How to Concatenate Strings in C++: Simple Syntax and Examples

In C++, you can concatenate strings using the + operator or the append() method of the std::string class. Both ways join two or more strings into one combined string.

Syntax

There are two common ways to concatenate strings in C++:

• string3 = string1 + string2; — uses the + operator to join strings.
• string1.append(string2); — adds string2 to the end of string1.

Both string1 and string2 must be std::string objects or convertible to strings.

cpp

std::string string1 = "Hello, ";
std::string string2 = "World!";

// Using + operator
std::string string3 = string1 + string2;

// Using append method
string1.append(string2);

Example

This example shows how to concatenate two strings using both the + operator and the append() method, then prints the results.

cpp

#include <iostream>
#include <string>

int main() {
    std::string greeting = "Hello, ";
    std::string name = "Alice!";

    // Using + operator
    std::string message1 = greeting + name;
    std::cout << message1 << std::endl;

    // Using append method
    std::string message2 = greeting;
    message2.append(name);
    std::cout << message2 << std::endl;

    return 0;
}

Output

Hello, Alice!
Hello, Alice!

Common Pitfalls

Common mistakes when concatenating strings in C++ include:

• Trying to use + with C-style strings (char arrays) without converting to std::string, which causes errors.
• Modifying string literals directly, which is not allowed.
• Forgetting that append() changes the original string, while + creates a new string.

cpp

#include <iostream>
#include <string>

int main() {
    const char* cstr1 = "Hello, ";
    const char* cstr2 = "World!";

    // Wrong: cannot use + directly on C-style strings
    // std::string result = cstr1 + cstr2; // Error

    // Correct: convert to std::string first
    std::string result = std::string(cstr1) + std::string(cstr2);
    std::cout << result << std::endl;

    return 0;
}

Output

Hello, World!

Quick Reference

Summary tips for string concatenation in C++:

• Use + to create a new combined string.
• Use append() to add to an existing string.
• Convert C-style strings to std::string before concatenation.
• Remember string literals are immutable; always use std::string objects.

Key Takeaways

Use the + operator or append() method to concatenate std::string objects in C++.

Convert C-style strings to std::string before concatenation to avoid errors.

append() modifies the original string, while + creates a new string.

Never try to modify string literals directly; use std::string instead.