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str_replace只替换一次字符串的方法_php技巧

May 17, 2016 am 09:05 AM
str_replace

   我们都知道,在PHP里Strtr,strreplace等函数都可以用来替换,不过他们每次替换的时候都是全部替换,举个例子:
"abcabbc",这个字符串如果使用上边的函数来把其中的b替换掉,那么他会全部替换掉,但是如果你想只替换一个或两个怎么办呢?看下边的解决方法:
     这是个比较有点意思的问题,正好之前也做过类似的处理,当时我是直接利用preg_replace实现的。

mixed preg_replace ( mixed pattern, mixed replacement, mixed subject [, int limit] )
     在 subject 中搜索 pattern 模式的匹配项并替换为 replacement。如果指定了 limit,则仅替换 limit 个匹配,如果省略 limit 或者其值为 -1,则所有的匹配项都会被替换。
     因为preg_replace的第四个参数可以实现替换次数的限制,所以这个问题这样处理很方便。但是在查看php.net上关于str_replace的函数评论后,从中居然也可以挑出几个有代表性的函数来。

str_replace_once
思路首先是找到待替换的关键词的位置,然后利用substr_replace函数直接替换之。

复制代码 代码如下:

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

// Looks for the first occurence 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
还是利用preg_replace,只不过它的参数更象preg_replace了,而且对某些特殊字符做了转义处理,通用性更好。

复制代码 代码如下:

 

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); 

?> 

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