For循环解决方案

<?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;
}

可以用preg_replace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[Limit]。从文档中可以看到:

[极限]-最大可能 每个中的每个模式的替换 主题字符串。默认为-1 (no 限制)。

不过，请参阅zombat的回答以获得更有效的方法(大约快3-4倍)。

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));
}

For循环解决方案

<?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;
}

不幸的是，我不知道任何PHP函数可以做到这一点。 你可以像这样很容易地自己卷:

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));
}

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