Manual Pages for UNIX Operating System command usage for man ffi_call

The function provides a simple mechanism for invoking a  function
without  requiring  knowledge of the function's interface at com-
pile time.  is called with the values retrieved from the pointers
in  the array. The return value from is placed in storage pointed
to by contains information describing the data types,  sizes  and
alignments  of the arguments to and return value from and must be
initialized with before it is used with  must  point  to  storage
that  is  sizeof(ffi_arg) or larger for non-floating point types.
For smaller-sized return value types, the or integral  type  must
be  used  to  hold  the  return value.  #include  #include


unsigned char foo(unsigned int, float);

int main(int argc, const char **argv) {
    ffi_cif cif;
    ffi_type *arg_types[2];
    void *arg_values[2];
    ffi_status status;

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

    // Specify the data type of each  argument.  Available  types
are defined
    // in .
    arg_types[0] = &ffi_type_uint;
    arg_types[1] = &ffi_type_float;

    // Prepare the ffi_cif structure.
    if ((status = ffi_prep_cif(&cif, FFI_DEFAULT_ABI,
        2, &ffi_type_uint8, arg_types)) != FFI_OK)
    {
        // Handle the ffi_status error.
    }

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

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

    // Invoke the function.
    ffi_call(&cif, FFI_FN(foo), &result, arg_values);

    // The  ffi_arg  '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; }