Its address can be used whenever an C<SV*> is needed. Make sure that
+you don't try to compare a random sv with C<&PL_sv_undef>. For example
+when interfacing Perl code, it'll work correctly for:
+
+  foo(undef);
+
+But won't work when called as:
+
+  $x = undef;
+  foo($x);
+
+So to repeat always use SvOK() to check whether an sv is defined.

 
 

-There are also the two values C<PL_sv_yes> and C<PL_sv_no>, which contain Boolean
-TRUE and FALSE values, respectively.  Like C<PL_sv_undef>, their addresses can
-be used whenever an C<SV*> is needed.
+Also you have to be careful when using C<&PL_sv_undef> as a value in
+AVs or HVs (see L<AVs, HVs and undefined values>).
+
+There are also the two values C<PL_sv_yes> and C<PL_sv_no>, which contain
+boolean TRUE and FALSE values, respectively.  Like C<PL_sv_undef>, their
+addresses can be used whenever an C<SV*> is needed.

 
 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>.
 Take this code:
 
 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>.
 Take this code:


@@ -208,8 +234,8 @@ Take this code:
 This code tries to return a new SV (which contains the value 42) if it should
 return a real value, or undef otherwise.  Instead it has returned a NULL
 pointer which, somewhere down the line, will cause a segmentation violation,
 This code tries to return a new SV (which contains the value 42) if it should
 return a real value, or undef otherwise.  Instead it has returned a NULL
 pointer which, somewhere down the line, will cause a segmentation violation,

-bus error, or just weird results.  Change the zero to C<&PL_sv_undef> in the first
-line and all will be well.
+bus error, or just weird results.  Change the zero to C<&PL_sv_undef> in the
+first line and all will be well.

 
 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>.  Normally this
 call is not necessary (see L<Reference Counts and Mortality>).
 
 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>.  Normally this
 call is not necessary (see L<Reference Counts and Mortality>).


@@ -247,12 +273,12 @@ portion of the string between the "real" and the "fake" beginnings is
 shown in parentheses, and the values of C<SvCUR> and C<SvLEN> reflect
 the fake beginning, not the real one.
 
 shown in parentheses, and the values of C<SvCUR> and C<SvLEN> reflect
 the fake beginning, not the real one.
 

-Something similar to the offset hack is perfomed on AVs to enable
+Something similar to the offset hack is performed on AVs to enable

 efficient shifting and splicing off the beginning of the array; while
 C<AvARRAY> points to the first element in the array that is visible from
 Perl, C<AvALLOC> points to the real start of the C array. These are
 usually the same, but a C<shift> operation can be carried out by
 efficient shifting and splicing off the beginning of the array; while
 C<AvARRAY> points to the first element in the array that is visible from
 Perl, C<AvALLOC> points to the real start of the C array. These are
 usually the same, but a C<shift> operation can be carried out by

-increasing C<AvARRAY> by one and decreasing C<AvFILL> and C<AvLEN>.
+increasing C<AvARRAY> by one and decreasing C<AvFILL> and C<AvMAX>.

 Again, the location of the real start of the C array only comes into
 play when freeing the array. See C<av_shift> in F<av.c>.
 
 Again, the location of the real start of the C array only comes into
 play when freeing the array. See C<av_shift> in F<av.c>.
 


@@ -278,7 +304,7 @@ The are various ways in which the private and public flags may differ.
 For example, a tied SV may have a valid underlying value in the IV slot
 (so SvIOKp is true), but the data should be accessed via the FETCH
 routine rather than directly, so SvIOK is false. Another is when
 For example, a tied SV may have a valid underlying value in the IV slot
 (so SvIOKp is true), but the data should be accessed via the FETCH
 routine rather than directly, so SvIOK is false. Another is when

-numeric conversion has occured and precision has been lost: only the
+numeric conversion has occurred and precision has been lost: only the

 private flag is set on 'lossy' values. So when an NV is converted to an
 IV with loss, SvIOKp, SvNOKp and SvNOK will be set, while SvIOK wont be.
 
 private flag is set on 'lossy' values. So when an NV is converted to an
 IV with loss, SvIOKp, SvNOKp and SvNOK will be set, while SvIOK wont be.
 


@@ -341,7 +367,7 @@ then nothing is done.
 If you know the name of an array variable, you can get a pointer to its AV
 by using the following:
 
 If you know the name of an array variable, you can get a pointer to its AV
 by using the following:
 

-    AV*  get_av("package::varname", FALSE);
+    AV*  get_av("package::varname", 0);

 
 This returns NULL if the variable does not exist.
 
 
 This returns NULL if the variable does not exist.
 


@@ -405,7 +431,7 @@ specified below.
             /* Get the key from an HE structure and also return
                the length of the key string */
     SV*    hv_iterval(HV*, HE* entry);
             /* Get the key from an HE structure and also return
                the length of the key string */
     SV*    hv_iterval(HV*, HE* entry);

-            /* Return a SV pointer to the value of the HE
+            /* Return an SV pointer to the value of the HE

                structure */
     SV*    hv_iternextsv(HV*, char** key, I32* retlen);
             /* This convenience routine combines hv_iternext,
                structure */
     SV*    hv_iternextsv(HV*, char** key, I32* retlen);
             /* This convenience routine combines hv_iternext,


@@ -416,7 +442,7 @@ specified below.
 If you know the name of a hash variable, you can get a pointer to its HV
 by using the following:
 
 If you know the name of a hash variable, you can get a pointer to its HV
 by using the following:
 

-    HV*  get_hv("package::varname", FALSE);
+    HV*  get_hv("package::varname", 0);

 
 This returns NULL if the variable does not exist.
 
 
 This returns NULL if the variable does not exist.
 


@@ -478,6 +504,58 @@ reference count of the stored C<val>, which is the caller's responsibility.
 If these functions return a NULL value, the caller will usually have to
 decrement the reference count of C<val> to avoid a memory leak.
 
 If these functions return a NULL value, the caller will usually have to
 decrement the reference count of C<val> to avoid a memory leak.
 

+=head2 AVs, HVs and undefined values
+
+Sometimes you have to store undefined values in AVs or HVs. Although
+this may be a rare case, it can be tricky. That's because you're
+used to using C<&PL_sv_undef> if you need an undefined SV.
+
+For example, intuition tells you that this XS code:
+
+    AV *av = newAV();
+    av_store( av, 0, &PL_sv_undef );
+
+is equivalent to this Perl code:
+
+    my @av;
+    $av[0] = undef;
+
+Unfortunately, this isn't true. AVs use C<&PL_sv_undef> as a marker
+for indicating that an array element has not yet been initialized.
+Thus, C<exists $av[0]> would be true for the above Perl code, but
+false for the array generated by the XS code.
+
+Other problems can occur when storing C<&PL_sv_undef> in HVs:
+
+    hv_store( hv, "key", 3, &PL_sv_undef, 0 );
+
+This will indeed make the value C<undef>, but if you try to modify
+the value of C<key>, you'll get the following error:
+
+    Modification of non-creatable hash value attempted
+
+In perl 5.8.0, C<&PL_sv_undef> was also used to mark placeholders
+in restricted hashes. This caused such hash entries not to appear
+when iterating over the hash or when checking for the keys
+with the C<hv_exists> function.
+
+You can run into similar problems when you store C<&PL_sv_true> or
+C<&PL_sv_false> into AVs or HVs. Trying to modify such elements
+will give you the following error:
+
+    Modification of a read-only value attempted
+
+To make a long story short, you can use the special variables
+C<&PL_sv_undef>, C<&PL_sv_true> and C<&PL_sv_false> with AVs and
+HVs, but you have to make sure you know what you're doing.
+
+Generally, if you want to store an undefined value in an AV
+or HV, you should not use C<&PL_sv_undef>, but rather create a
+new undefined value using the C<newSV> function, for example:
+
+    av_store( av, 42, newSV(0) );
+    hv_store( hv, "foo", 3, newSV(0), 0 );
+

 =head2 References
 
 References are a special type of scalar that point to other data types
 =head2 References
 
 References are a special type of scalar that point to other data types


@@ -522,11 +600,11 @@ The most useful types that will be returned are:
     SVt_PVGV  Glob (possible a file handle)
     SVt_PVMG  Blessed or Magical Scalar
 
     SVt_PVGV  Glob (possible a file handle)
     SVt_PVMG  Blessed or Magical Scalar
 

-    See the sv.h header file for more details.
+See the F<sv.h> header file for more details.

 
 =head2 Blessed References and Class Objects
 
 
 =head2 Blessed References and Class Objects
 

-References are also used to support object-oriented programming.  In the
+References are also used to support object-oriented programming.  In perl's

 OO lexicon, an object is simply a reference that has been blessed into a
 package (or class).  Once blessed, the programmer may now use the reference
 to access the various methods in the class.
 OO lexicon, an object is simply a reference that has been blessed into a
 package (or class).  Once blessed, the programmer may now use the reference
 to access the various methods in the class.


@@ -535,8 +613,8 @@ A reference can be blessed into a package with the following function:
 
     SV* sv_bless(SV* sv, HV* stash);
 
 
     SV* sv_bless(SV* sv, HV* stash);
 

-The C<sv> argument must be a reference.  The C<stash> argument specifies
-which class the reference will belong to.  See
+The C<sv> argument must be a reference value.  The C<stash> argument
+specifies which class the reference will belong to.  See

 L<Stashes and Globs> for information on converting class names into stashes.
 
 /* Still under construction */
 L<Stashes and Globs> for information on converting class names into stashes.
 
 /* Still under construction */


@@ -589,9 +667,9 @@ to write:
 To create a new Perl variable with an undef value which can be accessed from
 your Perl script, use the following routines, depending on the variable type.
 
 To create a new Perl variable with an undef value which can be accessed from
 your Perl script, use the following routines, depending on the variable type.
 

-    SV*  get_sv("package::varname", TRUE);
-    AV*  get_av("package::varname", TRUE);
-    HV*  get_hv("package::varname", TRUE);
+    SV*  get_sv("package::varname", GV_ADD);
+    AV*  get_av("package::varname", GV_ADD);
+    HV*  get_hv("package::varname", GV_ADD);

 
 Notice the use of TRUE as the second parameter.  The new variable can now
 be set, using the routines appropriate to the data type.
 
