LANGUAGE » CPP

Regex

Last updated:
Reference:devdocs.io

Usage ​

cpp
#include <regex>

Match ​

Check for a full match (returns bool):

cpp
std::string text = "Welcome";
std::regex pattern("[A-Za-z]+");

if (std::regex_match(text, pattern)) {
    fmt::println("Match found!");
} else {
    fmt::println("Match not found.");
}

Check for a partial match (returns bool):

cpp
std::string text = "Code coverage is 87.49%";
std::regex pattern("\\d{2}\\.\\d{2}%");

if (std::regex_search(text, pattern)) {
    fmt::println("Match found!");
} else {
    fmt::println("Match not found.");
}

To get the value of the matched text, use a std::smatch variable as the second parameter.

cpp
std::string text = "Code coverage is 87.49%";
std::regex pattern("\\d{2}\\.\\d{2}%");
std::smatch match;

if (std::regex_search(text, match, pattern)) {
    fmt::println("Match found! It is {}", match.str());
} else {
    fmt::println("Match not found.");
}

To get the value of capture groups is pretty much the same code structure:

cpp
std::string text = "My name is Tom, I'm 25 years old";
std::regex pattern("My name is ([A-Za-z]+), I'm ([0-9]+) years old");
std::smatch match;

if (std::regex_search(text, match, pattern)) {
    fmt::println("Full match: {}", match[0].str());
    fmt::println("Capture group 1: {}", match[1].str());
    fmt::println("Capture group 2: {}", match[2].str());
} else {
    fmt::println("Match not found.");
}

Replace ​

Using regex replace to create a copy of a std::string with the whitespace trimmed:

cpp
std::string ltrim(const std::string &s) {
    return std::regex_replace(s, std::regex("^\\s+"), std::string(""));
}

std::string rtrim(const std::string &s) {
    return std::regex_replace(s, std::regex("\\s+$"), std::string(""));
}

std::string trim(const std::string &s) {
    return ltrim(rtrim(s));
}