String Functions in C++

String functions are functions and methods used to perform operations on text stored in a std::string.

For example:

std::string name = "Rahul";

std::cout << name.length();

The length() function returns the number of characters in the string.

To use std::string, include the string header.

#include <iostream>
#include <string>

You can then create and manipulate string objects.

The length() function returns the number of characters in a string.

std::string text = "Hello";

std::cout << text.length();

Output:

5

The size() function also returns the number of characters in a std::string.

std::string text = "Computer";

std::cout << text.size();

Output:

8

For std::string, size() and length() return the same count.

The empty() function checks whether a string contains no characters.

std::string name;

if (name.empty()) {

    std::cout << "String is empty";
}

It returns true if the string is empty.

The clear() function removes all characters from a string.

std::string message = "Hello World";

message.clear();

std::cout << message;

After calling clear(), the string becomes empty.

The at() function accesses a character at a specified position.

std::string word = "Hello";

std::cout << word.at(1);

Output:

e

Indexes start from 0.

Characters can also be accessed using the square bracket operator.

std::string word = "Hello";

std::cout << word[0];

Output:

H

Both at() and [] can access characters, but they differ in their handling of an out-of-range index.

The find() function searches for a character or substring.

std::string text = "Hello World";

std::size_t position = text.find("World");

if (position != std::string::npos) {

    std::cout << "Found";
}

If the text is not found, find() returns std::string::npos.

std::string word = "Computer";

std::size_t position = word.find('p');

std::cout << position;

The function returns the index of the first matching character.

For "Computer", the character p is found at index 3.

You can specify where the search should start.

std::string text = "apple apple";

std::size_t position =
    text.find("apple", 1);

std::cout << position;

The search starts from index 1, so the second occurrence can be found.

The rfind() function searches for the last occurrence of a character or substring.

std::string text = "apple apple";

std::size_t position =
    text.rfind("apple");

std::cout << position;

It searches from the end of the string toward the beginning.

The substr() function extracts part of a string.

std::string text = "Programming";

std::string part =
    text.substr(0, 7);

std::cout << part;

Output:

Program

The first argument is the starting position and the second is the number of characters.

If the second argument is omitted, substr() returns the characters from the starting position to the end.

std::string text = "Hello World";

std::string part =
    text.substr(6);

std::cout << part;

Output:

World

The append() function adds text to the end of a string.

std::string text = "Hello";

text.append(" World");

std::cout << text;

Output:

Hello World

The insert() function adds text at a specified position.

std::string text = "Hello World";

text.insert(6, "C++ ");

std::cout << text;

Output:

Hello C++ World

The erase() function removes characters from a string.

std::string text = "Hello World";

text.erase(5, 6);

std::cout << text;

Output:

Hello

The first argument is the starting position and the second is the number of characters to remove.

The replace() function replaces part of a string with another string.

std::string text = "I like Java";

text.replace(7, 4, "C++");

std::cout << text;

Output:

I like C++

The compare() function compares two strings.

std::string first = "Apple";
std::string second = "Apple";

if (first.compare(second) == 0) {

    std::cout << "Strings are equal";
}

A result of 0 means the strings are equal.

Strings can also be compared using operators such as ==, !=, <, and >.

std::string a = "Apple";
std::string b = "Banana";

if (a < b) {

    std::cout << "Apple comes before Banana";
}

String comparisons are based on the ordering of their character values.

The swap() function exchanges the contents of two strings.

std::string first = "Hello";
std::string second = "World";

first.swap(second);

std::cout << first << std::endl;
std::cout << second;

Output:

World
Hello

The push_back() function adds one character to the end of a string.

std::string text = "Hell";

text.push_back('o');

std::cout << text;

Output:

Hello

The pop_back() function removes the last character from a non-empty string.

std::string text = "Hello";

text.pop_back();

std::cout << text;

Output:

Hell

The c_str() function provides access to a null-terminated character sequence representing the string.

std::string text = "Hello";

const char* value = text.c_str();

std::cout << value;

It is useful when interacting with APIs that require a C-style string.

A loop and at() or indexing can be used to count how many times a character appears.

std::string text = "banana";

int count = 0;

for (int i = 0; i < text.length(); i++) {

    if (text[i] == 'a') {
        count++;
    }
}

std::cout << "Count = "
          << count;

Output:

Count = 3

• Forgetting to include <string>.
• Using an invalid string index.
• Confusing the string length with the last index.
• Forgetting that find() returns std::string::npos when the item is not found.
• Calling pop_back() on an empty string.
• Using std::cin >> when a complete line with spaces is required.
• Using incorrect positions with erase(), insert(), or replace().

#include <iostream>
#include <string>

int main() {

    std::string sentence;

    std::cout << "Enter a sentence: ";

    std::getline(std::cin, sentence);

    std::string searchText;

    std::cout << "Enter text to search: ";

    std::getline(std::cin, searchText);

    std::size_t position =
        sentence.find(searchText);

    if (position != std::string::npos) {

        std::cout << "Text found at index "
                  << position;
    }
    else {

        std::cout << "Text not found";
    }

    return 0;
}

#include <iostream>
#include <string>

int main() {

    std::string text = "Hello World";

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

    std::cout << text << std::endl;

    text.append(" Programming");

    std::cout << text;

    return 0;
}

Output:

Hello C++
Hello C++ Programming

• Use std::string for normal string processing.
• Use length() or size() when you need the string length.
• Check the result of find() against std::string::npos.
• Use substr() to extract portions of text.
• Use append() or += to add text.
• Use erase() and replace() carefully with correct positions.
• Use empty() before operations that require a non-empty string when appropriate.
• Use std::getline() when input can contain spaces.