gnulib/doc/posix-functions/environ.texi

@node environ
@section @code{environ}
@findex environ

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9699919799/functions/environ.html}

Gnulib module: environ

Portability problems fixed by Gnulib:
@itemize
@item
POSIX does not require this variable to be declared, and it is indeed not
declared on some platforms:
Mac OS X 10.5, FreeBSD 6.0, NetBSD 5.0, OpenBSD 3.8, IRIX 6.5, Solaris 11.4.
@item
On Mac OS X 10, this variable is not declared.  Up to Mac OS X 10.4, one can use
@smallexample
extern char **environ;
@end smallexample
to get the variable declared.  This does not work any more, however, in
shared libraries on Mac OS X 10.5.  Here is a workaround: Instead, one can use
@smallexample
#include <crt_externs.h>
#define environ (*_NSGetEnviron())
@end smallexample
This works at all versions of Mac OS X.
@item
On Cygwin in 64-bit mode, references to this variable cause a link error when
the option @code{-Wl,--disable-auto-import} is in use.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
The address of this variable is not a compile-time constant on some platforms:
mingw.
@item
Assigning NULL to @code{environ} to clear all variables is not
portable; better is to assign @code{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 @code{PATH}) to be present in order to operate
consistently.
@end itemize