eval() 函数把字符串按照 PHP 代码来计算。
该字符串必须是合法的 PHP 代码，且必须以分号结尾。
如果没有在代码字符串中调用 return 语句，则返回 NULL。如果代码中存在解析错误，则 eval() 函数返回 false。
for example:
<code><span><span>class</span><span>Pass</span>{</span><span>private</span><span>$var1</span>;
<span>private</span><span>$var2</span>;
<span>public</span><span><span>function</span><span>__construct</span><span>(<span>$var1</span>,<span>$var2</span>)</span>{</span><span>$varchar</span>=<span>"this is a construct function,is hava two varchar $var1 and $var2"</span>;
<span>eval</span>(<span>"\$varchar=\".$varchar.\";"</span>);
<span>echo</span><span>$varchar</span>;
}
}
<span>$P</span>=<span>new</span> Pass(<span>"HELLO"</span>, <span>"WORLD"</span>);</code>输出结果： this is a construct function,is hava two varchar HELLO and WORLD.
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