# ffi_call - Invoke a foreign function. - man(3) - [phpMan]


## 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  re‐
       trieved  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  align‐
       ments 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)](https://www.chedong.com/phpMan.php/man/ffi/3/markdown), [_ffi_prep_cif_(3)](https://www.chedong.com/phpMan.php/man/ffiprepcif/3/markdown)

                                          February 15, 2008                              [_ffi_call_(3)](https://www.chedong.com/phpMan.php/man/fficall/3/markdown)