PHP防止SQL注入的方法（1）

（1）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
使用方法如下：

<code>$sql = "<span><span>select</span><span>count</span>(*) <span>as</span> ctr <span>from</span> users <span>where</span> username =<span>'".mysql_real_escape_string($username)."'</span><span>and</span> password=<span>'". mysql_real_escape_string($pw)."'</span> limit <span>1</span><span>";</span></span></code>

使用

<code><span><span>mysql_real_escape_string</span><span>()</span></span></code>

作为用户输入的包装器，就可以避免用户输入中的任何恶意 SQL 注入。
（2） 打开magic_quotes_gpc来防止SQL注入
php.ini中有一个设置：magic_quotes_gpc = Off
　　这个默认是关闭的，如果它打开后将自动把用户提交对sql的查询进行转换，
　　比如把 ’ 转为 \’等，对于防止sql注射有重大作用。
如果magic_quotes_gpc=Off，则使用addslashes()函数
（3）自定义函数

<code><span><span>function</span><span>inject_check</span><span>(<span>$sql_str</span>)</span> {</span><span>return</span> eregi(<span>'select|insert|and|or|update|delete|\'|\/\*|\*|\.\.\/|\.\/|union|into|load_file|outfile'</span>, <span>$sql_str</span>);
} 

<span><span>function</span><span>verify_id</span><span>(<span>$id</span>=null)</span> {</span><span>if</span>(!<span>$id</span>) {
        <span>exit</span>(<span>'没有提交参数！'</span>); 
    } <span>elseif</span>(inject_check(<span>$id</span>)) { 
        <span>exit</span>(<span>'提交的参数非法！'</span>);
    } <span>elseif</span>(!is_numeric(<span>$id</span>)) { 
        <span>exit</span>(<span>'提交的参数非法！'</span>); 
    } 
    <span>$id</span> = intval(<span>$id</span>); 

    <span>return</span><span>$id</span>; 
} 


<span><span>function</span><span>str_check</span><span>( <span>$str</span> )</span> {</span><span>if</span>(!get_magic_quotes_gpc()) { 
        <span>$str</span> = addslashes(<span>$str</span>); <span>// 进行过滤 </span>
    } 
    <span>$str</span> = str_replace(<span>"_"</span>, <span>"\_"</span>, <span>$str</span>); 
    <span>$str</span> = str_replace(<span>"%"</span>, <span>"\%"</span>, <span>$str</span>); 

   <span>return</span><span>$str</span>; 
} 


<span><span>function</span><span>post_check</span><span>(<span>$post</span>)</span> {</span><span>if</span>(!get_magic_quotes_gpc()) { 
        <span>$post</span> = addslashes(<span>$post</span>);
    } 
    <span>$post</span> = str_replace(<span>"_"</span>, <span>"\_"</span>, <span>$post</span>); 
    <span>$post</span> = str_replace(<span>"%"</span>, <span>"\%"</span>, <span>$post</span>); 
    <span>$post</span> = nl2br(<span>$post</span>); 
    <span>$post</span> = htmlspecialchars(<span>$post</span>); 

    <span>return</span><span>$post</span>; 
}</code>

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