php如何实现字符串大小写转换

php如何实现字符串大小写转换，下面web建站小编给大家简单介绍以下2个语法的运用！

1、利用strtoupper转成大写

<?php
header('content-type:text/html;charset=utf-8');  
echo strtoupper("Hello WORLD!");
?>

2、利用mb_convert_case大小写转换

<?php
$str = "mary had a Little lamb and she loved it so";
$str = mb_convert_case($str, MB_CASE_UPPER, "UTF-8");
echo $str."<br>"; // 输出 MARY HAD A LITTLE LAMB AND SHE LOVED IT SO
$str = mb_convert_case($str, MB_CASE_TITLE, "UTF-8");
echo $str; // 输出 Mary Had A Little Lamb And She Loved It So
?>

// MB_CASE_UPPER —— 转换为大写
// MB_CASE_LOWER —— 转换为小写
// MB_CASE_TITLE —— 单词首字母转换为大写