C++ String Methods

C++ string methods are built-in functions you call on a std::string value. They help you inspect, search, extract, and change text without writing all the character-by-character logic yourself.

You call a method with dot syntax, such as word.length() or message.find("C++").

Checking Size

Use length() or size() to count characters in a string. Use empty() to check whether a string has no characters.

#include <iostream>
#include <string>

int main(void) {
    std::string word = "compiler";
    std::string blank = "";

    std::cout << "Word: " << word << std::endl;
    std::cout << "Length: " << word.length() << std::endl;
    std::cout << "Size: " << word.size() << std::endl;
    std::cout << "Blank is empty: " << blank.empty() << std::endl;

    return 0;
}

Output:

Word: compiler
Length: 8
Size: 8
Blank is empty: 1

For std::string, length() and size() return the same value. The empty() method returns a Boolean value; when printed with std::cout, true appears as 1 and false appears as 0.

Searching A String

Use find() to search for text inside a string. It returns the index where the match begins. If the text is not found, it returns the special value std::string::npos.

#include <iostream>
#include <string>

int main(void) {
    std::string fileName = "notes-final.txt";

    std::size_t finalPos = fileName.find("final");
    std::size_t draftPos = fileName.find("draft");

    std::cout << "final position: " << finalPos << std::endl;

    if (draftPos == std::string::npos) {
        std::cout << "draft was not found" << std::endl;
    }

    return 0;
}

Output:

final position: 6
draft was not found

String indexes start at 0, so final starts at index 6 in "notes-final.txt". Searches are case-sensitive: find("Final") would not match "final".

Extracting Part Of A String

The substr() method returns a new string made from part of another string. The form substr(start, count) starts at start and copies up to count characters.

#include <iostream>
#include <string>

int main(void) {
    std::string code = "CPP-2026-BASICS";

    std::string topic = code.substr(0, 3);
    std::string year = code.substr(4, 4);
    std::string level = code.substr(9);

    std::cout << "Topic: " << topic << std::endl;
    std::cout << "Year: " << year << std::endl;
    std::cout << "Level: " << level << std::endl;

    return 0;
}

Output:

Topic: CPP
Year: 2026
Level: BASICS

If you call substr() with only the starting index, it returns everything from that index to the end of the string.

Changing A String

Unlike many string operations in some other languages, several C++ string methods change the original string. Common methods include append(), insert(), erase(), and replace().

Method	What it does
append(text)	Adds text to the end.
insert(index, text)	Adds text before an index.
erase(index, count)	Removes characters.
replace(index, count, text)	Replaces characters with new text.

#include <iostream>
#include <string>

int main(void) {
    std::string title = "C++ Strings";

    title.append(" Course");
    title.insert(0, "Learn ");
    title.replace(6, 3, "Modern C++");
    title.erase(16, 8);

    std::cout << title << std::endl;

    return 0;
}

Output:

Learn Modern C++ Course

In this example, each method updates title. The indexes used by insert(), replace(), and erase() are zero-based.

Common Mistakes

• Forgetting to include <string> before using std::string.
• Checking find() against 0 instead of std::string::npos when text is not found.
• Mixing up substr(start, count) with an ending index. The second value is a character count.
• Using indexes that are outside the string.

Takeaway: C++ string methods let you check, search, extract, and update text while keeping your code short and readable.