php内置了98个字符串函数（除了基于正则表达式的函数，正则表达式在此不在讨论范围），能够处理字符串中能遇到的每一个方面内容，本文对常用字符串函数进行简单的小结，主要包含以下8部分：1.确定字符串长度、2.比较字符串、3.分割连接反转、4.html与字符串相互转化、5.填充和剔除字符串、6.统计字符和单词个数、7.查找替换截取、8.大小写处理。

确定字符串长度

strlen函数和mb_strlen函数，后者需要开启mbstring扩展

<?php 
    header(\'content-type:text/html;charset=utf-8\');
    $str = \'abcdef\';
    echo strlen($str); // 6
    echo "<br/>";
    $str = \' ab cd \';
    echo mb_strlen($str); // 7
    echo "<br/>";
    //strlen 是计算字符串"字节"长度 
    //mb_strlen,是根据编码,计算字符串的"字符"个数. 

    $str=\'中华人民共和国\';
    echo "字节长度是".strlen($str);//在 UTF-8编码下，一个汉字占3个字节 在gbk中一个汉字占2个字节
    echo "<br/>";
    echo "字符长度是".mb_strlen($str,\'utf-8\');
 ?>

比较字符串

strcmp函数、strcasecmp函数、strspn函数、strcspn函数

<?php 
	$pwd="userpwd";
	$pwd2="Userpwd";
	//区分大小写
	if (strcmp($pwd, $pwd2) !=0) {
		echo "password do not match";
	} else{
		echo "password match";
	}

	$email1="www.baidu.com";
	$email2="WWW.BAIDU.COM";
	//不区分大小写
	if (!strcasecmp($email1, $email2)) {
		echo "ok",\'<br>\';
	}
	//求两个字符串相同的部分
	$password="1233345";
	if (strspn($password,"1234567890")==strlen($password)) {
		echo "the password connot consist solely of numbers";
	}
	//
	$password="a12345";
	if (strcspn($password, "1234567890")==0) {
		echo "the password connot consist solely of numbers";
	}
	
 ?>

分割连接反转

str_split函数、split函数、explode函数和implode函数

<?php 
header(\'content-type:text/html;charset=utf-8\');
	$str = "Hello Friend";

	$arr1 = str_split($str);
	print_r($arr1);

	$arr2 = str_split($str, 3);
	print_r($arr2);

	$str = \'abc,中国,美国,日本\'; 
	// explode,是根据指定的分割符,把字符串拆成数组. 
	$arr = explode(\',\',$str); 
	print_r($arr); 
	// implode,是根据指定的连接符,把数组再拼接成字符串 
	$arr = explode(\',\',$str); 
	echo implode(\'~\',$arr),\'<br />\'; 
	// 你可以只传一个数组做参数,不指定连接符, 
	// 这样,将把数组单元直接拼接起来 
	echo implode($arr);

 ?>

html与字符串相互转化

htmlspecialchars函数、strip_tags函数、get_html_translation_table函数和addcslashes函数和htmlentities函数

<?php 

	$str = "hello \', world"; 
	echo $str,\'<br />\';
	echo $str= addslashes($str),\'<br />\';
	echo stripslashes($str),\'<br />\';
	$str = \'<ab>\'; 
	echo $str,\'<br />\'; 
	echo htmlspecialchars($str); 
	echo "</br>";
	$str="Email <a href=\'admin@qq.com\'>example@qq.com</a>";
	echo strip_tags($str);

 ?>

填充和剔除字符串

trim函数、ltrim函数、rtrim函数、str_pad函数、chunk_split函数

<?php 
	$str = \'12345678\'; 
	echo chunk_split($str,3,\',\');
	echo "<br>";
	$text   = "\t\tThese are a few words :) ...  ";
	echo trim($text);
	echo "<br>";
	echo ltrim($text,\'\t\'),\'<br>\';
	echo rtrim($text,\'\r\'),\'<br>\';
	echo str_pad(\'apple\', 6)."is good.";
 ?>

统计字符和单词个数

count_chars函数和str_word_count

<?php 
    $data = "Two Ts and one F.";

    foreach (count_chars($data, 1) as $i => $val) {
       echo "There were $val instance(s) of \"" , chr($i) , "\" in the string.\n";
    }

    echo "<hr>";
    $str = "Hello fri3nd, you\'re looking good today!";

    print_r(str_word_count($str, 1));

 ?>

查找替换截取

strpos函数、str_replace函数、substr_replace函数、substr函数、strstr函数

<?php 
	$substr = "index.html";
	$log = <<< logfile
	192.168.1.11:/www/htdocs/index.html:[2016/08/10:21:58:27]
	192.168.1.11:/www/htdocs/index.html:[2016/08/18:01:51:37]
	192.168.1.11:/www/htdocs/index.html:[2016/08/20:11:48:27]
logfile;

    $pos =strpos($log, $substr);
    $pos2=strpos($log,"\n",$pos);
    $pos=$pos+strlen($substr)+1;
    $timestamp=substr($log,$pos,$pos2-$pos);
    echo "The file $substr was first accessed on:$timestamp";
    echo "<br>";
    $author="lester@example.com";
    $author=str_replace("@", "at", $author);
    echo "connect the author of this article at $author";
    echo "<br>";
    echo ltrim(strstr($author,"@"), "@");

 ?>

大小写处理

strtolower函数、strtoupper函数、ucfirst函数、ucwords函数

<?php 
	$url="http://WWWW.BAIDU.COM";
	echo strtolower($url),\'<br>\';
	$str="hello world";
	echo strtoupper($str),\'<br>\';
	$str="php is the most popular language ";
	echo ucfirst($str),\'<br>\';
	echo ucwords($str);
 ?>