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Groups > comp.lang.c > #107810
| From | David Brown <david.brown@hesbynett.no> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: How to fix: [-Wformat-nonliteral] |
| Date | 2017-04-07 13:35 +0200 |
| Organization | A noiseless patient Spider |
| Message-ID | <oc7tcd$vi2$1@dont-email.me> (permalink) |
| References | <oc7g6c$lpq$1@dont-email.me> <oc7nm7$d6i$1@dont-email.me> <87shlkv6om.fsf@bsb.me.uk> |
On 07/04/17 12:43, Ben Bacarisse wrote:
> David Brown <david.brown@hesbynett.no> writes:
>
>> On 07/04/17 09:50, MehdiAmini wrote:
> <snip>
>>> vfprintf(stderr,s,args);
> <snip>
>>> I get:
>>> warning: format string is not a string literal [-Wformat-nonliteral]
>>> vfprintf(stderr,s,args);
> <snip>
>
>> Another poster showed you how to disable the warning.
> <snip>
>> So it would be /much/ safer to have the function as:
>>
>> noreturn void my_err_s(const char * const s)
>> {
>> if ((s == NULL) || (*s == '\0')) {
>> fprintf(stderr, "Please provide a proper message for "
>> "my_err function.\n");
>> exit(EXIT_FAILURE);
>> }
>> fprintf(stderr, "%s\n", s);
>> exit(EXIT_FAILURE);
>> }
>>
>> #define my_errPrintfBuffLen 256
>> #define my_err(f, x...) \
>> do { \
>> char buff[my_errPrintfBuffLen]; \
>> snprintf(buff, sizeof(buff) - 1, f, ## x); \
>> buff[my_errPrintfBuffLen - 1] = 0; \
>> my_err_s(buff); \
>> } while (0)
>>
>> This makes any formatting be handled locally in the function that calls
>> my_err, where the compiler can see the format string as a literal and
>> check the format against the actual parameters used. (There is, IIRC, a
>> slight gcc'ism in the token pasting here to get the commas right even if
>> my_err is called with no extra parameters. But I expect clang supports
>> the same feature.)
>
> There are two GNUisms -- one is the comma pasting trick to handle zero
> variable arguments, and the other is naming the variable arguments as x.
>
> In fact, you don't need either as there is always one required
> argument. This is standard C99 and up:
>
> #define my_err(...) \
> do { \
> char buff[my_errPrintfBuffLen]; \
> snprintf(buff, sizeof(buff) - 1, __VA_ARGS__); \
> buff[my_errPrintfBuffLen - 1] = 0; \
> my_err_s(buff); \
> } while (0)
>
Good point. The macro was a modified copy of something from my own
code, which in this case already has plenty of GNUisms - a couple more
won't affect portability! And while the OP here is using clang, which I
believe supports these extensions, removing them makes the code more
portable for other people.
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How to fix: [-Wformat-nonliteral] MehdiAmini <atorrses@gmail.com> - 2017-04-07 12:20 +0430
Re: How to fix: [-Wformat-nonliteral] Barry Schwarz <schwarzb@dqel.com> - 2017-04-07 01:28 -0700
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-07 11:58 +0200
Re: How to fix: [-Wformat-nonliteral] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-04-07 11:43 +0100
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-07 13:35 +0200
Re: How to fix: [-Wformat-nonliteral] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-04-07 13:50 +0100
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-07 15:54 +0200
Re: How to fix: [-Wformat-nonliteral] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-04-07 19:35 +0100
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-08 13:41 +0200
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-10 13:52 -0700
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-11 00:18 +0200
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-10 15:43 -0700
Re: How to fix: [-Wformat-nonliteral] Keith Thompson <kst-u@mib.org> - 2017-04-10 16:10 -0700
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-10 16:26 -0700
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-11 11:33 +0200
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-11 08:37 -0700
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-13 00:20 +0200
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-12 15:55 -0700
Re: How to fix: [-Wformat-nonliteral] Keith Thompson <kst-u@mib.org> - 2017-04-12 18:17 -0700
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-14 12:27 +0200
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-14 11:57 -0700
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-17 18:08 +0200
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-17 09:38 -0700
Re: How to fix: [-Wformat-nonliteral] Keith Thompson <kst-u@mib.org> - 2017-04-12 18:13 -0700
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-13 07:37 -0700
Re: How to fix: [-Wformat-nonliteral] Keith Thompson <kst-u@mib.org> - 2017-04-13 08:43 -0700
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-13 11:24 -0700
Re: How to fix: [-Wformat-nonliteral] Keith Thompson <kst-u@mib.org> - 2017-04-13 11:49 -0700
Re: How to fix: [-Wformat-nonliteral] Robert Wessel <robertwessel2@yahoo.com> - 2017-04-13 14:43 -0500
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-13 13:26 -0700
Re: How to fix: [-Wformat-nonliteral] Keith Thompson <kst-u@mib.org> - 2017-04-13 13:32 -0700
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-13 14:27 -0700
Re: How to fix: [-Wformat-nonliteral] Robert Wessel <robertwessel2@yahoo.com> - 2017-04-13 17:39 -0500
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-13 16:16 -0700
Re: How to fix: [-Wformat-nonliteral] Tim Rentsch <txr@alumni.caltech.edu> - 2017-04-16 17:53 -0700
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-13 13:19 -0700
Re: How to fix: [-Wformat-nonliteral] Tim Rentsch <txr@alumni.caltech.edu> - 2017-04-16 17:49 -0700
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-17 18:14 +0200
Re: How to fix: [-Wformat-nonliteral] Keith Thompson <kst-u@mib.org> - 2017-04-17 11:54 -0700
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-17 22:41 +0200
Re: How to fix: [-Wformat-nonliteral] Keith Thompson <kst-u@mib.org> - 2017-04-17 15:02 -0700
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-14 12:40 +0200
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-14 12:10 -0700
Re: How to fix: [-Wformat-nonliteral] Keith Thompson <kst-u@mib.org> - 2017-04-14 13:22 -0700
Re: How to fix: [-Wformat-nonliteral] supercat@casperkitty.com - 2017-04-14 17:14 -0700
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-13 00:20 +0200
Re: How to fix: [-Wformat-nonliteral] MehdiAmini <atorrses@gmail.com> - 2017-04-07 20:29 +0430
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-07 18:42 +0200
Re: How to fix: [-Wformat-nonliteral] MehdiAmini <atorrses@gmail.com> - 2017-04-08 08:04 +0430
Re: How to fix: [-Wformat-nonliteral] Richard Heathfield <rjh@cpax.org.uk> - 2017-04-08 07:51 +0100
Re: How to fix: [-Wformat-nonliteral] MehdiAmini <atorrses@gmail.com> - 2017-04-08 12:11 +0430
Re: How to fix: [-Wformat-nonliteral] Richard Heathfield <rjh@cpax.org.uk> - 2017-04-08 11:38 +0100
Re: How to fix: [-Wformat-nonliteral] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-04-08 18:52 +0100
Re: How to fix: [-Wformat-nonliteral] David Brown <david.brown@hesbynett.no> - 2017-04-08 13:48 +0200
Re: How to fix: [-Wformat-nonliteral] MehdiAmini <atorrses@gmail.com> - 2017-04-08 20:34 +0430
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