最简单的方法是使用正则表达式。

另一种方法是用strpos()找到字符串的位置，然后用substr_replace()

但我真的会选择RegExp。

对于字符串

$string = 'OOO.OOO.OOO.S';
$search = 'OOO';
$replace = 'B';

//replace ONLY FIRST occurance of "OOO" with "B"
    $string = substr_replace($string,$replace,0,strlen($search));
    //$string => B.OOO.OOO.S

//replace ONLY LAST occurance of "OOOO" with "B"
    $string = substr_replace($string,$replace,strrpos($string,$search),strlen($search)) 
    //$string => OOO.OOO.B.S

    //replace ONLY LAST occurance of "OOOO" with "B"
    $string = strrev(implode(strrev($replace),explode(strrev($search),strrev($string),2)))
    //$string => OOO.OOO.B.S

对于单个字符

$string[strpos($string,$search)] = $replace;


//EXAMPLE

$string = 'O.O.O.O.S';
$search = 'O';
$replace = 'B';

//replace ONLY FIRST occurance of "O" with "B" 
    $string[strpos($string,$search)] = $replace;  
    //$string => B.O.O.O.S

//replace ONLY LAST occurance of "O" with "B" 
    $string[strrpos($string,$search)] = $replace; 
    // $string => B.O.O.B.S

我想知道哪一个是最快的，所以我都测试了。

下面你会发现:

这个页面上的所有功能的综合列表 对每个贡献进行基准测试(平均执行时间超过10,000次运行) 链接到每个答案(完整代码)

所有功能都在相同的设置下进行测试:

$string = 'OOO.OOO.OOO.S';
$search = 'OOO'; 
$replace = 'B';

仅替换字符串中字符串第一次出现的函数:

substr_replace($string, $replace, 0, strlen($search)); [CONTRIBUTED BY] => zombat [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000062883 [SLOWER BY] => FASTEST replace_first($search, $replace, $string); [CONTRIBUTED BY] => too much php [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000073902 [SLOWER BY] => 17.52% preg_replace($search, $replace, $string, 1); [CONTRIBUTED BY] => karim79 [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000077519 [SLOWER BY] => 23.27% str_replace_once($search, $replace, $string); [CONTRIBUTED BY] => happyhardik [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000082286 [SLOWER BY] => 30.86% str_replace_limit($search, $replace, $string, $count, 1); [CONTRIBUTED BY] => bfrohs - expanded renocor [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000083342 [SLOWER BY] => 32.54% str_replace_limit($search, $replace, $string, 1); [CONTRIBUTED BY] => renocor [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000093116 [SLOWER BY] => 48.08% str_replace_limit($string, $search, $replace, 1, 0); [CONTRIBUTED BY] => jayoaK [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000093862 [SLOWER BY] => 49.26%

仅替换字符串中最后一次出现的字符串的函数:

Substr_replace ($string， $replace, strrpos($string， $search)， strlen($search)); [贡献BY] => oLinkSoftware - modified僵尸 [OOO.OOO.OOO。S] => ooo [平均时间]=> 0.0000068083 [慢]=>最快 Strrev (implode(Strrev ($replace)， explosion (Strrev ($search)， Strrev ($string)， 2))); [贡献BY] => oLinkSoftware [OOO.OOO.OOO。S] => ooo [平均时间]=> 0.0000084460 [慢]=> 24.05%

这个函数很大程度上受到@ renoor回答的启发。 它使函数多字节安全。

function str_replace_limit($search, $replace, $string, $limit)
{
    $i = 0;
    $searchLength = mb_strlen($search);

    while(($pos = mb_strpos($string, $search)) !== false && $i < $limit)
    {
        $string = mb_substr_replace($string, $replace, $pos, $searchLength);
        $i += 1;
    }

    return $string;
}

function mb_substr_replace($string, $replacement, $start, $length = null, $encoding = null)
{
    $string = (array)$string;
    $encoding = is_null($encoding) ? mb_internal_encoding() : $encoding;
    $length = is_null($length) ? mb_strlen($string) - $start : $length;

    $string = array_map(function($str) use ($replacement, $start, $length, $encoding){

        $begin = mb_substr($str, 0, $start, $encoding);
        $end = mb_substr($str, ($start + $length), mb_strlen($str), $encoding);

        return $begin . $replacement . $end;

    }, $string);

    return ( count($string) === 1 ) ? $string[0] : $string;
}

最简单的方法是使用正则表达式。

另一种方法是用strpos()找到字符串的位置，然后用substr_replace()

但我真的会选择RegExp。

下面是我创建的一个简单类，用于包装稍作修改的str_replace()函数。

我们的php::str_rreplace()函数还允许执行反向的、有限的str_replace()，这在试图只替换字符串的最后X个实例时非常方便。

这些例子都使用了preg_replace()。

<?php
class php {

    /**
    * str_replace() from the end of a string that can also be limited e.g. replace only the last instance of '</div>' with ''
    *
    * @param string   $find
    * @param string   $replace
    * @param string   $subject
    * @param int      $replacement_limit | -1 to replace all references
    *
    * @return string
    */
    public static function str_replace($find, $replace, $subject, $replacement_limit = -1) {
        $find_pattern = str_replace('/', '\/', $find);
        return preg_replace('/' . $find_pattern . '/', $replace, $subject, $replacement_limit);
    }

    /**
    * str_replace() from the end of a string that can also be limited e.g. replace only the last instance of '</div>' with ''
    *
    * @param string   $find
    * @param string   $replace
    * @param string   $subject
    * @param int      $replacement_limit | -1 to replace all references
    *
    * @return string
    */
    public static function str_rreplace($find, $replace, $subject, $replacement_limit = -1) {
        return strrev( self::str_replace(strrev($find), strrev($replace), strrev($subject), $replacement_limit) );
    }
}