php常用[字符串]函数

nl2br 
功能：化换行符为<br>

<?php
$str = "cat isn't 
 dog";
$result = nl2br($str);
echo $result;
/**结果
cat isn't
dog
*/

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
14
11
*/

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!
16
12
*/

str_ireplace
功能：替换

<?php
$str = "zhang san";
$result = str_ireplace("zhang","li",$str);
echo $str."<br>";
echo $result;
/**结果
zhang san
li 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!
3
Array ( [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 zhangsan
hello 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
a
abcde
cde
de
d
*/

 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
*/