mb_strtolower

(PHP 4 >= 4.3.0, PHP 5, PHP 7, PHP 8)

mb_strtolower — 使字符串小写

说明

mb_strtolower ( string $str , string $encoding = mb_internal_encoding() ) : string

返回所有字母字符转换成小写的 str。

参数

str

要被小写的字符串。

encoding

encoding 参数为字符编码。如果省略或是 null，则使用内部字符编码。

返回值

所有字母字符已被转换成小写的 str。

Unicode

更多关于 Unicode 属性的信息，请参见 » http://www.unicode.org/reports/tr21/。

和 strtolower() 不同的是，"字母"字符的检测是根据字符的 Unicode 属性。 因此函数的行为不会受语言设置的影响，能偶转换任意具有"字母"属性的字符，例如元音变音 A（?）。

范例

Example #1 mb_strtolower() 例子

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

Example #2 非拉丁 UTF-8 文本的 mb_strtolower() 例子

<?php
$str = "Τ?χιστη αλ?πηξ βαφ?? ψημ?νη γη, δρασκελ?ζει υπ?ρ νωθρο? κυν??";
$str = mb_strtolower($str, 'UTF-8');
echo $str; // 输出 τ?χιστη αλ?πηξ βαφ?? ψημ?νη γη, δρασκελ?ζει υπ?ρ νωθρο? κυν??
?>

参见

User Contributed Notes

Ukio 25-Nov-2015 09:32
Maybe it help someone.
Make up case with first char, low case for other.

<?php
function str_split_unicode($str, $l = 0) {
    if ($l > 0) {
        $ret = array();
        $len = mb_strlen($str, "UTF-8");
        for ($i = 0; $i < $len; $i += $l) {
            $ret[] = mb_substr($str, $i, $l, "UTF-8");
        }
        return $ret;
    }
    return preg_split("//u", $str, -1, PREG_SPLIT_NO_EMPTY);
}

function ToCorrectCase($str){

    $str = mb_strtolower($str);
    $str_array = str_split_unicode($str);
    $str_array[0] = mb_strtoupper($str_array[0]);
    $str = '';
    foreach ($str_array as $key){
        $str = $str.$key;
    }
    return $str;
}
?>
fisharebest at gmail dot com 18-Apr-2012 04:27
There is not a one-to-one correspondence between upper and lower case letters.

Turkish is a good example of this.  In Turkish, the letter I/i has a dotted-upper-case form (?) and a dotless-lower-case form (?).

https://en.wikipedia.org/wiki/Dotted_and_dotless_I

This means that you cannot correctly convert between upper-case and lower-case without also knowing the locale of the data.

Since the function does not let you specify a locale, you should only use this function for text written in languages that follow the same orthography as English.

Although it does handle some digraphs, such as the Dutch ij (?), it does not handle others, such as the Polish dz (?).
akniep at linklift dot net 12-Sep-2011 08:42
Please, note that when using with UTF-8 mb_strtolower will only convert upper case characters to lower case which are marked with the Unicode property "Upper case letter" ("Lu"). However, there are also letters such as "Letter numbers" (Unicode property "Nl") that also have lower case and upper case variants. These characters will not be converted be mb_strtolower!

Example:
The Roman letters Ⅰ, Ⅱ, Ⅲ, ..., ? (UTF-8 code points 8544 through 8559) also exist in their respective lower case variants ⅰ, ⅱ, ⅲ, ..., ? (UTF-8 code points 8560 through 8575) and should, in my opinion, also be converted by mb_strtolower, but they are not!

Big internet-companies (like Google) do match both variants as semantically equal (since the representations only differ in case).

Since I was not finding any proper solution in the internet on how to map all UTF8-strings to their lowercase counterpart in PHP, I offer the following hard-coded extended mb_strtolower function for UTF-8 strings:

The function wraps the existing function mb_strtolower() and additionally replaces uppercase UTF8-characters for which there is a lowercase representation. Since there is no proper Unicode uppercase and lowercase character-table in the internet that I was able to find, I checked the first million UTF8-characters against the Google-search and -KeywordTool and identified the following 78 characters as uppercase-characters, not being replaced by mb_strtolower, but having a UTF8 lowercase counterpart.

