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1.1     ! root        1: .TI F77/LINK_TO_C "Sep. 4, 1985"
        !             2: Linking to C Procedures
        !             3: 
        !             4: C is a commonly used programming language in UNIX.  "A Portable
        !             5: Fortran 77 Compiler" gives complete specification of the C/Fortran
        !             6: interface.  This help file summarizes the basics for simple cases and
        !             7: gives a simple example.
        !             8: 
        !             9: The following table from that paper lists corresponding Fortran and C 
        !            10: declarations:
        !            11: 
        !            12: .nf
        !            13:        Fortran                 C
        !            14:        -----------             ---------
        !            15:        integer*2 x             short int x;
        !            16:        integer x               long int x;
        !            17:        logical x               long int x;
        !            18:        real x                  float x;
        !            19:        double precision x      double x;
        !            20:        complex x               struct { float r, i; } x;
        !            21:        double complex x        struct { double dr, di; } x;
        !            22:        character*6 x           char x[6];
        !            23: .fi
        !            24: 
        !            25: 
        !            26: The following Fortran statements calls a procedure fill() that
        !            27: sets the first 10 elements of ix() to the value 20:
        !            28: 
        !            29: .nf
        !            30:                integer ix(100)
        !            31:        c
        !            32:                call fill(ix, 10,  20)
        !            33: .fi
        !            34: 
        !            35: In creating external symbols for subprogram and common block names,
        !            36: f77 adds an underscore before and after external names,
        !            37: while the C compiler only adds an underscore before the name.
        !            38: Thus the C name fill_() corresponds to the f77 name fill();
        !            39: and the corresponding C procedure is:
        !            40: 
        !            41: .nf
        !            42:        fill_( vec, nvec, val)
        !            43:        long *vec, *nvec, *val;
        !            44:        {
        !            45:                long nv = *nvec;
        !            46:        
        !            47:                while (nv-- > 0) *vec++ = *val;
        !            48:        }
        !            49: .fi
        !            50: 
        !            51: Since Fortran passes variables by address, the C procedure treats the
        !            52: parameters as pointers.  This also means that a temporary must be used.
        !            53: If a temporary is not used, as in:
        !            54: 
        !            55:        while ((*nvec)-- > 0) *vec++ = *val;
        !            56: 
        !            57: the value of the third parameter in the call would be destroyed.
        !            58: 
        !            59: When mixing C and Fortran, if I/O is done in both languages and
        !            60: the main program is in C, then call 'f_init()' in the
        !            61: Fortran I/O library to initialize units 0, 5, and 6 to standard error,
        !            62: standard input and standard output and to line-buffer standard error.
        !            63: 
        !            64: C stores arrays in row-major order with subscripts starting at 0
        !            65: while Fortran stores arrays in column-major order with subscripts
        !            66: starting (by default) at 1.

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