C++ Strings

C++ strings are handled by the std::string class from <string>. Unlike C character arrays, std::string manages its own memory, grows automatically and supports operators like + and ==.

Creating and Joining Strings

#include <iostream>
#include <string>

int main() {
    std::string first = "Naeem";
    std::string last = "Amin";
    std::string full = first + " " + last;
    full += "!";
    std::cout << full << " has " << full.size() << " characters\n";
}

Naeem Amin! has 11 characters

Accessing Characters

Use [] for fast access or .at() for bounds-checked access that throws an exception if the index is invalid.

#include <iostream>
#include <string>

int main() {
    std::string word = "Code";
    word[0] = 'M';
    std::cout << word << ' ' << word.at(3) << ' ' << word.back() << '\n';
}

Mode e e

Useful std::string Methods

#include <iostream>
#include <string>

int main() {
    std::string s = "learn modern c++";
    std::cout << s.substr(6, 6) << '\n';     // from index 6, 6 chars
    std::cout << s.find("c++") << '\n';      // position
    s.replace(0, 5, "master");
    std::cout << s << '\n';
    std::cout << std::boolalpha << s.starts_with("master") << '\n'; // C++20
}

modern
13
master modern c++
true

Numbers and Strings

std::to_string turns a number into text, and std::stoi / std::stod parse text into numbers.

#include <iostream>
#include <string>

int main() {
    int n = std::stoi("41") + 1;
    std::string msg = "Answer: " + std::to_string(n);
    std::cout << msg << '\n';
}

Answer: 42

Comparing Strings

With std::string you can compare using ==, !=, < and >, which compare the text alphabetically. This is much simpler than C's strcmp.

Frequently asked questions

What is the difference between size() and length() for std::string?

There is no difference; both return the number of characters. size() is consistent with other containers.

How do I convert an int to a string in C++?

Use std::to_string(number), or std::format("{}", number) in C++20.

What does find return if the text is not found?

It returns std::string::npos, a special very large value. Always compare the result with npos before using it.