=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.
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
-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* newSVuv(UV);
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*);
-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_setpvn(SV*, const char*, int)
+ void sv_setpvn(SV*, const char*, STRLEN)
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
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.
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:
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>).
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
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 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.
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 */
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.
"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:
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);
=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,
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:
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.
-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
-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
-referr
ring 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<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);
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
+This MGVTBL structure is set at compile-time in
F<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.
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_clear Clear something the SV represents.
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
~ PERL_MAGIC_ext (none) Available for use by extensions
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.
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
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
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)>
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(newSVuv(an_unsigned_integer)))
+ PUSHs(sv_2mortal(newSVnv(a_double)))
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:
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>.
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.
=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
order to satisfy allocation requests more quickly. However, on some
platforms, it may cause spurious malloc or free errors.
+The following three macros are used to initially allocate memory :
+
New(x, pointer, number, type);
Newc(x, pointer, number, type, cast);
Newz(x, pointer, number, type);
-These three macros are used to initially allocate memory.
-
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
Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
to zero out all the newly allocated memory.
+=head3 Reallocation
+
Renew(pointer, number, type);
Renewc(pointer, number, type, cast);
Safefree(pointer)
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);
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:
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.
+
+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:
-On a related note, if you do use C<(X)PUSH[npi]>, then you're going to
+ 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*>
-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
(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
=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:
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 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
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
+Two 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,
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
details of the interpreter's context. THX stands for "thread", "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:
- 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 */
- 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:
- sv_setsv(foo, bar);
+ sv_setiv(foo, bar);
and still have it work under all the modes Perl could have been
compiled with.
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:
- Perl_sv_setsv(Perl_get_context(), asv, bsv);
+ Perl_sv_setiv(Perl_get_context(), sv, num);
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
=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,
-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
-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
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 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).
+
=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
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 neccessary 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
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
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
+characters, and the one Perl uses is called UTF-8. UTF-8 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/
-=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.
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
+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 UTF8.
+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
+As mentioned above, UTF-8 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
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";
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.
-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 */
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
*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!
-=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
slightly differently. If a string has been identified as being UTF-8
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 is 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
The C<char*> string does not tell you the whole story, and you can't
copy or reconstruct an SV just by copying the string value. Check if the
-old SV has the UTF8 flag set, and act accordingly:
+old SV has the UTF-8 flag set, and act accordingly:
p = SvPV(sv, len);
frobnicate(p);
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.
-=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 UTF-8 flags, even less right is just
+passing a C<char *> to an XS function.
+
+=head2 How do I convert a string to UTF-8?
-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
+If you're mixing UTF-8 and non-UTF-8 strings, you might find it 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);
strings that came into the operator, and, while it shouldn't be noticeable
by the end user, it can cause problems.
-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
=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 *
-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 *
-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 *
-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
+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. There are tricks you can use to
+delay deciding whether you need to use a UTF-8 string until you get to a
high character - C<HALF_UPGRADE> is one of those.
=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
=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.
-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)
https://perl5.git.perl.org / perl5.git / blobdiff