php教程

trim

(PHP 4, PHP 5, PHP 7)

trim — 去除字符串首尾处的空白字符（或者其他字符）

说明

trim ( string $str [, string $character_mask = " \t\n\r\0\x0B" ] ) : string

此函数返回字符串 str 去除首尾空白字符后的结果。如果不指定第二个参数，trim() 将去除这些字符：

  • " " (ASCII 32 (0x20))，普通空格符。
  • "\t" (ASCII 9 (0x09))，制表符。
  • "\n" (ASCII 10 (0x0A))，换行符。
  • "\r" (ASCII 13 (0x0D))，回车符。
  • "\0" (ASCII 0 (0x00))，空字节符。
  • "\x0B" (ASCII 11 (0x0B))，垂直制表符。

参数

str

待处理的字符串。

character_mask

可选参数，过滤字符也可由 character_mask 参数指定。一般要列出所有希望过滤的字符，也可以使用 ".." 列出一个字符范围。

返回值

过滤后的字符串。

范例

Example #1 trim() 使用范例

<?php

$text   = "\t\tThese are a few words :) ...  ";
$binary = "\x09Example string\x0A";
$hello  = "Hello World";
var_dump($text, $binary, $hello);

print "\n";

$trimmed = trim($text);
var_dump($trimmed);

$trimmed = trim($text, " \t.");
var_dump($trimmed);

$trimmed = trim($hello, "Hdle");
var_dump($trimmed);

// 清除 $binary 首位的 ASCII 控制字符
// （包括 0-31）
$clean = trim($binary, "\x00..\x1F");
var_dump($clean);

?>

以上例程会输出：

string(32) "        These are a few words :) ...  "
string(16) "    Example string
"
string(11) "Hello World"

string(28) "These are a few words :) ..."
string(24) "These are a few words :)"
string(5) "o Wor"
string(14) "Example string"

Example #2 使用 trim() 清理数组值

<?php
function trim_value(&$value) 
{ 
    $value = trim($value); 
}

$fruit = array('apple','banana ', ' cranberry ');
var_dump($fruit);

array_walk($fruit, 'trim_value');
var_dump($fruit);

?>

以上例程会输出：

array(3) {
  [0]=>
  string(5) "apple"
  [1]=>
  string(7) "banana "
  [2]=>
  string(11) " cranberry "
}
array(3) {
  [0]=>
  string(5) "apple"
  [1]=>
  string(6) "banana"
  [2]=>
  string(9) "cranberry"
}

注释

Note: Possible gotcha: removing middle characters

Because trim() trims characters from the beginning and end of a string, it may be confusing when characters are (or are not) removed from the middle. trim('abc', 'bad') removes both 'a' and 'b' because it trims 'a' thus moving 'b' to the beginning to also be trimmed. So, this is why it "works" whereas trim('abc', 'b') seemingly does not.

参见

  • ltrim() - 删除字符串开头的空白字符（或其他字符）
  • rtrim() - 删除字符串末端的空白字符（或者其他字符）
  • str_replace() - 子字符串替换

User Contributed Notes

roger21 at free dot fr 04-Apr-2019 11:02
It is worth mentioning that trim, ltrim and rtrim are NOT multi-byte safe, meaning that trying to remove an utf-8 encoded non-breaking space for instance will result in the destruction of utf-8 characters than contain parts of the utf-8 encoded non-breaking space, for instance:

non breaking-space is "\u{a0}" or "\xc2\xa0" in utf-8, "μ" is "\u{b5}" or "\xc2\xb5" in utf-8 and "à" is "\u{e0}" or "\xc3\xa0" in utf-8

$input = "\u{a0}μ déjà\u{a0}"; // " μ déjà "
$output = trim($input, "\u{a0}"); // "? déj?" or whatever how the interpretation of broken utf-8 characters is performed

$output got both "\u{a0}" characters removed but also both "μ" and "à" characters destroyed
igor dot pellegrini at berlinonline dot de 04-Apr-2019 10:36
Beware with trimming apparently innocent characters. It is NOT a Unicode-safe function:

<?php
echo trim('≈ [Approximation sign]', '- [en-dash]');  // ?? [Approximation sig
?>

The en-dash here is breaking the Unicode characters.

