support gmtime_r, timegm functions on windows mingw32

Question

I am trying to build legacy C program under Windows using mingw32 port. But gcc compiller informs me about next errors:

gmtime_r(const time_t*, struct tm*); //implicit declaration of function 
timegm(struct tm*); //implicit declaration of function 

I tried to declare _mkgmtime as suggested here but then I get the same error about declaration. I also tried to declare gmtime_r based on gmtime_s as descibed here but is seems that mingw does not support gmtime_s as well.

Is there any idea? Might need to replace them to some equivalents?

mingw-32 gcc 5.3.0-3 windows 7

Answer 1

It's 2022 and the problem persists with GCC-10/MinGW64.

The solution is to define _POSIX_C_SOURCE which enables gmtime_r .

On command line:

x86_64-w64-mingw32-gcc -D_POSIX_C_SOURCE

autoconf/make:

CFLAGS=-D_POSIX_C_SOURCE

cmake:

add_compile_definitions(_POSIX_C_SOURCE)