C++ Strings

In C++, the string is an object of the std::string class that represents a sequence of characters. We can perform many operations on strings, such as concatenation, comparison, conversion, etc.

C++ utilizes string as a sequential collection of characters dedicated to handling textual data storage and manipulation. The primary programming function of strings enables developers to process names along with messages, sentences, and additional textual data in an efficient way. Strings occupy one continuous memory block to store their characters, yet they differ fundamentally from single-valued data types , such as int or char.

Simple String Example

Let us see a simple example of a C++ string.

Example

#include <iostream>  

using namespace std;  //using the standard namespace

int main( ) {  

    string s1 = "Hello";    //using string

        char ch[] = { 'C', '+', '+'};    

        string s2 = string(ch);  // Convert the character array ch to a string object s2

        cout<<s1<<endl; // Output the value of s1 to the console

        cout<<s2<<endl; // Output the value of s2 to the console

}

Output:

Hello

C++

Explanation:

The C++ program demonstrates string initialization, where s1 is assigned a string literal, and s2 is created from a character array using the string constructor. After that, it prints both strings as output.

Types of Strings in C++

C++ supports two primary types of strings:

1. C-Style Strings (Character Arrays)

C-style strings contain sequential characters stopped by a terminating null character (\0). The utilization of this string type demands both memory handling functions from the <cstring> library and user-controlled memory management.

Example:

char str[] = "Hello";

2. C++ Strings (std::string from the Standard Library)

Strings processed through std::string demonstrate better flexibility and safety than Standard Template Library (STL). The built-in functions length, append, substr and replace help users efficiently manipulate strings as a matter of standard. Standard Library strings manage memory automatically so developers avoid encountering buffer overflows.

Example:

std::string str = "Hello, C++!";

Creating and Initialize Strings in C++

In C++, strings can be created and initialized using C-style character arrays or std::string from the <string> library.

a. Initializing C-Style Strings:

char str1[] = "Hello";  // Implicit null character '\0'

char str2[6] = {'H', 'e', 'l', 'l', 'o', '\0'};  // Explicit null character

char str3[10] = "Hello";  // Extra space for modification

b. Initializing std::string:

std::string str1 = "Hello";  // Direct initialization

std::string str2("World");   // Constructor-based initialization

std::string str3(5, 'A');    // Creates "AAAAA"

std::string str4 = str1 + " " + str2;  // Concatenation: "Hello World"

Example:

Let us take an example to illustrate the creating and initializing string in C++.

Example

#include <iostream>

#include <string>  // Include string library for std::string

int main() {

    // (a) Initializing C-Style Strings

    char str1[] = "Hello";  

    char str2[6] = {'H', 'e', 'l', 'l', 'o', '\0'};  

    char str3[10] = "Hello";  

    std::cout << "C-Style Strings:" << std::endl;

    std::cout << "str1: " << str1 << std::endl;

    std::cout << "str2: " << str2 << std::endl;

    std::cout << "str3: " << str3 << std::endl;

    // (b) Initializing std::string

    std::string s1 = "Hello";  

    std::string s2("World");  

    std::string s3(5, 'A');  // Creates "AAAAA"

    std::string s4 = s1 + " " + s2;  // Concatenation of s1 and s2

    std::cout << "\nstd::string Initialization:" << std::endl;

    std::cout << "s1: " << s1 << std::endl;

    std::cout << "s2: " << s2 << std::endl;

    std::cout << "s3: " << s3 << std::endl;

    std::cout << "s4: " << s4 << std::endl;

    return 0;

}

Output:

C-Style Strings:

str1: Hello

str2: Hello

str3: Hello

std::string Initialization:

s1: Hello

s2: World

s3: AAAAA

s4: Hello World

Explanation:

The program demonstrates different ways to initialize C-style strings using character arrays and std::string using direct assignment, constructors, and concatenation. It prints the initialized values to show their usage in C++ string handling.

