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   <title> strtolower.php </title>
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<?php
 $str = "I want To FLY";
 echo $str;
 echo '<br>';
 $str2 = strtolower($str);
 echo $str;
 echo '<br>';
 echo $str2;
 ?>
  </body>
 </html>
I want To FLY
 I want To FLY
 i want to fly 1．字符串大小写转换函数
 （1）strtolower()函数。该函数将传入的字符串参数所有的字符都转换成小写，并以小写形式放回这个字符串。该函数声明如下：
 string strtolower(string str)