str_replace method to replace a string only once_PHP tutorial-PHP Tutorial-php.cn

str_replace method to replace a string only once_PHP tutorial

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Release： 2016-07-21 15:12:25

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We all know that in PHP, Strtr, strreplace and other functions can be used to replace, but they replace all of them every time. For example:
"abcabbc", if this string is used as above function to replace b among them, then it will replace them all, but what if you want to replace only one or two? See the solution below:
This is a rather interesting question, just before I have also done similar processing. At that time, I directly used preg_replace to implement it.

mixed preg_replace (mixed pattern, mixed replacement, mixed subject [, int limit] )
Search for a match of the pattern pattern in subject and replace it with replacement. If limit is specified, only limit matches are replaced; if limit is omitted or has a value of -1, all matches are replaced.
Because the fourth parameter of preg_replace can limit the number of replacements, it is very convenient to deal with this problem in this way. But after looking at the function comments about str_replace on php.net, we can actually pick out a few representative functions.

str_replace_once
The idea is to first find the location of the keyword to be replaced, and then use the substr_replace function to directly replace it.

Copy code The code is as follows:

function str_replace_once($needle, $replace, $haystack) {

// Looks for the first occurrence of $needle in $haystack

// and replaces it with $replace.

$pos = strpos($haystack, $needle);

if ($pos === false) {

return $haystack;

}

return substr_replace($haystack, $replace, $pos, strlen($needle));

}

str_replace_limit
Still uses preg_replace, but its parameters are more like preg_replace, and some special characters are escaped, making it more versatile.

Copy code The code is as follows:

function str_replace_limit($search, $replace, $subject, $limit=-1) {

// constructing mask(s)...

if (is_array($search)) {

foreach ($search as $k=>$v) {

$search[$k] = ''' . preg_quote($search[$k],''') . ''';

}

else {

$search = '`' . preg_quote($search,''') . '`';

}

//replacement

return preg_replace($search, $replace, $subject, $limit);