## Basic FFI usage

Before diving into the details of the FFI API, lets take a look at a few examples demonstrating the simplicity of the FFI API usage for regular tasks.

> Note: Some of these examples require libc.so.6 and as such will not work on systems where it is not available.

Example #1 Calling a function from shared library

`<?php
// create FFI object, loading libc and exporting function printf()
$ffi = FFI::cdef(
"int printf(const char *format, ...);", // this is a regular C declaration
"libc.so.6");
// call C's printf()
$ffi->printf("Hello %s!\n", "world");
?>`

The above example will output:

    Hello world!

> Note: Note that some C functions need specific calling conventions, e.g. `__fastcall`, `__stdcall` or `,__vectorcall`.

Example #2 Calling a function, returning a structure through an argument

`<?php
// create gettimeofday() binding
$ffi = FFI::cdef("
typedef unsigned int time_t;
typedef unsigned int suseconds_t;
struct timeval {
time_t tv_sec;
suseconds_t tv_usec;
};
struct timezone {
int tz_minuteswest;
int tz_dsttime;
};
int gettimeofday(struct timeval *tv, struct timezone *tz);
", "libc.so.6");
// create C data structures
$tv = $ffi->new("struct timeval");
$tz = $ffi->new("struct timezone");
// call C's gettimeofday()
var_dump($ffi->gettimeofday(FFI::addr($tv), FFI::addr($tz)));
// access field of C data structure
var_dump($tv->tv_sec);
// print the whole C data structure
var_dump($tz);
?>`

The above example will output something similar to:

    int(0)
    int(1555946835)
    object(FFI\CData:struct timezone)#3 (2) {
      ["tz_minuteswest"]=>
      int(0)
      ["tz_dsttime"]=>
      int(0)
    }

Example #3 Accessing existing C variables

`<?php
// create FFI object, loading libc and exporting errno variable
$ffi = FFI::cdef(
"int errno;", // this is a regular C declaration
"libc.so.6");
// print C's errno
var_dump($ffi->errno);
?>`

The above example will output:

    int(0)

Example #4 Creating and Modifying C variables

`<?php
// create a new C int variable
$x = FFI::new("int");
var_dump($x->cdata);
// simple assignment
$x->cdata = 5;
var_dump($x->cdata);
// compound assignment
$x->cdata += 2;
var_dump($x->cdata);
?>`

The above example will output:

    int(0)
    int(5)
    int(7)

Example #5 Working with C arrays

`<?php
// create C data structure
$a = FFI::new("long[1024]");
// work with it like with a regular PHP array
for ($i = 0; $i < count($a); $i++) {
$a[$i] = $i;
}
var_dump($a[25]);
$sum = 0;
foreach ($a as $n) {
$sum += $n;
}
var_dump($sum);
var_dump(count($a));
var_dump(FFI::sizeof($a));
?>`

The above example will output:

    int(25)
    int(523776)
    int(1024)
    int(8192)

Example #6 Working with C enums

`<?php
$a = FFI::cdef('typedef enum _zend_ffi_symbol_kind {
ZEND_FFI_SYM_TYPE,
ZEND_FFI_SYM_CONST = 2,
ZEND_FFI_SYM_VAR,
ZEND_FFI_SYM_FUNC
} zend_ffi_symbol_kind;
');
var_dump($a->ZEND_FFI_SYM_TYPE);
var_dump($a->ZEND_FFI_SYM_CONST);
var_dump($a->ZEND_FFI_SYM_VAR);
?>`

The above example will output:

    int(0)
    int(2)
    int(3)

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