String manipulation functions in C++ are used to perform various operations on strings, allowing developers to manipulate, analyze, and process string data easily. The C++ Standard Library provides a robust set of functions and methods for working with strings, particularly through the std::string class. Below is an overview of common string manipulation functions and methods available in C++.

1. Common std::string Member Functions

The std::string class offers various member functions to facilitate string manipulation. Here are some of the most frequently used functions:

a. Length and Size

• length() / size(): Returns the number of characters in the string.

std::string str = "Hello, World!";
std::cout << "Length: " << str.length() << std::endl; // Output: 13

b. Accessing Characters

• operator[]: Accesses a character at a specific index.

char firstChar = str[0]; // 'H'

• at(index): Similar to operator[], but it performs bounds checking and throws an exception if the index is out of range.

char secondChar = str.at(1); // 'e'

c. Appending Strings

• append(): Appends a string or character to the end of the current string.

str.append(" How are you?");
std::cout << str << std::endl; // Output: Hello, World! How are you?

• operator+=: Concatenates another string or character to the current string.

str += " Have a nice day!";

d. Inserting Strings

• insert(index, str): Inserts a string at the specified index.

str.insert(7, "Beautiful "); // Inserts "Beautiful " at index 7

e. Erasing Strings

• erase(index, count): Removes characters from the string starting at the specified index for the given count.

str.erase(7, 10); // Removes "Beautiful "

f. Finding Substrings

• find(substr): Returns the index of the first occurrence of the specified substring. Returns std::string::npos if not found.

size_t position = str.find("World");
if (position != std::string::npos) {
    std::cout << "Found 'World' at position: " << position << std::endl; // Output: 7
}

g. Replacing Substrings

• replace(start, length, str): Replaces a portion of the string with another string.

str.replace(7, 5, "Everyone"); // Replaces "World" with "Everyone"

h. Substrings

• substr(start, length): Returns a new string containing a substring from the original string, starting at the specified index and extending for the given length.

std::string sub = str.substr(0, 5); // Extracts "Hello"

i. Comparing Strings

• compare(str): Compares the current string with another string and returns an integer value indicating the relationship.

if (str.compare("Hello, Everyone!") == 0) {
    std::cout << "Strings are equal." << std::endl;
} else {
    std::cout << "Strings are not equal." << std::endl;
}

j. Converting to C-style String

• c_str(): Returns a pointer to a null-terminated character array representing the string.

const char* cStr = str.c_str(); // Convert to C-style string

2. Example of String Manipulation

Here’s a comprehensive example demonstrating various string manipulation functions:

#include <iostream>
#include <string>

int main() {
    std::string str = "Hello, World!";

    // Print the original string
    std::cout << "Original String: " << str << std::endl;

    // Length of the string
    std::cout << "Length: " << str.length() << std::endl;

    // Accessing characters
    std::cout << "First character: " << str[0] << std::endl;

    // Appending
    str.append(" How are you?");
    std::cout << "After append: " << str << std::endl;

    // Inserting
    str.insert(7, "Beautiful ");
    std::cout << "After insert: " << str << std::endl;

    // Erasing
    str.erase(7, 10); // Removes "Beautiful "
    std::cout << "After erase: " << str << std::endl;

    // Finding a substring
    size_t pos = str.find("World");
    if (pos != std::string::npos) {
        std::cout << "'World' found at position: " << pos << std::endl;
    }

    // Replacing a substring
    str.replace(7, 5, "Everyone");
    std::cout << "After replace: " << str << std::endl;

    // Substring extraction
    std::string sub = str.substr(0, 5);
    std::cout << "Substring: " << sub << std::endl; // Output: Hello

    // Comparing strings
    if (str.compare("Hello, Everyone!") == 0) {
        std::cout << "Strings are equal." << std::endl;
    } else {
        std::cout << "Strings are not equal." << std::endl;
    }

    // Convert to C-style string
    const char* cStr = str.c_str();
    std::cout << "C-style string: " << cStr << std::endl;

    return 0;
}