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* [Bug c/106988] New: subscripting a string literal is not an integer constant expression but __builtin_strlen is
@ 2022-09-20 20:27 msebor at gcc dot gnu.org
2022-09-21 0:57 ` [Bug c/106988] " pinskia at gcc dot gnu.org
2022-09-22 16:12 ` msebor at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: msebor at gcc dot gnu.org @ 2022-09-20 20:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106988
Bug ID: 106988
Summary: subscripting a string literal is not an integer
constant expression but __builtin_strlen is
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
In C mode, GCC rejects a subscript expression whose operand is a string literal
in contexts where an integer constant expression is required but accepts an
equivalent expression involving __builtin_strlen. Although conforming, it's
inconsistent and unnecessarily restrictive. Accepting both (either with
-Wpedantic) would also be conforming and more useful to programmers who need it
but don't think of using the built-in workaround.
$ cat a.c && gcc -S -Wall -Wpedantic a.c
#define EMPTY1(S) (__builtin_strlen(S) == 0)
_Static_assert(!EMPTY1("1"), ""); // ok
#define EMPTY2(S) (S[0] == 0)
_Static_assert(!EMPTY2("1"), ""); // error
a.c:5:16: error: expression in static assertion is not constant
5 | _Static_assert(!EMPTY2("1"), ""); // error
| ^
^ permalink raw reply [flat|nested] 3+ messages in thread* [Bug c/106988] subscripting a string literal is not an integer constant expression but __builtin_strlen is 2022-09-20 20:27 [Bug c/106988] New: subscripting a string literal is not an integer constant expression but __builtin_strlen is msebor at gcc dot gnu.org @ 2022-09-21 0:57 ` pinskia at gcc dot gnu.org 2022-09-22 16:12 ` msebor at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: pinskia at gcc dot gnu.org @ 2022-09-21 0:57 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106988 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |DUPLICATE See Also| |https://gcc.gnu.org/bugzill | |a/show_bug.cgi?id=44094 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- This is an exact dup of bug 89408 and basically the same as PR 44094. *** This bug has been marked as a duplicate of bug 89408 *** ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c/106988] subscripting a string literal is not an integer constant expression but __builtin_strlen is 2022-09-20 20:27 [Bug c/106988] New: subscripting a string literal is not an integer constant expression but __builtin_strlen is msebor at gcc dot gnu.org 2022-09-21 0:57 ` [Bug c/106988] " pinskia at gcc dot gnu.org @ 2022-09-22 16:12 ` msebor at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: msebor at gcc dot gnu.org @ 2022-09-22 16:12 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106988 Martin Sebor <msebor at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|DUPLICATE |--- Status|RESOLVED |UNCONFIRMED Keywords|diagnostic |rejects-valid --- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> --- After experimenting with this some more I think the decision to reject this and the other similar requests should be reconsidered. GCC accepts many equivalent nonconstant expressions in contexts where they are required (see below). Rejecting the simplest of them seems arbitrary and is (as is evident from the duplicate requests) unhelpful to C programmers and surprising those used to the C++ behavior. $ cat a.c && gcc -S -Wall -Wpedantic a.c #include <string.h> _Static_assert (memcmp ("", "", 1) == 0, ""); // okay in C mode only _Static_assert (memchr ("", 0, 1) != 0, ""); // okay in C mode only _Static_assert (strlen ("") == 0, ""); // okay in C and C++ _Static_assert (strcmp ("", "") == 0, ""); // okay in C and C++ _Static_assert ("" == "", ""); // okay in C and C++ _Static_assert (*"" == 0, ""); // error in C only a.c:3:36: warning: expression in static assertion is not an integer constant expression [-Wpedantic] 3 | _Static_assert (memcmp ("", "", 1) == 0, ""); // okay in C mode only | ~~~~~~~~~~~~~~~~~~~^~~~ a.c:4:35: warning: expression in static assertion is not an integer constant expression [-Wpedantic] 4 | _Static_assert (memchr ("", 0, 1) != 0, ""); // okay in C mode only | ~~~~~~~~~~~~~~~~~~^~~~ a.c:5:29: warning: expression in static assertion is not an integer constant expression [-Wpedantic] 5 | _Static_assert (strlen ("") == 0, ""); // okay in C and C++ | ~~~~~~~~~~~~^~~~ a.c:6:33: warning: expression in static assertion is not an integer constant expression [-Wpedantic] 6 | _Static_assert (strcmp ("", "") == 0, ""); // okay in C and C++ | ~~~~~~~~~~~~~~~~^~~~ a.c:7:20: warning: comparison with string literal results in unspecified behavior [-Waddress] 7 | _Static_assert ("" == "", ""); // okay in C and C++ | ^~ a.c:7:20: warning: expression in static assertion is not an integer constant expression [-Wpedantic] 7 | _Static_assert ("" == "", ""); // okay in C and C++ | ~~~^~~~~ a.c:9:21: error: expression in static assertion is not constant 9 | _Static_assert (*"" == 0, ""); // error in C only | ~~~~^~~~ ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-09-22 16:12 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-09-20 20:27 [Bug c/106988] New: subscripting a string literal is not an integer constant expression but __builtin_strlen is msebor at gcc dot gnu.org 2022-09-21 0:57 ` [Bug c/106988] " pinskia at gcc dot gnu.org 2022-09-22 16:12 ` msebor at gcc dot gnu.org
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