author Marco Bonardo <mbonardo@mozilla.com>
Fri, 08 Jan 2010 13:57:46 +0100
changeset 36951 765335600809c6fe847897351ea6b6cb17c913da
parent 32998 eb97628a701b7c0673c9a7aa6ad83d8c0abe90cb
child 36955 1b205e684e065ba98042eb2e9063fede1709cb5f
permissions -rw-r--r--
Bug 537271 - Add .pyo files to .hgignore, r=ted

.Dd February 15, 2008
.Dt ffi_call 3
.Nm ffi_call
.Nd Invoke a foreign function.
.In ffi.h
.Ft void
.Fo ffi_call
.Fa "ffi_cif *cif"
.Fa "void (*fn)(void)"
.Fa "void *rvalue"
.Fa "void **avalue"
.Nm ffi_call
function provides a simple mechanism for invoking a function without
requiring knowledge of the function's interface at compile time.
.Fa fn
is called with the values retrieved from the pointers in the
.Fa avalue
array. The return value from
.Fa fn
is placed in storage pointed to by
.Fa rvalue .
.Fa cif
contains information describing the data types, sizes and alignments of the
arguments to and return value from
.Fa fn ,
and must be initialized with
.Nm ffi_prep_cif
before it is used with
.Nm ffi_call .
.Fa rvalue
must point to storage that is sizeof(long) or larger. For smaller
return value sizes, the
.Nm ffi_arg
.Nm ffi_sarg
integral type must be used to hold
the return value.
.Bd -literal
#include <ffi/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;
.Xr ffi 3 ,
.Xr ffi_prep_cif 3