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NAME
       ffi_call	-- Invoke a foreign function.

SYNOPSIS
       #include	<ffi.h>

       void
       ffi_call(ffi_cif	*cif, void (*fn)(void),	void *rvalue, void **avalue);

DESCRIPTION
       The  ffi_call function provides a simple	mechanism for invoking a func-
       tion 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 initialized with ffi_prep_cif	before it is used with ffi_call.

       rvalue must point to storage that is sizeof(ffi_arg) or larger for non-
       floating	point types. For smaller-sized return value types, the ffi_arg
       or ffi_sarg integral type must be used to hold the return value.

EXAMPLES
       #include	<ffi.h>
       #include	<stdio.h>

       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 <ffi/ffi.h>.
	   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;
       }

SEE ALSO
       ffi(3), ffi_prep_cif(3)

			       February	15, 2008		   ffi_call(3)

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