And also prevents the open-square-bracket from being seen as part of the characters to trim on the left side, letting it untouched in the resulting string.
Mark-Centurion at ya dot ru 16-Feb-2019 05:54
utf-8:
trim($text, " \t\n\r\0\x0B\xC2\xA0");
solaimanshah059 at gmail dot com 18-Aug-2018 10:02
Simple Example I hope you will understand easily:

<?php

// Inserting empty variable;

$name = "";

if( !(empty( $name )) )
{
   $sql = "INSERT INTO `users`( name ) VALUE( '$name' );";
}

// But is not empty that will be inserted but space

$name2 = "     ";

if( !(empty( $name )) )
{
   $sql = "INSERT INTO `users`( name ) VALUE( '$name' );";
}

// Now that will not be inserted by using trim() function

$name3 = "     ";

if( !(empty( trim($name) )) )
{
   $sql = "INSERT INTO `users`( name ) VALUE( '$name' );";
}

?>
aalhad at NOSPAM dot gmail dot com 11-Jan-2018 11:28
When specifying the character mask,
make sure that you use double quotes

<?php
  $hello = "
      Hello World   "; //here is a string with some trailing and leading whitespace

  $trimmed_correct   = trim($hello, " \t\n\r"); //<--------OKAY
  $trimmed_incorrect = trim($hello, ' \t\n\r'); //<--------NOT AS EXPECTED

  print("----------------------------");
  print("TRIMMED OK:".PHP_EOL);
  print_r($trimmed_correct.PHP_EOL);
  print("----------------------------");
  print("TRIMMING NOT OK:".PHP_EOL);
  print_r($trimmed_incorrect.PHP_EOL);
  print("----------------------------".PHP_EOL);
?>

Here is the output:

----------------------------TRIMMED OK:
Hello World
----------------------------TRIMMING NOT OK:

      Hello World
----------------------------
johovich at yandex dot ru 30-Jul-2017 10:17
trim is the fastest way to remove first and last char.

Benchmark comparsion 4 different ways to trim string with  '/'
4 functions with the same result - array exploded by '/'

<?php
$s = '/catalog/lyustry/svet/dom-i-svet/';

$times = 100000;

print cycle("str_preg('$s');", $times);
print cycle("str_preg2('$s');", $times);
print cycle("str_sub_replace('$s');", $times);
print cycle("str_trim('$s');", $times);
print cycle("str_clear('$s');", $times);

//print_r(str_preg2($s));

function cycle($function, $times){
    $count = 0;
    if($times < 1){
        return false;
    }
    $start = microtime(true);
    while($times > $count){
        eval($function);
        $count++;
    }
    $end = microtime(true) - $start;
    return "\n $function exec time: $end";
}

function str_clear($s){
    $s = explode('/', $s);
    $s = array_filter($s, function ($s){if(!empty($s)) return true;});
    return $s;
}

function str_preg2($s){
    $s = preg_replace('/((?<!.)\/(?=.))?((?<=.)\/(?!.))?/i', '', $s);
    $s = explode('/', $s);
    return $s;
}

function str_preg($s){
    $s = preg_replace('/^(\/?)(.*?)(\/?)$/i', '$2', $s);
    $s = explode('/', $s);
    return $s;
}

function str_sub_replace($s){
    $s = str_replace('/' , '' , mb_substr( $s , 0, 1)) . mb_substr( $s , 1, -1) . str_replace('/', '', mb_substr(  $s , -1));
    $s = explode('/', $s);
    return $s;
}

function str_trim($s){
    $s = trim($s, '/');
    $s = explode('/', $s);
    return $s;
}
tongcheong77 at gmail dot com 09-Jul-2017 12:39
if you are using trim and you still can't remove the whitespace then check if your closing tag inside the html document is NOT at the next line.

