gcc and GCVT(3)

[d3vv]

Code example:

#include <stdlib.h>

void main()
{
	char buf[50];
	char * str = gcvt(3.141592653589793238462643383279502884197169399375, 49, buf);
}

And we have:

$ gcc msys2_err.c
msys2_err.c: In function ‘main’:
msys2_err.c:6:15: warning: implicit declaration of function ‘gcvt’ [-Wimplicit-function-declaration]
    6 |  char * str = gcvt(3.141592653589793238462643383279502884197169399375, 49, buf);
      |               ^~~~
msys2_err.c:6:15: warning: initialization of ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]

1. Why we have "implicit declaration of function"? If from:

MSVC: https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/gcvt?view=vs-2019
Linux man: http://man7.org/linux/man-pages/man3/gcvt.3.html
And from IBM: https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.bpxbd00/rgcvt.htm

gcvt must be into stdlib.h as well!

2. Why we have "incompatible integer to pointer conversion"? If declaration from all standards looks like:

char *gcvt(double number, int ndigit, char *buf);

And where is the "int" here? What include must be into MSYS2 for gcvt?

[d3vv]

I post all found issues here:

https://cygwin.com/ml/cygwin/2019-08/msg00030.html

but mys post to mail-list looks like not readable :(((