String Container Overview

Basic Concepts

The string type in C++ represents a sequence of characters and is implemented as a class rather than a raw pointer like char*. It encapsulates a dynamic array of characters, offering built-in methods for manipulation.

Key characteristics:

• Encapsulates internal memory management
• Provides extensive member functions for operations like searching, copying, replacing, and inserting
• Safeguards against buffer overflows and invalid access through its internal mechanisms

Constructor Usage

The string class offers several constructors for initialization:

string();                     // Default constructor
string(const char* s);        // From C-style string
string(const string& s);      // Copy constructor
string(size_t count, char c); // Repeat character

Example usage:

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

void test_constructors() {
    string empty_str;               // Empty string
    cout << "Empty: " << empty_str << endl;

    const char* literal = "Hello";
    string from_cstr(literal);      // Initialize from C-string
    cout << "From C-string: " << from_cstr << endl;

    string copy_str(from_cstr);     // Copy construction
    cout << "Copy: " << copy_str << endl;

    string repeated(5, 'A');        // Five A's
    cout << "Repeated: " << repeated << endl;
}

Assignment Operations

Assigning values to strings can be done via overloaded operators or dedicated funcsions:

string& operator=(const char* s);
string& operator=(const string& s);
string& operator=(char c);
string& assign(const char* s);
string& assign(const char* s, size_t count);
string& assign(const string& s);
string& assign(size_t count, char c);

Example:

void test_assignment() {
    string s1 = "Hello";             // Assignment from C-string
    string s2 = s1;                  // Assignment from string
    cout << "s1: " << s1 << " s2: " << s2 << endl;

    string s3;
    s3 = 'X';                        // Assign single character
    cout << "Single char: " << s3 << endl;

    string s4;
    s4.assign("World");              // Using assign function
    cout << "Assigned: " << s4 << endl;

    string s5;
    s5.assign("World", 3);          // Assign first 3 chars
    cout << "Partial assign: " << s5 << endl;

    string s6;
    s6.assign(4, 'Y');               // 4 Y's
    cout << "Repeated: " << s6 << endl;
}

Concatenation Methods

Strings can be joined using various approaches:

string& operator+=(const string& s);
string& operator+=(const char* s);
string& operator+=(char c);
string& append(const char* s);
string& append(const char* s, size_t count);
string& append(const string& s);
string& append(const string& s, size_t pos, size_t count);

Example:

void test_concatenation() {
    string s1 = "Start";
    s1 += "End";                    // Append string
    cout << "Concatenated: " << s1 << endl;

    s1 += '!' ;                      // Append character
    cout << "With exclamation: " << s1 << endl;

    string s2 = "Middle";
    s1 += s2;                       // Append another string
    cout << "Final: " << s1 << endl;

    s1.append(" Final");           // Using append method
    cout << "Appended: " << s1 << endl;
}

Search and Replace

Finding and replacing substrings within a string:

int find(const string& str, size_t pos = 0);
int find(const char* s, size_t pos = 0);
int rfind(const string& str, size_t pos = string::npos);
string& replace(size_t pos, size_t count, const string& str);

Example:

void test_search_replace() {
    string text = "abcdefgde";
    int pos = text.find("de");       // Find first occurrence
    if (pos != string::npos)
        cout << "Found at position: " << pos << endl;

    pos = text.rfind("de");         // Find last occurrence
    cout << "Last found at: " << pos << endl;

    string replaced = text;
    replaced.replace(3, 3, "XYZ");   // Replace 3 chars starting at index 3
    cout << "Replaced: " << replaced << endl;
}

String Comparison

Comparison is performed based on ASCII values:

int compare(const string& s) const;
int compare(const char* s) const;

Example:

void test_comparison() {
    string a = "Apple";
    string b = "Banana";
    int result = a.compare(b);

    if (result == 0)
        cout << "Equal" << endl;
    else if (result > 0)
        cout << "Greater" << endl;
    else
        cout << "Less" << endl;
}

Character Access

Access individual characters using either operator[] or at():

char& operator[](size_t pos);
char& at(size_t pos);

Example:

void test_access() {
    string str = "Hello";
    cout << "Length: " << str.length() << endl;

    for (size_t i = 0; i < str.length(); ++i)
        cout << str[i] << " ";
    cout << endl;

    for (size_t i = 0; i < str.length(); ++i)
        cout << str.at(i) << " ";
    cout << endl;

    str[0] = 'h';                   // Modify first character
    str.at(1) = 'E';                // Modify second character
    cout << "Modified: " << str << endl;
}

Insertion and Deletion

Operations for modifying the string in-place:

string& insert(size_t pos, const string& s);
string& insert(size_t pos, size_t count, char c);
string& erase(size_t pos, size_t count = string::npos);

Example:

void test_insert_delete() {
    string s = "Hello";
    s.insert(1, "XX");              // Insert at index 1
    cout << "After insert: " << s << endl;

    s.erase(1, 2);                  // Delete 2 chars from index 1
    cout << "After delete: " << s << endl;
}

Substring Extraction

Extract parts of a string using substr:

string substr(size_t pos = 0, size_t count = string::npos) const;

Example:

void test_substring() {
    string email = "user@example.com";
    size_t at_pos = email.find('@');
    string username = email.substr(0, at_pos);
    cout << "Username: " << username << endl;
}