[FFmpeg-devel] [PATCH] checkasm: Silence warnings about unused return value from read()

[Martin Storsjö]

On Fri, 5 Aug 2022, Martin Storsjö wrote:

> On Wed, 27 Jul 2022, Andreas Rheinhardt wrote:
>
>> Swinney, Jonathan:
>>> This patch looks good to me. I would appreciate its merging.
>>> 
>
>>  } while (0)
>>  #define PERF_STOP(t) do {                               \
>> +    int ret;                                            \
>>      ioctl(sysfd, PERF_EVENT_IOC_DISABLE, 0);            \
>> -    read(sysfd, &t, sizeof(t));                         \
>> +    ret = read(sysfd, &t, sizeof(t));                   \
>> +    (void)ret;                                          \
>>  } while (0)
>
>> Why do you use this extra variable instead of just casting the return
>> value of read to void?
>
> Because if I just cast the return value of read to void, it still warns about 
> it being unused, at least with GCC 9. I believe the rules for "used vs 
> unused" for variables (where you can cast it to void to mark it as used) and 
> "must not ignore return value" (-Wunused-result) differ. Apparently, in order 
> to appease the compiler for a return value to not be ignored, it either has 
> to be stored or compared.

Pushed this now.

// Martin