Accessing Strings in C++

String elements can be accessed by their position through indexing in a string. C-style strings access elements through array notation, yet std::string gives users multiple functions to retrieve characters. The traversal methods within loops enable users to manipulate or retrieve information from strings.

a) Accessing C-Style Strings:

Using array indexing:

We can access the C-Style Strings using array indexing in C++.

char str[] = "Hello"; 

std::cout << str[index];

Using pointers:

We can access the C-Style Strings using pointers in C++.

char str[] = "Hello"; 

char *ptr = str; 

std::cout << *ptr;

b) Accessing std::string:

Using operator:

We can access the std::strings using operator in C++.

std::string str = "Hello"; 

std::cout << str[index];

Using .at(index):

We can also access the std::strings using .at(index) in C++.

std::cout << str.at(index);

Using .front and .back:

We can also access the std::strings using .front and .back function in C++.

std::cout << str.front(); // First character 

std::cout << str.back();  // Last character

Example:

Let us take an example to illustrate the accessing string in C++.

Example

#include <iostream>

#include <string>

int main() {

    // Accessing C-Style Strings

    char cstr[] = "Hello";

    char *ptr = cstr;

    std::cout << "C-Style String Access:\n";

    std::cout << "Using array indexing: " << cstr[0] << "\n"; // Output: H

    std::cout << "Using pointer: " << *ptr << "\n";          // Output: H

    std::cout << "Using pointer arithmetic: " << *(cstr + 1) << "\n"; // Output: e

    std::cout << "Using loop traversal: ";

    for (int i = 0; cstr[i] != '\0'; i++) {

        std::cout << cstr[i];

    }

    std::cout << "\n";

    // Accessing std::string

    std::string str = "Hello";

    std::cout << "\nstd::string Access:\n";

    std::cout << "Using [] operator: " << str[1] << "\n";    // Output: e

    std::cout << "Using .at(): " << str.at(2) << "\n";      // Output: l

    std::cout << "Using .front(): " << str.front() << "\n";  // Output: H

    std::cout << "Using .back(): " << str.back() << "\n";    // Output: o

    std::cout << "Using iterators: ";

    for (std::string::iterator it = str.begin(); it != str.end(); ++it) {

        std::cout << *it;

    }

    std::cout << "\n";

    std::cout << "Using range-based for loop: ";

    for (char ch : str) {

        std::cout << ch;

    }

    std::cout << "\n";

    std::cout << "Using .c_str(): " << str.c_str() << "\n";

    return 0;

}

Output:

C-Style String Access:

Using array indexing: H

Using pointer: H

Using pointer arithmetic: e

Using loop traversal: Hello

std::string Access:

Using [] operator: e

Using .at(): l

Using .front(): H

Using .back(): o

Using iterators: Hello

Using range-based for loop: Hello

Using .c_str(): Hello

Explanation:

This C++ program demonstrates various ways to access C-style strings using indexing, pointers, and loops , and std::string using methods like .at, .front, .back, iterators, and range-based loops. It also converts std::string to a C-style string using .c_str.

Updating Strings in C++

A string can be modified by altering specific characters and by adding new sections or substituting existing text. C-style strings need proper memory management during modifications because buffer overflows can occur, while std::string includes automatic functions to add, insert, delete, and swap parts within its strings.

a) Updating C-Style Strings:

Using operator:

In C++, we can update the C-Style string using operator.

char str[] = "Hello";

str[0] = 'M';

std::cout << str; // Output: Mello

b) Updating std::string:

Using or .at:

In C++, we can update the C-Style string using operator.

std::string str = "Hello";

str[0] = 'M';

std::cout << str; // Output: Mello

Example:

Let us take an example to illustrate how to update the string in C++.