 Notice the use of TRUE as the second parameter.  The new variable can now
 be set, using the routines appropriate to the data type.


@@ -599,17 +677,32 @@ be set, using the routines appropriate to the data type.
 There are additional macros whose values may be bitwise OR'ed with the
 C<TRUE> argument to enable certain extra features.  Those bits are:
 
 There are additional macros whose values may be bitwise OR'ed with the
 C<TRUE> argument to enable certain extra features.  Those bits are:
 

-    GV_ADDMULTI        Marks the variable as multiply defined, thus preventing the
-               "Name <varname> used only once: possible typo" warning.
-    GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
-               the variable did not exist before the function was called.
+=over
+
+=item GV_ADDMULTI
+
+Marks the variable as multiply defined, thus preventing the:
+
+  Name <varname> used only once: possible typo
+
+warning.
+
+=item GV_ADDWARN
+
+Issues the warning:
+
+  Had to create <varname> unexpectedly
+
+if the variable did not exist before the function was called.
+
+=back

 
 If you do not specify a package name, the variable is created in the current
 package.
 
 =head2 Reference Counts and Mortality
 
 
 If you do not specify a package name, the variable is created in the current
 package.
 
 =head2 Reference Counts and Mortality
 

-Perl uses an reference count-driven garbage collection mechanism. SVs,
+Perl uses a reference count-driven garbage collection mechanism. SVs,

 AVs, or HVs (xV for short in the following) start their life with a
 reference count of 1.  If the reference count of an xV ever drops to 0,
 then it will be destroyed and its memory made available for reuse.
 AVs, or HVs (xV for short in the following) start their life with a
 reference count of 1.  If the reference count of an xV ever drops to 0,
 then it will be destroyed and its memory made available for reuse.


@@ -660,9 +753,9 @@ later be decremented twice.
 
 "Mortal" SVs are mainly used for SVs that are placed on perl's stack.
 For example an SV which is created just to pass a number to a called sub
 
 "Mortal" SVs are mainly used for SVs that are placed on perl's stack.
 For example an SV which is created just to pass a number to a called sub

-is made mortal to have it cleaned up automatically when stack is popped.
-Similarly results returned by XSUBs (which go in the stack) are often
-made mortal.
+is made mortal to have it cleaned up automatically when it's popped off
+the stack. Similarly, results returned by XSUBs (which are pushed on the
+stack) are often made mortal.

 
 To create a mortal variable, use the functions:
 
 
 To create a mortal variable, use the functions:
 


@@ -674,7 +767,7 @@ The first call creates a mortal SV (with no value), the second converts an exist
 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
 third creates a mortal copy of an existing SV.
 Because C<sv_newmortal> gives the new SV no value,it must normally be given one
 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
 third creates a mortal copy of an existing SV.
 Because C<sv_newmortal> gives the new SV no value,it must normally be given one

-via C<sv_setpv>, C<sv_setiv> etc. :
+via C<sv_setpv>, C<sv_setiv>, etc. :

 
     SV *tmp = sv_newmortal();
     sv_setiv(tmp, an_integer);
 
     SV *tmp = sv_newmortal();
     sv_setiv(tmp, an_integer);


@@ -699,8 +792,8 @@ C<sv_2mortal> or C<sv_mortalcopy> routines.
 
 =head2 Stashes and Globs
 
 
 =head2 Stashes and Globs
 

-A "stash" is a hash that contains all of the different objects that
-are contained within a package.  Each key of the stash is a symbol
+A B<stash> is a hash that contains all variables that are defined
+within a package.  Each key of the stash is a symbol

 name (shared by all the different types of objects that have the same
 name), and each value in the hash table is a GV (Glob Value).  This GV
 in turn contains references to the various objects of that name,
 name (shared by all the different types of objects that have the same
 name), and each value in the hash table is a GV (Glob Value).  This GV
 in turn contains references to the various objects of that name,


@@ -713,20 +806,20 @@ including (but not limited to) the following:
     Format
     Subroutine
 
     Format
     Subroutine
 

-There is a single stash called "PL_defstash" that holds the items that exist
-in the "main" package.  To get at the items in other packages, append the
-string "::" to the package name.  The items in the "Foo" package are in
-the stash "Foo::" in PL_defstash.  The items in the "Bar::Baz" package are
-in the stash "Baz::" in "Bar::"'s stash.
+There is a single stash called C<PL_defstash> that holds the items that exist
+in the C<main> package.  To get at the items in other packages, append the
+string "::" to the package name.  The items in the C<Foo> package are in
+the stash C<Foo::> in PL_defstash.  The items in the C<Bar::Baz> package are
+in the stash C<Baz::> in C<Bar::>'s stash.

 
 To get the stash pointer for a particular package, use the function:
 
 
 To get the stash pointer for a particular package, use the function:
 

-    HV*  gv_stashpv(const char* name, I32 create)
-    HV*  gv_stashsv(SV*, I32 create)
+    HV*  gv_stashpv(const char* name, I32 flags)
+    HV*  gv_stashsv(SV*, I32 flags)

 
 The first function takes a literal string, the second uses the string stored
 in the SV.  Remember that a stash is just a hash table, so you get back an
 
 The first function takes a literal string, the second uses the string stored
 in the SV.  Remember that a stash is just a hash table, so you get back an

-C<HV*>.  The C<create> flag will create a new package if it is set.
+C<HV*>.  The C<flags> flag will create a new package if it is set to GV_ADD.

 
 The name that C<gv_stash*v> wants is the name of the package whose symbol table
 you want.  The default package is called C<main>.  If you have multiply nested
 
 The name that C<gv_stash*v> wants is the name of the package whose symbol table
 you want.  The default package is called C<main>.  If you have multiply nested


@@ -785,7 +878,7 @@ following code:
     extern int  dberror;
     extern char *dberror_list;
 
     extern int  dberror;
     extern char *dberror_list;
 

-    SV* sv = get_sv("dberror", TRUE);
+    SV* sv = get_sv("dberror", GV_ADD);

     sv_setiv(sv, (IV) dberror);
     sv_setpv(sv, dberror_list[dberror]);
     SvIOK_on(sv);
     sv_setiv(sv, (IV) dberror);
     sv_setpv(sv, dberror_list[dberror]);
     SvIOK_on(sv);


@@ -808,9 +901,9 @@ linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
         U16         mg_private;
         char        mg_type;
         U8          mg_flags;
         U16         mg_private;
         char        mg_type;
         U8          mg_flags;

+        I32         mg_len;

         SV*         mg_obj;
         char*       mg_ptr;
         SV*         mg_obj;
         char*       mg_ptr;

-        I32         mg_len;

     };
 
 Note this is current as of patchlevel 0, and could change at any time.
     };
 
 Note this is current as of patchlevel 0, and could change at any time.


@@ -833,17 +926,20 @@ SV.
 
 The C<name> and C<namlen> arguments are used to associate a string with
 the magic, typically the name of a variable. C<namlen> is stored in the
 
 The C<name> and C<namlen> arguments are used to associate a string with
 the magic, typically the name of a variable. C<namlen> is stored in the

-C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
-copy of the name is stored in C<mg_ptr> field.
+C<mg_len> field and if C<name> is non-null then either a C<savepvn> copy of
+C<name> or C<name> itself is stored in the C<mg_ptr> field, depending on
+whether C<namlen> is greater than zero or equal to zero respectively.  As a
+special case, if C<(name && namlen == HEf_SVKEY)> then C<name> is assumed
+to contain an C<SV*> and is stored as-is with its REFCNT incremented.

 
 The sv_magic function uses C<how> to determine which, if any, predefined
 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
 
 The sv_magic function uses C<how> to determine which, if any, predefined
 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.

-See the "Magic Virtual Table" section below.  The C<how> argument is also
+See the L<Magic Virtual Tables> section below.  The C<how> argument is also

 stored in the C<mg_type> field. The value of C<how> should be chosen
 stored in the C<mg_type> field. The value of C<how> should be chosen

-from the set of macros C<PERL_MAGIC_foo> found perl.h. Note that before
+from the set of macros C<PERL_MAGIC_foo> found in F<perl.h>. Note that before

 these macros were added, Perl internals used to directly use character
 literals, so you may occasionally come across old code or documentation
 these macros were added, Perl internals used to directly use character
 literals, so you may occasionally come across old code or documentation

-referrring to 'U' magic rather than C<PERL_MAGIC_uvar> for example.
+referring to 'U' magic rather than C<PERL_MAGIC_uvar> for example.

 
 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
 structure.  If it is not the same as the C<sv> argument, the reference
 
 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
 structure.  If it is not the same as the C<sv> argument, the reference


@@ -851,6 +947,9 @@ count of the C<obj> object is incremented.  If it is the same, or if
 the C<how> argument is C<PERL_MAGIC_arylen>, or if it is a NULL pointer,
 then C<obj> is merely stored, without the reference count being incremented.
 
 the C<how> argument is C<PERL_MAGIC_arylen>, or if it is a NULL pointer,
 then C<obj> is merely stored, without the reference count being incremented.
 

+See also C<sv_magicext> in L<perlapi> for a more flexible way to add magic
+to an SV.
+

 There is also a function to add magic to an C<HV>:
 
     void hv_magic(HV *hv, GV *gv, int how);
 There is also a function to add magic to an C<HV>:
 
     void hv_magic(HV *hv, GV *gv, int how);


@@ -866,12 +965,13 @@ was initially made magical.
 
 =head2 Magic Virtual Tables
 
 
 =head2 Magic Virtual Tables
 

-The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
+The C<mg_virtual> field in the C<MAGIC> structure is a pointer to an

 C<MGVTBL>, which is a structure of function pointers and stands for
 "Magic Virtual Table" to handle the various operations that might be
 applied to that variable.
 
 C<MGVTBL>, which is a structure of function pointers and stands for
 "Magic Virtual Table" to handle the various operations that might be
 applied to that variable.
 