<textarea class="form-control" rows="5"><?php echo trim($comment);?></textarea>

there should be no spaces at the beginning and end of your echo statement, else trim will not work as expected.
ivijan dot stefan at gmail dot com 03-Jul-2017 09:06
Standard trim() functions can be a problematic when come HTML entities. That's why i wrote "Super Trim" function what is used to handle with this problem and also you can choose is trimming from the begin, end or booth side of string.
<?php
function strim($str,$charlist=" ",$option=0){
    if(is_string($str))
    {
        // Translate HTML entities
        $return = strtr($str, array_flip(get_html_translation_table(HTML_ENTITIES, ENT_QUOTES)));
        // Remove multi whitespace
        $return = preg_replace("@\s+\s@Ui"," ",$return);
        // Choose trim option
        switch($option)
        {
            // Strip whitespace (and other characters) from the begin and end of string
            default:
            case 0:
                $return = trim($return,$charlist);
            break;
            // Strip whitespace (and other characters) from the begin of string
            case 1:
                $return = ltrim($return,$charlist);
            break;
            // Strip whitespace (and other characters) from the end of string
            case 2:
                $return = rtrim($return,$charlist);
            break;
               
        }
    }
    return $return;
}
?>
Anonymous 11-Jun-2017 04:45
The comment of "ludko2 at gmail dot com" for trimming non-breaking spaces is wrong due the the way UTF-8 works. For example, it breaks on `"&nbsp;abà"`.
jianglong at qiyi dot com 13-May-2015 08:09
Trim full width space will return mess character,  when target string starts with '《'

@example 
echo trim("《", "　");

@return
?

php version 5.4.27

[EDIT by cmb AT php DOT net: it is not necessarily safe to use trim with multibyte character encodings. The given example is equivalent to echo trim("\xe3\80\8a", "\xe3\x80\x80").]
ludko2 at gmail dot com 09-Jul-2010 02:28
Non-breaking spaces can be troublesome with trim:

<?php
// turn some HTML with non-breaking spaces into a "normal" string
$myHTML = "&nbsp;abc";
$converted = strtr($myHTML, array_flip(get_html_translation_table(HTML_ENTITIES, ENT_QUOTES)));

// this WILL NOT work as expected
// $converted will still appear as " abc" in view source
// (but not in od -x)
$converted = trim($converted);

// &nbsp; are translated to 0xA0, so use:
$converted = trim($converted, "\xA0"); // <- THIS DOES NOT WORK

// EDITED>>
// UTF encodes it as chr(0xC2).chr(0xA0)
$converted = trim($converted,chr(0xC2).chr(0xA0)); // should work

// PS: Thanks to John for saving my sanity!
?>
Piopier 12-Jan-2007 06:06
It may be useful to know that trim() returns an empty string when the argument is an unset/null variable.
dmr37 at cornell dot edu 17-May-2005 12:47
If you want to check whether something ONLY has whitespaces, use the following:

<?php

if (trim($foobar)=='') {
   echo 'The string $foobar only contains whitespace!';
}

?>
Hayley Watson 07-Feb-2005 04:46
Another way to trim all the elements of an array
<?php
$newarray = array_map('trim', $array);
?>
jubi at irc dot pl 20-Apr-2004 06:48
To remove multiple occurences of whitespace characters in a string an convert them all into single spaces, use this:

<?

$text = preg_replace('/\s+/', ' ', $text);

?>

------------
JUBI
http://www.jubi.buum.pl
HW 05-Jun-2003 06:32
You can combine character ranges and individual characters in trim()'s second argument (ditto for ltrim and rtrim). All of the specified characters and ranges will be used concurrently (i.e., if a character on either end of the string matches any of the specified charaters or character ranges, it will be trimmed). The characters and character ranges can be in any order (except of course that the character ranges need to be specified in increasing order) and may overlap.
E.g., trim any nongraphical non-ASCII character:
trim($text,"\x7f..\xff\x0..\x1f");

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