str_replace 用替换词替换所有出现的单词。
preg_replace 用替换替换出现的模式，并采用可选的限制参数。
我不需要模式匹配，但想要一个限制参数的便利。我应该使用什么？
【问题讨论】：
str_replace 的最后一个参数有什么问题？
标签： php
有更好的方法来做到这一点
<?
$str = 'abcdef abcdef abcdef';
// pattern, replacement, string, limit
echo preg_replace('/abc/', '123', $str, 1); // outputs '123def abcdef abcdef'
?>
【讨论】：
function str_replace2($find, $replacement, $subject, $limit = 0){
if ($limit == 0)
return str_replace($find, $replacement, $subject);
$ptn = '/' . preg_quote($find,'/') . '/';
return preg_replace($ptn, $replacement, $subject, $limit);
}
这将允许您限制替换次数。字符串应使用preg_quote 进行转义，以确保任何特殊字符都不会被解释为模式字符。
如果您有兴趣，here's a version 包含 &$count 参数：
function str_replace2($find, $replacement, $subject, $limit = 0, &$count = 0){
if ($limit == 0)
return str_replace($find, $replacement, $subject, $count);
$ptn = '/' . preg_quote($find,'/') . '/';
return preg_replace($ptn, $replacement, $subject, $limit, $count);
}
【讨论】：
strpos 和 substrs 来匹配，但它会做更多的工作（并且可以说更快/花，因为你正在处理在发动机本身之外）。这取决于您，但看到基准比较会很有趣。
$count 应该在$limit 之前，以便与str_replace() 向后兼容。此外，您的代码仅支持字符串，而 str_replace() 支持 $search、$replace 和 $subject 的数组。
str_replace2 （可以使用它来代替 str_replace；0 用于“无限制”，而不是标准的 -1；您使用自己的变量名，与str_replace 不匹配；并且您的变量名不一致（缩写为“模式”$ptn 而其余变量使用完整的单词）。是的，这是我的意见，但它也会如果我对您的答案投了赞成票，请发表我的看法。如果您解决了其中一些问题，我很乐意投赞成票:)
$str = implode($replace, explode($search, $subject, $count + 1));
快速概念验证：
$str =
"To be, or not to be, that is the question:
Whether 'tis Nobler in the mind to suffer
The Slings and Arrows of outrageous Fortune,
Or to take Arms against a Sea of troubles,
And by opposing end them";
/* Replace the first 2 occurrences of 'to' with 'CAN IT' in $str. */
echo implode('CAN IT', explode('to', $str, 3));
输出（强调）：
成为，还是可以成为，这是个问题：
头脑中的贵族是否可以受苦
令人发指的命运的弹弓和箭，
或者 拿起武器对抗麻烦之海，
并通过反对结束他们
请注意，此方法区分大小写。
【讨论】：
最初来自https://stackoverflow.com/a/11400172/526741
我编写了一个与str_replace() 100% 向后兼容的函数。也就是说，您可以用str_replace_limit() 替换所有 次出现的str_replace()，而不会搞砸任何事情，即使是那些使用$search、$replace 和/或$subject 的数组。
函数可以完全独立，如果你想用($string===strval(intval(strval($string))))替换函数调用，但我建议不要这样做，因为valid_integer()在处理时是一个相当有用的函数整数作为字符串提供。
注意：只要有可能，str_replace_limit() 将使用 str_replace()，因此所有对 str_replace() 的调用都可以替换为 str_replace_limit()，而无需担心达到性能。
<?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 个替换 -- bbcbbc
$limit = 1; // Limit of 1
$new_string = str_replace_limit($search, $replace, $subject, $count, $limit);
echo $count.' replacements -- '.$new_string;
1 个替换 -- bbcabc
$limit = 10; // Limit of 10
$new_string = str_replace_limit($search, $replace, $subject, $count, $limit);
echo $count.' replacements -- '.$new_string;
2 个替换 -- bbcbbc
<?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;
}
}
【讨论】：
这是@brad-christie 的答案的增强版本，其中将数组的兼容性宣传为 $find 和 $replace 值：
function str_replace_limit($find, $replacement, $subject, $limit = 0) {
if ($limit == 0)
return str_replace($find, $replacement, $subject);
for ($i = 0; $i < count($find); $i++) {
$find[$i] = '/' . preg_quote($find[$i],'/') . '/';
}
return preg_replace($find, $replacement, $subject, $limit);
}
【讨论】：