<?php

//the numbers in the in-line-comments display the characters' Unicode code-points (CP).
function strtolower_utf8_extended( $utf8_string )
{
    $additional_replacements    = array
        ( "?"    => "?"        //   453 ->   454
        , "?"    => "?"        //   456 ->   457
        , "?"    => "?"        //   459 ->   460
        , "?"    => "?"        //   498 ->   499
        , "?"    => "?"        //  1015 ->  1016
        , "?"    => "?"        //  1017 ->  1010
        , "?"    => "?"        //  1018 ->  1019
        , "?"    => "?"        //  8072 ->  8064
        , "?"    => "?"        //  8073 ->  8065
        , "?"    => "?"        //  8074 ->  8066
        , "?"    => "?"        //  8075 ->  8067
        , "?"    => "?"        //  8076 ->  8068
        , "?"    => "?"        //  8077 ->  8069
        , "?"    => "?"        //  8078 ->  8070
        , "?"    => "?"        //  8079 ->  8071
        , "?"    => "?"        //  8088 ->  8080
        , "?"    => "?"        //  8089 ->  8081
        , "?"    => "?"        //  8090 ->  8082
        , "?"    => "?"        //  8091 ->  8083
        , "?"    => "?"        //  8092 ->  8084
        , "?"    => "?"        //  8093 ->  8085
        , "?"    => "?"        //  8094 ->  8086
        , "?"    => "?"        //  8095 ->  8087
        , "?"    => "?"        //  8104 ->  8096
        , "?"    => "?"        //  8105 ->  8097
        , "?"    => "?"        //  8106 ->  8098
        , "?"    => "?"        //  8107 ->  8099
        , "?"    => "?"        //  8108 ->  8100
        , "?"    => "?"        //  8109 ->  8101
        , "?"    => "?"        //  8110 ->  8102
        , "?"    => "?"        //  8111 ->  8103
        , "?"    => "?"        //  8124 ->  8115
        , "?"    => "?"        //  8140 ->  8131
        , "?"    => "?"        //  8188 ->  8179
        , "Ⅰ"    => "ⅰ"        //  8544 ->  8560
        , "Ⅱ"    => "ⅱ"        //  8545 ->  8561
        , "Ⅲ"    => "ⅲ"        //  8546 ->  8562
        , "Ⅳ"    => "ⅳ"        //  8547 ->  8563
        , "Ⅴ"    => "ⅴ"        //  8548 ->  8564
        , "Ⅵ"    => "ⅵ"        //  8549 ->  8565
        , "Ⅶ"    => "ⅶ"        //  8550 ->  8566
        , "Ⅷ"    => "ⅷ"        //  8551 ->  8567
        , "Ⅸ"    => "ⅸ"        //  8552 ->  8568
        , "Ⅹ"    => "ⅹ"        //  8553 ->  8569
        , "Ⅺ"    => "?"        //  8554 ->  8570
        , "Ⅻ"    => "?"        //  8555 ->  8571
        , "?"    => "?"        //  8556 ->  8572
        , "?"    => "?"        //  8557 ->  8573
        , "?"    => "?"        //  8558 ->  8574
        , "?"    => "?"        //  8559 ->  8575
        , "?"    => "?"        //  9398 ->  9424
        , "?"    => "?"        //  9399 ->  9425
        , "?"    => "?"        //  9400 ->  9426
        , "?"    => "?"        //  9401 ->  9427
        , "?"    => "?"        //  9402 ->  9428
        , "?"    => "?"        //  9403 ->  9429
        , "?"    => "?"        //  9404 ->  9430
        , "?"    => "?"        //  9405 ->  9431
        , "?"    => "?"        //  9406 ->  9432
        , "?"    => "?"        //  9407 ->  9433
        , "?"    => "?"        //  9408 ->  9434
        , "?"    => "?"        //  9409 ->  9435
        , "?"    => "?"        //  9410 ->  9436
        , "?"    => "?"        //  9411 ->  9437
        , "?"    => "?"        //  9412 ->  9438
        , "?"    => "?"        //  9413 ->  9439
        , "?"    => "?"        //  9414 ->  9440
        , "?"    => "?"        //  9415 ->  9441
        , "?"    => "?"        //  9416 ->  9442
        , "?"    => "?"        //  9417 ->  9443
        , "?"    => "?"        //  9418 ->  9444
        , "?"    => "?"        //  9419 ->  9445
        , "?"    => "?"        //  9420 ->  9446
        , "?"    => "?"        //  9421 ->  9447
        , "?"    => "?"        //  9422 ->  9448
        , "?"    => "?"        //  9423 ->  9449
        , "??"    => "??"        // 66598 -> 66638
        , "??"    => "??"        // 66599 -> 66639
        );
   
