The following example shows a partial Fortran routine that calls a C++ function. The called C++ function contains the extern "FORTRAN" linkage specification for the C++ function CFCN and the function definition for the C++ function.

INTEGER*4 INDEX
REAL*8 LIST(0:99)
REAL*8 VALUE
REAL*8 CFCN
⋮
VALUE=CFCN(INDEX, LIST)

extern "FORTRAN" 
   {double cfcn(int *, double *);}
⋮
double cfcn(int *index, double list [])
{
⋮
return list[*index];
}