strtolower

(PHP 4, PHP 5, PHP 7)

strtolower — 将字符串转化为小写

说明

strtolower ( string $string ) : string

将 string 中所有的字母字符转换为小写并返回。

注意 "字母" 与当前所在区域有关。例如，在默认的 "C" 区域，字符 umlaut-A（?）就不会被转换。

参数

string

输入字符串。

返回值

返回转换后的小写字符串。

范例

Example #1 strtolower() 范例

<?php
$str = "Mary Had A Little Lamb and She LOVED It So";
$str = strtolower($str);
echo $str; // 打印 mary had a little lamb and she loved it so
?>

注释

Note: 此函数可安全用于二进制对象。

参见

User Contributed Notes

Daniel Klein 07-May-2016 10:33
When the locale is set to "utf8" or "C" I can't get strtolower() to convert accented characters encoded as UTF-8, so here is my workaround.

<?php
function tolower($string) {
  if ($old_locale = setlocale(LC_CTYPE, 0)) {
    // 'fr_FR.ISO-8859-1' for *nix, 'French_France.1252' fallback for Windows
    if ($newlocale = setlocale(LC_CTYPE, 'fr_FR.ISO-8859-1', 'French_France.1252')) {
      preg_match('/\.(?<encoding>.+)$/', $newlocale, $match);
      $string = utf8_encode(strtolower(utf8_decode($string)));
    }
    setlocale(LC_CTYPE, $old_locale);
  }
  return $string;
}

print(tolower('DéJà-VU'));  // prints déjà-vu
?>

Change the language-country codes if you want some language other than French.
helvete at bahno dot net 26-Nov-2014 01:05
It is worth noting that
<?php
var_dump(strtolower(null))
?>
returns:
string(0) ""
RCube 31-Mar-2011 04:57
To convert an entire array to lower, I prefer this method;

<?php
function arraytolower(array $array, $round = 0){
  return unserialize(strtolower(serialize($array)));
}
?>

3 lines of code seem a lot less overhead than 10-40.
If there's any intrinsic problem with this method, please post it.
marcin at maydesign dot pl 22-Jun-2010 03:16
strtolower(); doesn't work for polish chars

<?php strtolower("m?kA"); ?>
will return: m?ka;

the best solution - use mb_strtolower()

<?php mb_strtolower("m?kA",'UTF-8'); ?>
will return: m?ka
leha_grobov 25-Jun-2009 08:03
the strtolower version to support most amount of languages including russian, french and so on:

<?php
function strtolower_utf8($string){
  $convert_to = array(
    "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u",
    "v", "w", "x", "y", "z", "à", "á", "a", "?", "?", "?", "?", "?", "è", "é", "ê", "?", "ì", "í", "?", "?",
    "e", "?", "ò", "ó", "?", "?", "?", "?", "ù", "ú", "?", "ü", "y", "а", "б", "в", "г", "д", "е", "ё", "ж",
    "з", "и", "й", "к", "л", "м", "н", "о", "п", "р", "с", "т", "у", "ф", "х", "ц", "ч", "ш", "щ", "ъ", "ы",
    "ь", "э", "ю", "я"
  );
  $convert_from = array(
    "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U",
    "V", "W", "X", "Y", "Z", "à", "á", "?", "?", "?", "?", "?", "?", "è", "é", "ê", "?", "ì", "í", "?", "?",
    "D", "?", "ò", "ó", "?", "?", "?", "?", "ù", "ú", "?", "ü", "Y", "А", "Б", "В", "Г", "Д", "Е", "Ё", "Ж",
    "З", "И", "Й", "К", "Л", "М", "Н", "О", "П", "Р", "С", "Т", "У", "Ф", "Х", "Ц", "Ч", "Ш", "Щ", "Ъ", "Ъ",
    "Ь", "Э", "Ю", "Я"
  );

  return str_replace($convert_from, $convert_to, $string);
}
?>
coder at bulgaria dot bg 03-Apr-2009 04:08
for cyrillic and UTF 8 use  mb_convert_case

exampel

<?php
$string = "Австралия";
$string = mb_convert_case($string, MB_CASE_LOWER, "UTF-8");
echo $string;

//output is: австралия
?>
dbers26 at gmail dot com 07-Jan-2009 01:34
the function  arraytolower will create duplicate entries since keys are case sensitive. 

