String Concatenation in C++

String concatenation refers to the process of combining two or more strings into a single string. Generally, one string is appended at the end of the other string. In this article, we will learn how to concatenate two strings in C++.

The simplest method to concatenate two strings in C++ is by using + operator. Let’s take a look at an example:

#include <bits/stdc++.h>
using namespace std;

int main() {
    string s1("Hello");
    string s2(" World");

    // Concatenation s1 and s2
    s1 = s1 + s2;

    cout << s1;
    return 0;
}

Hello World

Explanation: The ‘+’ operator combines two string objects and returns the resulting concatenated string. However, this method only works for C++ style strings (std::string) and is not applicable to C-style character arrays.

There are also many other different ways to concatenate two strings in C++:

Using String append()

The string append() function is a member of the string class that is used to concatenate two string objects in C++. It provides an efficient way to concatenate two strings.

#include <bits/stdc++.h>
using namespace std;

int main() {
    string s1("Hello");
    string s2(" World");

    // Concatenation str1 and str2
    s1.append(s2);

    cout << s1;
    return 0;
}

Hello World

When to use?

Use this method when you need an efficient, in-place concatenation of std::string objects.

Using strcat()

The strcat() function is a standard library function in C that is also available in C++. It is used to concatenate (append) one C-style string (character array) to another and adds a null terminator at the end. It is defined inside the <cstring> header file.

#include <bits/stdc++.h>
using namespace std;

int main() {
    char s1[] = "Hello";
    char s2[] = " World";

    // Concatenating s1 and s2
    strcat(s1, s2);

    cout << s1;
    return 0;
}

Hello World

When to use?

Use this method when concatenating C-style strings (character arrays). Also suitable for legacy code that may run in C compilers.

Using for Loop

In this method, characters from one string are appended manually one by one to another while iterating through both strings using loops. The final result is a concatenated string that combines both original string.

#include <bits/stdc++.h>
using namespace std;

int main() {
    string s1("Hello");
    string s2(" World");

    // Adding characters of s2 at the end of s1
    for (auto i : s2)
        s1 += i;

    cout << s1;
    return 0;
}

Hello World

When to use?

Use this method for manual control over concatenation, such as with custom string structures or some processing before concatenation. It is also suitable when direct library functions aren’t available or for specific logic during concatenation.

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