environ (GNU Gnulib)

Gnulib module: environ

Portability problems fixed by Gnulib:

POSIX does not require this variable to be declared, and it is indeed not declared on some platforms: macOS 14, FreeBSD 14.0, NetBSD 5.0, OpenBSD 3.8, Solaris 11.4.
On macOS, this variable is not declared. Up to Mac OS X 10.4, one can use
```
extern char **environ;
```
to get the variable declared. This does not work any more, however, in shared libraries on macOS 10.5. Here is a workaround: Instead, one can use
```
#include <crt_externs.h>
#define environ (*_NSGetEnviron())
```
This works at all versions of macOS.
On Cygwin in 64-bit mode, references to this variable cause a link error when the option -Wl,--disable-auto-import is in use.

Portability problems not fixed by Gnulib:

The address of this variable is not a compile-time constant on some platforms: mingw.
Assigning NULL to environ to clear all variables is not portable; better is to assign environ to one-element array containing a NULL pointer. That said, an empty environment is not portable either, as some systems may require particular environment variables (such as PATH) to be present in order to operate consistently.