In C++, the try-catch block is used to catch and handle exceptions (errors) that may occur during the execution of a program.

An exception is an unexpected event that interrupts the normal flow of the program. The purpose of the try-catch block is to allow the program to respond to errors in a controlled manner, rather than terminating abruptly.

Basic Structure

The basic structure of try-catch is as follows:

try {
    // Code that may throw an exception
}
catch (const std::exception& e) {
    // Code to handle the exception
}

Basic Example

Let’s see it with a simple example, where we attempt to divide two numbers and handle a possible division by zero:

#include <iostream>
#include <stdexcept>

int main() {
    try {
        int divisor = 0;
        if (divisor == 0) {
            throw std::runtime_error("Error: Division by zero not allowed.");
        }
        int result = 10 / divisor;
    }
    catch (const std::runtime_error& e) {
        std::cout << e.what() << std::endl;  // Displays the exception message
    }
    return 0;
}

Capturing Multiple Exceptions

You can have multiple catch blocks to handle different types of exceptions specifically:

#include <iostream>
#include <stdexcept>

int main() {
    try {
        // Code that may throw exceptions
        throw std::logic_error("Logical error");
    }
    catch (const std::logic_error& e) {
        std::cout << "Caught: " << e.what() << std::endl;
    }
    catch (const std::runtime_error& e) {
        std::cout << "Caught: " << e.what() << std::endl;
    }
    catch (...) {
        std::cout << "Unknown error" << std::endl;
    }
    return 0;
}

General catch

Sometimes, it is useful to have a catch block that can handle any type of exception. This is achieved using the catch(...) syntax, which captures any exception regardless of its type.

try {
    throw 10.5;
} catch (...) {
    std::cerr << "An exception has been caught." << std::endl;
}

Practical Examples

Handling Exceptions in I/O Operations

In this example, we use try-catch to handle exceptions related to reading a file.

We capture two types of exceptions: std::ios_base::failure if there is an I/O error, and std::exception for other general issues.

#include <iostream>
#include <fstream>
#include <stdexcept>

int main() {
    try {
        std::ifstream file("file.txt");
        if (!file) {
            throw std::ios_base::failure("Error: Cannot open the file.");
        }

        std::string line;
        while (std::getline(file, line)) {
            std::cout << line << std::endl;
        }
    }
    catch (const std::ios_base::failure& e) {
        std::cout << "File error: " << e.what() << std::endl;
    }
    catch (const std::exception& e) {
        std::cout << "General error: " << e.what() << std::endl;
    }
    return 0;
}