php常用字符串函数小结

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);
?>