Lesson of 18 February 2011

Example of linking with foreign language (and decoration)

A Fortran routine making simple addition

File add.f

	subroutine add( a, b, c )
	real*8 a(*), b(*), c(*)
	do i=1,3
	  c(i) = a(i) + b(i)
	end do
	return
	end

A simple C++ code with use external routine

File testDecoration.cc

// to compile on unix/OSX use
// g++ -c testDecoration.cc (for generation of testDecoration.o)
// g95 -c add.f             (for generation of test.o a fortran routine)
// g++ testDecoration.o add.o -o test
// ./test (to run)
//

#include <iostream>

using namespace std ;

typedef struct {
  double x, y, z ;
} Point3D ;

// routine 1
void
add( Point3D const * const a,  // pointer to a structure, pointer non modificable
     Point3D const * const b,
     Point3D       * const c ) {
  c -> x = a -> x + b -> x ;
  c -> y = a -> y + b -> y ;
  c -> z = a -> z + b -> z ;
}

// routine 2
void
add( Point3D const & a,
     Point3D const & b,
     Point3D       & c ) {
  c.x = a.x + b.x ;
  c.y = a.y + b.y ;
  c.z = a.z + b.z ;
}

#define F77NAME(A) A##_

// routine 3
// make a prototype of the external routine
extern "C" void F77NAME(add)( double * a, double * b, double * c ) ;

int
main( int argc, char const * argv []) {
  double a[3] = {1,2,3} ;
  double b[3] = {3,4,5} ;
  double c[3] ;
  
  F77NAME(add)( a, b, c ) ; // only routine 3 match the prototype
  
  cout << "c = [ " << c[0] << ", " << c[1] << ", " << c[2] << " ]\n" ;  

  return 0 ;
}

The C decoration A simple code which use an external printOnTerminal C routine

File testDecoration2.cc

// to compile on unix/OSX use
// g++ -c testDecoration2.cc testDecoration2b.c -o test (for generation of testDecoration.o)
// ./test (to run)
//

#include <iostream>

using namespace std ;

// declare a prototype for a C++ routine
void printOnTerminal( char const msg[] ) ;

int
main( int argc, char const * argv []) {
  char theMessage[] = "Ciao Mamma!\n" ;
  printOnTerminal( theMessage ) ;
  return 0 ;
}

A C code which define _Z15printOnTerminalPKc. The code link (on GNU compiler) because the name fit the decoration of C++:

File testDecoration2b.c

// to compile on unix/OSX use
// g++ -c testDecoration2.cc
// gcc -c testDecoration2b.c
// g++ testDecoration2.o testDecoration2b.o -o test (for generation of testDecoration.o)
// ./test (to run)
//

#include <stdio.h>

void 
_Z15printOnTerminalPKc( char const msg[] ) {
  printf(msg) ;
}

Another example of Fortran linking A simple code which use an external print Fortran routine

File testFortranLink.cc

// to compile on unix/OSX use
// g++ -c testDecoration.cc (for generation of testDecoration.o)
// g95 -c test.f            (for generation of test.o a fortran routine)
// g++ testDecoration.o test.o -o test
// ./test (to run)
//

#include <cstdlib>
#include <cstring>

using namespace std ;

#define F77NAME(A) A##_

// make a prototype of the external routine
extern "C" void F77NAME(print)( char const * msg, int * value, unsigned long msgLen ) ;

int
main( int argc, char const * argv []) {
  char msg[] = "I am a C message!" ;
  int  value = 199 ;
  F77NAME(print)( msg, &value, strlen(msg) ) ;
  return 0 ;
}

The fortran routine for which a parameter is a variable length string:

File print.f

	subroutine print( msg, value )
	integer       value
	character*(*) msg
	print *,msg,value
	return
	end

---