Example

#include <iostream>

#include <string>  // Include string library for std::string

int main() {

    // (a) Updating C-Style String

    char cstr[] = "Hello";  // C-style string (character array)

    cstr[0] = 'M';          // Modifying the first character

    std::cout << "Updated C-Style String: " << cstr << std::endl; 

    // (b) Updating std::string

    std::string str = "Hello"; // Declare a std::string variable

    // Using index operator []

    str[0] = 'M'; 

    std::cout << "After modifying using []: " << str << std::endl; 

    // Using .at() method (safe version of indexing)

    str.at(1) = 'a'; 

    std::cout << "After modifying using at(): " << str << std::endl; 

    return 0;

}

Output:

Updated C-Style String: Mello

After modifying using []: Mello

After modifying using at(): Mallo

Explanation:

This C++ program demonstrates updating both C-style strings and std::string in C++. It modifies specific characters using indexing ('') and the '.at' method, showing how string values can be changed safely.

Appending strings using .append or +=

Strings allow new characters or words to be appended to their ends through either C-style manual concatenation or std::string built-in operations.

Using .append method:

We can append the string using the .append method in C++.

std::string str = "Hello";

str.append(" World");

std::cout << str;  // Output: Hello World

Using += operator:

We can append the string using the += operator in C++.

std::string str = "Hello";

str += " World";

std::cout << str;  // Output: Hello World

Example:

Let us take an example to illustrate how to append the string in C++.

Example

#include <iostream>

#include <string>  // Include the string library

int main() {

    // Initialize a string

    std::string str = "Hello";

    // Using .append() to add a word at the end

    str.append(" World"); 

    std::cout << "After append(): " << str << std::endl; 

    // Using += operator to add more text

    str += "!!!";  

    std::cout << "After += operator: " << str << std::endl; 

    return 0;

}

Output:

After append(): Hello World

After += operator: Hello World!!!

Explanation:

The '.append' method adds " World" to the original string "Hello", updating it to "Hello World". The '+=' operator then further appends "!!!", resulting in the final output "Hello World!!!".

Replacing substrings using .replace

The substring within a string can be exchanged for a different string through direct manual edits in C-style strings and integrated functions in std::string.

std::string str = "Hello World";

str.replace(6, 5, "C++");

std::cout << str; // Output: Hello C++

Example:

Let us take an example to illustrate how to replace the substring using .replace function in C++.

Example

#include <iostream>

#include <string>  // Include the string library

int main() {

    // Initialize a string

    std::string str = "Hello World";

    // Using .replace() to replace "World" with "C++"

    str.replace(6, 5, "C++"); 

    std::cout << "After replace(): " << str << std::endl; 

    return 0;

}

Output:

After replace(): Hello C++

Explanation:

The 'std::string::replace' method replaces a portion of the string starting from index '6' with a length of '5' characters (i.e., "World") with "C++". It modifies the original string to "Hello C++", demonstrating how substring replacement works in C++.

Other examples of C++ String

Several another examples of C++ string are as follows:

1. C++ String Compare Example:

Let's see the simple example of string comparison using the strcmp function.

Example

#include <iostream>  

#include <cstring>  

using namespace std;  

int main ()  

{  

  char key[] = "mango";  // Define the correct answer as a C-string

  char buffer[50];  // // Buffer to store user input

  do {  

     cout<<"What is my favourite fruit? ";  

     cin>>buffer;  

  } while (strcmp (key, buffer) != 0);  // Compare input with key;

 cout<<"Answer is correct!!"<<endl;  

  return 0;  

}

Output:

What is my favourite fruit? apple

What is my favourite fruit? banana

What is my favourite fruit? mango

The answer is correct!!

Explanation:

In this program, the user input is compared with predefined string "mango" using strcmp function. This will check the equality among two strings. When the user inputs "mango", strcmp returns 0, causing the loop to terminate and displaying "Answer is correct!!".

2. C++ String Concat Example:

Let's see the simple example of string concatenation using the strcat function.

