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HomeBackend DevelopmentPHP Tutorialphp preg_replace替换实例讲解_PHP

复制代码 代码如下:
mixed preg_replace ( mixed $pattern , mixed $replacement , mixed $subject [, int $limit = -1 [, int &$count ]] )

是执行一个正则表达式的搜索和替换的用函数,平时我们用它时多是一次替换结束,今天又看php手册发现了一个较为难理解(自认为)的例子分享给大家。
复制代码 代码如下:
 $subject = array('1', 'a', '2', 'b', '3', 'A', 'B', '4');
 $pattern = array('/\d/', '/[a-z]/', '/[1a]/');
 $replace = array('A:$0', 'B:$0', 'C:$0');

 echo "preg_replace returns\n

";
 print_r(preg_replace($pattern, $replace, $subject));
 ?>
 
结果如下:

php preg_replace替换实例讲解_PHP
咋一看,我就看晕了
一般 若匹配模式和替换内容这两项都是数组的话它们应该相对应,如果replacement中的元素比pattern中的少, 多出来的pattern使用空字符串进行替换.
$pattern就像个扫描器,扫到匹配的就用于之对应的$replace替换
对于上例替换过程如下:
/\d/扫描$subject里的1,匹配了,匹配内容为$0(也就是1)就把1替换为A:1
然后用/[a-z]/扫描A:1不匹配,就不替换,继续用[1a]扫描A:1,匹配内容为1(也就是$0),就把A:1中1换为C:1
第一项最终被替换为A:C:1
简化过程:

1->A:1->A:C:1
a->B:a->B:C:a
2->A:2
b->B:b
A(没有符合匹配的就不替换了)
B(同上)
4->A:4
总结一点,拿$pattern里的每一个模式依次去匹配$subject里的每一个元素,匹配到了就用与$pattern对应的那个$replace对换,如上例,可能不止一次替换

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