A Custom Exception Built at Run Time

1#include <iostream>
2#include <stdexcept>
3#include <string>
4 
5class UnknownCommand : public std::runtime_error {
6public:
7    explicit UnknownCommand(const std::string& name)
8        : std::runtime_error("unknown command: " + name) {}
9};
10 
11void run(const std::string& command) {
12    if (command != "start" && command != "stop") {
13        throw UnknownCommand(command);
14    }
15    std::cout << "running " << command << "\n";
16}
17 
18int main() {
19    std::string commands[] = {"start", "jump", "stop", "fly"};
20    for (const std::string& command : commands) {
21        try {
22            run(command);
23        } catch (const std::runtime_error& e) {
24            std::cout << e.what() << "\n";
25        }
26    }
27    return 0;
28}