GCC, C dialects, and srand48

[jbrody2 at umbc dot edu]

I've run in to some interesting things using GCC on a couple of
different solaris machines.  The first machine is a Solaris 2.5 box
running gcc 2.6.3.  The second is a Solaris 2.6 box running gcc
2.8.1.  I've written a program which uses srand48 and drand48; I want
to get the prototypes for these by #including stdlib.h.  stdlib.h has
these prototypes guarded by the following conditions:
 #if defined(__EXTENSIONS__) || \
	 (__STDC__ == 0 && !defined(_POSIX_C_SOURCE)) || \
	 (defined(_XOPEN_SOURCE) && (_XOPEN_VERSION - 0 == 4))

The strange behaviour is this: On the 2.6 machine everything is fine;
I include <stdlib.h> and the protype seems to get read.  On the other
machine, however, the prototype isn't read.  What's even stranger is
that I wrote a test program to see which of the above conditions were
being met on the 2.6 machine:  the answer seems to be none!  Here's
the program:

#include <stdio.h>
#include <stdlib.h>

int main() {
  int i;

#if defined(__EXTENSIONS__)
  printf("extensions\n");
#endif

#if defined(_POSIX_C_SOURCE)
  printf("posix\n");
#endif
  
#if defined(_XOPEN_SOURCE)
  printf("Xopen version %d\n", _XOPEN_VERSION);
#endif

#if (__STDC__ == 0)
  printf("__STDC__ == 0\n");
#endif
  
#if defined(__STDC__)
  printf("STDC = %d\n", __STDC__);
#endif

  srand48(23423);
  for(i=0; i < 10; i++) printf("%g\n", drand48());
}


Here's a test compile and run from the 2.6 machine:
Script started on Tue Aug 31 08:29:43 1999
sunserver1[2] gcc -Wall test3.c
test3.c: In function `main':
test3.c:29: warning: control reaches end of non-void function
sunserver1[3] a.out
STDC = 1
0.973304
0.372346
0.706783
0.764237
0.855564
0.396148
0.337794
0.69388
0.313063
0.610031
sunserver1[4] exit
exit
script done on Tue Aug 31 08:29:58 1999


And here's the output from the 2.5 machine:
Script started on Tue Aug 31 08:29:41 1999
w[345] gcc -Wall test3.c
test3.c: In function `main':
test3.c:27: warning: implicit declaration of function `srand48'
test3.c:28: warning: implicit declaration of function `drand48'
test3.c:28: warning: double format, different type arg (arg 2)
test3.c:29: warning: control reaches end of non-void function
w[346] a.out
STDC = 1
3.33909e-319
2.12203e-314
4.24402e-314
6.36602e-314
8.48802e-314
1.061e-313
1.2732e-313
1.4854e-313
1.6976e-313
1.9098e-313
w[347] exit
script done on Tue Aug 31 08:29:59 1999

Anyone know what's going on???  I'd also be interested if anyone knows
where the numbers produced by the 2.5 machine are coming from - I know
this is probably undefined behaviour - still curious though...