fficall(3) BSD Library Functions Manual fficall(3)

NAME
     ffffiiccaallll - Invoke a foreign function.

SYNOPSIS
     ##iinncclluuddee <>

     void
     ffffiiccaallll(fficif *cif, void (*fn)(void), void *rvalue, void **avalue);

DESCRIPTION
     The ffffiiccaallll function provides a simple mechanism for invoking a function
     without requiring knowledge of the function's interface at compile time.
     fn is called with the values retrieved from the pointers in the avalue
     array. The return value from fn is placed in storage pointed to by
     rvalue.  cif contains information describing the data types, sizes and
     alignments of the arguments to and return value from fn, and must be ini-
     tialized with ffffiipprreeppcciiff before it is used with ffffiiccaallll.

     rvalue must point to storage that is sizeof(long) or larger. For smaller
     return value sizes, the ffffiiaarrgg or ffffiissaarrgg integral type must be used to
     hold the return value.

EEXXAAMMPPLLEESS
     #define MACOSX  // for fficonfig.h on Darwin

     #include 
     #include 

     unsigned char
     foo(unsigned int, float);

     int
     main(int argc, const char **argv)
     {
         fficif cif;
         ffitype *argtypes[2];
         void *argvalues[2];
         ffistatus status;

         // Because the return value from foo() is smaller than sizeof(long), it
         // must be passed as ffiarg or ffisarg.
         ffiarg result;

         // Specify the data type of each argument. Available types are defined
         // in .
         argtypes[0] = &ffitypeuint;
         argtypes[1] = &ffitypefloat;

         // Prepare the fficif structure.
         if ((status = ffiprepcif(&cif, FFIDEFAULTABI,
             2, &ffitypeuint8, argtypes)) != FFIOK)
         {
             // Handle the ffistatus error.
         }

         // Specify the values of each argument.
         unsigned int arg1 = 42;
         float arg2 = 5.1;

         argvalues[0] = &arg1;
         argvalues[1] = &arg2;

         // Invoke the function.
         fficall(&cif, FFIFN(foo), &result, argvalues);

         // The ffiarg 'result' now contains the unsigned char returned from foo(),
         // which can be accessed by a typecast.
         printf("result is %hhu", (unsigned char)result);

         return 0;
     }

     // The target function.
     unsigned char
     foo(unsigned int x, float y)
     {
         unsigned char result = x - y;
         return result;
     }

SEE ALSO
     ffi(3), ffiprepcif(3)

Darwin                           July 20, 2007                          Darwin