Shulou(Shulou.com)05/31 Report--

This article mainly introduces the relevant knowledge of how to use regular expressions in C++. The content is detailed and easy to understand, easy to operate, and has a certain reference value. I believe that you will gain something after reading this C++ article on how to use regular expressions. Let's take a look.

Introduction

The C++ regular expressions tutorial explains the work of regular expressions in C++, including regular expression matching, search, replacement, input validation, and tagging.

Almost all programming languages support regular expressions. C++ has directly supported regular expressions since Clipper 11. In addition to programming languages, most text processors, such as lexical analyzers, advanced text editors, and so on, use regular expressions.

1. Regular expressions (Regex) in C++

A regular expression is an expression that contains a series of characters that define specific search patterns that can be used for string search algorithms, find or find / replace algorithms, and so on. Regular expressions are also used for input validation.

Most programming languages provide either built-in functionality for regular expressions or through libraries. Since Category 11, C++ has provided regular expression support through the standard library.

The regular expression processor used to parse the regular expression converts it to an internal representation that is executed and matches a string that represents the text being searched. Caching 11 uses the ECMAScript syntax as the default syntax for regular expressions. ECMAScript is simple, but it provides powerful regular expression capabilities. Let's take a look at some of the patterns we specify in regular expressions, such as range specifications, repetition patterns, and so on.

1.1 scope specification

Specifying a range of characters or text is one of the simplest criteria used in regular expressions.

For example, we can specify a range of lowercase letters from a to z, as follows: [amurz], which will match only one lowercase character.

The following conditions: [A-Za-z0-9]

The above expression specifies a range of uppercase letters, lowercase letters, and numbers between 0 and 9.

The square brackets ([]) in the above expression have a special meaning, that is, they are used to specify the scope. If you want to include a parenthesis as part of the expression, you need to escape it.

So the following expression, [\ [0-9]

The above expression represents a left parenthesis and a number in the range of 0 to 9 as a regular expression.

Note, however, that when we program with C++, we need to use C++-specific escape sequences, as follows: [\ [0-9]

1.2 repetition pattern

The range example we specified above matches only one character or text. If we want to match multiple characters, we usually specify an "expression modifier" in the pattern, making it a repeating pattern.

The expression modifier can be +, which means that a pattern appears one or more times, or it can be *, which means that a pattern appears zero or more times.

For example, the following expression

[a Murz] + matches strings such as a, aaa, abcd, softwaretestinghelp, etc. Note that it never matches a blank string.

[amurz] * will match a blank string or any of the above strings.

If you want to specify that a set of characters match one or more times, you can use parentheses as follows: (Xyz) +

The above expression will match Xyz, XyzXyz, XyzXyz, and so on.

2. An example of C++ regular expression

Consider a regular expression that matches the name of the MS-DOS file, as shown below.

Char regex_filename [] = "[a-zA-Z0-9] [a-zA-Z_0-9] [a-zA-Z0-9] +"

The above regular expression can be explained as follows:

Matches a letter (lowercase, then uppercase) or underscore. Then match zero or more characters, each of which can be a letter, underscore, or number. Then match the text dot (.). After the dot, one or more characters are matched, where each character can be a letter or number that represents the file extension.

3. Function templates used in C++ regular expressions

Now let's discuss some important function templates when writing regular expressions in C++.

3.1 regex_match ()

This function template is used to match a given pattern. If the given expression matches a string, this function returns true. Otherwise, the function returns false.

The following is a C++ programming example that demonstrates the regex_match function.

# include # include # include using namespace std; int main () {if (regex_match ("softwareTesting", regex ("(soft) (. *) cout

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.