perldelta for #47047 / 1de22db27a

[perl5.git] / pod / perlpacktut.pod

diff --git a/pod/perlpacktut.pod b/pod/perlpacktut.pod
index 3b138ef..f40d1c2 100644 (file)
--- a/pod/perlpacktut.pod
+++ b/pod/perlpacktut.pod
@@ -176,7 +176,8 @@ template doesn't match the incoming data, Perl will scream and die.
 
 Hence, putting it all together:
 
-    my($date,$description,$income,$expend) = unpack("A10xA27xA7xA*", $_);
+    my ($date, $description, $income, $expend) =
+        unpack("A10xA27xA7xA*", $_);
 
 Now, that's our data parsed. I suppose what we might want to do now is
 total up our income and expenditure, and add another line to the end of
@@ -184,7 +185,8 @@ our ledger - in the same format - saying how much we've brought in and
 how much we've spent:
 
     while (<>) {
-        my($date, $desc, $income, $expend) = unpack("A10xA27xA7xA*", $_);
+        my ($date, $desc, $income, $expend) =
+            unpack("A10xA27xA7xA*", $_);
         $tot_income += $income;
         $tot_expend += $expend;
     }
@@ -196,7 +198,8 @@ how much we've spent:
 
     # OK, let's go:
 
-    print pack("A10xA27xA7xA*", $date, "Totals", $tot_income, $tot_expend);
+    print pack("A10xA27xA7xA*", $date, "Totals",
+        $tot_income, $tot_expend);
 
 Oh, hmm. That didn't quite work. Let's see what happened:
 
@@ -219,7 +222,8 @@ What we actually need to do is expand the width of the fields. The C<A>
 format pads any non-existent characters with spaces, so we can use the
 additional spaces to line up our fields, like this:
 
-    print pack("A11 A28 A8 A*", $date, "Totals", $tot_income, $tot_expend);
+    print pack("A11 A28 A8 A*", $date, "Totals",
+        $tot_income, $tot_expend);
 
 (Note that you can put spaces in the template to make it more readable,
 but they don't translate to spaces in the output.) Here's what we got
@@ -238,7 +242,8 @@ can get C<sprintf> to do it:
     $tot_income = sprintf("%.2f", $tot_income); 
     $tot_expend = sprintf("%12.2f", $tot_expend);
     $date = POSIX::strftime("%m/%d/%Y", localtime); 
-    print pack("A11 A28 A8 A*", $date, "Totals", $tot_income, $tot_expend);
+    print pack("A11 A28 A8 A*", $date, "Totals",
+        $tot_income, $tot_expend);
 
 This time we get the right answer:
 
@@ -454,7 +459,7 @@ or even:
 
 and pass C<$buf> to your send routine. Some protocols demand that the
 count should include the length of the count itself: then just add 4
-to the data length. (But make sure to read L<"Lengths and Widths"> before
+to the data length. (But make sure to read L</"Lengths and Widths"> before
 you really code this!)
 
 
@@ -482,7 +487,7 @@ obviously works for C<E<lt>>, where the "little end" touches the code.
 
 You will probably find these modifiers even more useful if you have
 to deal with big- or little-endian C structures. Be sure to read
-L<"Packing and Unpacking C Structures"> for more on that.
+L</"Packing and Unpacking C Structures"> for more on that.
 
 
 =head2 Floating point Numbers
@@ -491,14 +496,19 @@ For packing floating point numbers you have the choice between the
 pack codes C<f>, C<d>, C<F> and C<D>. C<f> and C<d> pack into (or unpack
 from) single-precision or double-precision representation as it is provided
 by your system. If your systems supports it, C<D> can be used to pack and
-unpack extended-precision floating point values (C<long double>), which
-can offer even more resolution than C<f> or C<d>. C<F> packs an C<NV>,
-which is the floating point type used by Perl internally. (There
-is no such thing as a network representation for reals, so if you want
-to send your real numbers across computer boundaries, you'd better stick
-to ASCII representation, unless you're absolutely sure what's on the other
-end of the line. For the even more adventuresome, you can use the byte-order
-modifiers from the previous section also on floating point codes.)
+unpack (C<long double>) values, which can offer even more resolution
+than C<f> or C<d>.  B<Note that there are different long double formats.>
+
+C<F> packs an C<NV>, which is the floating point type used by Perl
+internally.
+
+There is no such thing as a network representation for reals, so if
+you want to send your real numbers across computer boundaries, you'd
+better stick to text representation, possibly using the hexadecimal
+float format (avoiding the decimal conversion loss), unless you're
+absolutely sure what's on the other end of the line. For the even more
+adventuresome, you can use the byte-order modifiers from the previous
+section also on floating point codes.
 
 
 
@@ -791,7 +801,8 @@ C</> is not implemented in Perls before 5.6, so if your code is required to
 work on older Perls you'll need to C<unpack( 'Z* Z* C')> to get the length,
 then use it to make a new unpack string. For example
 
-   # pack a message: ASCIIZ, ASCIIZ, length, string, byte (5.005 compatible)
+   # pack a message: ASCIIZ, ASCIIZ, length, string, byte
+   # (5.005 compatible)
    my $msg = pack( 'Z* Z* C A* C', $src, $dst, length $sm, $sm, $prio );
 
    # unpack
@@ -1136,7 +1147,7 @@ where a pointer is expected. The read(2) system call comes to mind:
 After reading L<perlfunc> explaining how to use C<syscall> we can write
 this Perl function copying a file to standard output:
 
-    require 'syscall.ph';
+    require 'syscall.ph'; # run h2ph to generate this file
     sub cat($){
         my $path = shift();
         my $size = -s $path;