The code is very easy. I'm trying to call a fortran function from C.

The code is as follow:

=========C code=========
#include "stdio.h"

extern float r_ (int * d, float *b);

main ()
{
     float a = 1.5, b = 1.05, c = 1;
     int d = 2;
     c = r_ (&d, &b);
     printf ("%f\n", c);

      print *, m, t
      r = 0.1*t+46
      print *, r

      return
      end
================================

It doesn't matter what the fortran code does...but when I compile it
with g77, the result can't be passed back to the C code, but with
gfortran, it can. Here are the outputs:

***fortran code compiled by gfortran****
[du@brutus qr]$ gfortran -funroll-all-loops -O3 -c ceiling.f -o
ceiling.o;gcc -funroll-all-loops -O3 -c testint.c -o testint.o;g77 -o
testint.x testint.o ceiling.o -L/pkgs/intel/mkl/9.0/lib/em64t -L/home/
du/lib/hpl/lib/LINUX_XEON_QUAD -L/usr/lib/gcc/x86_64-redhat-linux/
3.4.6/ -L/usr/lib/gcc/x86_64-redhat-linux/4.1.1 -L. -lgfortran

[du@brutus qr]$ ./testint.x
           2   1.050000
   46.10500   <----------- result in Fortran function
46.105000  <--------- result received by C code

***fortran code compiled by g77****
[du@brutus qr]$ g77 -funroll-all-loops -O3 -c ceiling.f -o
ceiling.o;gcc -funroll-all-loops -O3 -c testint.c -o testint.o;g77 -o
testint.x testint.o ceiling.o -L/pkgs/intel/mkl/9.0/lib/em64t -L/home/
du/lib/hpl/lib/LINUX_XEON_QUAD -L/usr/lib/gcc/x86_64-redhat-linux/
3.4.6/ -L/usr/lib/gcc/x86_64-redhat-linux/4.1.1 -L. -lgfortran
[du@brutus qr]$ ./testint.x
 2  1.04999995
  46.1049995
-0.000000 <----------- but here I get 0, with the only difference in
the way the fortran code is compiled.

Here are the versions:
[du@brutus qr]$ g77 -v
Reading specs from /usr/lib/gcc/x86_64-redhat-linux/3.4.6/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --
infodir=/usr/share/info --enable-shared --enable-threads=posix --
disable-checking --with-system-zlib --enable-__cxa_atexit --disable-
libunwind-exceptions --enable-languages=c,c++,f77 --disable-libgcj --
host=x86_64-redhat-linux
Thread model: posix
gcc version 3.4.6 20060404 (Red Hat 3.4.6-4)

[du@brutus qr]$ gfortran -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --
infodir=/usr/share/info --enable-shared --enable-threads=posix --
enable-checking=release --with-system-zlib --enable-__cxa_atexit --
disable-libunwind-exceptions --enable-libgcj-multifile --enable-
languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --
disable-dssi --enable-plugin --with-java-home=/usr/lib/jvm/java-1.4.2-
gcj-1.4.2.0/jre --with-cpu=generic --host=x86_64-redhat-linux
Thread model: posix
gcc version 4.1.2 20070626 (Red Hat 4.1.2-13)

[du@brutus qr]$ gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --
infodir=/usr/share/info --enable-shared --enable-threads=posix --
enable-checking=release --with-system-zlib --enable-__cxa_atexit --
disable-libunwind-exceptions --enable-libgcj-multifile --enable-
languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --
disable-dssi --enable-plugin --with-java-home=/usr/lib/jvm/java-1.4.2-
gcj-1.4.2.0/jre --with-cpu=generic --host=x86_64-redhat-linux
Thread model: posix
gcc version 4.1.2 20070626 (Red Hat 4.1.2-13)