# mysql_real_escape_string

(PHP 4 >= 4.3.0, PHP 5)

mysql_real_escape_string — 转义 SQL 语句中使用的字符串中的特殊字符，并考虑到连接的当前字符集

Warning

本扩展自 PHP 5.5.0 起已废弃，并在自 PHP 7.0.0 开始被移除。应使用 MySQLi 或 PDO_MySQL 扩展来替换之。参见 MySQL：选择 API 指南以及相关 FAQ 来获取更多信息。用以替代本函数的有：

- mysqli_real_escape_string()
- PDO::quote()

### 说明

mysql_real_escape_string ( string `$unescaped_string` [, resource `$link_identifier` = NULL ] ) : string

本函数将 `unescaped_string` 中的特殊字符转义，并计及连接的当前字符集，因此可以安全用于 mysql_query()。

mysql_real_escape_string() 调用mysql库的函数 mysql_real_escape_string, 在以下字符前添加反斜杠: \x00, \n, \r, \, ', " 和 \x1a.

为了安全起见，在像MySQL传送查询前，必须调用这个函数（除了少数例外情况）。

Caution

# 安全提示: 默认字符集

The character set must be set either at the server level, or with the API function mysql_set_charset() for it to affect mysql_real_escape_string(). See the concepts section on character sets for more information.

### 参数

`unescaped_string`

  The string that is to be escaped.

`link_identifier`

  MySQL 连接。如不指定连接标识，则使用由 mysql_connect() 最近打开的连接。如果没有找到该连接，会尝试不带参数调用 mysql_connect() 来创建。如没有找到连接或无法建立连接，则会生成 `E_WARNING` 级别的错误。

### 返回值

Returns the escaped string, or `FALSE` on error.

### 错误／异常

Executing this function without a MySQL connection present will also emit `E_WARNING` level PHP errors. Only execute this function with a valid MySQL connection present.

### 范例

Example #1 mysql_real_escape_string() 例子

    <?php
    // Connect
    $link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password')
        OR die(mysql_error());

    // Query
    $query = sprintf("SELECT * FROM users WHERE user='%s' AND password='%s'",
                mysql_real_escape_string($user),
                mysql_real_escape_string($password));
    ?>

Example #2 mysql_real_escape_string() requires a connection example

This example demonstrates what happens if a MySQL connection is not present when calling this function.

    <?php
    // We have not connected to MySQL

    $lastname  = "O'Reilly";
    $_lastname = mysql_real_escape_string($lastname);

    $query = "SELECT * FROM actors WHERE last_name = '$_lastname'";

    var_dump($_lastname);
    var_dump($query);
    ?>

以上例程的输出类似于：

    Warning: mysql_real_escape_string(): No such file or directory in /this/test/script.php on line 5
    Warning: mysql_real_escape_string(): A link to the server could not be established in /this/test/script.php on line 5

    bool(false)
    string(41) "SELECT * FROM actors WHERE last_name = ''"

Example #3 An example SQL Injection Attack

    <?php
    // We didn't check $_POST['password'], it could be anything the user wanted! For example:
    $_POST['username'] = 'aidan';
    $_POST['password'] = "' OR ''='";

    // Query database to check if there are any matching users
    $query = "SELECT * FROM users WHERE user='{$_POST['username']}' AND password='{$_POST['password']}'";
    mysql_query($query);

    // This means the query sent to MySQL would be:
    echo $query;
    ?>

The query sent to MySQL:

    SELECT * FROM users WHERE user='aidan' AND password='' OR ''=''

This would allow anyone to log in without a valid password.

### 注释

> Note:

> A MySQL connection is required before using mysql_real_escape_string() otherwise an error of level `E_WARNING` is generated, and `FALSE` is returned. If `link_identifier` isn't defined, the last MySQL connection is used.

> Note:

> If magic_quotes_gpc is enabled, first apply stripslashes() to the data. Using this function on data which has already been escaped will escape the data twice.

> Note:

> If this function is not used to escape data, the query is vulnerable to SQL Injection Attacks.

> Note: mysql_real_escape_string() does not escape % and _. These are wildcards in MySQL if combined with LIKE, GRANT, or REVOKE.

### 参见

- mysql_set_charset() - 设置客户端的字符集
- mysql_client_encoding() - 返回字符集的名称
- addslashes() - 使用反斜线引用字符串
- stripslashes() - 反引用一个引用字符串
- The magic_quotes_gpc directive
- The magic_quotes_runtime directive