what does -Wimplicit-function-declaration mean?

Andrew Udvare audvare at gmail.com
Sat Oct 29 20:21:47 UTC 2022

On 29/10/2022 13:05, Murray Eisenberg wrote:
> During successful reinstall of a number of ports (under Ventura), I see 
> message:
> Warning: Configuration logfiles contain indications of 
> -Wimplicit-function-declaration; check that features were not 
> accidentally disabled:
> and then a list of what would appear to be cariou variables found in the 
> config.log.
> What is that all about?


You should file tickets about the packages especially if functionality 
gets disabled unexpectedly.

The flag is for a compiler like GCC or Clang to warn when a function is 
being used from its declaration, usually caused by not including the 
correct header. You can call printf() in GCC/Clang without #include-ing 
<stdio.h> but this is not standard.

Apple has made implicit declarations as of Xcode 12 Clang to be an 
error. So if something were to test for a function without including the 
correct header, it could fail and disable functionality. The port might 
still build.
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