Re: [PATCH] build: avoid printf format mismatch warnings

[Jim Meyering]

Joel E. Denny wrote:
> On Tue, 29 Sep 2009, Jim Meyering wrote:
>> I tried to bootstrap/build "master" today, without
>> success, so switched to branch-2.5.  There, ./bootstrap
>> succeeded, but the build failed with two like this:
>>
>>   Sbitset.c: In function 'Sbitset__fprint':
>>   Sbitset.c:75: error: format '%d' expects type 'int', but argument 3
>>     has type 'Sbitset__Index
>
> Thanks for the report.  I'm not seeing those failures with either gcc
> 4.2.4 or 4.3.4.  Which gcc are you using?

Hi Joel,

I'm using the stock gcc on an up-to-date Fedora 11 system:

  gcc version 4.4.1 20090725 (Red Hat 4.4.1-2) (GCC)

>> With the change below, the build and "make check" succeeded.
...
>> -      fprintf (file, " %d", i);
>> +      fprintf (file, " %d", (int) i);
>>      }
>>    fprintf (file, " }");
>>  }
>
> Because Sbitset__index is a size_t, wouldn't the following patch be
> better?
>
>>From 47eced3099712180364f4e01b839242027d9a9d8 Mon Sep 17 00:00:00 2001
> From: Joel E. Denny <address@hidden>
> Date: Tue, 29 Sep 2009 06:54:38 -0400
> Subject: [PATCH] Use the correct conversion specifier for size_t.
>
> Reported by Jim Meyering.
> * src/Sbitset.h (SBITSET__INDEX__CONVERSION_SPEC): New, "zu"
> because Sbitset__Index is size_t.
> * src/Sbitset.c (Sbitset__fprint): Use it instead of %d.
...
> -      fprintf (file, " %d", i);
> +      fprintf (file, " %" SBITSET__INDEX__CONVERSION_SPEC, i);
...
> +#define SBITSET__INDEX__CONVERSION_SPEC "zu"

I didn't know (and didn't dig) if it could be negative,
presumed that the author chose %d for a good reason,
and took the quick and dirty add-cast approach.

I'm glad there was a better say.