php中preg正则函数使用

1.preg_match和preg_match_all的区别
preg_match和 preg_match_all区别是preg_match只匹配一次。而preg_match_all全部匹配，直到字符串结束。例：

 string 'abcde' (length=5)

array (size=1)
  0 =>
    array (size=3)
      0 => string 'abcde' (length=5)
      1 => string 'abcde' (length=5)
      2 => string 'abcde' (length=5)
 */
?>

2.贪婪模式和非贪婪模式的区别
如：String str="abcaxc";
　　Patter p="ab*c";
贪婪匹配:正则表达式一般趋向于最大长度匹配，也就是所谓的贪婪匹配。如上面使用模式p匹配字符串str，结果就是匹配到：abcaxc(ab*c)。
非贪婪匹配：就是匹配到结果就好，较少的匹配字符。如上面使用模式p匹配字符串str，结果就是匹配到：abc(ab*c)。
例：

 string 'http://www.baidu/.com?url=www.sina.com' (length=38)
  1 => string '//www.baidu/.com?url=www.sina.' (length=30)

array (size=2)
  0 => string 'http://www.baidu/.com' (length=21)
  1 => string '//www.baidu/.' (length=13)
 */
?>

3.preg_match_all参数PREG_PATTERN_ORDER(默认)和PREG_SET_ORDER的区别

]+>(.*)]+>U",
    "start: this is a testend",
    $out1);
var_dump($out1);

echo('PREG_SET_ORDER');
preg_match_all("<[^>]+>(.*)]+>U",
    "start: this is a testend",
    $out2, PREG_SET_ORDER);
var_dump($out2);

/*
PREG_PATTERN_ORDER
array (size=2)
  0 =>
    array (size=3)
      0 => string 'start: ' (length=14)
      1 => string 'this is a test' (length=21)
      2 => string 'end' (length=10)
  1 =>
    array (size=3)
      0 => string 'start: ' (length=7)
      1 => string 'this is a test' (length=14)
      2 => string 'end' (length=3)

PREG_SET_ORDER
array (size=3)
  0 =>
    array (size=2)
      0 => string 'start: ' (length=14)
      1 => string 'start: ' (length=7)
  1 =>
    array (size=2)
      0 => string 'this is a test' (length=21)
      1 => string 'this is a test' (length=14)
  2 =>
    array (size=2)
      0 => string 'end' (length=10)
      1 => string 'end' (length=3)
 */
?>

延伸阅读：preg_match_all使用实例