-The C<MGVTBL> has five pointers to the following routine types:
+The C<MGVTBL> has five (or sometimes eight) pointers to the following
+routine types:

 
     int  (*svt_get)(SV* sv, MAGIC* mg);
     int  (*svt_set)(SV* sv, MAGIC* mg);
 
     int  (*svt_get)(SV* sv, MAGIC* mg);
     int  (*svt_set)(SV* sv, MAGIC* mg);


@@ -879,19 +979,28 @@ The C<MGVTBL> has five pointers to the following routine types:
     int  (*svt_clear)(SV* sv, MAGIC* mg);
     int  (*svt_free)(SV* sv, MAGIC* mg);
 
     int  (*svt_clear)(SV* sv, MAGIC* mg);
     int  (*svt_free)(SV* sv, MAGIC* mg);
 

-This MGVTBL structure is set at compile-time in C<perl.h> and there are
-currently 19 types (or 21 with overloading turned on).  These different
-structures contain pointers to various routines that perform additional
-actions depending on which function is being called.
+    int  (*svt_copy)(SV *sv, MAGIC* mg, SV *nsv, const char *name, I32 namlen);
+    int  (*svt_dup)(MAGIC *mg, CLONE_PARAMS *param);
+    int  (*svt_local)(SV *nsv, MAGIC *mg);
+
+
+This MGVTBL structure is set at compile-time in F<perl.h> and there are
+currently 32 types.  These different structures contain pointers to various
+routines that perform additional actions depending on which function is
+being called.

 
     Function pointer    Action taken
     ----------------    ------------
 
     Function pointer    Action taken
     ----------------    ------------

-    svt_get             Do something after the value of the SV is retrieved.
+    svt_get             Do something before the value of the SV is retrieved.

     svt_set             Do something after the SV is assigned a value.
     svt_len             Report on the SV's length.
     svt_set             Do something after the SV is assigned a value.
     svt_len             Report on the SV's length.

-    svt_clear          Clear something the SV represents.
+    svt_clear           Clear something the SV represents.

     svt_free            Free any extra storage associated with the SV.
 
     svt_free            Free any extra storage associated with the SV.
 

+    svt_copy            copy tied variable magic to a tied element
+    svt_dup             duplicate a magic structure during thread cloning
+    svt_local           copy magic to local value during 'local'
+

 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
 to an C<mg_type> of C<PERL_MAGIC_sv>) contains:
 
 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
 to an C<mg_type> of C<PERL_MAGIC_sv>) contains:
 


@@ -903,56 +1012,69 @@ called.  All the various routines for the various magical types begin
 with C<magic_>.  NOTE: the magic routines are not considered part of
 the Perl API, and may not be exported by the Perl library.
 
 with C<magic_>.  NOTE: the magic routines are not considered part of
 the Perl API, and may not be exported by the Perl library.
 

+The last three slots are a recent addition, and for source code
+compatibility they are only checked for if one of the three flags
+MGf_COPY, MGf_DUP or MGf_LOCAL is set in mg_flags. This means that most
+code can continue declaring a vtable as a 5-element value. These three are
+currently used exclusively by the threading code, and are highly subject
+to change.
+

 The current kinds of Magic Virtual Tables are:
 
     mg_type
 The current kinds of Magic Virtual Tables are:
 
     mg_type

-    (old-style char and macro)   MGVTBL         Type of magic
-    --------------------------   ------         ----------------------------
-    \0 PERL_MAGIC_sv             vtbl_sv        Special scalar variable
-    A  PERL_MAGIC_overload       vtbl_amagic    %OVERLOAD hash
+    (old-style char and macro)   MGVTBL          Type of magic
+    --------------------------   ------          -------------
+    \0 PERL_MAGIC_sv             vtbl_sv         Special scalar variable
+    A  PERL_MAGIC_overload       vtbl_amagic     %OVERLOAD hash

     a  PERL_MAGIC_overload_elem  vtbl_amagicelem %OVERLOAD hash element
     a  PERL_MAGIC_overload_elem  vtbl_amagicelem %OVERLOAD hash element

-    c  PERL_MAGIC_overload_table (none)         Holds overload table (AMT)
-                                               on stash
-    B  PERL_MAGIC_bm             vtbl_bm        Boyer-Moore (fast string search)
-    D  PERL_MAGIC_regdata        vtbl_regdata   Regex match position data
-                                               (@+ and @- vars)
-    d  PERL_MAGIC_regdatum       vtbl_regdatum  Regex match position data
-                                               element
-    E  PERL_MAGIC_env            vtbl_env       %ENV hash
-    e  PERL_MAGIC_envelem        vtbl_envelem   %ENV hash element
-    f  PERL_MAGIC_fm             vtbl_fm        Formline ('compiled' format)
-    g  PERL_MAGIC_regex_global   vtbl_mglob     m//g target / study()ed string
-    I  PERL_MAGIC_isa            vtbl_isa       @ISA array
-    i  PERL_MAGIC_isaelem        vtbl_isaelem   @ISA array element
-    k  PERL_MAGIC_nkeys          vtbl_nkeys     scalar(keys()) lvalue
-    L  PERL_MAGIC_dbfile         (none)         Debugger %_<filename
-    l  PERL_MAGIC_dbline         vtbl_dbline    Debugger %_<filename element
-    m  PERL_MAGIC_mutex          vtbl_mutex     ???
-    o  PERL_MAGIC_collxfrm       vtbl_collxfrm  Locale collate transformation
-    P  PERL_MAGIC_tied           vtbl_pack      Tied array or hash
-    p  PERL_MAGIC_tiedelem       vtbl_packelem  Tied array or hash element
-    q  PERL_MAGIC_tiedscalar     vtbl_packelem  Tied scalar or handle
-    r  PERL_MAGIC_qr             vtbl_qr        precompiled qr// regex
-    S  PERL_MAGIC_sig            vtbl_sig       %SIG hash
-    s  PERL_MAGIC_sigelem        vtbl_sigelem   %SIG hash element
-    t  PERL_MAGIC_taint          vtbl_taint     Taintedness
-    U  PERL_MAGIC_uvar           vtbl_uvar      Available for use by extensions
-    v  PERL_MAGIC_vec            vtbl_vec       vec() lvalue
-    x  PERL_MAGIC_substr         vtbl_substr    substr() lvalue
-    y  PERL_MAGIC_defelem        vtbl_defelem   Shadow "foreach" iterator
-                                               variable / smart parameter
-                                               vivification
-    *  PERL_MAGIC_glob           vtbl_glob      GV (typeglob)
-    #  PERL_MAGIC_arylen         vtbl_arylen    Array length ($#ary)
-    .  PERL_MAGIC_pos            vtbl_pos       pos() lvalue
-    <  PERL_MAGIC_backref        vtbl_backref   ???
-    ~  PERL_MAGIC_ext            (none)         Available for use by extensions
+    c  PERL_MAGIC_overload_table (none)          Holds overload table (AMT)
+                                                 on stash
+    B  PERL_MAGIC_bm             vtbl_bm         Boyer-Moore (fast string search)
+    D  PERL_MAGIC_regdata        vtbl_regdata    Regex match position data
+                                                 (@+ and @- vars)
+    d  PERL_MAGIC_regdatum       vtbl_regdatum   Regex match position data
+                                                 element
+    E  PERL_MAGIC_env            vtbl_env        %ENV hash
+    e  PERL_MAGIC_envelem        vtbl_envelem    %ENV hash element
+    f  PERL_MAGIC_fm             vtbl_fm         Formline ('compiled' format)
+    g  PERL_MAGIC_regex_global   vtbl_mglob      m//g target / study()ed string
+    H  PERL_MAGIC_hints          vtbl_hints      %^H hash
+    h  PERL_MAGIC_hintselem      vtbl_hintselem  %^H hash element
+    I  PERL_MAGIC_isa            vtbl_isa        @ISA array
+    i  PERL_MAGIC_isaelem        vtbl_isaelem    @ISA array element
+    k  PERL_MAGIC_nkeys          vtbl_nkeys      scalar(keys()) lvalue
+    L  PERL_MAGIC_dbfile         (none)          Debugger %_<filename
+    l  PERL_MAGIC_dbline         vtbl_dbline     Debugger %_<filename element
+    o  PERL_MAGIC_collxfrm       vtbl_collxfrm   Locale collate transformation
+    P  PERL_MAGIC_tied           vtbl_pack       Tied array or hash
+    p  PERL_MAGIC_tiedelem       vtbl_packelem   Tied array or hash element
+    q  PERL_MAGIC_tiedscalar     vtbl_packelem   Tied scalar or handle
+    r  PERL_MAGIC_qr             vtbl_qr         precompiled qr// regex
+    S  PERL_MAGIC_sig            vtbl_sig        %SIG hash
+    s  PERL_MAGIC_sigelem        vtbl_sigelem    %SIG hash element
+    t  PERL_MAGIC_taint          vtbl_taint      Taintedness
+    U  PERL_MAGIC_uvar           vtbl_uvar       Available for use by extensions
+    v  PERL_MAGIC_vec            vtbl_vec        vec() lvalue
+    V  PERL_MAGIC_vstring        (none)          v-string scalars
+    w  PERL_MAGIC_utf8           vtbl_utf8       UTF-8 length+offset cache
+    x  PERL_MAGIC_substr         vtbl_substr     substr() lvalue
+    y  PERL_MAGIC_defelem        vtbl_defelem    Shadow "foreach" iterator
+                                                 variable / smart parameter
+                                                 vivification
+    #  PERL_MAGIC_arylen         vtbl_arylen     Array length ($#ary)
+    .  PERL_MAGIC_pos            vtbl_pos        pos() lvalue
+    <  PERL_MAGIC_backref        vtbl_backref    back pointer to a weak ref 
+    ~  PERL_MAGIC_ext            (none)          Available for use by extensions
+    :  PERL_MAGIC_symtab         (none)          hash used as symbol table
+    %  PERL_MAGIC_rhash          (none)          hash used as restricted hash
+    @  PERL_MAGIC_arylen_p       vtbl_arylen_p   pointer to $#a from @a
+

 
 When an uppercase and lowercase letter both exist in the table, then the
 
 When an uppercase and lowercase letter both exist in the table, then the

-uppercase letter is used to represent some kind of composite type (a list
-or a hash), and the lowercase letter is used to represent an element of
-that composite type. Some internals code makes use of this case
-relationship.
+uppercase letter is typically used to represent some kind of composite type
+(a list or a hash), and the lowercase letter is used to represent an element
+of that composite type. Some internals code makes use of this case
+relationship.  However, 'v' and 'V' (vec and v-string) are in no way related.

