g77 - GNU Project FORTRAN Compiler

Computer History Notes - Herong's Tutorial Notes

∟1957 - FORTRAN Language Developed by IBM

∟g77 - GNU Project FORTRAN Compiler

This section provides a quick introduction of g77, the GNU Project FORTRAN Compiler. A sample session of compilation, linking and executing a FORTRAN 77 program is also provided.

"g77" is a free and open source compiler for FORTRAN 77 language developed by the GNU project. "g77" is actually a front-end program that calls "gcc", the GNU C Compiler to compile FORTRAN 77 programs.

Here is an interesting compilation, linking and execution session of a FORTRAN 77 program using "g77" on a Linux system:

%cat swap.f
      SUBROUTINE SWAP(X, Y, N)
      DIMENSION X(*), Y(*)
      DO 100 I = 1, N
         T = X(I)
         X(I) = Y(I)
         Y(I) = T
  100 CONTINUE
      END

%g77 -c swap.f -o swap.o -v
g77 version 0.5.21
 gcc -c -xf77 swap.f -o swap.o -v
Reading specs from /usr/lib/gcc-lib/i486.../2.7.2.3/specs
gcc version 2.7.2.3
...

%cat test.f
      PROGRAM TEST
      DIMENSION A(10), B(10)
      M = 7
      DO 100 I = 1, M
         A(I) = 10.0 + RAND()
         B(I) = 20.0 + RAND()
  100 CONTINUE
      CALL SWAP(A, B, M)
      DO 200 I = 1, M
         WRITE(6,10) A(I), B(I)
  200 CONTINUE
   10 FORMAT(2F7.2)
      END

%g77 -c testf -o test.o

%g77 test.o swap.o -o test -v
g77 version 0.5.21
 gcc -c -xf77 swap.f -o swap.o -v
...

%./test
  20.54  10.13
  20.58  10.41
  20.96  10.17
  20.29  10.69
  20.11  10.56
  20.71  10.82
  20.48  10.84

Notice that:

The "-v" option tells "g77" to show the "gcc" command line.
The "-c" option tells "g77" to compile the source code only, no linking.
The "-o" option tells "g77" to store output to the specified file.
Actually, compiling and linking of multiple source code files can be in a single command: "g77 test.f swap.f -o test".