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 ().

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 '

Single quotation mark (')

Double quotation mark (")

Backslash(\)

NULL

strip_tags(); Function strips HTML, XML and PHP tags.

<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>";
?>

number_format(); The function formats a number by grouping thousands.

<?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,&#39;.&#39;,&#39;,&#39;)."<br>";
?>

strrev(); Function to reverse a string

<?php
$str="Hello World!";
 
echo $str."<br>";
echo strrev($str)."<br>";
?>

md5();

Function calculates the MD5 hash of a string.

The md5() function uses RSA data security, including the MD5 message digest algorithm.

Returns the calculated MD5 hash if successful, false if failed.

<?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.

Returns the calculated MD5 hash if successful, false if failed.

3. String comparison function

strcmp(); The function compares two strings.

0 - if the two strings are equal

>0 - 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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