Now we move on to regular expressions in C++. Our first step will be to understand the purpose of this library.

Regular expressions are a language for describing text patterns. They need the header <regex>.

Regular expressions are a powerful tool for the following tasks:

  • Check if a text matches a text pattern: std::regex_match

  • Search for a text pattern in a text: std::regex_search

  • Replace a text pattern with a text: std::regex_replace

  • Iterate through all text patterns in a text: std::regex_iterator and std::regex_token_iterator

C++ supports six different grammars for regular expressions. By default, the ECMAScript grammar is used. This one is the most powerful of the six grammars, and is quite similar to the grammar used in Perl 5. The other five grammars are the basic, extended, awk, grep, and egrep grammars.

🔑 Use raw strings
Use raw string literals in regular expressions. The regular expression for the text in C++ is quite ugly: C\\+\\+. We have to use two backslashes for each + sign. First, the + sign is a special character in a regular expression. Second, the backslash is a special character in a string. Therefore one backslash escapes the + sign, the other backslash escapes the backslash. By using a raw string literal, the second backslash is not necessary anymore, because the backslash is not interpreted in the string.

#include <regex>
std::string regExpr("C\\+\\+");
std::string regExprRaw(R"(C\+\+)");

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