我想要一个str_replace()的版本，只替换$subject中$search的第一次出现。是否有一个简单的解决方案，或者我需要一个黑客解决方案？

没有任何版本，但解决方案一点也不黑。

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

相当简单，而且省去了正则表达式的性能损失。

奖励：如果您想替换 last 出现，只需使用 strrpos 代替 strpos。

可以用preg_replace来完成。

function str_replace_first($search, $replace, $subject)
{
    $search = '/'.preg_quote($search, '/').'/';
    return preg_replace($search, $replace, $subject, 1);
}

echo str_replace_first('abc', '123', 'abcdef abcdef abcdef'); 
// outputs '123def abcdef abcdef'

神奇之处在于可选的第四个参数[限制]。来自文档。

[Limit] - 每个主题字符串中每个模式的最大可能替换。默认为-1（无限制）。

不过，请参阅zombat的回答，以了解更有效的方法（大致上，3-4倍的速度）。

编辑：两个答案都已更新，现在是正确的。我将留下这个答案，因为函数的时序仍然有用。

"僵尸 "和 "太多的php "的答案很不幸地不正确。这是对僵尸发布的答案的修改（因为我没有足够的声誉来发布评论）。

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

注意strlen($needle)，而不是strlen($replace)。Zombat的例子只有在needle和replace长度相同的情况下才能正确工作。

在一个与PHP自己的str_replace签名相同的函数中，也有同样的功能。

function str_replace_first($search, $replace, $subject) {
    $pos = strpos($subject, $search);
    if ($pos !== false) {
        return substr_replace($subject, $replace, $pos, strlen($search));
    }
    return $subject;
}

这是修订后的 "太多的php "的答案。

implode($replace, explode($search, $subject, 2));

注意末尾的2而不是1，或者说是函数格式。

function str_replace_first($search, $replace, $subject) {
    return implode($replace, explode($search, $subject, 2));
}

我对这两个函数进行了计时，当没有找到匹配的时候，第一个函数的速度是两倍。当找到匹配的时候，它们的速度是一样的。

我想知道哪一个是最快的，所以我把它们都测试了一遍。

下面你将会发现。

• 所有被贡献到本页面的功能的全面列表
• 每项对比的基准测试（10,000次运行的平均执行时间）。
• 每个答案的链接（用于完整的代码）。

所有功能都在相同的设置下进行了测试。

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

只替换一个字符串中第一个出现的字符串的函数。

• 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%
  

只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));

  [CONTRIBUTED BY] => oLinkSoftware - modified zombat
  [OOO.OOO.OOO.S] => OOO.OOO.B.S
  [AVERAGE TIME] => 0.0000068083
  [SLOWER BY] => FASTEST
  

• strrev(implode(strrev($replace), explode(strrev($search), strrev($string), 2)));

  [CONTRIBUTED BY] => oLinkSoftware
  [OOO.OOO.OOO.S] => OOO.OOO.B.S
  [AVERAGE TIME] => 0.0000084460
  [SLOWER BY] => 24.05%
  

不幸的是，我不知道有什么PHP函数可以做到这一点。
你可以像这样相当容易地推出你自己的函数。

function replace_first($find, $replace, $subject) {
    // stolen from the comments at PHP.net/str_replace
    // Splits $subject into an array of 2 items by $find,
    // and then joins the array with $replace
    return implode($replace, explode($find, $subject, 2));
}

我创建了这个小函数，用limit来替换字符串（区分大小写），不需要Regexp。它运行良好。

function str_replace_limit($search, $replace, $string, $limit = 1) {
    $pos = strpos($string, $search);

    if ($pos === false) {
        return $string;
    }

    $searchLen = strlen($search);

    for ($i = 0; $i < $limit; $i++) {
        $string = substr_replace($string, $replace, $pos, $searchLen);

        $pos = strpos($string, $search);

        if ($pos === false) {
            break;
        }
    }

    return $string;
}

举例说明用法。

$search  = 'foo';
$replace = 'bar';
$string  = 'foo wizard makes foo brew for evil foo and jack';
$limit   = 2;

$replaced = str_replace_limit($search, $replace, $string, $limit);

echo $replaced;
// bar wizard makes bar brew for evil foo and jack

$str = "/property/details&id=202&test=123#tab-6p";
$position = strpos($str,"&");
echo substr_replace($str,"?",$position,1);

使用substr_replace，我们可以只替换字符串中出现的第一个字符。由于&重复了多次，但只在第一个位置出现，我们必须将&替换为?

