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

FreeBSD Manual Pages

  
 
  

home | help 
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 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 ar-
     ray. 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)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=ffi_call&sektion=3&manpath=FreeBSD+Ports+15.1.quarterly>

home | help