pack with a human face: the sequel

Message-ID: <20020221213337.A23848@math.ohio-state.edu>

p4raw-id: //depot/perl@14824

2 files changed, 17 insertions, 7 deletions

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 0c87d94643..6d8e9407f7 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -2313,6 +2313,12 @@ supplied.  See L<perlform>.
 of Perl.  Check the #! line, or manually feed your script into Perl
 yourself.
 
+=item %s not allowed in length fields
+
+(F) The count in the (un)pack template may be replaced by C<[TEMPLATE]> only if
+C<TEMPLATE> always matches the same amount of packed bytes.  Redesign
+the template.
+
 =item no UTC offset information; assuming local time is UTC
 
 (S) A warning peculiar to VMS.  Perl was unable to find the local
diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod
index 56ad58f474..dfacad5146 100644
--- a/pod/perlfunc.pod
+++ b/pod/perlfunc.pod
@@ -3169,7 +3169,7 @@ of values, as follows:
     x	A null byte.
     X	Back up a byte.
     @	Null fill to absolute position.
-    (	Beginning of a ()-group.
+    (	Start of a ()-group.
 
 The following rules apply:
 
@@ -3179,12 +3179,16 @@ The following rules apply:
 
 Each letter may optionally be followed by a number giving a repeat
 count.  With all types except C<a>, C<A>, C<Z>, C<b>, C<B>, C<h>,
-C<H>, and C<P> the pack function will gobble up that many values from
-the LIST.  A C<*> for the repeat count means to use however many items are
-left, except for C<@>, C<x>, C<X>, where it is equivalent
-to C<0>, and C<u>, where it is equivalent to 1 (or 45, what is the
-same).  A numeric repeat count may optionally be enclosed in brackets, as in
-C<pack 'C[80]', @arr>.
+C<H>, C<@>, C<x>, C<X> and C<P> the pack function will gobble up that
+many values from the LIST.  A C<*> for the repeat count means to use
+however many items are left, except for C<@>, C<x>, C<X>, where it is
+equivalent to C<0>, and C<u>, where it is equivalent to 1 (or 45, what
+is the same).  A numeric repeat count may optionally be enclosed in
+brackets, as in C<pack 'C[80]', @arr>.
+
+One can replace the numeric repeat count by a template enclosed in brackets;
+then the packed length of this template in bytes is used as a count.
+For example, C<x[L]> skips a long (it skips the number of bytes in a long).
 
 When used with C<Z>, C<*> results in the addition of a trailing null
 byte (so the packed result will be one longer than the byte C<length>