=> 代码已被修改，所以考虑到一些评论太旧了

并且感谢大家帮助我改进这一点

任何BUG，请与我联系；我将立即解决这个问题。

因此，让我们为之努力。

将第一个 'o' 替换为 'ea' 例如：

$s='I love you';
$s=str_replace_first('o','ea',$s);
echo $s;

//output: I leave you

该功能。

function str_replace_first($this,$that,$s)
{
    $w=strpos($s,$this);
    if($w===false)return $s;
    return substr($s,0,$w).$that.substr($s,$w+strlen($this));
}

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()进行替换。

但是，我真的会选择正则表达法。

function str_replace_once($search, $replace, $subject) {
    $pos = strpos($subject, $search);
    if ($pos === false) {
        return $subject;
    }

    return substr($subject, 0, $pos) . $replace . substr($subject, $pos + strlen($search));
}

$string = 'this is my world, not my world';
$find = 'world';
$replace = 'farm';
$result = preg_replace("/$find/",$replace,$string,1);
echo $result;

为了扩展@renocor 的答案，我编写了一个与str_replace() 100% 向后兼容的函数。也就是说，您可以用str_replace_limit() 替换所有 次出现的str_replace()，而不会搞砸任何事情，即使是那些为$search、$replace 和/或$subject 使用数组的人。

如果你想用($string===strval(intval(strval($string))))代替函数调用，该函数可以完全自成一体，但我建议不要这样做，因为在处理以字符串形式提供的整数时，valid_integer()是一个相当有用的函数。

注意：只要有可能，str_replace_limit()将使用str_replace()代替，因此所有对str_replace()的调用都可以用str_replace_limit()代替，而不必担心对性能的打击。

Usage

<?php
$search = 'a';
$replace = 'b';
$subject = 'abcabc';

$limit = -1; // No limit
$new_string = str_replace_limit($search, $replace, $subject, $count, $limit);
echo $count.' replacements -- '.$new_string;

2名替补 -- -- bbcbbc

$limit = 1; // Limit of 1
$new_string = str_replace_limit($search, $replace, $subject, $count, $limit);
echo $count.' replacements -- '.$new_string;

1名替代者 -- -- BBCABC

$limit = 10; // Limit of 10
$new_string = str_replace_limit($search, $replace, $subject, $count, $limit);
echo $count.' replacements -- '.$new_string;

2名替补 -- -- bbcbbc

Function

<?php

/**
 * Checks if $string is a valid integer. Integers provided as strings (e.g. '2' vs 2)
 * are also supported.
 * @param mixed $string
 * @return bool Returns boolean TRUE if string is a valid integer, or FALSE if it is not 
 */
function valid_integer($string){
    // 1. Cast as string (in case integer is provided)
    // 1. Convert the string to an integer and back to a string
    // 2. Check if identical (note: 'identical', NOT just 'equal')
    // Note: TRUE, FALSE, and NULL $string values all return FALSE
    $string = strval($string);
    return ($string===strval(intval($string)));
}

/**
 * Replace $limit occurences of the search string with the replacement string
 * @param mixed $search The value being searched for, otherwise known as the needle. An
 * array may be used to designate multiple needles.
 * @param mixed $replace The replacement value that replaces found search values. An
 * array may be used to designate multiple replacements.
 * @param mixed $subject The string or array being searched and replaced on, otherwise
 * known as the haystack. If subject is an array, then the search and replace is
 * performed with every entry of subject, and the return value is an array as well. 
 * @param string $count If passed, this will be set to the number of replacements
 * performed.
 * @param int $limit The maximum possible replacements for each pattern in each subject
 * string. Defaults to -1 (no limit).
 * @return string This function returns a string with the replaced values.
 */
function str_replace_limit(
        $search,
        $replace,
        $subject,
        &$count,
        $limit = -1
    ){