Example

#include <iostream>  

#include <cstring>  

using namespace std;  

int main()  

{  

    char key[25], buffer[25];  

    cout << "Enter the key string: ";  

    cin.getline(key, 25);  

    cout << "Enter the buffer string: ";  

     cin.getline(buffer, 25);  

    strcat(key, buffer);   

    cout << "Key = " << key << endl;  

    cout << "Buffer = " << buffer<<endl;  

    return 0;  

}

Output:

Enter the key string: Welcome to

Enter the buffer string: C++ Programming.

Key = Welcome to C++ Programming.

Buffer = C++ Programming.

Explanation:

This program concatenates two C-style strings using the 'strcat' function, which appends the 'buffer' string to the 'key' string. After concatenation, the updated 'key' contains both strings combined, while 'buffer' remains unchanged.

3. C++ String Copy Example:

Let's see the simple example of copying the string using the strcpy function.

Example

#include <iostream>  

#include <cstring>  

using namespace std;  

int main()  

{  

    char key[25], buffer[25];  

    cout << "Enter the key string: ";  

    cin.getline(key, 25);  

    strcpy(buffer, key);  

    cout << "Key = "<< key << endl;  

    cout << "Buffer = "<< buffer<<endl;  

    return 0;  

}

Output:

Enter the key string: C++ Tutorial

Key = C++ Tutorial

Buffer = C++ Tutorial

Explanation:

This program copies the content of the 'key' string into the 'buffer' string using the 'strcpy' function. After copying, both 'key' and 'buffer' contain the same string.

4. C++ String Length Example:

Let's see the simple example of finding the string length using the strlen function.

Example

#include <iostream>  

#include <cstring>  

using namespace std;  

int main()  

{  

    char ary[] = "Welcome to C++ Programming";  

    cout << "Length of String = " << strlen(ary)<<endl;  

    return 0;  

}

Output:

Length of String = 26

Explanation:

This program calculates the length of the string "Welcome to C++ Programming" using the 'strlen' function. It returns the number of characters in the string, excluding the null terminator ('\0').

Pass Strings to Functions in C++

a) Passing C-Style Strings to Functions:

C-style strings are passed as character arrays. It is good practice to use const to prevent modification inside the function.

void printCStr(const char str[]) {

    std::cout << str << std::endl;

}

int main() {

    char str[] = "Hello";

    printCStr(str);

    return 0;

}

b) Passing std::string to Functions:

The std::string class provides a safer and more flexible way to handle strings in C++. Passing by reference (const std::string&) avoids unnecessary copies.

#include <iostream>  

void printString(const std::string &str) {

    std::cout << str << std::endl;

}

int main() {

    std::string str = "Hello C++";

    printString(str);

    return 0;

}

Why Use Strings in C++?

• ✅ It sores textual data efficiently
• ✅ The string class provides multiple functional capabilities, such as string joining pattern search and substring retrieval.
• ✅ The use of std::string provides users with safer memory handling and simplified memory management operations.

C++ String Functions

Here is a table that contains several string functions in C++.

C++ String MCQs

1. What is a C++ string?

• ✅ A C++ string consists of a character sequence in which integers are stored in arrays.
• ✅ A sequence of characters takes residence in a character array that ends with a null terminator character (\0).
• ✅ A sequence of characters exists within std::string objects.
• ✅ Both B and C

1. In C++, which header file allows developers to use std::string?

• ✅ <string>
• ✅ <cstring>
• ✅ <iostream>
• ✅ <stdlib.h>

1. How does C++ organize string data within storage?

• ✅ A collection of integers
• ✅ A sequential collection of characters
• ✅ A pointer to a single character
• ✅ This data type contains only numerical content

1. Which character signifies the termination of a C-style string held in C++ memory?

• ✅ With a space character
• ✅ With a special delimiter
• ✅ With a null character (\0)
• ✅ With a newline character (\n)

1. Which standard function determines the length value of C++ strings utilizing std::string?

• ✅ size
• ✅ length
• ✅ strlen
• ✅ Both a and b