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* [Bug c/99950] New: Option -Wchar-subscripts leads to wrong fixes
@ 2021-04-07 6:46 roland.illig at gmx dot de
2021-04-07 7:26 ` [Bug c/99950] " egallager at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: roland.illig at gmx dot de @ 2021-04-07 6:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99950
Bug ID: 99950
Summary: Option -Wchar-subscripts leads to wrong fixes
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: roland.illig at gmx dot de
Target Milestone: ---
When code calls the functions from <ctype.h> with an expression of type 'char',
GCC and Clang warn:
> array subscript has type char
Since the function prototypes expect an 'int', inexperienced programmers cast
the argument to 'int', which silences the warning:
https://github.com/search?q=%22isspace+int%22&type=code
More experienced programmers who heard something about 'unsigned' cast the
argument to 'unsigned int', which silences the warning as well:
https://github.com/search?q=%22isspace+unsigned+int%22&type=code
To get these programmers to fix their code properly, GCC should provide more
guidance in this area. As a quick prototype I implemented a check for these
wrong "fixes" in NetBSD's lint, which results in warnings like these:
warning: argument to 'function from <ctype.h>' must be cast to 'unsigned char',
not to 'int' [342]
The implementation is here, including a test:
https://github.com/NetBSD/src/blob/fdd2c09ca474/usr.bin/xlint/lint1/ckctype.c
https://github.com/NetBSD/src/blob/fdd2c09ca474/tests/usr.bin/xlint/lint1/msg_341.c
https://github.com/NetBSD/src/blob/fdd2c09ca474/tests/usr.bin/xlint/lint1/msg_341.exp
Maybe GCC can implement a similar check to prevent these wrong fixes in the
future.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/99950] Option -Wchar-subscripts leads to wrong fixes
2021-04-07 6:46 [Bug c/99950] New: Option -Wchar-subscripts leads to wrong fixes roland.illig at gmx dot de
@ 2021-04-07 7:26 ` egallager at gcc dot gnu.org
2021-04-07 15:47 ` msebor at gcc dot gnu.org
2022-04-28 11:59 ` [Bug c/99950] Option -Wchar-subscripts leads to wrong fixes when used with functions from <ctype.h> egallager at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: egallager at gcc dot gnu.org @ 2021-04-07 7:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99950
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=94182
Keywords| |diagnostic
CC| |egallager at gcc dot gnu.org
--- Comment #1 from Eric Gallager <egallager at gcc dot gnu.org> ---
related to bug 94182
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/99950] Option -Wchar-subscripts leads to wrong fixes
2021-04-07 6:46 [Bug c/99950] New: Option -Wchar-subscripts leads to wrong fixes roland.illig at gmx dot de
2021-04-07 7:26 ` [Bug c/99950] " egallager at gcc dot gnu.org
@ 2021-04-07 15:47 ` msebor at gcc dot gnu.org
2022-04-28 11:59 ` [Bug c/99950] Option -Wchar-subscripts leads to wrong fixes when used with functions from <ctype.h> egallager at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: msebor at gcc dot gnu.org @ 2021-04-07 15:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99950
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
CC| |msebor at gcc dot gnu.org
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=78155
Last reconfirmed| |2021-04-07
Severity|normal |enhancement
Status|UNCONFIRMED |NEW
--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
Adding a note after the warning suggesting to cast the argument to unsigned
char would help. Enabling the warning also when the char argument is cast to a
wider type might also be worth considering. See also pr78155 for a related
request to enable the warning for calls to the character classification
built-ins.
$ cat pr99950.c && gcc -O2 -S -Wall -Wchar-subscripts pr99950.c
extern int a[255];
int f (char c)
{
return a[c]; // -Wchar-subscripts
}
int g (char c)
{
return a[(int)c]; // same bug, no warning
}
pr99950.c: In function ‘f’:
pr99950.c:5:11: warning: array subscript has type ‘char’ [-Wchar-subscripts]
5 | return a[c]; // -Wchar-subscripts
| ^
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/99950] Option -Wchar-subscripts leads to wrong fixes when used with functions from <ctype.h>
2021-04-07 6:46 [Bug c/99950] New: Option -Wchar-subscripts leads to wrong fixes roland.illig at gmx dot de
2021-04-07 7:26 ` [Bug c/99950] " egallager at gcc dot gnu.org
2021-04-07 15:47 ` msebor at gcc dot gnu.org
@ 2022-04-28 11:59 ` egallager at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: egallager at gcc dot gnu.org @ 2022-04-28 11:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99950
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|Option -Wchar-subscripts |Option -Wchar-subscripts
|leads to wrong fixes |leads to wrong fixes when
| |used with functions from
| |<ctype.h>
--- Comment #3 from Eric Gallager <egallager at gcc dot gnu.org> ---
retitling for searchability purposes
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-04-28 11:59 UTC | newest]
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2021-04-07 6:46 [Bug c/99950] New: Option -Wchar-subscripts leads to wrong fixes roland.illig at gmx dot de
2021-04-07 7:26 ` [Bug c/99950] " egallager at gcc dot gnu.org
2021-04-07 15:47 ` msebor at gcc dot gnu.org
2022-04-28 11:59 ` [Bug c/99950] Option -Wchar-subscripts leads to wrong fixes when used with functions from <ctype.h> egallager at gcc dot gnu.org
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