    // Set some defaults
    $count = 0;

    // Invalid $limit provided. Throw a warning.
    if(!valid_integer($limit)){
        $backtrace = debug_backtrace();
        trigger_error('Invalid $limit `'.$limit.'` provided to '.__function__.'() in '.
                '`'.$backtrace[0]['file'].'` on line '.$backtrace[0]['line'].'. Expecting an '.
                'integer', E_USER_WARNING);
        return $subject;
    }

    // Invalid $limit provided. Throw a warning.
    if($limit<-1){
        $backtrace = debug_backtrace();
        trigger_error('Invalid $limit `'.$limit.'` provided to '.__function__.'() in '.
                '`'.$backtrace[0]['file'].'` on line '.$backtrace[0]['line'].'. Expecting -1 or '.
                'a positive integer', E_USER_WARNING);
        return $subject;
    }

    // No replacements necessary. Throw a notice as this was most likely not the intended
    // use. And, if it was (e.g. part of a loop, setting $limit dynamically), it can be
    // worked around by simply checking to see if $limit===0, and if it does, skip the
    // function call (and set $count to 0, if applicable).
    if($limit===0){
        $backtrace = debug_backtrace();
        trigger_error('Invalid $limit `'.$limit.'` provided to '.__function__.'() in '.
                '`'.$backtrace[0]['file'].'` on line '.$backtrace[0]['line'].'. Expecting -1 or '.
                'a positive integer', E_USER_NOTICE);
        return $subject;
    }

    // Use str_replace() whenever possible (for performance reasons)
    if($limit===-1){
        return str_replace($search, $replace, $subject, $count);
    }

    if(is_array($subject)){

        // Loop through $subject values and call this function for each one.
        foreach($subject as $key => $this_subject){

            // Skip values that are arrays (to match str_replace()).
            if(!is_array($this_subject)){

                // Call this function again for
                $this_function = __FUNCTION__;
                $subject[$key] = $this_function(
                        $search,
                        $replace,
                        $this_subject,
                        $this_count,
                        $limit
                );

                // Adjust $count
                $count += $this_count;

                // Adjust $limit, if not -1
                if($limit!=-1){
                    $limit -= $this_count;
                }

                // Reached $limit, return $subject
                if($limit===0){
                    return $subject;
                }

            }

        }

        return $subject;

    } elseif(is_array($search)){
        // Only treat $replace as an array if $search is also an array (to match str_replace())

        // Clear keys of $search (to match str_replace()).
        $search = array_values($search);

        // Clear keys of $replace, if applicable (to match str_replace()).
        if(is_array($replace)){
            $replace = array_values($replace);
        }

        // Loop through $search array.
        foreach($search as $key => $this_search){

            // Don't support multi-dimensional arrays (to match str_replace()).
            $this_search = strval($this_search);

            // If $replace is an array, use the value of $replace[$key] as the replacement. If
            // $replace[$key] doesn't exist, just an empty string (to match str_replace()).
            if(is_array($replace)){
                if(array_key_exists($key, $replace)){
                    $this_replace = strval($replace[$key]);
                } else {
                    $this_replace = '';
                }
            } else {
                $this_replace = strval($replace);
            }

            // Call this function again for
            $this_function = __FUNCTION__;
            $subject = $this_function(
                    $this_search,
                    $this_replace,
                    $subject,
                    $this_count,
                    $limit
            );

            // Adjust $count
            $count += $this_count;

            // Adjust $limit, if not -1
            if($limit!=-1){
                $limit -= $this_count;
            }

            // Reached $limit, return $subject
            if($limit===0){
                return $subject;
            }

        }

        return $subject;

    } else {
        $search = strval($search);
        $replace = strval($replace);

        // Get position of first $search
        $pos = strpos($subject, $search);