 
 The C<PERL_MAGIC_ext> and C<PERL_MAGIC_uvar> magic types are defined
 specifically for use by extensions and will not be used by perl itself.
 
 The C<PERL_MAGIC_ext> and C<PERL_MAGIC_uvar> magic types are defined
 specifically for use by extensions and will not be used by perl itself.


@@ -988,6 +1110,17 @@ sv_magic, so you can safely allocate it on the stack.
         uf.uf_index = 0;
         sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf));
 
         uf.uf_index = 0;
         sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf));
 

+Attaching C<PERL_MAGIC_uvar> to arrays is permissible but has no effect.
+
+For hashes there is a specialized hook that gives control over hash
+keys (but not values).  This hook calls C<PERL_MAGIC_uvar> 'get' magic
+if the "set" function in the C<ufuncs> structure is NULL.  The hook
+is activated whenever the hash is accessed with a key specified as
+an C<SV> through the functions C<hv_store_ent>, C<hv_fetch_ent>,
+C<hv_delete_ent>, and C<hv_exists_ent>.  Accessing the key as a string
+through the functions without the C<..._ent> suffix circumvents the
+hook.  See L<Hash::Util::Fieldhash/Guts> for a detailed description.
+

 Note that because multiple extensions may be using C<PERL_MAGIC_ext>
 or C<PERL_MAGIC_uvar> magic, it is important for extensions to take
 extra care to avoid conflict.  Typically only using the magic on
 Note that because multiple extensions may be using C<PERL_MAGIC_ext>
 or C<PERL_MAGIC_uvar> magic, it is important for extensions to take
 extra care to avoid conflict.  Typically only using the magic on


@@ -1034,7 +1167,7 @@ you find yourself actually applying such information in this section, be
 aware that the behavior may change in the future, umm, without warning.
 
 The perl tie function associates a variable with an object that implements
 aware that the behavior may change in the future, umm, without warning.
 
 The perl tie function associates a variable with an object that implements

-the various GET, SET etc methods.  To perform the equivalent of the perl
+the various GET, SET, etc methods.  To perform the equivalent of the perl

 tie function from an XSUB, you must mimic this behaviour.  The code below
 carries out the necessary steps - firstly it creates a new hash, and then
 creates a second hash which it blesses into the class which will implement
 tie function from an XSUB, you must mimic this behaviour.  The code below
 carries out the necessary steps - firstly it creates a new hash, and then
 creates a second hash which it blesses into the class which will implement


@@ -1053,7 +1186,7 @@ to do this.
     CODE:
         hash = newHV();
         tie = newRV_noinc((SV*)newHV());
     CODE:
         hash = newHV();
         tie = newRV_noinc((SV*)newHV());

-        stash = gv_stashpv("MyTie", TRUE);
+        stash = gv_stashpv("MyTie", GV_ADD);

         sv_bless(tie, stash);
         hv_magic(hash, (GV*)tie, PERL_MAGIC_tied);
         RETVAL = newRV_noinc(hash);
         sv_bless(tie, stash);
         hv_magic(hash, (GV*)tie, PERL_MAGIC_tied);
         RETVAL = newRV_noinc(hash);


@@ -1128,7 +1261,7 @@ This construction is I<approximately> equivalent to
 
 The biggest difference is that the first construction would
 reinstate the initial value of $var, irrespective of how control exits
 
 The biggest difference is that the first construction would
 reinstate the initial value of $var, irrespective of how control exits

-the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
+the block: C<goto>, C<return>, C<die>/C<eval>, etc. It is a little bit

 more efficient as well.
 
 There is a way to achieve a similar task from C via Perl API: create a
 more efficient as well.
 
 There is a way to achieve a similar task from C via Perl API: create a


@@ -1246,7 +1379,8 @@ Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
 
 Duplicates the current value of C<SV>, on the exit from the current
 C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
 
 Duplicates the current value of C<SV>, on the exit from the current
 C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>

-using the stored value.
+using the stored value. It doesn't handle magic. Use C<save_scalar> if
+magic is affected.

 
 =item C<void save_list(SV **sarg, I32 maxsarg)>
 
 
 =item C<void save_list(SV **sarg, I32 maxsarg)>
 


@@ -1255,7 +1389,7 @@ C<sarg> of C<SV*> of length C<maxsarg>.
 
 =item C<SV* save_svref(SV **sptr)>
 
 
 =item C<SV* save_svref(SV **sptr)>
 

-Similar to C<save_scalar>, but will reinstate a C<SV *>.
+Similar to C<save_scalar>, but will reinstate an C<SV *>.

 
 =item C<void save_aptr(AV **aptr)>
 
 
 =item C<void save_aptr(AV **aptr)>
 


@@ -1297,11 +1431,13 @@ where C<SP> is the macro that represents the local copy of the stack pointer,
 and C<num> is the number of elements the stack should be extended by.
 
 Now that there is room on the stack, values can be pushed on it using C<PUSHs>
 and C<num> is the number of elements the stack should be extended by.
 
 Now that there is room on the stack, values can be pushed on it using C<PUSHs>

-macro. The values pushed will often need to be "mortal" (See L</Reference Counts and Mortality>).
+macro. The pushed values will often need to be "mortal" (See
+L</Reference Counts and Mortality>):

 
     PUSHs(sv_2mortal(newSViv(an_integer)))
 
     PUSHs(sv_2mortal(newSViv(an_integer)))

+    PUSHs(sv_2mortal(newSVuv(an_unsigned_integer)))
+    PUSHs(sv_2mortal(newSVnv(a_double)))

     PUSHs(sv_2mortal(newSVpv("Some String",0)))
     PUSHs(sv_2mortal(newSVpv("Some String",0)))

-    PUSHs(sv_2mortal(newSVnv(3.141592)))

 
 And now the Perl program calling C<tzname>, the two values will be assigned
 as in:
 
 And now the Perl program calling C<tzname>, the two values will be assigned
 as in:


@@ -1317,8 +1453,9 @@ This macro automatically adjust the stack for you, if needed.  Thus, you
 do not need to call C<EXTEND> to extend the stack.
 
 Despite their suggestions in earlier versions of this document the macros
 do not need to call C<EXTEND> to extend the stack.
 
 Despite their suggestions in earlier versions of this document the macros

-C<PUSHi>, C<PUSHn> and C<PUSHp> are I<not> suited to XSUBs which return
-multiple results, see L</Putting a C value on Perl stack>.
+C<(X)PUSH[iunp]> are I<not> suited to XSUBs which return multiple results.
+For that, either stick to the C<(X)PUSHs> macros shown above, or use the new
+C<m(X)PUSH[iunp]> macros instead; see L</Putting a C value on Perl stack>.

 
 For more information, consult L<perlxs> and L<perlxstut>.
 
 
 For more information, consult L<perlxs> and L<perlxstut>.
 


@@ -1342,7 +1479,7 @@ trapped, and how to treat return values.
 All four routines return the number of arguments that the subroutine returned
 on the Perl stack.
 
 All four routines return the number of arguments that the subroutine returned
 on the Perl stack.
 

-These routines used to be called C<perl_call_sv> etc., before Perl v5.6.0,
+These routines used to be called C<perl_call_sv>, etc., before Perl v5.6.0,

 but those names are now deprecated; macros of the same name are provided for
 compatibility.
 
 but those names are now deprecated; macros of the same name are provided for
 compatibility.
 


@@ -1367,6 +1504,8 @@ consult L<perlcall>.
 
 =head2 Memory Allocation
 
 
 =head2 Memory Allocation
 

+=head3 Allocation
+

 All memory meant to be used with the Perl API functions should be manipulated
 using the macros described in this section.  The macros provide the necessary
 transparency between differences in the actual malloc implementation that is
 All memory meant to be used with the Perl API functions should be manipulated
 using the macros described in this section.  The macros provide the necessary
 transparency between differences in the actual malloc implementation that is


@@ -1377,29 +1516,26 @@ with Perl.  It keeps pools of various sizes of unallocated memory in
 order to satisfy allocation requests more quickly.  However, on some
 platforms, it may cause spurious malloc or free errors.
 
 order to satisfy allocation requests more quickly.  However, on some
 platforms, it may cause spurious malloc or free errors.
 

-    New(x, pointer, number, type);
-    Newc(x, pointer, number, type, cast);
-    Newz(x, pointer, number, type);
+The following three macros are used to initially allocate memory :

 
 

-These three macros are used to initially allocate memory.
+    Newx(pointer, number, type);
+    Newxc(pointer, number, type, cast);
+    Newxz(pointer, number, type);

 
 

-The first argument C<x> was a "magic cookie" that was used to keep track
-of who called the macro, to help when debugging memory problems.  However,
-the current code makes no use of this feature (most Perl developers now
-use run-time memory checkers), so this argument can be any number.
-
-The second argument C<pointer> should be the name of a variable that will
+The first argument C<pointer> should be the name of a variable that will

 point to the newly allocated memory.
 
 point to the newly allocated memory.
 

-The third and fourth arguments C<number> and C<type> specify how many of
+The second and third arguments C<number> and C<type> specify how many of

 the specified type of data structure should be allocated.  The argument
 the specified type of data structure should be allocated.  The argument

-C<type> is passed to C<sizeof>.  The final argument to C<Newc>, C<cast>,
+C<type> is passed to C<sizeof>.  The final argument to C<Newxc>, C<cast>,

 should be used if the C<pointer> argument is different from the C<type>
 argument.
 
 should be used if the C<pointer> argument is different from the C<type>
 argument.
 

-Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
+Unlike the C<Newx> and C<Newxc> macros, the C<Newxz> macro calls C<memzero>

 to zero out all the newly allocated memory.
 
 to zero out all the newly allocated memory.
 

+=head3 Reallocation
+

     Renew(pointer, number, type);
     Renewc(pointer, number, type, cast);
     Safefree(pointer)
     Renew(pointer, number, type);
     Renewc(pointer, number, type, cast);
     Safefree(pointer)


@@ -1409,6 +1545,8 @@ piece of memory no longer needed.  The arguments to C<Renew> and C<Renewc>
 match those of C<New> and C<Newc> with the exception of not needing the
 "magic cookie" argument.
 
 match those of C<New> and C<Newc> with the exception of not needing the
 "magic cookie" argument.
 

+=head3 Moving
+

     Move(source, dest, number, type);
     Copy(source, dest, number, type);
     Zero(dest, number, type);
     Move(source, dest, number, type);
     Copy(source, dest, number, type);
     Zero(dest, number, type);


@@ -1446,7 +1584,7 @@ corresponding parts of its I<target> and puts the I<target> on stack.
 
 The macro to put this target on stack is C<PUSHTARG>, and it is
 directly used in some opcodes, as well as indirectly in zillions of
 
 The macro to put this target on stack is C<PUSHTARG>, and it is
 directly used in some opcodes, as well as indirectly in zillions of

-others, which use it via C<(X)PUSH[pni]>.
+others, which use it via C<(X)PUSH[iunp]>.

 
 Because the target is reused, you must be careful when pushing multiple
 values on the stack. The following code will not do what you think:
 
 Because the target is reused, you must be careful when pushing multiple
 values on the stack. The following code will not do what you think:


@@ -1458,12 +1596,30 @@ This translates as "set C<TARG> to 10, push a pointer to C<TARG> onto
 the stack; set C<TARG> to 20, push a pointer to C<TARG> onto the stack".
 At the end of the operation, the stack does not contain the values 10
 and 20, but actually contains two pointers to C<TARG>, which we have set
 the stack; set C<TARG> to 20, push a pointer to C<TARG> onto the stack".
 At the end of the operation, the stack does not contain the values 10
 and 20, but actually contains two pointers to C<TARG>, which we have set

-to 20. If you need to push multiple different values, use C<XPUSHs>,
-which bypasses C<TARG>.
+to 20.

 
 

-On a related note, if you do use C<(X)PUSH[npi]>, then you're going to
+If you need to push multiple different values then you should either use
+the C<(X)PUSHs> macros, or else use the new C<m(X)PUSH[iunp]> macros,
+none of which make use of C<TARG>.  The C<(X)PUSHs> macros simply push an
+SV* on the stack, which, as noted under L</XSUBs and the Argument Stack>,
+will often need to be "mortal".  The new C<m(X)PUSH[iunp]> macros make
+this a little easier to achieve by creating a new mortal for you (via
+C<(X)PUSHmortal>), pushing that onto the stack (extending it if necessary
+in the case of the C<mXPUSH[iunp]> macros), and then setting its value.
+Thus, instead of writing this to "fix" the example above:
+
+    XPUSHs(sv_2mortal(newSViv(10)))
+    XPUSHs(sv_2mortal(newSViv(20)))
+
+you can simply write:
+
+    mXPUSHi(10)
+    mXPUSHi(20)
+
+On a related note, if you do use C<(X)PUSH[iunp]>, then you're going to

 need a C<dTARG> in your variable declarations so that the C<*PUSH*>
 need a C<dTARG> in your variable declarations so that the C<*PUSH*>

-macros can make use of the local variable C<TARG>.
+macros can make use of the local variable C<TARG>.  See also C<dTARGET>
+and C<dXSTARG>.

 
 =head2 Scratchpads
 
 
 =head2 Scratchpads
 


@@ -1490,7 +1646,7 @@ the scratchpad AV. In fact it contains a pointer to an AV of
 (initially) one element, and this element is the scratchpad AV. Why do
 we need an extra level of indirection?
 
 (initially) one element, and this element is the scratchpad AV. Why do
 we need an extra level of indirection?
 

-The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
+The answer is B<recursion>, and maybe B<threads>. Both

 these can create several execution pointers going into the same
 subroutine. For the subroutine-child not write over the temporaries
 for the subroutine-parent (lifespan of which covers the call to the
 these can create several execution pointers going into the same
 subroutine. For the subroutine-child not write over the temporaries
 for the subroutine-parent (lifespan of which covers the call to the


@@ -1537,8 +1693,8 @@ is the same as in our example.
 
 =head2 Examining the tree
 
 
 =head2 Examining the tree
 

-If you have your perl compiled for debugging (usually done with C<-D
-optimize=-g> on C<Configure> command line), you may examine the
+If you have your perl compiled for debugging (usually done with
+C<-DDEBUGGING> on the C<Configure> command line), you may examine the

 compiled tree by specifying C<-Dx> on the Perl command line.  The
 output takes several lines per node, and for C<$b+$c> it looks like
 this:
 compiled tree by specifying C<-Dx> on the Perl command line.  The
 output takes several lines per node, and for C<$b+$c> it looks like
 this:


@@ -1607,6 +1763,9 @@ complicate matters, if a C<UNOP> is actually a C<null> op after
 optimization (see L</Compile pass 2: context propagation>) it will still
 have children in accordance with its former type.
 
 optimization (see L</Compile pass 2: context propagation>) it will still
 have children in accordance with its former type.
 

+Another way to examine the tree is to use a compiler back-end module, such
+as L<B::Concise>.
+

 =head2 Compile pass 1: check routines
 
 The tree is created by the compiler while I<yacc> code feeds it
 =head2 Compile pass 1: check routines
 
 The tree is created by the compiler while I<yacc> code feeds it


@@ -1670,10 +1829,10 @@ are subject to the same restrictions as in the pass 2.
 =head2 Pluggable runops
 
 The compile tree is executed in a runops function.  There are two runops
 =head2 Pluggable runops
 
 The compile tree is executed in a runops function.  There are two runops

-functions in F<run.c>.  C<Perl_runops_debug> is used with DEBUGGING and
-C<Perl_runops_standard> is used otherwise.  For fine control over the
-execution of the compile tree it is possible to provide your own runops
-function.
+functions, in F<run.c> and in F<dump.c>.  C<Perl_runops_debug> is used
+with DEBUGGING and C<Perl_runops_standard> is used otherwise.  For fine
+control over the execution of the compile tree it is possible to provide
+your own runops function.

 
 It's probably best to copy one of the existing runops functions and
 change it to suit your needs.  Then, in the BOOT section of your XS
 
 It's probably best to copy one of the existing runops functions and
 change it to suit your needs.  Then, in the BOOT section of your XS


@@ -1695,7 +1854,7 @@ C<sv_dump> to produce debugging output from Perl-space, so users of that
 module should already be familiar with its format.
 
 C<Perl_op_dump> can be used to dump an C<OP> structure or any of its
 module should already be familiar with its format.
 
 C<Perl_op_dump> can be used to dump an C<OP> structure or any of its

-derivatives, and produces output similiar to C<perl -Dx>; in fact,
+derivatives, and produces output similar to C<perl -Dx>; in fact,

 C<Perl_dump_eval> will dump the main root of the code being evaluated,
 exactly like C<-Dx>.
 
 C<Perl_dump_eval> will dump the main root of the code being evaluated,
 exactly like C<-Dx>.
 


@@ -1731,13 +1890,39 @@ interpreters, with one interpreter represented either as a C structure,
 or inside a thread-specific structure.  These structures contain all
 the context, the state of that interpreter.
 
 or inside a thread-specific structure.  These structures contain all
 the context, the state of that interpreter.
 

-Three macros control the major Perl build flavors: MULTIPLICITY, and
-USE_5005THREADS.  The MULTIPLICITY build has a C structure
-that packages all the interpreter state, and there is a similar thread-specific
-data structure under USE_5005THREADS.  In both cases,
-PERL_IMPLICIT_CONTEXT is also normally defined, and enables the
-support for passing in a "hidden" first argument that represents all three
-data structures.
+One macro controls the major Perl build flavor: MULTIPLICITY. The
+MULTIPLICITY build has a C structure that packages all the interpreter
+state. With multiplicity-enabled perls, PERL_IMPLICIT_CONTEXT is also
+normally defined, and enables the support for passing in a "hidden" first
+argument that represents all three data structures. MULTIPLICITY makes
+mutli-threaded perls possible (with the ithreads threading model, related
+to the macro USE_ITHREADS.)
+
+Two other "encapsulation" macros are the PERL_GLOBAL_STRUCT and
+PERL_GLOBAL_STRUCT_PRIVATE (the latter turns on the former, and the
+former turns on MULTIPLICITY.)  The PERL_GLOBAL_STRUCT causes all the
+internal variables of Perl to be wrapped inside a single global struct,
+struct perl_vars, accessible as (globals) &PL_Vars or PL_VarsPtr or
+the function  Perl_GetVars().  The PERL_GLOBAL_STRUCT_PRIVATE goes
+one step further, there is still a single struct (allocated in main()
+either from heap or from stack) but there are no global data symbols
+pointing to it.  In either case the global struct should be initialised
+as the very first thing in main() using Perl_init_global_struct() and
+correspondingly tear it down after perl_free() using Perl_free_global_struct(),
+please see F<miniperlmain.c> for usage details.  You may also need
+to use C<dVAR> in your coding to "declare the global variables"
+when you are using them.  dTHX does this for you automatically.
+
+To see whether you have non-const data you can use a BSD-compatible C<nm>:
+
+  nm libperl.a | grep -v ' [TURtr] '
+
+If this displays any C<D> or C<d> symbols, you have non-const data.
+
+For backward compatibility reasons defining just PERL_GLOBAL_STRUCT
+doesn't actually hide all symbols inside a big global struct: some
+PerlIO_xxx vtables are left visible.  The PERL_GLOBAL_STRUCT_PRIVATE
+then hides everything (see how the PERLIO_FUNCS_DECL is used).

