C++ string Library - The Coding College

Welcome to The Coding College! In this tutorial, we’ll explore the C++ string library provided by <string>. This library simplifies working with strings by offering robust tools for string manipulation, comparison, concatenation, and more.

What is the `<string>` Library?

The <string> library in C++ allows developers to work with C++ string objects instead of traditional C-style strings (char[]). String objects are part of the Standard Template Library (STL) and provide numerous functionalities to handle text efficiently.

To use the string library, include it in your program:

#include <string>

Features of `<string>`

Here are some key features of the C++ string library:

Dynamic Size: String objects can grow or shrink as needed.
Rich Functions: Provides methods like concatenation, substring extraction, and string comparison.
Safe and Flexible: Simplifies memory management and avoids buffer overflow issues common with C-style strings.

Declaring a String Object

A string object is created using the std::string data type:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string greeting = "Hello, World!";
    cout << greeting << endl;
    return 0;
}

Common String Operations

The string library offers several functions to manipulate and interact with strings. Let’s go through some of the most important ones.

1. String Initialization

You can initialize strings in multiple ways:

string str1 = "Hello";          // Direct initialization
string str2("World");           // Constructor initialization
string str3 = str1 + " " + str2; // Concatenation

2. Concatenation

Strings can be concatenated using the + operator or append() method:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string firstName = "John";
    string lastName = "Doe";

    string fullName = firstName + " " + lastName; // Using +
    cout << "Full Name: " << fullName << endl;

    fullName.append(" Jr."); // Using append()
    cout << "Updated Name: " << fullName << endl;

    return 0;
}

Output:

Full Name: John Doe
Updated Name: John Doe Jr.

3. Accessing Characters

Use the [] operator or the at() method to access specific characters:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string text = "Hello";

    cout << "First character: " << text[0] << endl;
    cout << "Last character: " << text.at(text.size() - 1) << endl;

    return 0;
}

4. String Length

Use the size() or length() method to get the number of characters in a string:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string message = "The Coding College";
    cout << "Length of string: " << message.size() << endl;

    return 0;
}

5. Substrings

Extract parts of a string using the substr() method:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string text = "The Coding College";

    string word = text.substr(4, 6); // Extracts "Coding"
    cout << "Extracted word: " << word << endl;

    return 0;
}

6. String Comparison

Use ==, <, >, or the compare() method to compare strings:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string str1 = "Hello";
    string str2 = "World";

    if (str1 == str2) {
        cout << "Strings are equal." << endl;
    } else {
        cout << "Strings are not equal." << endl;
    }

    cout << "Comparison result: " << str1.compare(str2) << endl;

    return 0;
}

7. Finding and Replacing

Use find() and replace() for searching and modifying strings:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string text = "I love programming.";

    // Find position of "love"
    size_t pos = text.find("love");
    cout << "'love' found at position: " << pos << endl;

    // Replace "love" with "enjoy"
    text.replace(pos, 4, "enjoy");
    cout << "Updated text: " << text << endl;

    return 0;
}

8. Clearing and Emptying Strings

Use clear() to remove all characters or empty() to check if a string is empty:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string text = "Hello, World!";
    text.clear();

    if (text.empty()) {
        cout << "String is now empty." << endl;
    }

    return 0;
}

Practical Example: Palindrome Check

#include <iostream>
#include <string>
using namespace std;

bool isPalindrome(string str) {
    int start = 0;
    int end = str.size() - 1;

    while (start < end) {
        if (str[start] != str[end]) {
            return false;
        }
        start++;
        end--;
    }
    return true;
}

int main() {
    string text = "madam";
    if (isPalindrome(text)) {
        cout << text << " is a palindrome." << endl;
    } else {
        cout << text << " is not a palindrome." << endl;
    }

    return 0;
}

Summary of Common String Functions

Function	Description	Example
`size()` / `length()`	Returns the length of the string.	`"Hello".size() → 5`
`substr(pos, len)`	Extracts a substring starting at `pos`.	`"Hello".substr(1, 3)`
`find(str)`	Finds the first occurrence of `str`.	`"Hello".find("l") → 2`
`append(str)`	Appends `str` to the string.	`"Hi".append(" there")`
`clear()`	Clears the string content.	`str.clear()`
`empty()`	Checks if the string is empty.	`"".empty() → true`
`compare(str)`	Compares two strings lexicographically.	`"a".compare("b") → -1`

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What is the <string> Library?

Features of <string>