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($str1,&#39;1&#39;)."<br>";
//删除所有的数字  0..9表示范围
echo ltrim($str1,&#39;0..9&#39;)."<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 (65e199e482cf6f44f7f2441f7a10f472).

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 '
1c5c63ed842c46e2468a1261bea229410 - if string1 is greater than string2

strcasecmp( );

strnatcmp();

<?php
$str1="abcd";
$str2="abcd";
 
if(strcmp($str1,$str2)==0){
  echo &#39;$str1=$str2&#39;;
}elseif(strcmp(str1,$str2)>0){
  echo &#39;$str1>$str2&#39;;
}else{
  echo &#39;$str1<$str2&#39;;
}
?>

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