## 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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