    $utf8_string    = mb_strtolower( $utf8_string, "UTF-8");
   
    $utf8_string    = strtr( $utf8_string, $additional_replacements );
   
    return $utf8_string;
} //strtolower_utf8_extended()

?>
Ken Shiro 31-Jul-2010 02:07
[If you get this error:]
Fatal error: Call to undefined function: mb_strtolower() in ????.php on line ??

The PHP mbstring extension, which is required to handle international character sets, is not available on your server. Check your PHP configuration and make sure that PHP has been compiled with --enable-mbstring.

It's also apply to
Call to undefined function mb_eregi() / mb_strtolower()
Philipp H 01-Nov-2007 10:11
Note that mb_strtolower() is very SLOW, if you have a database connection, you may want to use it to convert your strings to lower case. Even latin1/9 (iso-8859-1/15) and other encodings are possible.

Have a look at my simple benchmark:

<?php

$text = "L?rem ip?üm d?l?r ?it ?met, c?n?ectetüer ?dipi?cing elit. Sed ligül?. Pr?e?ent jü?t? tellü?, gr?vid? eü, tempü? ?, m?tti? n?n, ?rci. N?m qüi? l?rem. N?m ?liqüet elit ?ed elit. Ph??ellü? venen?ti? jü?t? eget enim. D?nec ni?l. Pr?in m?tti? venen?ti? jü?t?. Sed ?liqü?m p?rt? ?rci. Cr?? elit ni?l, c?nv?lli? qüi?, tincidünt ?t, vehicül? ?ccüm??n, ?di?. Sed m?le?tie. Eti?m m?lli? feügi?t elit. Ve?tibülüm ?nte ip?üm primi? in f?ücibü? ?rci lüctü? et ültrice? p??üere cübili? Cür?e; M?ecen?? n?n nüll?.";

// mb_strtolower()
$timeMB = microtime(true);    
             
    for($i=0;$i<30000;$i++)
        $lower = mb_strtolower("$text/no-cache-$i");

$timeMB = microtime(true) - $timeMB;

// MySQL lower()
$timeSQL = microtime(true);   

    mysql_query("set names latin1");              
    for($i=0;$i<30000;$i++) {
        $r = mysql_fetch_row(mysql_query("select lower('$text/no-cache-$i')"));
        $lower = $r[0];
    }

$timeSQL = microtime(true) - $timeSQL;

echo "mb: ".sprintf("%.5f",$timeMB)." sek.<br />";
echo "sql: ".sprintf("%.5f",$timeSQL)." sek.<br />";

// Result on my notebook:
// mb: 11.50642 sek.
// sql: 5.44143 sek.

?>
btherl at yahoo dot com dot au 15-Nov-2005 09:12
If you use this function on a unicode string without telling PHP that it is unicode, then you will corrupt your string.  In particular, the uppercase 'A' with tilde, common in 2-byte UTF-8 characters, is converted to lowercase 'a' with tilde.

This can be handled correctly by:
$str = mb_strtolower($str, mb_detect_encoding($str));

Or if you know your data is UTF-8, just use the string "UTF-8" as the second argument.

You should check also that mb_detect_encoding() is checking the encodings you want it to check, and is detecting the correct encodings.