 
 All this obviously requires a way for the Perl internal functions to be
 either subroutines taking some kind of structure as the first
 
 All this obviously requires a way for the Perl internal functions to be
 either subroutines taking some kind of structure as the first


@@ -1772,9 +1957,9 @@ A public function (i.e. part of the internal API, but not necessarily
 sanctioned for use in extensions) begins like this:
 
   void
 sanctioned for use in extensions) begins like this:
 
   void

-  Perl_sv_setsv(pTHX_ SV* dsv, SV* ssv)
+  Perl_sv_setiv(pTHX_ SV* dsv, IV num)

 
 

-C<pTHX_> is one of a number of macros (in perl.h) that hide the
+C<pTHX_> is one of a number of macros (in F<perl.h>) that hide the

 details of the interpreter's context.  THX stands for "thread", "this",
 or "thingy", as the case may be.  (And no, George Lucas is not involved. :-)
 The first character could be 'p' for a B<p>rototype, 'a' for B<a>rgument,
 details of the interpreter's context.  THX stands for "thread", "this",
 or "thingy", as the case may be.  (And no, George Lucas is not involved. :-)
 The first character could be 'p' for a B<p>rototype, 'a' for B<a>rgument,


@@ -1791,19 +1976,19 @@ macro without the trailing underscore is used when there are no additional
 explicit arguments.
 
 When a core function calls another, it must pass the context.  This
 explicit arguments.
 
 When a core function calls another, it must pass the context.  This

-is normally hidden via macros.  Consider C<sv_setsv>.  It expands into
+is normally hidden via macros.  Consider C<sv_setiv>.  It expands into

 something like this:
 
 something like this:
 

-    ifdef PERL_IMPLICIT_CONTEXT
-      define sv_setsv(a,b)      Perl_sv_setsv(aTHX_ a, b)
+    #ifdef PERL_IMPLICIT_CONTEXT
+      #define sv_setiv(a,b)      Perl_sv_setiv(aTHX_ a, b)

       /* can't do this for vararg functions, see below */
       /* can't do this for vararg functions, see below */

-    else
-      define sv_setsv           Perl_sv_setsv
-    endif
+    #else
+      #define sv_setiv           Perl_sv_setiv
+    #endif

 
 This works well, and means that XS authors can gleefully write:
 
 
 This works well, and means that XS authors can gleefully write:
 

-    sv_setsv(foo, bar);
+    sv_setiv(foo, bar);

 
 and still have it work under all the modes Perl could have been
 compiled with.
 
 and still have it work under all the modes Perl could have been
 compiled with.


@@ -1843,20 +2028,20 @@ built with PERL_IMPLICIT_CONTEXT enabled.
 
 There are three ways to do this.  First, the easy but inefficient way,
 which is also the default, in order to maintain source compatibility
 
 There are three ways to do this.  First, the easy but inefficient way,
 which is also the default, in order to maintain source compatibility

-with extensions: whenever XSUB.h is #included, it redefines the aTHX
+with extensions: whenever F<XSUB.h> is #included, it redefines the aTHX

 and aTHX_ macros to call a function that will return the context.
 Thus, something like:
 
 and aTHX_ macros to call a function that will return the context.
 Thus, something like:
 

-        sv_setsv(asv, bsv);
+        sv_setiv(sv, num);

 
 in your extension will translate to this when PERL_IMPLICIT_CONTEXT is
 in effect:
 
 
 in your extension will translate to this when PERL_IMPLICIT_CONTEXT is
 in effect:
 

-        Perl_sv_setsv(Perl_get_context(), asv, bsv);
+        Perl_sv_setiv(Perl_get_context(), sv, num);

 
 or to this otherwise:
 
 
 or to this otherwise:
 

-        Perl_sv_setsv(asv, bsv);
+        Perl_sv_setiv(sv, num);

 
 You have to do nothing new in your extension to get this; since
 the Perl library provides Perl_get_context(), it will all just
 
 You have to do nothing new in your extension to get this; since
 the Perl library provides Perl_get_context(), it will all just


@@ -1870,9 +2055,9 @@ your Foo.xs:
         #include "perl.h"
         #include "XSUB.h"
 
         #include "perl.h"
         #include "XSUB.h"
 

-        static my_private_function(int arg1, int arg2);
+        STATIC void my_private_function(int arg1, int arg2);

 
 

-        static SV *
+        STATIC void

         my_private_function(int arg1, int arg2)
         {
             dTHX;       /* fetch context */
         my_private_function(int arg1, int arg2)
         {
             dTHX;       /* fetch context */


@@ -1910,9 +2095,9 @@ the Perl guts:
         #include "XSUB.h"
 
         /* pTHX_ only needed for functions that call Perl API */
         #include "XSUB.h"
 
         /* pTHX_ only needed for functions that call Perl API */

-        static my_private_function(pTHX_ int arg1, int arg2);
+        STATIC void my_private_function(pTHX_ int arg1, int arg2);

 
 

-        static SV *
+        STATIC void

         my_private_function(pTHX_ int arg1, int arg2)
         {
             /* dTHX; not needed here, because THX is an argument */
         my_private_function(pTHX_ int arg1, int arg2)
         {
             /* dTHX; not needed here, because THX is an argument */


@@ -1940,6 +2125,13 @@ Never add a comma after C<pTHX> yourself--always use the form of the
 macro with the underscore for functions that take explicit arguments,
 or the form without the argument for functions with no explicit arguments.
 
 macro with the underscore for functions that take explicit arguments,
 or the form without the argument for functions with no explicit arguments.
 

+If one is compiling Perl with the C<-DPERL_GLOBAL_STRUCT> the C<dVAR>
+definition is needed if the Perl global variables (see F<perlvars.h>
+or F<globvar.sym>) are accessed in the function and C<dTHX> is not
+used (the C<dTHX> includes the C<dVAR> if necessary).  One notices
+the need for C<dVAR> only with the said compile-time define, because
+otherwise the Perl global variables are visible as-is.
+

 =head2 Should I do anything special if I call perl from multiple threads?
 
 If you create interpreters in one thread and then proceed to call them in
 =head2 Should I do anything special if I call perl from multiple threads?
 
 If you create interpreters in one thread and then proceed to call them in


@@ -1966,14 +2158,14 @@ Just as PERL_IMPLICIT_CONTEXT provides a way to bundle up everything
 that the interpreter knows about itself and pass it around, so too are
 there plans to allow the interpreter to bundle up everything it knows
 about the environment it's running on.  This is enabled with the
 that the interpreter knows about itself and pass it around, so too are
 there plans to allow the interpreter to bundle up everything it knows
 about the environment it's running on.  This is enabled with the

-PERL_IMPLICIT_SYS macro.  Currently it only works with USE_ITHREADS
-and USE_5005THREADS on Windows (see inside iperlsys.h).
+PERL_IMPLICIT_SYS macro.  Currently it only works with USE_ITHREADS on
+Windows.

 
 This allows the ability to provide an extra pointer (called the "host"
 environment) for all the system calls.  This makes it possible for
 all the system stuff to maintain their own state, broken down into
 seven C structures.  These are thin wrappers around the usual system
 
 This allows the ability to provide an extra pointer (called the "host"
 environment) for all the system calls.  This makes it possible for
 all the system stuff to maintain their own state, broken down into
 seven C structures.  These are thin wrappers around the usual system

-calls (see win32/perllib.c) for the default perl executable, but for a
+calls (see F<win32/perllib.c>) for the default perl executable, but for a

 more ambitious host (like the one that would do fork() emulation) all
 the extra work needed to pretend that different interpreters are
 actually different "processes", would be done here.
 more ambitious host (like the one that would do fork() emulation) all
 the extra work needed to pretend that different interpreters are
 actually different "processes", would be done here.


@@ -1985,19 +2177,20 @@ more "hosts", with free association between them.
 =head1 Internal Functions
 
 All of Perl's internal functions which will be exposed to the outside
 =head1 Internal Functions
 
 All of Perl's internal functions which will be exposed to the outside

-world are be prefixed by C<Perl_> so that they will not conflict with XS
+world are prefixed by C<Perl_> so that they will not conflict with XS

 functions or functions used in a program in which Perl is embedded.
 Similarly, all global variables begin with C<PL_>. (By convention,
 functions or functions used in a program in which Perl is embedded.
 Similarly, all global variables begin with C<PL_>. (By convention,

-static functions start with C<S_>)
+static functions start with C<S_>.)

 
 Inside the Perl core, you can get at the functions either with or
 without the C<Perl_> prefix, thanks to a bunch of defines that live in
 F<embed.h>. This header file is generated automatically from
 
 Inside the Perl core, you can get at the functions either with or
 without the C<Perl_> prefix, thanks to a bunch of defines that live in
 F<embed.h>. This header file is generated automatically from

-F<embed.pl>. F<embed.pl> also creates the prototyping header files for
-the internal functions, generates the documentation and a lot of other
-bits and pieces. It's important that when you add a new function to the
-core or change an existing one, you change the data in the table at the
-end of F<embed.pl> as well. Here's a sample entry from that table:
+F<embed.pl> and F<embed.fnc>. F<embed.pl> also creates the prototyping
+header files for the internal functions, generates the documentation
+and a lot of other bits and pieces. It's important that when you add
+a new function to the core or change an existing one, you change the
+data in the table in F<embed.fnc> as well. Here's a sample entry from
+that table:

 
     Apd |SV**   |av_fetch   |AV* ar|I32 key|I32 lval
 
 
     Apd |SV**   |av_fetch   |AV* ar|I32 key|I32 lval
 


@@ -2008,16 +2201,18 @@ after that are the arguments. The first column is a set of flags:
 
 =item A
 
 
 =item A
 

-This function is a part of the public API.
+This function is a part of the public API. All such functions should also
+have 'd', very few do not.

 
 =item p
 
 
 =item p
 

-This function has a C<Perl_> prefix; ie, it is defined as C<Perl_av_fetch>
+This function has a C<Perl_> prefix; i.e. it is defined as
+C<Perl_av_fetch>.

