php 使用 str_replace 使其仅作用于第一个匹配项？
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Using str_replace so that it only acts on the first match?
提问by Nick Heiner
I want a version of str_replace()that only replaces the first occurrence of $searchin the $subject. Is there an easy solution to this, or do I need a hacky solution?
我想的一个版本str_replace()是只替换第一次出现$search的$subject。有没有一个简单的解决方案，或者我需要一个hacky解决方案？
回答by zombat
There's no version of it, but the solution isn't hacky at all.
没有它的版本，但解决方案一点也不笨拙。
$pos = strpos($haystack, $needle);
if ($pos !== false) {
$newstring = substr_replace($haystack, $replace, $pos, strlen($needle));
}
Pretty easy, and saves the performance penalty of regular expressions.
非常简单，并节省了正则表达式的性能损失。
Bonus: If you want to replace lastoccurrence, just use strrposin place of strpos.
奖励：如果你想替换最后一次出现，只需使用strrpos代替strpos.
回答by karim79
Can be done with preg_replace:
可以用preg_replace完成：
function str_replace_first($from, $to, $content)
{
$from = '/'.preg_quote($from, '/').'/';
return preg_replace($from, $to, $content, 1);
}
echo str_replace_first('abc', '123', 'abcdef abcdef abcdef');
// outputs '123def abcdef abcdef'
The magic is in the optional fourth parameter [Limit]. From the documentation:
神奇之处在于可选的第四个参数 [Limit]。从文档：
[Limit] - The maximum possible replacements for each pattern in each subject string. Defaults to -1 (no limit).
[限制] - 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）。
Though, see zombat's answerfor a more efficient method (roughly, 3-4x faster).
不过，请参阅zombat 的答案以了解更有效的方法（大约快 3-4 倍）。
回答by Bas
Edit: both answers have been updated and are now correct. I'll leave the answer since the function timings are still useful.
编辑：两个答案都已更新，现在是正确的。我会留下答案，因为功能计时仍然有用。
The answers by 'zombat' and 'too much php' are unfortunately not correct. This is a revision to the answer zombat posted (as I don't have enough reputation to post a comment):
不幸的是，'zombat' 和 'too much php' 的答案是不正确的。这是对 zombat 发布的答案的修订（因为我没有足够的声誉发表评论）：
$pos = strpos($haystack,$needle);
if ($pos !== false) {
$newstring = substr_replace($haystack,$replace,$pos,strlen($needle));
}
Note the strlen($needle), instead of strlen($replace). Zombat's example will only work correctly if needle and replace are the same length.
注意 strlen($needle)，而不是 strlen($replace)。Zombat 的示例只有在针和替换的长度相同时才能正常工作。
Here's the same functionality in a function with the same signature as PHP's own str_replace:
这是与 PHP 自己的 str_replace 具有相同签名的函数中的相同功能：
function str_replace_first($search, $replace, $subject) {
$pos = strpos($subject, $search);
if ($pos !== false) {
return substr_replace($subject, $replace, $pos, strlen($search));
}
return $subject;
}
This is the revised answer of 'too much php':
这是'太多php'的修订答案：
implode($replace, explode($search, $subject, 2));
Note the 2 at the end instead of 1. Or in function format:
注意末尾的 2 而不是 1。 或者在函数格式中：
function str_replace_first($search, $replace, $subject) {
return implode($replace, explode($search, $subject, 2));
}
I timed the two functions and the first one is twice as fast when no match is found. They are the same speed when a match is found.
我为这两个函数计时，当找不到匹配项时，第一个函数的速度是它的两倍。当找到匹配时，它们的速度相同。
回答by oLinkWebDevelopment
I wondered which one was the fastest, so I tested them all.
