C # Network application programming basic exercises and Answers (vii)

Programming | network

　　1. Explanation of regular expression <a\s+href\s*=\s* ""? ([^ ">]+)" "?> (. +) </a> The meaning of each part of the representative.

"Answer" this regular expression is used to match a string that is similar to the Sohu news in the source file, and each part means:

\s+ one or more whitespace characters

HREF is followed by the exact text in the HTML anchor point

\s* 0 or more white space characters

= followed by the exact text in the HTML anchor point

\s* 0 or more white space characters

""? 0 or no quotes (escaped)

(The starting point of the group that defines the substring (anchor URL).

[^ ' ">]+ one or more occurrences of any character, except for the characters in parentheses.

Defines the end of the first group of substrings

""? 0 or no quotes (escaped)

> followed by the exact text in the HTML anchor point

(. +) A group that matches any character (anchored point text).

End the exact text of an HTML anchor point

　　2. The following is a regular expression that checks whether the input string is a valid e-mail message:

^ ([\w-]+\.) *? [\w-]+@[\w-]+\. ([\w-]+\.) *? [\w]+$

Try to explain the meaning of each part.

Troubleshooting

[\w-]+

One or more arbitrary characters (A-Z, A-Z, 0-9, and underscores) or dashes. On both sides of the @ character, make sure the address form is name@domainname.

\.

An escape point number. (without a backslash, a point number matches any single character except the newline character.) To ensure that there is at least one point number in the domain name.

*?

For the previous expression, not greedy (non-greedy, or minimal) to find 0 or more matches.

([\w-]+\.) *?

Combination of the above three expressions:

For an expression that contains one or more arbitrary characters (A-Z, A-Z, 0-9, and underscores) or dashes, followed by only a point number, it is not greedy to find 0 or more occurrences.

　　3. Write out regular expressions that meet the following requirements:

1 requires 4-8 letters in English.

2) cannot contain letters, at least 1 characters.

3) at least 3 digits.

4) at least 3 characters.

5) At least 3 English letters.

6) any character.

7) 3 letters or numbers, such as 123,R3A.

8) 3 points.

9 @ There are at least 1 characters before @, @ after at least 3 characters.

10) You must enter an opening parenthesis.

Troubleshooting

1) [a-za-z]{4,8}

2) [^a-za-z]{1,}

3) [0-9]{3,}

4) {3,}

5) [A-za-z]{3,}

6). {0,}

7) [A-za-z0-9]{3}

8) \. {3}

9). {1,}@. {3,}

10) \ (