php手册里有一个函数叫做substr_count，是用来计算一个字符串在指定的字符串中出现的次数。
http://www.php.net/manual/en/function.substr-count.php
- <?php
- $text = 'This is a test';
- echo strlen($text); // 14
- echo substr_count($text, 'is'); // 2
- // the string is reduced to 's is a test', so it prints 1
- echo substr_count($text, 'is', 3);
- // the text is reduced to 's i', so it prints 0
- echo substr_count($text, 'is', 3, 3);
- // generates a warning because 5+10 > 14
- echo substr_count($text, 'is', 5, 10);
- // prints only 1, because it doesn't count overlapped substrings
- $text2 = 'gcdgcdgcd';
- echo substr_count($text2, 'gcdgcd');
- ?>
最后一个例子很深刻的说明了，就算字符串重复再多，但是真要显示的话，也只显示一次，不重复计算。