How to convert all strings to lowercase in php

3 conversion methods: 1. Use strtolower() function for conversion, syntax "strtolower(string)"; 2. Use mb_strtolower() function for conversion, syntax "mb_strtolower(string, character encoding) "; 3. Use the mb_convert_case() function to convert, the syntax is "mb_convert_case(string, MB_CASE_LOWER, character encoding)".

The operating environment of this tutorial: windows7 system, PHP version 8.1, DELL G3 computer

In PHP, you want to convert a string into To convert all the letters to lowercase, you can use the strtolower(), mb_strtolower() or mb_convert_case() function

Method 1: Use the strtolower() function to convert

strtolower() function can convert letters in a string to lowercase. The syntax format is as follows:

strtolower($string)

Among them, $string is a parameter of string type. This function can convert the parameter $string Convert the letters in to lowercase and return the converted string.

The sample code is as follows:

<?php
header("Content-type:text/html;charset=utf-8");
$str = "HTTPS://WWW.PHP.CN/";
echo "原字符串：<br> $str <br><br>";
$str = strtolower($str);
echo "转换后：<br> $str";
?>

The running results are as follows:

Method 2 : Use the mb_strtolower() function for conversion

The function of the mb_strtolower() function is similar to the strtolower() function. It can also convert letters in the string to lowercase, and the mb_strtolower() function You can also set the character encoding of the parameter. The syntax format is as follows:

mb_strtolower($str [, $encoding = mb_internal_encoding()])

Among them, $str is the string that needs to be converted, and $encoding is an optional parameter used to set the character encoding of the parameter.

The difference from the strtolower() function is that the detection of alphabetic characters in $str is based on the Unicode attribute of the character. The behavior of the function is therefore independent of the language setting and can convert any character with a "letter" attribute, such as the umlaut A (Ä).

Example 1:

<?php
header("Content-type:text/html;charset=utf-8");
$str = "HELLO";
echo "原字符串：<br> $str <br><br>";
$str = mb_strtolower($str, &#39;UTF-8&#39;);
echo "转换后：<br> $str";
?>

Example 2:

<?php
header("Content-type:text/html;charset=utf-8");
$str = "Τάχιστη αλώπηξ βαφής ψημένη γη, δρασκελίζει υπέρ νωθρού κυνός";
echo "原字符串：<br> $str <br><br>";
$str = mb_strtolower($str, &#39;UTF-8&#39;);
echo "转换后：<br> $str";
?>

Method 3: Use the mb_convert_case() function to convert

The mb_convert_case() function can convert strings from upper to lower case. The syntax format is as follows :

mb_convert_case($str, $mode [, $encoding = mb_internal_encoding()])

Among them, $str is the string that needs to be converted; $mode is the conversion mode, which can be MB_CASE_UPPER (all converted to uppercase), MB_CASE_LOWER (all One of MB_CASE_TITLE (convert the first letter to uppercase); $encoding is the character encoding of the parameter and can be omitted.

Compared with the strtolower() and strtoupper() functions, the mb_convert_case() function performs case conversion based on Unicode character attributes. Therefore, the behavior of the mb_convert_case() function is not affected by the locale setting and can convert any character with a "letter" attribute, such as the umlaut A (Ä).

The sample code is as follows:

<?php
header("Content-type:text/html;charset=utf-8");
$str = "ABCDEFG";
echo "原字符串：<br> $str <br><br>";
$str = mb_convert_case($str,MB_CASE_LOWER, &#39;UTF-8&#39;);
echo "转换后：<br> $str";
?>

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