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Detailed explanation of PHP's built-in string processing functions
Detailed explanation of PHP's built-in string processing functions
Characteristics of strings
1. Other types of data used in string type processing functions will automatically be converted into strings and processed
<?php
echo substr("abcdefghijklmn",2,4),"<br>"; //cdef
//使用数字会自动转化为字符串
echo substr(123456,2,4); //3456
?>2. Yes Treat strings as arrays and character sets
<?php
$str="abcdefg";
//下面这两种方法都可以输出想要的字符
echo $str[2]."<br>";
//但是为了区分数组我们常用下面一种
echo $str{2}."<br>";
?>Powerful built-in string processing functions
1. Commonly used string output functions
echo()
print()
die()----exit()
printf() Format string
sprintf() Return formatted string
2. Commonly used String formatting function
Remove characters
ltrim(); Remove the string on the left (spaces are removed by default)
rtrim(); Remove the string on the right
trim(); Remove the strings on both sides
<?php $str=" abc "; echo strlen($str)."<br>"; echo strlen(ltrim($str))."<br>"; echo strlen(rtrim($str))."<br>"; echo strlen(trim($str))."<br>"; $str1="123This is Test"; //第二个参数指定要删除的字符（串） echo ltrim($str1,'1')."<br>"; //删除所有的数字 0..9表示范围 echo ltrim($str1,'0..9')."<br>"; ?>
Add string
str_pad(); Add string (added on the right by default)
<?php $str="hello"; //默认从右边补充 echo str_pad($str,10,"@")."<br>"; //两边补充 echo str_pad($str,10,"@",STR_PAD_BOTH)."<br>"; //从左边补充 echo str_pad($str,10,"@",STR_PAD_LEFT)."<br>"; ?>
Case conversion
strtolower(); All characters are converted to lowercase
strtoupper(); All characters are converted to uppercase
ucfirst(); The first letter of each word is converted to uppercase
ucword(); The first letter of each word is converted Into uppercase
<?php $str="My name is TOM!"; echo strtoupper($str)."<br>"; echo strtolower($str)."<br>"; echo ucfirst($str)."<br>"; echo ucwords($str)."<br>"; ?>
String formatting related to HTML tags
nl2br(); The function inserts an HTML newline character (< before each new line (\n) in the string) br />).
htmlentities(); Function converts characters into HTML entities.
htmllspeciachars(); The function converts some predefined characters into HTML entities.
The predefined characters are:
& (ampersand) becomes &
"" (double quote) becomes "
'' (single quote) becomes '
< ( Less than) becomes< Add a backslash before the specified predefined characters:
<form>
input:<input type="text" name="str" size="100">
<input type="submit" name="sub" value="提交">
<br>
</form>
<?php
echo $_GET["str"]."<br>";
//函数把字符转换为 HTML 实体。
echo htmlentities($_GET["str"],ENT_NOQUOTES)."<br>";
//函数把一些预定义的字符转换为 HTML 实体。
echo htmlspecialchars($_GET["str"])."<br>";
//去掉由addslashes()函数加的 \
echo stripslashes($_GET["str"])."<br>";
//结合使用
echo htmlentities(stripslashes($_GET["str"]))."<br>";
// 函数剥去 HTML、XML 以及 PHP 的标签。
echo strip_tags($_GET["str"])."<br>";
?><?php $a=1000000.12345; echo $a."<br>"; echo number_format($a)."<br>"; //小数点保留三位，千分位用“,”隔开，小数点用“.” echo number_format($a,3,'.',',')."<br>"; ?>
<?php $str="Hello World!"; echo $str."<br>"; echo strrev($str)."<br>"; ?>
<?php $pass="1234#!_56"; if(md5($pass)=="a8affa3d7aca3a35a39f674e1e5f0cc7") echo "Ok!"; ?>
md5_file();
The function calculates the MD5 hash of the file.
The md5() function uses RSA data security, including the MD5 message digest algorithm.
<?php
$str1="abcd";
$str2="abcd";
if(strcmp($str1,$str2)==0){
echo '$str1=$str2';
}elseif(strcmp(str1,$str2)>0){
echo '$str1>$str2';
}else{
echo '$str1<$str2';
}
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