Cpp Programming String Handling Functions Complete Guide

Example 1: Using std::string and Basic Functions

Description: This example demonstrates how to declare, initialize and use basic functions such as length(), substr(), find(), and replace a std::string.

#include <iostream>
#include <string>

int main() {
    // Step 1: Declare and initialize a std::string variable
    std::string str = "Welcome to C++ Programming";

    // Step 2: Display the original string
    std::cout << "Original String: " << str << std::endl;

    // Step 3: Get and display the length of the string
    int len = str.length();
    std::cout << "Length of the String: " << len << std::endl;

    // Step 4: Get and display a substring from the original string
    std::string substr = str.substr(7, 2);  // Starting from index 7, take next 2 characters
    std::cout << "Substring (from index 7, of length 2): " << substr << std::endl;

    // Step 5: Find a substring within the original string
    size_t pos = str.find("C++");
    if (pos != std::string::npos) {
        std::cout << "Substring 'C++' found at position: " << pos << std::endl;
    } else {
        std::cout << "Substring 'C++' not found." << std::endl;
    }

    // Step 6: Replace a part of the string
    str.replace(pos, 3, "Java");  // Replace 'C++' with 'Java'
    std::cout << "After Replacement: " << str << std::endl;

    return 0;
}

Explanation:

• Step 1: We include the <string> library and declare a std::string object named str and initialize it.
• Step 2: We output the original string.
• Step 3: We use length() to get the number of characters in the string.
• Step 4: substr(starting_index, length_of_substring) takes two parameters and returns the substring from the specified starting index and of the specified length.
• Step 5: find(substring) searches for the specified substring and returns its position. It returns std::string::npos if the substring is not found.
• Step 6: replace(position, length_of_text_to_replace, replacement_text) replaces a portion of the string with another string.

Example 2: Concatenation of Strings

Description: This example shows how to concatenate strings using std::string.

#include <iostream>
#include <string>

int main() {
    // Step 1: Initialize two std::string objects
    std::string firstName = "John";
    std::string lastName = "Doe";

    // Step 2: Concatenate firstName and lastName into fullName
    std::string fullName = firstName + " " + lastName;

    // Step 3: Output the full name
    std::cout << "Full Name: " << fullName << std::endl;

    // Step 4: Append suffix to the full name
    fullName += ", Jr.";
    std::cout << "Full Name after appending suffix: " << fullName << std::endl;

    return 0;
}

Explanation:

• Step 1: Two strings, firstName and lastName, are initialized.
• Step 2: Strings can be concatenated using the + operator.
• Step 3: Print the concatenated string.
• Step 4: The += operator can be used to append a string to the end of another string.

Example 3: String Comparison

Description: This example illustrates how to compare strings using std::string.

#include <iostream>
#include <string>

int main() {
    // Step 1: Initialize two std::string objects
    std::string str1 = "apple";
    std::string str2 = "banana";

    // Step 2: Compare the strings for inequality
    if (str1 != str2) {
        std::cout << "Strings '" << str1 << "' and '" << str2 << "' are not equal." << std::endl;
    }

    // Step 3: Compare the strings for equality
    if (str1 == "apple") {
        std::cout << "String '" << str1 << "' is equal to 'apple'." << std::endl;
    }

    // Step 4: Use comparison operators to compare lexicographical order
    if (str1 < str2) {
        std::cout << "String '" << str1 << "' comes before '" << str2 << "' in lexicographical order." << std::endl;
    } else {
        std::cout << "String '" << str2 << "' comes before '" << str1 << "' in lexicographical order." << std::endl;
    }

    return 0;
}

Explanation:

• Step 1: Two string variables, str1 and str2, are declared and initialized.
• Step 2: Use != operator to check if two strings are not equal.
• Step 3: Use == operator to check if a string equals a given value.
• Step 4: Use <, >, <=, >= operators to determine the lexicographical order of strings (similar to dictionary order).

Example 4: Converting C-Style Strings to STL Strings

Description: This example shows how to convert between C-style strings (char*) and STL strings (std::string).

#include <iostream>
#include <string>

int main() {
    // Step 1: Define a C-style string (null-terminated character array)
    char cStyleStr[] = "Hello";

    // Step 2: Convert C-style string to std::string
    std::string stlStr(cStyleStr);
    std::cout << "STL String after conversion from C-style string: " << stlStr << std::endl;

    // Step 3: Convert std::string back to C-style string with .c_str()
    const char* convertedBack = stlStr.c_str();
    std::cout << "C-style string after converting back from STL string: " << convertedBack << std::endl;

    return 0;
}

Explanation:

• Step 1: A C-style string is declared as a char array.
• Step 2: An std::string can be created from a C-style string simply by passing the C-style string to the constructor of std::string.
• Step 3: The c_str() member function of std::string can be used to obtain a C-style string version of the std::string.

Example 5: Using getline to Read a Full Line Including Spaces

Description: This example reads a line of text from the user which includes spaces using std::getline.

#include <iostream>
#include <string>

int main() {
    // Step 1: Declare a std::string to store the full line input
    std::string line;

    // Step 2: Prompt the user for input
    std::cout << "Enter a line including spaces: ";

    // Step 3: Read the whole line of text (including spaces) using std::getline
    std::getline(std::cin, line);

    // Step 4: Output the read text
    std::cout << "You entered: " << line << std::endl;

    return 0;
}

Explanation:

• Step 1: Initialize an std::string object that will hold the user's input.
• Step 2 & 3: Use std::getline(std::cin, line) to read an entire line of input from the user, preserving spaces and other characters until a newline (\n) is encountered.
• Step 4: Output the contents of the line object.