Strings & String Functions

std::string is a powerful class in the C++ Standard Library that represents a sequence of characters. It's an alternative to C-style character arrays (like char[]) and provides many helpful functions for string manipulation.

To use std::string, you need to include the <string> header file:

#include <iostream>
#include <string>

int main() {
    std::string hello = "Hello world!";
    std::cout << hello << std::endl;

    return 0;
}

Common String Methods

Length and Capacity

Length or Size: length() or size() returns the number of characters in the string.

#include <iostream>
#include <string>

int main() {
    std::string s = "hello";
    std::cout << s.length();  // Output: 5

    return 0;
}

Empty: empty() returns true if the string has no characters, otherwise false.

#include <iostream>
#include <string>

int main() {
    std::string emptyString = "";
    if (emptyString.empty()) {
        std::cout << "The string is empty!" << std::endl;
    }

    return 0;
}

Accessing Characters

Indexing characters: at(index) or operator[](index) returns a reference to the character at a given position. Indices start from 0, just like arrays.

#include <iostream>
#include <string>

int main() {
    std::string str = "hello";
    char first = str.at(0);        // 'h'
    char second = str.operator[](1); // 'e'
    char third = str[2];             // 'l'

    std::cout << first << std::endl;
    std::cout << second << std::endl;
    std::cout << third << std::endl;

    return 0;
}

Note: Using an index out of bounds will result in undefined behavior.

Modifying Strings

Appending strings: append(str) or operator+=(str) appends another string or character to the end of the current string.

#include <iostream>
#include <string>

int main() {
    std::string greeting = "Hello ";
    greeting.append("world!");          // "Hello world!"
    greeting += "! How are you today?"; // "Hello world! How are you today?"

    std::cout << greeting << std::endl;

    return 0;
}

Inserting characters: insert(pos, str) inserts a string or character at a specified position.

#include <iostream>
#include <string>

int main() {
    std::string message = "We love C";
    message.insert(7, "++"); // "We love C++"

    std::cout << message << std::endl;

    return 0;
}

Erasing characters: erase(pos, count) Erases count characters from the position pos. If count is not provided, it erases all characters until the end of the string.

#include <iostream>
#include <string>

int main() {
    std::string text = "I like bananas";
    text.erase(7, 8); // "I like"

    std::cout << text << std::endl;

    return 0;
}

Searching and Comparing

Finding occurrences: find(str) Searches for the first occurrence of a substring and returns its starting position. If not found, it returns the std::string::npos constant (or -1).

#include <iostream>
#include <string>

int main() {
    std::string sentence = "C++ is fun!";
    size_t pos = sentence.find("fun");
    if (pos != std::string::npos) {
        std::cout << "Found 'fun' at position: " << pos << std::endl;
    }

    return 0;
}

Comparing strings: compare(str) Compares two strings. Returns 0 if they're equal, a positive value if the first string is greater than the second one, and a negative value otherwise.

#include <iostream>
#include <string>

int main() {
    std::string s1 = "apple", s2 = "banana";
    int result = s1.compare(s2);
    if (result == 0) {
        std::cout << "s1 equals s2" << std::endl;
    } else if (result > 0) {
        std::cout << "s1 is greater than s2" << std::endl;
    } else {
        std::cout << "s1 is less than s2" << std::endl;
    }

    return 0;
}

Conclusion

std::string is a versatile and easy-to-use class for string manipulation in C++. It provides many functions to access, modify, search, and compare strings. Using std::string instead of C-style character arrays can make your code safer and more readable.