如果你的字符串不包含任何多字节字符，如果你只想替换一个字符，你可以简单地使用strpos

这里是处理错误的函数

/**
 * Replace the first occurence of given string
 *
 * @param  string $search  a char to search in `$subject`
 * @param  string $replace a char to replace in `$subject`
 * @param  string $subject
 * @return string
 *
 * @throws InvalidArgumentException if `$search` or `$replace` are invalid or if `$subject` is a multibytes string
 */
function str_replace_first(string $search , string $replace , string $subject) : string {
    // check params
    if(strlen($replace) != 1 || strlen($search) != 1) {
        throw new InvalidArgumentException('$search & $replace must be char');
    }elseif(mb_strlen($subject) != strlen($subject)){
        throw new InvalidArgumentException('$subject is an multibytes string');
    }
    // search 
    $pos = strpos($subject, $search);
    if($pos === false) {
        // not found
        return $subject;
    }

    // replace
    $subject[$replace] = $subject;

    return $subject;
}

它没有版本，但解决方案一点也不俗气。

$pos = strpos($haystack, $needle);
if ($pos !== false) {
    $newstring = substr_replace($haystack, $replace, $pos, strlen($needle));
}

非常简单，并且节省了正则表达式的性能损失。

额外的好处:如果你想替换上次出现的字符串，只需使用strrpos来代替strpos。

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%

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。

补充一下人们所说的，记住整个字符串是一个数组:

$string = "Lorem ipsum lá lá lá";

$string[0] = "B";

echo $string;

“Borem ipsum there there”

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) );
    }
}