我想知道哪个最快，所以我测试了它们。
Below you will find:
下面你会发现：
- A comprehensive list of all the functions that have been contributed onto this page
- Benchmark testing for each contrubution (average execution time over 10,000 runs)
- Links to each answer (for the full code)
- 已贡献到此页面的所有功能的完整列表
- 每个 contrubution 的基准测试（平均执行时间超过 10,000 次运行）
- 每个答案的链接（完整代码）
All functions were tested with the same settings:
所有功能都使用相同的设置进行测试：
$string = 'OOO.OOO.OOO.S';
$search = 'OOO';
$replace = 'B';
Functions that only replace the firstoccurrence of a string within a string:
仅替换字符串中第一次出现的字符串的函数：
substr_replace($string, $replace, 0, strlen($search));[CONTRIBUTED BY] => zombat [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000062883 [SLOWER BY] => FASTESTreplace_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, $replace, 1, 0);[CONTRIBUTED BY] => jayoaK [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000093862 [SLOWER BY] => 49.26%
substr_replace($string, $replace, 0, strlen($search));[CONTRIBUTED BY] => zombat [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000062883 [SLOWER BY] => FASTESTreplace_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, $replace, 1, 0);[CONTRIBUTED BY] => jayoaK [OOO.OOO.OOO.S] => B.OOO.OOO.S [AVERAGE TIME] => 0.0000093862 [SLOWER BY] => 49.26%
Functions that only replace the lastoccurrence of a string within a string:
仅替换字符串中最后一次出现的字符串的函数：
substr_replace($string, $replace, strrpos($string, $search), strlen($search));[CONTRIBUTED BY] => oLinkSoftware - modified zombat [OOO.OOO.OOO.S] => OOO.OOO.B.S [AVERAGE TIME] => 0.0000068083 [SLOWER BY] => FASTESTstrrev(implode(strrev($replace), explode(strrev($search), strrev($string), 2)));[CONTRIBUTED BY] => oLinkSoftware [OOO.OOO.OOO.S] => OOO.OOO.B.S [AVERAGE TIME] => 0.0000084460 [SLOWER BY] => 24.05%
substr_replace($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] => FASTESTstrrev(implode(strrev($replace), explode(strrev($search), strrev($string), 2)));[CONTRIBUTED BY] => oLinkSoftware [OOO.OOO.OOO.S] => OOO.OOO.B.S [AVERAGE TIME] => 0.0000084460 [SLOWER BY] => 24.05%
回答by too much php
Unfortunately, I don't know of any PHP function which can do this.
You can roll your own fairly easily like this:
不幸的是，我不知道有任何 PHP 函数可以做到这一点。
您可以像这样轻松地推出自己的产品：
function replace_first($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, $subject, 2));
}
回答by Parziphal
I created this littlefunction that replaces string on string (case-sensitive) with limit, without the need of Regexp. It works fine.
我创建了这个小函数，它用限制替换字符串上的字符串（区分大小写），不需要正则表达式。它工作正常。
function str_replace_limit($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;
}
Example usage:
用法示例：
$search = 'foo';
$replace = 'bar';
$string = 'foo wizard makes foo brew for evil foo and Hyman';
$limit = 2;
$replaced = str_replace_limit($search, $replace, $string, $limit);
echo $replaced;
// bar wizard makes bar brew for evil foo and Hyman
回答by luchaninov
function str_replace_once($search, $replace, $subject) {
$pos = strpos($subject, $search);
if ($pos === false) {
return $subject;
}
return substr($subject, 0, $pos) . $replace . substr($subject, $pos + strlen($search));
}
回答by PYK
=> CODE WAS REVISED, so consider some comments too old
=> 代码已修改，因此请考虑一些过时的评论
And thanks everyoneon helping me to improve that
Any BUG, please communicate me; I'll fix that up right after
并感谢大家帮助我改进
有BUG请私信我；我会马上解决这个问题
So, lets go for:
所以，让我们去：
Replacing the first 'o'to 'ea'for example:
例如，将第一个'o'替换为'ea'：
$s='I love you';
$s=str_replace_first('o','ea',$s);
echo $s;
//output: I leave you
The function:
功能：
function str_replace_first($a,$b,$s)
{
$w=strpos($s,$a);
if($w===false)return $s;
return substr($s,0,$w).$b.substr($s,$w+strlen($a));
}
回答by Rufinus
The easiest way would be to use regular expression.
最简单的方法是使用正则表达式。
The other way is to find the position of the string with strpos() and then an substr_replace()
另一种方法是使用 strpos() 找到字符串的位置，然后使用 substr_replace()
But i would really go for the RegExp.
但我真的会选择 RegExp。
回答by zack
$string = 'this is my world, not my world';
$find = 'world';
$replace = 'farm';
$result = preg_replace("/$find/",$replace,$string,1);
echo $result;