 
 =item d
 
 This function has documentation using the C<apidoc> feature which we'll
 
 =item d
 
 This function has documentation using the C<apidoc> feature which we'll

-look at in a second.
+look at in a second.  Some functions have 'd' but not 'A'; docs are good.

 
 =back
 
 
 =back
 


@@ -2027,12 +2222,13 @@ Other available flags are:
 
 =item s
 
 
 =item s
 

-This is a static function and is defined as C<S_whatever>, and usually
-called within the sources as C<whatever(...)>.
+This is a static function and is defined as C<STATIC S_whatever>, and
+usually called within the sources as C<whatever(...)>.

 
 =item n
 
 
 =item n
 

-This does not use C<aTHX_> and C<pTHX> to pass interpreter context. (See
+This does not need a interpreter context, so the definition has no
+C<pTHX>, and it follows that callers don't use C<aTHX>.  (See

 L<perlguts/Background and PERL_IMPLICIT_CONTEXT>.)
 
 =item r
 L<perlguts/Background and PERL_IMPLICIT_CONTEXT>.)
 
 =item r


@@ -2056,19 +2252,36 @@ or disappear without notice.
 This function should not have a compatibility macro to define, say,
 C<Perl_parse> to C<parse>. It must be called as C<Perl_parse>.
 
 This function should not have a compatibility macro to define, say,
 C<Perl_parse> to C<parse>. It must be called as C<Perl_parse>.
 

-=item j
-
-This function is not a member of C<CPerlObj>. If you don't know
-what this means, don't use it.
-

 =item x
 
 This function isn't exported out of the Perl core.
 
 =item x
 
 This function isn't exported out of the Perl core.
 

+=item m
+
+This is implemented as a macro.
+
+=item X
+
+This function is explicitly exported.
+
+=item E
+
+This function is visible to extensions included in the Perl core.
+
+=item b
+
+Binary backward compatibility; this function is a macro but also has
+a C<Perl_> implementation (which is exported).
+
+=item others
+
+See the comments at the top of C<embed.fnc> for others.
+

 =back
 
 =back
 

-If you edit F<embed.pl>, you will need to run C<make regen_headers> to
-force a rebuild of F<embed.h> and other auto-generated files.
+If you edit F<embed.pl> or F<embed.fnc>, you will need to run
+C<make regen_headers> to force a rebuild of F<embed.h> and other
+auto-generated files.

 
 =head2 Formatted Printing of IVs, UVs, and NVs
 
 
 =head2 Formatted Printing of IVs, UVs, and NVs
 


@@ -2114,6 +2327,39 @@ and
         AV *av = ...;
         UV  uv = PTR2UV(av);
 
         AV *av = ...;
         UV  uv = PTR2UV(av);
 

+=head2 Exception Handling
+
+There are a couple of macros to do very basic exception handling in XS
+modules. You have to define C<NO_XSLOCKS> before including F<XSUB.h> to
+be able to use these macros:
+
+        #define NO_XSLOCKS
+        #include "XSUB.h"
+
+You can use these macros if you call code that may croak, but you need
+to do some cleanup before giving control back to Perl. For example:
+
+        dXCPT;    /* set up necessary variables */
+
+        XCPT_TRY_START {
+          code_that_may_croak();
+        } XCPT_TRY_END
+
+        XCPT_CATCH
+        {
+          /* do cleanup here */
+          XCPT_RETHROW;
+        }
+
+Note that you always have to rethrow an exception that has been
+caught. Using these macros, it is not possible to just catch the
+exception and ignore it. If you have to ignore the exception, you
+have to use the C<call_*> function.
+
+The advantage of using the above macros is that you don't have
+to setup an extra function for C<call_*>, and that using these
+macros is faster than using C<call_*>.
+

 =head2 Source Documentation
 
 There's an effort going on to document the internal functions and
 =head2 Source Documentation
 
 There's an effort going on to document the internal functions and


@@ -2137,6 +2383,26 @@ source, like this:
 Please try and supply some documentation if you add functions to the
 Perl core.
 
 Please try and supply some documentation if you add functions to the
 Perl core.
 

+=head2 Backwards compatibility
+
+The Perl API changes over time. New functions are added or the interfaces
+of existing functions are changed. The C<Devel::PPPort> module tries to
+provide compatibility code for some of these changes, so XS writers don't
+have to code it themselves when supporting multiple versions of Perl.
+
+C<Devel::PPPort> generates a C header file F<ppport.h> that can also
+be run as a Perl script. To generate F<ppport.h>, run:
+
+    perl -MDevel::PPPort -eDevel::PPPort::WriteFile
+
+Besides checking existing XS code, the script can also be used to retrieve
+compatibility information for various API calls using the C<--api-info>
+command line switch. For example:
+
+  % perl ppport.h --api-info=sv_magicext
+
+For details, see C<perldoc ppport.h>.
+

 =head1 Unicode Support
 
 Perl 5.6.0 introduced Unicode support. It's important for porters and XS
 =head1 Unicode Support
 
 Perl 5.6.0 introduced Unicode support. It's important for porters and XS


@@ -2163,34 +2429,35 @@ to one character.
 To fix this, some people formed Unicode, Inc. and
 produced a new character set containing all the characters you can
 possibly think of and more. There are several ways of representing these
 To fix this, some people formed Unicode, Inc. and
 produced a new character set containing all the characters you can
 possibly think of and more. There are several ways of representing these

-characters, and the one Perl uses is called UTF8. UTF8 uses
-a variable number of bytes to represent a character, instead of just
-one. You can learn more about Unicode at http://www.unicode.org/
+characters, and the one Perl uses is called UTF-8. UTF-8 uses
+a variable number of bytes to represent a character. You can learn more
+about Unicode and Perl's Unicode model in L<perlunicode>.

 
 

-=head2 How can I recognise a UTF8 string?
+=head2 How can I recognise a UTF-8 string?

 
 

-You can't. This is because UTF8 data is stored in bytes just like
-non-UTF8 data. The Unicode character 200, (C<0xC8> for you hex types)
+You can't. This is because UTF-8 data is stored in bytes just like
+non-UTF-8 data. The Unicode character 200, (C<0xC8> for you hex types)

 capital E with a grave accent, is represented by the two bytes
 C<v196.172>. Unfortunately, the non-Unicode string C<chr(196).chr(172)>
 has that byte sequence as well. So you can't tell just by looking - this
 is what makes Unicode input an interesting problem.
 
 capital E with a grave accent, is represented by the two bytes
 C<v196.172>. Unfortunately, the non-Unicode string C<chr(196).chr(172)>
 has that byte sequence as well. So you can't tell just by looking - this
 is what makes Unicode input an interesting problem.
 

-The API function C<is_utf8_string> can help; it'll tell you if a string
-contains only valid UTF8 characters. However, it can't do the work for
-you. On a character-by-character basis, C<is_utf8_char> will tell you
-whether the current character in a string is valid UTF8.
+In general, you either have to know what you're dealing with, or you
+have to guess.  The API function C<is_utf8_string> can help; it'll tell
+you if a string contains only valid UTF-8 characters. However, it can't
+do the work for you. On a character-by-character basis, C<is_utf8_char>
+will tell you whether the current character in a string is valid UTF-8. 

 
 

-=head2 How does UTF8 represent Unicode characters?
+=head2 How does UTF-8 represent Unicode characters?

 
 

-As mentioned above, UTF8 uses a variable number of bytes to store a
-character. Characters with values 1...128 are stored in one byte, just
-like good ol' ASCII. Character 129 is stored as C<v194.129>; this
+As mentioned above, UTF-8 uses a variable number of bytes to store a
+character. Characters with values 0...127 are stored in one byte, just
+like good ol' ASCII. Character 128 is stored as C<v194.128>; this

 continues up to character 191, which is C<v194.191>. Now we've run out of
 bits (191 is binary C<10111111>) so we move on; 192 is C<v195.128>. And
 so it goes on, moving to three bytes at character 2048.
 
 continues up to character 191, which is C<v194.191>. Now we've run out of
 bits (191 is binary C<10111111>) so we move on; 192 is C<v195.128>. And
 so it goes on, moving to three bytes at character 2048.
 

-Assuming you know you're dealing with a UTF8 string, you can find out
+Assuming you know you're dealing with a UTF-8 string, you can find out

 how long the first character in it is with the C<UTF8SKIP> macro:
 
     char *utf = "\305\233\340\240\201";
 how long the first character in it is with the C<UTF8SKIP> macro:
 
     char *utf = "\305\233\340\240\201";


@@ -2200,19 +2467,21 @@ how long the first character in it is with the C<UTF8SKIP> macro:
     utf += len;
     len = UTF8SKIP(utf); /* len is 3 here */
 
     utf += len;
     len = UTF8SKIP(utf); /* len is 3 here */
 

-Another way to skip over characters in a UTF8 string is to use
+Another way to skip over characters in a UTF-8 string is to use

 C<utf8_hop>, which takes a string and a number of characters to skip
 over. You're on your own about bounds checking, though, so don't use it
 lightly.
 
 C<utf8_hop>, which takes a string and a number of characters to skip
 over. You're on your own about bounds checking, though, so don't use it
 lightly.
 

