How can I check if a function exists in waf?

[Sebastian Huber]

----- Am 2. Feb 2019 um 2:07 schrieb Chris Johns chrisj at rtems.org:

> On 1/2/19 8:19 pm, Sebastian Huber wrote:
>> 
>> So, there is no standard compile and link test for functions? If I use this
>> 
>>     conf.check_cc(fragment = 'int main(void) { strnlen("", 0); return 0; }',
>>                   header_name="string.h", features = 'c', mandatory = False)
>> 
>> waf outputs
>> 
>> Checking for header string.h                  : yes
>> 
>> I don't want to test for string.h, I want to test for strnlen(). In config.log
>> we have:
>> 
>> ---------------------------------------------
>> Checking for header string.h
>> ==>
>> int main(void) { strnlen("", 0); return 0; }
>> <==
>> [1/1] Compiling [32mbuild/.conf_check_6da1e91772980301eb2528a1d150a7ab/test.c[0m
>> 
>> ['/usr/bin/gcc', '../test.c', '-c',
>> '-o/scratch/git-rtems-tools/build/.conf_check_6da1e91772980301eb2528a1d150a7ab/testbuild/test.c.1.o']
>> 
>> err: ../test.c: In function ‘main’:
>> ../test.c:1:18: warning: implicit declaration of function ‘strnlen’
>> [-Wimplicit-function-declaration]
>>  int main(void) { strnlen("", 0); return 0; }
>>                   ^~~~~~~
>> 
>> yes
>> ---------------------------------------------
>> 
>> So, this test uses already quite some code and still is basically useless.
> 
> You have a powerful language available. I would create a function to handle
> repeated checks, for example:
> 
> https://git.rtems.org/chrisj/rtems_waf.git/tree/rtems.py?h=libbsd-libdl#n270
> 
> I think having the ability to perform checks for an RTEMS application highlights
> the power available.

Yes, I don't doubt that you can do a lot of things with Python, but it was a bit surprising to me that I have to write custom code for things which are covered by basic Autoconf macros and only because Microsoft is not able to ship an operating system with a strnlen() function.