Exceptions and Errors

Exceptions

Error handling in C++ is based on three keywords: try, throw, and catch.

Syntax

try {
    int divisor = 0;
    if (divisor == 0) {
        throw std::runtime_error("Error: division by zero"); // Throws an exception
    }
    int result = 10 / divisor; // Won't execute if divisor == 0
    std::cout << "Result: " << result << "\n";
}
 
catch (const std::runtime_error& e) { // Catches the specific exception
    std::cout << "Caught runtime_error: " << e.what() << "\n";
}
 
catch (const std::exception& e) { // Catches any other exception derived from std::exception
    std::cout << "Caught standard exception: " << e.what() << "\n";
}
 
catch (...) { // Catches any other unknown exception
    std::cout << "Caught unknown error\n";
}

Concepts

1. try: Block where an error may occur.
2. throw: Throws an exception.
3. catch: Catches the exception and handles it.
4. The catch(...) block catches any exception not handled by the previous catch blocks.

Note

catch blocks are evaluated in order, from most specific to most general. The exception is caught by the first matching catch.

STL Exceptions

The standard library defines predefined exceptions, such as std::out_of_range (out-of-bounds access) or std::invalid_argument:

std::vector<int> v = {1, 2, 3};
try {
    std::cout << v.at(10); // .at(10) throws std::out_of_range
} catch (const std::out_of_range& e) {
    std::cout << "Index out of bounds\n";
}

Warning

In C++ exceptions propagate automatically if not caught, which terminates the program (std::terminate) if there is no catch.

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