Re: environ on MacOS X

[Peter O'Gorman]

Bruno Haible wrote:

> 
> 2008-02-24  Bruno Haible  <address@hidden>
> 
>       * doc/posix-functions/environ.texi: Document the MacOS X problem.
> 
> *** doc/posix-functions/environ.texi.orig     2008-02-24 15:26:50.000000000 
> +0100
> --- doc/posix-functions/environ.texi  2008-02-24 15:25:16.000000000 +0100
> ***************
> *** 16,21 ****
> --- 16,33 ----
>   This variable is missing on some platforms:
>   MacOS X 10.3, FreeBSD 6.0, NetBSD 3.0, OpenBSD 3.8, IRIX 6.5, OSF/1 5.1, 
> Cygwin.
>   @item
> + On MacOS X 10, this variable is not declared.  Up to MacOS 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 MacOS X 10.5.  Here is a workaround: Instead, one can 
> use
> + @smallexample
> + #include <crt_externs.h>
> + #define environ (*_NSGetEnviron())
> + @end smallexample
> + This works at least on MacOS X 10.3 and newer.


Hi Bruno,

crt_externs.h and _NSGetEnviron works on all released versions of Mac OS X.

The environ symbol is available to every application, it is in the c
startup object crt1.o (on 10.5 crt1.10.5.o), but the static linker, when
set to not allow any undefined symbols (the default) does not know about
it when creating a shared library (because crt1.0 is only added when
creating an executable), so linking will fail with undefined references
to _environ in that case.

A library which allows undefined symbols (the GNU libtool default) will
not see this problem.

Thanks for writing this up, it is good to have the crt_externs.h
solution in the docs.

Peter
-- 
Peter O'Gorman
http://pogma.com