Symbol visibility problems with -std=

[Marco Atzeri]

Am 13.05.2020 um 12:21 schrieb Pavel Fedin via Cygwin:
>   Hello everyone!
> 
>   While compiling various software packages for Cygwin i notice that very often i have to add something like #define _GNU_SOURCE to
> them in order to compile correctly. Meanwhile on Linux they compile with no problems at all. I've narrowed it down to -std=???
> option using a simple test case:
> --- cut test.cpp ---
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> 
> int main(void)
> {
>          char *p = strdup("hello");
> 
>          printf("%s\n", p);
>          free(p);
>          return 0;
> }
> --- cut test.cpp ---
> 
> $ g++ test.cpp -o test - compiles OK
> $ g++ test.cpp -o test -std=c++14 - error: 'strdup' was not declared in this scope; did you mean 'strcmp'?
> 
>   By printing out predefined macros (-dM -E) i found out that -std=something option adds " #define __STRICT_ANSI__ 1" to builtin
> macros, but removes all *_SOURCE definitions, so _DEFAULT_SOURCE is not triggered any more.
>   I've compared the behavior with Linux system. On Linux -std=c++14 also defines __STRICT_ANSI__, but various *_SOURCE macros are not
> omitted.
>   Isn't this a Cygwin bug? By the way, clang does not suffer from this problem.
> 
> Kind regards,
> Pavel Fedin


strdup is an extension of C standard

so strictly behaviour of Cgywin is correct, see

  /usr/include/sys/features.h

for details