nl2br
功能：化换行符为<br>
<?php$str = "cat isn‘t \n dog";$result = nl2br($str);echo $result;/**结果cat isn‘tdog*/
rtrim
功能：清除右边的空白
<?php$str = "Hello world ??";echo strlen($str)."<br>";$result = rtrim($str);echo strlen($result);/**结果1411*/
strip_tags
功能：清除字符串中html和php的标记
<?php$str = "<font color = ‘red‘>Hello world</font>";$result = strip_tags($str);echo $result;/**结果Hello world*/
strtolower
strtoupper
功能：转换成大小写
<?php$str = "Hello World!";$result = strtolower($str);echo $result."<br>";$result = strtoupper($str);echo $result;/**结果hello world!HELLO WORLD!*/
trim
功能：去除首尾空格
<?php$str = " ?Hello World! ?";$result = trim($str);echo $str."<br>";echo $result."<br>";echo strlen($str)."<br>";echo strlen($result);/**结果Hello World!Hello World!1612*/
str_ireplace
功能：替换
<?php$str = "zhang san";$result = str_ireplace("zhang","li",$str);echo $str."<br>";echo $result;/**结果zhang sanli san*/
str_repeat
功能：将一个字符串重复多遍
<?php$str = "Hello jiqing!";$result = str_repeat($str,4);echo $str."<br>";echo $result;/**结果Hello jiqing!Hello jiqing!Hello jiqing!Hello jiqing!Hello jiqing!*/
str_replace
功能：区分大小写的替换
<?php$str = "hello jiqing!";$result1 = str_ireplace("Hello","Hi",$str); //不区分大小写$result2 = str_replace("Hello","Hi",$str); ?//区分大小写echo $str."<br>";echo $result1."<br>";echo $result2."<br>";/**结果hello jiqing!Hi jiqing!hello jiqing!*/
str_word_count
功能：返回字符串中单词的个数
<?php$str = "hello jiqing a!";$result1 = str_word_count($str); ???//返回个数$result2 = str_word_count($str,1); ?//返回数组echo $str."<br>";echo $result1."<br>";print_r($result2);/**结果hello jiqing a!3Array ( [0] => hello [1] => jiqing [2] => a )*/
strlen
功能：返回字符串长度
<?php$str = "hello jiqing a!";$result = strlen($str);echo $result;/**结果15*/
substr_count
功能：计算一个字符串在另一个字符串中的个数
<?php$str = "hello jiqing ,hello jim!";$result = substr_count($str,"hello");echo $result;/**结果2*/
substr_replace
功能：从某个位置开始替换
<?php$str = "hello jiqing ,hello jim!";$result = substr_replace($str,"zhangsan",6);echo $result."<br>";$result = substr_replace($str,"zhangsan",6,6);//从某个位置替换，替换几个字符串echo $result;/**结果hello zhangsanhello zhangsan ,hello jim!*/
substr
功能：获取子字符串
<?php$str = "abcdef";$result = substr($str,0,1); //从第0个开始，获取1个echo $result."<br>";$result = substr($str,0,-1);//从第0个开始，获取到除了最后一个的字符串echo $result."<br>";$result = substr($str,2,-1);//从第2个开始，获取到除了最后一个的字符串echo $result."<br>";$result = substr($str,-3,-1);//从第-3个开始，获取到除了最后一个的字符串echo $result."<br>";$result = substr($str,-3,1);//从第-3个开始，获取到除了最后一个的字符串echo $result."<br>";/**结果aabcdecdeded*/
implode
功能：将数组转化为字符串
<?php$array = array("2013","6","3");$date = implode("/",$array);echo $date;/**结果2013/6/3*/
md5
功能：对字符串进行md5加密
<?php$str = "Hello world";$result = md5($str);echo $result;/**结果3e25960a79dbc69b674cd4ec67a72c62*/
PHP常用字符串函数。
原文地址：http://www.cnblogs.com/Master-YQ/p/7677998.html