21.7　习题

一、填空题

1.___________实际上就是负责对字符串做解析对比，从而分析出字符串的构成，以便进一步并对字符串做相关的处理。

2.___________是正则表达式最基本的元素，它们是一组描述字符串特征的字符。

3.本章介绍的两种正则表达式函数分别是___________和___________。

4.注册一个网站时，我们经常需要输入用户名。用户名是含有字母、下划线和数字的任意个组合，写出一个检测用户名是否合法的正则表达式：___________。

二、上机实践

1.分别在字符串“PHP is the web scripting language of choice”和“PHP is the website scripting language of choice”中查找是否含有单独的单词web，进行表达式匹配。

【提示】

     $string=preg_match ("/\bweb\b/i", "PHP is the web scripting language of choice.",      $matches);                      //
匹配
     f ($string==true){                         //
判断匹配结果
        print "A match was found.<br>";         //
输出“A match was found
”
        print_r($matches);                      //
输出数组变量
        echo "<br>";                            //
换行
        } else {                                //
没有匹配上的情况
        print "A match was not found.<br>";     //
输出“A match was not found
”
        print_r($matches);                      //
输出数组变量
        echo "<br>";                            //
换行
        }       
        $string=preg_match ("/\bweb\b/i", "PHP is the website scripting language of                     choice.",$matches);
        if ($string==true) {                    //
判断匹配结果
         print "A match was found.";            //
输出“A match was found
”
        print_r($matches);                      //
输出数组变量
        echo "<br>";                            //
换行
        } else {                                //
没有匹配上的情况
         print "A match was not found.<br>";    //
输出“A match was not found
”
         print_r($matches);                     //
输出数组变量
        }

2.将字符串“The quick brown fox jumped over the lazy dog.”中的“quick”、“brown”、“fox”分别替换为“bear”、“black”、“slow”，然后将字符串逆序排列，再进行替换。

【提示】

        $string = "The quick brown fox jumped over the lazy dog.<br>";    
        $patterns[0] = "/quick/";               
        $patterns[1] = "/brown/";               
        $patterns[2] = "/fox/";                 
        $replacements[2] = "bear";      
        $replacements[1] = "black";     
        $replacements[0] = "slow";      
        print preg_replace($patterns, $replacements, $string);
        ksort($replacements);
        print preg_replace($patterns, $replacements, $string);