Strings in C++

In C++, strings are sequences of characters that are used to store words and text. They are also used to store data, such as numbers and other types of information in the form of text. Strings are provided by <string> header file in the form of std::string class.

Creating a String

Before using strings, first we are creating an instance of std::string class as shown:

string str_name;

where str_name is the name of the string.

Initializing a String

Initializing means assigning some initial value to the string. This can be done by using assignment operator and the text enclosed inside "" double quotes.

string str = "Some Text here";

The text inside "" is called string literal and it is the value that is assigned to the string variables. It can be any text that is the sequence of characters from the ASCII charset.

Printing a String

A string can be referred using its name anywhere in the scope once it is declared. For example, the below example prints string using cout:

#include <iostream>
using namespace std;

int main() {
    
    // Creating a string
    string greeting = "Welcome to GfG!";
    
    // Accessing string
    cout << greeting;

    return 0;
}

Welcome to GfG!

The individual characters of the strings can also be accessed using their position (or index) like arrays with [] square brackets. The index in C++ starts from 0 and goes till size - 1, so be careful not go outside this limit.

#include <iostream>
using namespace std;

int main() {
    string str = "Sonu";
    
    // Accessing 3rd character
    cout << str[2] << endl;
    
    // Accessing first character
    cout << str[0];

    return 0;
}

n
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Updating String

The string variable can be updated with new string literal in a similar way it is initialized.

#include <iostream>
using namespace std;

int main() {
    string str = "Tara";
    cout << str << endl;
    
    // Updating string
    str = "Singh";
    cout << str;

    return 0;
}

A single character can also be changed by first accessing the character and then using assignment operator to assign value.

#include <iostream>
using namespace std;

int main() {
    string str = "Tara";
    
    // Updating second character
    str[1] = 'o';
    cout << str;

    return 0;
}

Other String Operations

The following operations aims to improve your understanding of the strings in C++ and introduce you to some of the most commonly used operations:

• Find Length of a String
• Take String as Input
• Reverse a String
• String Concatenation
• Comparing two strings
• Different ways to copy a string
• Find Substring
• Tokenizing a string
• Comparing two strings

Pass Strings to Functions

The string can be passed to a function in the same was as any other type of variable.

#include <iostream>
using namespace std;

// Taking string as argument
void print(string s) {
    cout << s;
    return;
}

int main() {
    string s = "GeeksforGeeks";
    
    // Passing string
    print(s);
    return 0;
}

GeeksforGeeks

C Style Strings

C++ is a superset of C language, so it also inherits the way in which we used to create strings in C. In C, strings were nothing, but an array of characters terminated by a NULL character '\0'. They were created as:

char str[] = "Hello";

Due to being array, there were limitations on C strings:

• Fixed Size: Once declared, the size of the C string cannot be changed.
• Lack of Easy String Operations: No high-level operations like concatenation or substring extraction. Moreover, updating was also complex.

C++ strings resolve these issues by providing a lot of operations that are easy to perform. Internally, these strings are still implemented as dynamic array of characters (or more precisely vectors) Thats why we can access a single character by its index. But the std::string class act as a wrapper and provides lot of built-in functionality for easier and more efficient handling of strings.

C++ String vs C Strings

The main difference between a string and a character array is that strings are immutable, while character arrays are not.

Know more about the difference between strings and character arrays in C++

C++ String Functions

C++ provides some inbuilt functions which are used for string manipulation, such as the strcpy() and strcat() functions for copying and concatenating strings. Some of them are:

These functions are discussed in this article in more detail - String Function in C++