# random_bytes

(PHP 7)

random_bytes — Generates cryptographically secure pseudo-random bytes

### 说明

random_bytes ( int `$length` ) : string

Generates an arbitrary length string of cryptographic random bytes that are suitable for cryptographic use, such as when generating salts, keys or initialization vectors.

The sources of randomness used for this function are as follows:

- On Windows, » CryptGenRandom() will always be used. As of PHP 7.2.0, the » CNG-API will always be used instead.
- On Linux, the » getrandom(2) syscall will be used if available.
- On other platforms, /dev/urandom will be used.
- If none of the aforementioned sources are available, then an Exception will be thrown.

> Note: Although this function was added to PHP in PHP 7.0, a » userland implementation is available for PHP 5.2 to 5.6, inclusive.

### 参数

`length`

  The length of the random string that should be returned in bytes.

### 返回值

Returns a string containing the requested number of cryptographically secure random bytes.

### 错误／异常

- If an appropriate source of randomness cannot be found, an Exception will be thrown.
- If invalid parameters are given, a TypeError will be thrown.
- If an invalid `length` of bytes is given, an Error will be thrown.

### 范例

Example #1 random_bytes() example

    <?php
    $bytes = random_bytes(5);
    var_dump(bin2hex($bytes));
    ?>

以上例程的输出类似于：

    string(10) "385e33f741"

### 参见

- random_int() - Generates cryptographically secure pseudo-random integers
- openssl_random_pseudo_bytes() - 生成一个伪随机字节串
- bin2hex() - 函数把包含数据的二进制字符串转换为十六进制值