Exceptions: throw, try, catch

C++ error handling has two channels: return values for expected outcomes, and exceptions for conditions the caller cannot quietly ignore.

#include <stdexcept>

int parse_port(const std::string& s) {
    int value = std::stoi(s);          // throws std::invalid_argument
    if (value < 0 || value > 65535)
        throw std::out_of_range("port out of range: " + s);
    return value;
}

The throwing family you will actually use, all in <stdexcept>:

• std::invalid_argument — the input is not parseable
• std::out_of_range — parseable but outside the legal domain
• std::runtime_error — failures only visible at runtime (I/O, network)
• std::logic_error — the program broke its own contract

Throw by value, catch by const&:

try {
    int port = parse_port(user_input);
    use(port);
} catch (const std::out_of_range& e) {
    std::cerr << "bad port: " << e.what() << "\n";
} catch (const std::exception& e) {
    std::cerr << "error: " << e.what() << "\n";   // base-class fallback
}

Catch order matters: handlers are tried top-down, so put derived types before bases. A bare catch (...) swallows everything — reserve it for thread boundaries and last-resort barriers.