<?php
$array = array('test1' => 'asgAFasDAAd', 'TEST2' => 'ASddhshsDGb', 'TeSt3 '=> 'asdasda@asdadadASDASDgh');

$array = arraytolower($array);
?>
/*
Array
(
    [test1] => asgafasdaad
    [TEST2] => ASddhshsDGb
    [TeSt3] => asdasda@asdadadASDASDgh
    [test2] => asddhshsdgb
    [test3] => asdasda@asdadadasdasdgh
)
*/

I prefer this method

<?php
  function arraytolower($array, $include_leys=false) {
   
    if($include_leys) {
      foreach($array as $key => $value) {
        if(is_array($value))
          $array2[strtolower($key)] = arraytolower($value, $include_leys);
        else
          $array2[strtolower($key)] = strtolower($value);
      }
      $array = $array2;
    }
    else {
      foreach($array as $key => $value) {
        if(is_array($value))
          $array[$key] = arraytolower($value, $include_leys);
        else
          $array[$key] = strtolower($value);  
      }
    }
   
    return $array;
  }
?>

which when used like this

<?php
$array = $array = array('test1' => 'asgAFasDAAd', 'TEST2' => 'ASddhshsDGb', 'TeSt3 '=> 'asdasda@asdadadASDASDgh');

$array1 = arraytolower($array);
$array2 = arraytolower($array,true);

print_r($array1);
print_r($array2);
?>

will give output of

Array
(
    [test1] => asgafasdaad
    [TEST2] => asddhshsdgb
    [TeSt3] => asdasda@asdadadasdasdgh
)
Array
(
    [test1] => asgafasdaad
    [test2] => asddhshsdgb
    [test3] => asdasda@asdadadasdasdgh
)
rodrigoATsistemasparainternetDOTcomDOTbr 09-Sep-2008 06:25
<?php
function fullLower($str){
   // convert to entities
   $subject = htmlentities($str,ENT_QUOTES);
   $pattern = '/&([a-z])(uml|acute|circ';
   $pattern.= '|tilde|ring|elig|grave|slash|horn|cedil|th);/e';
   $replace = "'&'.strtolower('\\1').'\\2'.';'";
   $result = preg_replace($pattern, $replace, $subject);
   // convert from entities back to characters
   $htmltable = get_html_translation_table(HTML_ENTITIES);
   foreach($htmltable as $key => $value) {
      $result = ereg_replace(addslashes($value),$key,$result);
   }
   return(strtolower($result));
}

echo fullLower("? é ò ? úù?");

//results ? é ò ? úù?
//adapted from fullUpper on strtoupper manual
?>
patricia at steuerungb dot de 17-Oct-2007 06:29
When you're not sure, how the current locale is set, you might find the following function useful. It's strtolower for utf8-formatted text:

<?php
function strtolower_utf8($inputString) {
    $outputString    = utf8_decode($inputString);
    $outputString    = strtolower($outputString);
    $outputString    = utf8_encode($outputString);
    return $outputString;
}
?>

It's not suitable for every occasion, but it surely gets in handy. I use it for lowering German 'Umlauts' like ? and ?.
rok dot kralj at gmail dot com 04-Jun-2007 11:49
Slovenian characters

<?php
    function strtolower_slovenian($string)
    {
        $low=array("?" => "?", "?" => "?", "?" => "?");
        return strtolower(strtr($string,$low));
    }

