C++ string

String Operations

string first = "Hello";
string second = " World";
string result = first + second;

string text = "Hello";
int len = text.length();
int size = text.size();

string text = "Hello World";
int pos = text.find("World");
// pos = 6

string text = "Hello World";
string part = text.substr(0, 5);
// part = "Hello"

🔹 Basic String Operations

The C++ std::string class, from the <string> library, provides a rich set of member functions for safe and convenient text manipulation. Key operations include .length() or .size() to get the number of characters, .at() or the [] operator for safe character access, and .empty() to check if a string is empty. Unlike C-style character arrays, std::string handles its own memory management, automatically resizing as needed. This makes it the preferred choice for most text-processing tasks, from simple message display to complex parsing.

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

int main() {
    // Creating strings
    string greeting = "Hello";
    string name = "Alice";
    
    // String concatenation
    string message = greeting + ", " + name + "!";
    cout << "Message: " << message << endl;
    
    // String length
    cout << "Length of message: " << message.length() << endl;
    cout << "Size of message: " << message.size() << endl;
    
    // Accessing characters
    cout << "First character: " << message[0] << endl;
    cout << "Last character: " << message[message.length()-1] << endl;
    
    // Check if string is empty
    string empty = "";
    cout << "Is empty string empty? " << empty.empty() << endl;
    
    return 0;
}

🔹 String Search and Find

Searching within strings is a common requirement, and C++ provides several methods like find() and rfind() to locate substrings or characters. The find() method returns the index of the first occurrence of a substring (or string::npos if not found), while rfind() searches from the end. These methods are case-sensitive and essential for tasks like parsing URLs, extracting data from logs, validating input formats (e.g., checking for an '@' in an email), or implementing search functionality within a text editor or data processing application.

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

int main() {
    string sentence = "The quick brown fox jumps over the lazy dog";
    
    cout << "Original sentence: " << sentence << endl;
    cout << "Length: " << sentence.length() << endl << endl;
    
    // Find substring
    int pos = sentence.find("fox");
    if (pos != string::npos) {
        cout << "Found 'fox' at position: " << pos << endl;
    } else {
        cout << "'fox' not found" << endl;
    }
    
    // Find character
    int charPos = sentence.find('q');
    cout << "Found 'q' at position: " << charPos << endl;
    
    // Find last occurrence
    int lastPos = sentence.rfind("the");
    cout << "Last 'the' found at position: " << lastPos << endl;
    
    // Check if string contains substring
    if (sentence.find("dog") != string::npos) {
        cout << "Sentence contains 'dog'" << endl;
    }
    
    return 0;
}

🔹 String Modification

C++ strings are mutable, allowing in-place modification through methods that alter the content or structure of the string. Common operations include .append() to add text to the end, .insert() to add text at a specific position, .replace() to swap out a range of characters, and .erase() to remove characters. The .substr() function extracts a portion of the string without modifying the original. These powerful tools are used for tasks like building dynamic SQL queries, generating HTML/XML, cleaning user input, and implementing text templating systems.

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

int main() {
    string text = "Hello World";
    cout << "Original: " << text << endl;
    
    // Substring extraction
    string hello = text.substr(0, 5);
    string world = text.substr(6, 5);
    cout << "First part: " << hello << endl;
    cout << "Second part: " << world << endl;
    
    // Replace substring
    string replaced = text;
    replaced.replace(6, 5, "C++");
    cout << "After replace: " << replaced << endl;
    
    // Insert text
    string inserted = text;
    inserted.insert(5, " Beautiful");
    cout << "After insert: " << inserted << endl;
    
    // Erase part of string
    string erased = text;
    erased.erase(5, 6);  // Remove " World"
    cout << "After erase: " << erased << endl;
    
    // Append to string
    string appended = "Hello";
    appended.append(" World!");
    cout << "After append: " << appended << endl;
    
    return 0;
}

🔹 String Comparison

String comparison in C++ can be performed using relational operators (==, !=, <, etc.) or the .compare() member function. The operators provide a clear syntax for checking equality or lexicographical order (dictionary order), which is crucial for sorting alphabetically or validating passwords. The .compare() function offers more detailed results, returning zero for equality or a negative/positive number indicating order. Understanding comparison is vital for implementing search algorithms, sorting lists of names, managing access control, and organizing data in applications like phonebooks or file managers.

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

int main() {
    string str1 = "Apple";
    string str2 = "Banana";
    string str3 = "Apple";
    
    cout << "str1: " << str1 << endl;
    cout << "str2: " << str2 << endl;
    cout << "str3: " << str3 << endl << endl;
    
    // Equality comparison
    if (str1 == str3) {
        cout << "str1 equals str3" << endl;
    }
    
    if (str1 != str2) {
        cout << "str1 is not equal to str2" << endl;
    }
    
    // Lexicographic comparison
    if (str1 < str2) {
        cout << "str1 comes before str2 alphabetically" << endl;
    }
    
    // Using compare() method
    int result = str1.compare(str2);
    if (result < 0) {
        cout << "str1 is less than str2" << endl;
    } else if (result > 0) {
        cout << "str1 is greater than str2" << endl;
    } else {
        cout << "str1 equals str2" << endl;
    }
    
    return 0;
}