> From: Akim Demaille <[EMAIL PROTECTED]>
> Date: 08 Dec 2000 14:34:35 +0100
>
> | #include <assert.h>
> | /* Override any gcc2 internal prototype to avoid an error. */
> | #ifdef __cplusplus
> | extern "C"
> | #endif
> | /* We use char because int might match the return type of a gcc2
> | builtin and then its argument prototype would still apply. */
> | char mkdir ();
> | char (*f) ();
>
> BTW, I never quite understood this comment. Could someone explain it
> to me?
> first prototype it sees is compatible?
This comment highlights a confusing botch in autoconf.
Here's an example of the problem. Consider the following C program,
generated by AC_TRY_LINK_FUNC(abs):
int abs ();
main () { return abs (); }
This program does not conform to the C standard, as the C standard
does not let you redefine builtin C functions. So GCC warns about it.
To disable this warning, AC_TRY_LINK_FUNC does this instead:
char abs ();
int main () { return abs (); }
This program doesn't conform to the C standard, either! But GCC does
not warn about it so it's good enough for GCC users.
The real problem is that the autoconf AC_TRY_LINK_FUNC macro is
unportable, and is using the wrong assumptions. There is no reliable
way in general to see whether you can link a C function without
knowing the function's prototype. AC_TRY_LINK_FUNC is a hack that
sort of works, most of the time, but does not work in general.
AC_CHECK_FUNC, AC_TRY_LINK_FUNC, etc. should have arguments specifying
the function prototype, and should generate output that looks like
this instead:
... define PROTO in the usual way ...
int abs PROTO ((int));
int (*p) PROTO ((int)) = abs;
It's too late to fix this now for the next autoconf release, but
this problem will fester until fixed.
> Am I understanding that if __stub_foo exists, it means that foo
> doesn't really exist?
No, it means that foo exists, but if invoked foo will always fail with
ENOSYS.
