Combine Fortran program and C++ program into one

I have created a Visual C++ application (SDI).  I also have a Fortran application (routines) needed to be combine with the Visual C++ application under Visual Studio environment.  Could any one tell me how?  Do I need to compile Fortran routines into libraries in advance? How (by using Visual Studio)?  How do I call those functions in C++?  Thanks.

Richard
cw43Asked:
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hasmetCommented:
in your header file
extern int __stdcall myfunction(int n, double x);


then you compile and make a library of your fortran subroutines,
and link to VC++ project. then
use myfunction() in your cpp file
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cw43Author Commented:
In Fortran, function arguments are actually passed by reference.  So even when I call my Fortran subroutines in C++, which function takes variables in Fortran, should I pass pointers instead variables in my cpp file?  Also, how to make libraries of  Fortran subroutines in Visual Studio on Win95?  

Thanks.
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hasmetCommented:
you need a fortran compiler to create your library, can not use VC++
/*     File CMAIN.C   */

#include <stdio.h>

extern int __stdcall FACT (int n);
extern void __stdcall PYTHAGORAS (float a, float b, float *c);

main()
{
    float c;
    printf("Factorial of 7 is: %d\n", FACT(7));
    PYTHAGORAS (30, 40, &c);
    printf("Hypotenuse if sides 30, 40 is: %f\n", c);
}

C    File FORSUBS.FOR  "this is your fortran file, use fortran compiler to C  create library for this
C
      INTEGER*4 FUNCTION Fact (n)
      INTEGER*4 n [VALUE]
      INTEGER*4 i, amt
      amt = 1
      DO i = 1, n
        amt = amt * i
      END DO
      Fact = amt
      END

      SUBROUTINE Pythagoras (a, b, c)
      REAL*4 a [VALUE]
      REAL*4 b [VALUE]
      REAL*4 c [REFERENCE]  
      c = SQRT (a * a + b * b)
      END

as you see, you can specify value or reference
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cw43Author Commented:
I have compiled my Fortran code into a static libraty by using Digital Visual Fortran compiler, and called it in my C++ code like: extern void __stdcall myfunction().  Of course, I have linked the library in my Visual C++ 5.0 project.  However, it does not work.  The compiler complained about the unsolved external function.  What happened?
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hasmetCommented:
some fortran compilers are not creating compatible libs (such as watcom)
but digital visual fortran does create compatible one.

two if your fortran code doesnot specifically says [VALUE]
 the default is by reference so
extern void __stdcall PYTHAGORAS (float *a, floa t * b, float *c);

but above is for .c files, so if you are doing cpp project (C++ BUT NOT C)
then
extern "C" { void __stdcall PYTHAGORAS (float *a, floa t * b, float *c);}
 to say this is  C in C++

SO ABOVE ARE THREE problems you may have, other than these
it should run smoothly

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