-All bytes in a multi-byte UTF8 character will have the high bit set, so
-you can test if you need to do something special with this character
-like this:
+All bytes in a multi-byte UTF-8 character will have the high bit set,
+so you can test if you need to do something special with this
+character like this (the UTF8_IS_INVARIANT() is a macro that tests
+whether the byte can be encoded as a single byte even in UTF-8):

 
 

-    UV uv;
+    U8 *utf;
+    UV uv;     /* Note: a UV, not a U8, not a char */

 
 

-    if (utf & 0x80)
-        /* Must treat this as UTF8 */
+    if (!UTF8_IS_INVARIANT(*utf))
+        /* Must treat this as UTF-8 */

         uv = utf8_to_uv(utf);
     else
         /* OK to treat this character as a byte */
         uv = utf8_to_uv(utf);
     else
         /* OK to treat this character as a byte */


@@ -2220,9 +2489,9 @@ like this:
 
 You can also see in that example that we use C<utf8_to_uv> to get the
 value of the character; the inverse function C<uv_to_utf8> is available
 
 You can also see in that example that we use C<utf8_to_uv> to get the
 value of the character; the inverse function C<uv_to_utf8> is available

-for putting a UV into UTF8:
+for putting a UV into UTF-8:

 
 

-    if (uv > 0x80)
+    if (!UTF8_IS_INVARIANT(uv))

         /* Must treat this as UTF8 */
         utf8 = uv_to_utf8(utf8, uv);
     else
         /* Must treat this as UTF8 */
         utf8 = uv_to_utf8(utf8, uv);
     else


@@ -2230,19 +2499,21 @@ for putting a UV into UTF8:
         *utf8++ = uv;
 
 You B<must> convert characters to UVs using the above functions if
         *utf8++ = uv;
 
 You B<must> convert characters to UVs using the above functions if

-you're ever in a situation where you have to match UTF8 and non-UTF8
-characters. You may not skip over UTF8 characters in this case. If you
-do this, you'll lose the ability to match hi-bit non-UTF8 characters;
-for instance, if your UTF8 string contains C<v196.172>, and you skip
-that character, you can never match a C<chr(200)> in a non-UTF8 string.
+you're ever in a situation where you have to match UTF-8 and non-UTF-8
+characters. You may not skip over UTF-8 characters in this case. If you
+do this, you'll lose the ability to match hi-bit non-UTF-8 characters;
+for instance, if your UTF-8 string contains C<v196.172>, and you skip
+that character, you can never match a C<chr(200)> in a non-UTF-8 string.

 So don't do that!
 
 So don't do that!
 

-=head2 How does Perl store UTF8 strings?
+=head2 How does Perl store UTF-8 strings?

 
 Currently, Perl deals with Unicode strings and non-Unicode strings
 
 Currently, Perl deals with Unicode strings and non-Unicode strings

-slightly differently. If a string has been identified as being UTF-8
-encoded, Perl will set a flag in the SV, C<SVf_UTF8>. You can check and
-manipulate this flag with the following macros:
+slightly differently. A flag in the SV, C<SVf_UTF8>, indicates that the
+string is internally encoded as UTF-8. Without it, the byte value is the
+codepoint number and vice versa (in other words, the string is encoded
+as iso-8859-1). You can check and manipulate this flag with the
+following macros:

 
     SvUTF8(sv)
     SvUTF8_on(sv)
 
     SvUTF8(sv)
     SvUTF8_on(sv)


@@ -2254,8 +2525,8 @@ C<length>, C<substr> and other string handling operations will have
 undesirable results.
 
 The problem comes when you have, for instance, a string that isn't
 undesirable results.
 
 The problem comes when you have, for instance, a string that isn't

-flagged is UTF8, and contains a byte sequence that could be UTF8 -
-especially when combining non-UTF8 and UTF8 strings.
+flagged as UTF-8, and contains a byte sequence that could be UTF-8 -
+especially when combining non-UTF-8 and UTF-8 strings.

 
 Never forget that the C<SVf_UTF8> flag is separate to the PV value; you
 need be sure you don't accidentally knock it off while you're
 
 Never forget that the C<SVf_UTF8> flag is separate to the PV value; you
 need be sure you don't accidentally knock it off while you're


@@ -2281,14 +2552,18 @@ old SV has the UTF8 flag set, and act accordingly:
         SvUTF8_on(nsv);
 
 In fact, your C<frobnicate> function should be made aware of whether or
         SvUTF8_on(nsv);
 
 In fact, your C<frobnicate> function should be made aware of whether or

-not it's dealing with UTF8 data, so that it can handle the string
+not it's dealing with UTF-8 data, so that it can handle the string

 appropriately.
 
 appropriately.
 

-=head2 How do I convert a string to UTF8?
+Since just passing an SV to an XS function and copying the data of
+the SV is not enough to copy the UTF8 flags, even less right is just
+passing a C<char *> to an XS function.

 
 

-If you're mixing UTF8 and non-UTF8 strings, you might find it necessary
-to upgrade one of the strings to UTF8. If you've got an SV, the easiest
-way to do this is:
+=head2 How do I convert a string to UTF-8?
+
+If you're mixing UTF-8 and non-UTF-8 strings, it is necessary to upgrade
+one of the strings to UTF-8. If you've got an SV, the easiest way to do
+this is:

 
     sv_utf8_upgrade(sv);
 
 
     sv_utf8_upgrade(sv);
 


@@ -2299,9 +2574,9 @@ However, you must not do this, for example:
 
 If you do this in a binary operator, you will actually change one of the
 strings that came into the operator, and, while it shouldn't be noticeable
 
 If you do this in a binary operator, you will actually change one of the
 strings that came into the operator, and, while it shouldn't be noticeable

-by the end user, it can cause problems.
+by the end user, it can cause problems in deficient code.

 
 

-Instead, C<bytes_to_utf8> will give you a UTF8-encoded B<copy> of its
+Instead, C<bytes_to_utf8> will give you a UTF-8-encoded B<copy> of its

 string argument. This is useful for having the data available for
 comparisons and so on, without harming the original SV. There's also
 C<utf8_to_bytes> to go the other way, but naturally, this will fail if
 string argument. This is useful for having the data available for
 comparisons and so on, without harming the original SV. There's also
 C<utf8_to_bytes> to go the other way, but naturally, this will fail if


@@ -2316,38 +2591,37 @@ Not really. Just remember these things:
 
 =item *
 
 
 =item *
 

-There's no way to tell if a string is UTF8 or not. You can tell if an SV
-is UTF8 by looking at is C<SvUTF8> flag. Don't forget to set the flag if
-something should be UTF8. Treat the flag as part of the PV, even though
+There's no way to tell if a string is UTF-8 or not. You can tell if an SV
+is UTF-8 by looking at is C<SvUTF8> flag. Don't forget to set the flag if
+something should be UTF-8. Treat the flag as part of the PV, even though

 it's not - if you pass on the PV to somewhere, pass on the flag too.
 
 =item *
 
 it's not - if you pass on the PV to somewhere, pass on the flag too.
 
 =item *
 

-If a string is UTF8, B<always> use C<utf8_to_uv> to get at the value,
-unless C<!(*s & 0x80)> in which case you can use C<*s>.
+If a string is UTF-8, B<always> use C<utf8_to_uv> to get at the value,
+unless C<UTF8_IS_INVARIANT(*s)> in which case you can use C<*s>.

 
 =item *
 
 
 =item *
 

-When writing to a UTF8 string, B<always> use C<uv_to_utf8>, unless
-C<uv < 0x80> in which case you can use C<*s = uv>.
+When writing a character C<uv> to a UTF-8 string, B<always> use
+C<uv_to_utf8>, unless C<UTF8_IS_INVARIANT(uv))> in which case
+you can use C<*s = uv>.

 
 =item *
 
 
 =item *
 

-Mixing UTF8 and non-UTF8 strings is tricky. Use C<bytes_to_utf8> to get
-a new string which is UTF8 encoded. There are tricks you can use to
-delay deciding whether you need to use a UTF8 string until you get to a
-high character - C<HALF_UPGRADE> is one of those.
+Mixing UTF-8 and non-UTF-8 strings is tricky. Use C<bytes_to_utf8> to get
+a new string which is UTF-8 encoded, and then combine them.

 
 =back
 
 =head1 Custom Operators
 
 
 =back
 
 =head1 Custom Operators
 

-Custom operator support is a new experimental feature that allows you do
+Custom operator support is a new experimental feature that allows you to

 define your own ops. This is primarily to allow the building of
 interpreters for other languages in the Perl core, but it also allows
 optimizations through the creation of "macro-ops" (ops which perform the
 functions of multiple ops which are usually executed together, such as
 define your own ops. This is primarily to allow the building of
 interpreters for other languages in the Perl core, but it also allows
 optimizations through the creation of "macro-ops" (ops which perform the
 functions of multiple ops which are usually executed together, such as

-C<gvsv, gvsv, add>.) 
+C<gvsv, gvsv, add>.)

 
 This feature is implemented as a new op type, C<OP_CUSTOM>. The Perl
 core does not "know" anything special about this op type, and so it will
 
 This feature is implemented as a new op type, C<OP_CUSTOM>. The Perl
 core does not "know" anything special about this op type, and so it will


@@ -2379,26 +2653,19 @@ need to enter a name and description for your op at the appropriate
 place in the C<PL_custom_op_names> and C<PL_custom_op_descs> hashes.
 
 Forthcoming versions of C<B::Generate> (version 1.0 and above) should
 place in the C<PL_custom_op_names> and C<PL_custom_op_descs> hashes.
 
 Forthcoming versions of C<B::Generate> (version 1.0 and above) should

-directly support the creation of custom ops by name; C<Opcodes::Custom> 
-will provide functions which make it trivial to "register" custom ops to
-the Perl interpreter.
+directly support the creation of custom ops by name.

 
 =head1 AUTHORS
 
 Until May 1997, this document was maintained by Jeff Okamoto
 
 =head1 AUTHORS
 
 Until May 1997, this document was maintained by Jeff Okamoto

-<okamoto@corp.hp.com>.  It is now maintained as part of Perl itself
-by the Perl 5 Porters <perl5-porters@perl.org>.
+E<lt>okamoto@corp.hp.comE<gt>.  It is now maintained as part of Perl
+itself by the Perl 5 Porters E<lt>perl5-porters@perl.orgE<gt>.

 
 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
 Stephen McCamant, and Gurusamy Sarathy.
 
 
 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
 Stephen McCamant, and Gurusamy Sarathy.
 

-API Listing originally by Dean Roehrich <roehrich@cray.com>.
-
-Modifications to autogenerate the API listing (L<perlapi>) by Benjamin
-Stuhl.
-

 =head1 SEE ALSO
 
 perlapi(1), perlintern(1), perlxs(1), perlembed(1)
 =head1 SEE ALSO
 
 perlapi(1), perlintern(1), perlxs(1), perlembed(1)