util.h: fix broken casts in Perl_instr() parameters #23201
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Why broken? Because haystack/needle are effectively macros (they expand
to token sequences), so a call like
Perl_instr(a + b, x ? y : z)
expands to
strstr((char *)a + b, (char *)x ? y : z)
which is just wrong.
Normally I'd simply add the missing parentheses ((char *)(haystack),
etc), but it's not clear to me why the casts were added in the first
place (and fairly recently, too, in commit 4e52881).
Background:
instr() was originally implemented in pre-standard C (without const and
without a prototype) in util.c, perl-1.0. The consts were added fairly
early on in 08105a9 (1997): char *
instr(register const char *big, register const char *little);
The hand-written C code was replaced by a call to strstr() in
5d1d68e. It cast away const from the arguments to strstr() for no
reason I can see: strstr() takes pointers to const char (just like
Perl_instr), so the pointers were immediately implicitly re-consted by
the prototype of strstr().
Commit fea1d2d straight up turned instr() into an alias for strstr(),
which was apparently fine without any casts for 4.5 years. The C code in
Perl_instr() was moved from util.c to mathoms.c in commit 534dad4.
tonycoz
approved these changes
Apr 16, 2025
Contributor
|
The only reason I can think of for the casts is that some platform complained at the time. It could have just been carelessness |
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Why broken? Because haystack/needle are effectively macros (they expand to token sequences), so a call like
expands to
which is just wrong.
Normally I'd simply add the missing parentheses (
(char *)(haystack), etc), but it's not clear to me why the casts were added in the first place (and fairly recently, too, in commit 4e52881).Background:
instr() was originally implemented in pre-standard C (without const and without a prototype) in util.c, perl-1.0. The consts were added fairly early on in 08105a9 (1997):
char * instr(register const char *big, register const char *little);The hand-written C code was replaced by a call to strstr() in 5d1d68e. It cast away const from the arguments to strstr() for no reason I can see: strstr() takes pointers to const char (just like Perl_instr), so the pointers were immediately implicitly re-consted by the prototype of strstr().
Commit fea1d2d straight up turned instr() into an alias for strstr(), which was apparently fine without any casts for 4.5 years. The C code in Perl_instr() was moved from util.c to mathoms.c in commit 534dad4.