Anomaly in caller() returned values

[p5pRT]

Migrated from rt.perl.org#1790 (status was 'resolved')

Searchable as RT1790$

[p5pRT]

From Raphael.Manfredi@st.com

---

There is an anomaly in the way caller() returns its arguments.
Watch​:

  1 sub a {
  2 b();
  3 }
  4
  5 sub b {
  6 my ($pack, $file, $line, $sub) = caller(1);
  7 print "b() called from $sub/$line\n";
  8 }
  9
  10 a();

which produces​:

  b() called from main​::a/10

If caller(0) is used instead in line 6, I get​:

  b() called from main​::b/2

The anomaly is that $sub refers to the calling routine, but
not the line number. To get it, one must re-use caller()
with an (offset-1) with respect to the targetted call frame.

Raphael

---

---

Site configuration information for perl 5.00503​:

Configured by manfredi at Mon Aug 9 12​:37​:05 MET DST 1999.

Summary of my perl5 (5.0 patchlevel 5 subversion 3) configuration​:
  Platform​:
  osname=solaris, osvers=2.5.1, archname=sun4-solaris
  uname='sunos lod23 5.5.1 generic_103640-27 sun4u sparc sunw,ultra-60 '
  hint=previous, useposix=true, d_sigaction=define
  usethreads=undef useperlio=define d_sfio=undef
  Compiler​:
  cc='/apa/SUNWspro/bin/cc', optimize='-O', gccversion=
  cppflags='-I/home/manfredi/usr/BerkeleyDB/include'
  ccflags ='-I/home/manfredi/usr/BerkeleyDB/include'
  stdchar='unsigned char', d_stdstdio=define, usevfork=true
  intsize=4, longsize=4, ptrsize=4, doublesize=8
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
  alignbytes=8, usemymalloc=y, prototype=define
  Linker and Libraries​:
  ld='/apa/SUNWspro/bin/cc', ldflags ='-L/home/manfredi/usr/BerkeleyDB/lib'
  libpth=/lib /usr/lib /usr/ccs/lib /home/manfredi/usr/BerkeleyDB/lib
  libs=-lsocket -lnsl -ldl -lm -lc -lcrypt
  libc=/lib/libc.so, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags=' '
  cccdlflags='-KPIC', lddlflags='-G -L/home/manfredi/usr/BerkeleyDB/lib'

Locally applied patches​:
 

---

@​INC for perl 5.00503​:
  /home/manfredi/usr/lib/perl
  /home/manfredi/usr/lib/perl5/5.00503/sun4-solaris
  /home/manfredi/usr/lib/perl5/5.00503
  /home/manfredi/usr/lib/perl5/site_perl/5.005/sun4-solaris
  /home/manfredi/usr/lib/perl5/site_perl/5.005
  .

---

Environment for perl 5.00503​:
  HOME=/home/manfredi
  LANG=fr
  LANGUAGE (unset)
  LC_MESSAGES=C
  LC_MONETARY=C
  LC_NUMERIC=C
  LC_TIME=C
  LD_LIBRARY_PATH=/home/manfredi/usr/lib/X11​:/usr/openwin/lib
  LOGDIR (unset)
  PATH=/home/manfredi/bin/scripts​:/home/manfredi/bin/sun​:/home/manfredi/bin/sun/mh​:/home/manfredi/bin/scripts/mh​:/home/manfredi/bin/sun/fm2html​:/home/manfredi/bin/scripts/rdb​:/apa/gnu/SunOS5/bin​:/bin​:/usr/bin​:/sbin​:/usr/sbin​:/apa/SUNWspro/bin​:/usr/ccs/bin​:/usr/ucb​:/usr/contrib/bin​:/apa/comp/SunOS5/bin​:/apa/acroread/3.02/bin​:/apa/ddts/bin​:/apa/util/bin​:/etc​:/usr/bin/X11​:/usr/games​:/home/bruel/local/SunOS5/bin​:/home/manfredi​:.​:/home/manfredi/bin/acri
  PERL_BADLANG (unset)
  SHELL=/home/manfredi/bin/sun/ksh

[p5pRT]

From @gsar

On Wed, 17 Nov 1999 16​:31​:55 +0100, Raphael Manfredi wrote​:

There is an anomaly in the way caller() returns its arguments.
Watch​:

1  sub a \{
2      b\(\);
3  \}
4  
5  sub b \{
6      my \($pack\, $file\,  $line\, $sub\) = caller\(1\);
7      print "b\(\) called from $sub/$line\\n";
8  \}
9  

10 a();

which produces​:

b() called from main​::a/10

If caller(0) is used instead in line 6, I get​:

b() called from main​::b/2

The anomaly is that $sub refers to the calling routine, but
not the line number. To get it, one must re-use caller()
with an (offset-1) with respect to the targetted call frame.

FWIW, I don't think there's a bug here. What's probably
misleading is the way the message is written. caller() simply
reports the attributes of the executing context "frame", and
they look correct in the above. Try a message more like​:

  print "executing $sub() at $line\n";

and you'll see what I mean.

Sarathy
gsar@​ActiveState.com

[p5pRT]

From [Unknown Contact. See original ticket]

Quoting gsar@​activestate.com​:
:>The anomaly is that $sub refers to the calling routine, but
:>not the line number. To get it, one must re-use caller()
:>with an (offset-1) with respect to the targetted call frame.
:
:FWIW, I don't think there's a bug here. What's probably
:misleading is the way the message is written. caller() simply
:reports the attributes of the executing context "frame", and
:they look correct in the above. Try a message more like​:

I did not say it was a bug, I said it was an "anomaly". ;-)

Seriously, I was astonished by the behaviour, but you're right.
I had the "wording" wrong in my head, hence the interpretation
was also wrong.

Perhaps the example you gave me should go in the documentation?
Somehow, I thought caller(0) would give MY OWN stack frame, since
$subroutine is set to my name, but no, it's giving the name of
the subroutine called, which is mine!

Hence my confusion.

Raphael