?>
marco at recchiuti dot it 22-May-2007 12:43
Maybe it is not so elegant, but it Works.
It's just a fast Idea and it is what I need.
Any hacks for other characters (link !, ? etc etc) should help.

function RemoveShouting($string)
{
     $frase = "";   
     $astri = explode(".", $string);
     foreach ($astri as $elem)
    $frase .= " ".ucfirst(trim(strtolower($elem))).". ";
      
    return trim($frase);
}

Cheers!
M
spiceee ddotty spiceee com 06-Mar-2006 04:53
If you ever need to strtolower a string with href tags on it and doesn't want to mess with the characters inside a tag, this is for you.

<?php

function loweroutsidetags ($str) {
    $chars = preg_split ("//", $str);
    $tolower = true;
    $str = '';

    foreach ($chars as $k) {
        if ($k == '<') { $tolower = false; }
        if ($tolower) { $k = strtolower ($k); }
        $str .= $k;   
        if ($k == '>') { $tolower = true; }
    }
    return $str;
}

?>

this:
echo loweroutsidetags('aALalala <a href="?q=CASEsENSITIVINESSinURLSareSTUPID">')

will give:
aalalala <a href="?q=CASEsENSITIVINESSinURLSareSTUPID">
Patrick 19-Jan-2006 10:57
If you're considering using the below unhtmlentities function from phpContrib, I would suggest this one as an alternative:

<?php
function unhtmlentities($string)
{
   // replace numeric entities
   $string = preg_replace('~&#x([0-9a-f]+);~ei', 'chr(hexdec("\\1"))', $string);
   $string = preg_replace('~&#([0-9]+);~e', 'chr(\\1)', $string);
   // replace literal entities
   $trans_tbl = get_html_translation_table(HTML_ENTITIES);
   $trans_tbl = array_flip($trans_tbl);
   return strtr($string, $trans_tbl);
}
?>

That was copied exactly from the html_entity_decode manual page.  It'll handle numeric entities correctly, the below function won't.
mhuggins57 at yahoo dot com 19-Jul-2005 04:04
There's a ucfirst "function" to make the first character uppercase, but there's no "lcfirst" function to make the first character lowercase.  Here's my own code to accomplish this.

<?
function lcfirst($str) {
    return strtolower(substr($str, 0, 1)) . substr($str, 1);
}
?>

I found this particularly useful for generating XML nodes with the Reflection class.
kmcdermott at perimeterinstitute dot ca 08-Dec-2004 01:04
To do case insensitive comparisons in a database, strtolower() can be a quick and dirty solution:

$Sql = "SELECT * FROM tablename WHERE LOWER(column_name) = '".strtolower($my_var)."'";
bkimble at ebaseweb dot com 19-Jan-2003 10:39
Heres a small function I wrote to stop people from submitting data that is ALL IN CAPS SO THEY CAN GET MORE ATTENTION THAT THE REST OF THE USER SUBMITTED DATA on my website :) If you can make it better, by all means do so. This function splits up words delimited by a space, and makes only the first letter of each word capitalized. You can easily modify it so it's only the very first word of the string. I've also added some exceptions so you don't make things like roman numerals look like "Iii" or "Xcmii" or something.

function RemoveShouting($string)
{
 $lower_exceptions = array(
        "to" => "1", "a" => "1", "the" => "1", "of" => "1"
 );
 
 $higher_exceptions = array( 
        "I" => "1", "II" => "1", "III" => "1", "IV" => "1", 
        "V" => "1", "VI" => "1", "VII" => "1", "VIII" => "1",
        "XI" => "1", "X" => "1"
 );
 
 $words = split(" ", $string);
 $newwords = array();
 foreach ($words as $word)
 {
  if (!$higher_exceptions[$word]) $word = strtolower($word);
  if (!$lower_exceptions[$word]) $word[0] = strtoupper($word[0]);
  array_push($newwords, $word);
 }
 return join(" ", $newwords);
}

BK