Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
ffi_call(3)	       FreeBSD Library Functions Manual		   ffi_call(3)

     ffi_call -- Invoke	a foreign function.

     #include <ffi.h>

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

     The ffi_call 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 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.

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

     unsigned char
     foo(unsigned int, float);

     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;

     ffi(3), ffi_prep_cif(3)

			       February	15, 2008


Want to link to this manual page? Use this URL:

home | help