What's the best way to fix warnings from unused result

Fred Wright fw at fwright.net
Sun Apr 7 17:19:47 UTC 2019

On Sun, 7 Apr 2019, Eric S. Raymond via devel wrote:
> Hal Murray via devel <devel at ntpsec.org>:
>> ../../ntpd/nts.c:213:9: warning: ignoring return value of ???strerror_r???,
>> declared with attribute warn_unused_result [-Wunused-result]
>> I'm only getting this on Ubuntu, so a secondary question is why isn't that
>> check happening on other systems?
> Probablty compiler version. As GCC has evolved it has gotten stricter
> about this sort of thing.
>>> From the man page:
>>        int strerror_r(int errnum, char *buf, size_t buflen);
>>                    /* XSI-compliant */
>>        char *strerror_r(int errnum, char *buf, size_t buflen);
>>                    /* GNU-specific */
>> I don't know or care which version we get.  It's different on different
>> systems, so to save the result then say UNUSED_LOCAL gets slightly complicated.
> This is probably what you want:
> ./include/ntp_stdlib.h:162:#define IGNORE(r) do{if(r){}}while(0)

Does a simple void cast work?  E.g.:

 	(void) strerror_r(...)

It certainly works for unused function arguments, and it's an actual 
official language feature for explicitly discarding results.  Granted, I 
know of one compiler that doesn't like it, but it's an oddball.

Fred Wright

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