environ
=======

POSIX specification:
 https://pubs.opengroup.org/onlinepubs/9699919799/functions/environ.html

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 11.1, FreeBSD 14.0, NetBSD 5.0, OpenBSD 3.8, IRIX 6.5, 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 11.1.  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.