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PHP removes whitespace characters or other predefined characters on the left side of the string function ltrim()

黄舟Original: 2017-11-02 13:14:422545browse

Example

Remove characters on the left side of the string:

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

Definition and usage

ltrim() function removes blank characters or other characters on the left side of the string Predefined characters.

Related functions:

rtrim() - Removes whitespace characters or other predefined characters on the right side of a string.

trim() - Removes whitespace characters or other predefined characters on both sides of a string.

Syntax

ltrim(string,charlist)

Parameters Description

string Specifies the string to check.

charlist Optional. Specifies which characters are removed from a string. If this parameter is omitted, remove all the following characters:

"\ 0" -NULL

## "\ T" -The watch symbol

## "\ n"

"\ x0b" - Vertical forms

"\ r" -Elke

## "" " - 空

#Technical details

Return value: Return the modified string.

PHP Version: 4+

##Change Log: In PHP 4.1, new Added charlist parameter.

More examples

Example 1

Remove spaces on the left side of the string:

<?php
$str = " Hello World!";
echo "Without ltrim: " . $str;
echo "<br>";
echo "With ltrim: " . ltrim($str);
?>

HTML output of the above code As follows (view source code):

<!DOCTYPE html>
<html>
<body>

Without ltrim: Hello World!<br>With ltrim: Hello World!
</body>
</html>

The browser output of the above code is as follows:

Without ltrim: Hello World!
With ltrim: Hello World!

Example 2

Remove the newline character (\n) on the left side of the string :

<?php
$str = "nnnHello World!";
echo "Without ltrim: " . $str;
echo "<br>";
echo "With ltrim: " . ltrim($str);
?>

The HTML output of the above code is as follows (view source code):

<!DOCTYPE html>
<html>
<body>

Without ltrim: 


Hello World!<br>With ltrim: Hello World!
</body>
</html>

The browser output of the above code is as follows:

Without ltrim: Hello World!
With ltrim: Hello World!

string trim ( string $str [, string $charlist ] ) - 去除字符串首尾处的空白字符（或者其他字符）

　　trim()函数当第二个参数为空时，默认去掉空格、制表符、换行符、回车符、垂直制表符等，当加入第二个参数时

　　　　1) trim(' \"string\"', '\"sg');　　 // 最终输出：\"strin

　　　　2) trim(' \"string\" ', '\"sg'); // 最终输出：\"string\"

　　　　2)trim('\"string\"', '\"sg');　　　 // 最终输出：trin

　　所以trim()函数优先去掉字符首尾的空白字符，再过滤掉给定的要去除的字符(列表)，也适用于ltrim()、rtrim()函数

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