        // Return $subject if $search cannot be found
        if($pos===false){
            return $subject;
        }

        // Get length of $search, to make proper replacement later on
        $search_len = strlen($search);

        // Loop until $search can no longer be found, or $limit is reached
        for($i=0;(($i<$limit)||($limit===-1));$i++){

            // Replace 
            $subject = substr_replace($subject, $replace, $pos, $search_len);

            // Increase $count
            $count++;

            // Get location of next $search
            $pos = strpos($subject, $search);

            // Break out of loop if $needle
            if($pos===false){
                break;
            }

        }

        // Return new $subject
        return $subject;

    }

}

根据我的测试结果，我想投票给karim79提供的regular_express。(我现在没有足够的声誉来投票！)

zombat的解决方案使用了太多的函数调用，我甚至简化了代码。我用PHP5.4把两个方案都运行了10万次，结果是这样的。

$str = 'Hello abc, have a nice day abc! abc!';
$pos = strpos($str, 'abc');
$str = substr_replace($str, '123', $pos, 3);

======1.85秒

$str = 'Hello abc, have a nice day abc! abc!';
$str = preg_replace('/abc/', '123', $str, 1);

======1.35秒

正如你所看到的。preg_replace的性能并不像很多人认为的那么差。所以我建议，如果你的正则表达式不复杂的话，就用经典的方案。

为了扩展 zombat 的答案（我相信这是最好的答案），我创建了他的函数的递归版本，该函数接受 $limit 参数来指定要替换的出现次数。

function str_replace_limit($haystack, $needle, $replace, $limit, $start_pos = 0) {
    if ($limit <= 0) {
        return $haystack;
    } else {
        $pos = strpos($haystack,$needle,$start_pos);
        if ($pos !== false) {
            $newstring = substr_replace($haystack, $replace, $pos, strlen($needle));
            return str_replace_limit($newstring, $needle, $replace, $limit-1, $pos+strlen($replace));
        } else {
            return $haystack;
        }
    }
}

对于一个字符串来说

$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

对于单一的字符

$string[strpos($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

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 啦啦啦"。

这个函数在很大程度上受到了@renocor的回答的启发。 它使这个函数在多字节上是安全的。

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;
}

你可以使用这一点。

function str_replace_once($str_pattern, $str_replacement, $string){ 

        if (strpos($string, $str_pattern) !== false){ 
            $occurrence = strpos($string, $str_pattern); 
            return substr_replace($string, $str_replacement, strpos($string, $str_pattern), strlen($str_pattern)); 
        } 

        return $string; 
    } 

从php.net上找到了这个例子

使用方法。

$string = "Thiz iz an examplz";
var_dump(str_replace_once('z','Z', $string)); 

输出。

ThiZ iz an examplz

这可能会降低一点性能，但这是最简单的解决方案。

For Loop解决方案

<?php
echo replaceFirstMatchedChar("&", "?", "/property/details&id=202&test=123#tab-6");

function replaceFirstMatchedChar($searchChar, $replaceChar, $str)
{
    for ($i = 0; $i < strlen($str); $i++) {

        if ($str[$i] == $searchChar) {
            $str[$i] = $replaceChar;
            break;
        }
    }
    return $str;
}

我想用preg来代替。它有一个LIMIT参数，你可以把它设置为1。

preg_replace (regex, subst, string, limit) // default is -1

$str = "Hello there folks!"
$str_ex = explode("there, $str, 2);   //explodes $string just twice
                                      //outputs: array ("Hello ", " folks")
$str_final = implode("", $str_ex);    // glues above array together
                                      // outputs: str("Hello  folks")

还有一个额外的空间，但这并不重要，因为在我的案例中，它是用于后台脚本的。

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

这里有一个处理错误的函数

/**
 * 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;
}

这是我创建的一个简单的类，用来包装我们稍加修改的str_replace()函数。

我们的php::str_rreplace()函数也允许你进行反向的、有限的str_replace()，当试图只替换一个字符串的最后X个实例时，这将是非常方便的。

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) );
    }
}