我想要str_replace()的一个版本，它只替换$subject中第一次出现的$search。有一个简单的解决方案，还是我需要一个hack的解决方案?
当前回答
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 $subject;
}
其他回答
可以用preg_replace完成:
function str_replace_first($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)。
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 ($string)， 2))); [贡献BY] => oLinkSoftware [OOO.OOO.OOO。S] => ooo [平均时间]=> 0.0000084460 [慢]=> 24.05%
最简单的方法是使用正则表达式。
另一种方法是用strpos()找到字符串的位置，然后用substr_replace()
但我真的会选择RegExp。
这个函数很大程度上受到@ renoor回答的启发。 它使函数多字节安全。
function str_replace_limit($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] : $string;
}
为了扩展@ renoor的答案，我编写了一个与str_replace() 100%向后兼容的函数。也就是说，可以用str_replace_limit()替换所有出现的str_replace()，而不会搞砸任何事情，即使是使用数组进行$search、$replace和/或$subject。
如果您想用($string===strval(intval(strval($string))))))替换函数调用，则该函数可以完全自包含，但我不建议这样做，因为valid_integer()在处理作为字符串提供的整数时是一个相当有用的函数。
注意:只要可能，str_replace_limit()将使用str_replace()来代替，因此所有对str_replace()的调用都可以用str_replace_limit()来代替，而不用担心对性能的影响。
使用
<?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
函数
<?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;
}
}
