How to Find Length of String in C++: Simple Syntax & Example

In C++, you can find the length of a string using the length() or size() method on a std::string object. Both methods return the number of characters in the string as a size_t value.

Syntax

To get the length of a string in C++, use the length() or size() method on a std::string object.

• string.length(): Returns the number of characters in the string.
• string.size(): Does the same as length(), interchangeable.

cpp

std::string str = "Hello";
size_t len = str.length();

Example

This example shows how to create a string and print its length using length().

cpp

#include <iostream>
#include <string>

int main() {
    std::string greeting = "Hello, world!";
    std::cout << "The length of the string is: " << greeting.length() << std::endl;
    return 0;
}

Output

The length of the string is: 13

Common Pitfalls

Some common mistakes when finding string length in C++ include:

• Using strlen() on std::string objects, which is incorrect because strlen() works only with C-style strings (char*).
• Confusing length() with the size of the buffer or capacity of the string.
• Not including the <string> header, which is required for std::string.

cpp

#include <iostream>
#include <string>

int main() {
    std::string s = "Test";
    // Wrong: strlen(s.c_str()) - will work but is unnecessary
    // std::cout << strlen(s.c_str()) << std::endl;

    // Correct:
    std::cout << s.length() << std::endl;
    return 0;
}

Output

4

Quick Reference

Method	Description
string.length()	Returns the number of characters in the string.
string.size()	Same as length(), returns string length.
strlen(char*)	Use only for C-style strings, not std::string.

Key Takeaways

Use std::string's length() or size() method to get string length in C++.

Do not use strlen() on std::string objects; it works only with C-style strings.

Both length() and size() return the number of characters as size_t.

Always include header when working with std::string.

length() does not count any null terminator, just visible characters.