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Re: environ on MacOS X
From: |
Bruno Haible |
Subject: |
Re: environ on MacOS X |
Date: |
Sun, 24 Feb 2008 17:20:40 +0100 |
User-agent: |
KMail/1.5.4 |
Peter O'Gorman wrote:
> crt_externs.h and _NSGetEnviron works on all released versions of Mac OS X.
Thanks for this info. I'm updating the doc (see below).
> 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.
Well, there must be something different between MacOS X 10.[34] and 10.5.
The cited references mention a problem that cropped up with 10.5, not
earlier.
Attached you find the test script that I used to verify that both declarations
work on 10.3. (I cannot test 10.4 or 10.5.)
Bruno
--- doc/posix-functions/environ.texi.orig 2008-02-24 17:13:56.000000000
+0100
+++ doc/posix-functions/environ.texi 2008-02-24 17:13:47.000000000 +0100
@@ -23,7 +23,7 @@
#include <crt_externs.h>
#define environ (*_NSGetEnviron())
@end smallexample
-This works at least on MacOS X 10.3 and newer.
+This works at all versions of MacOS X.
@end itemize
Portability problems not fixed by Gnulib:
================================ fooshared.c ==================
#if 0
extern char **environ;
#else
#include <crt_externs.h>
#define environ (*_NSGetEnviron())
#endif
char *** environ_addr (void) { return &environ; }
===============================================================
================================= foo.c =======================
#include <stdio.h>
#include <unistd.h>
extern char ***environ_addr (void);
int main ()
{
printf ("%p\n", environ_addr());
{
char **env = *environ_addr();
if (env == NULL)
printf("env = NULL\n");
else {
char *s;
for (; (s = *env) && *s; env++)
printf ("%s\n", s);
}
}
return 0;
}
================================================================
$ libtool --mode=compile gcc -c fooshared.c
$ libtool --mode=link gcc -o libfoo.la fooshared.lo
$ gcc -c foo.c
$ libtool --mode=link gcc -o a.out foo.o libfoo.la
$ ./a.out