A Custom Exception With a Fixed Message

1#include <iostream>
2#include <exception>
3 
4class EmptyCartError : public std::exception {
5public:
6    const char* what() const noexcept override {
7        return "the cart is empty";
8    }
9};
10 
11void checkout(int items) {
12    if (items == 0) {
13        throw EmptyCartError();
14    }
15    std::cout << "charged for " << items << " item(s)\n";
16}
17 
18int main() {
19    try {
20        checkout(3);
21        checkout(0);
22        checkout(5);
23    } catch (const EmptyCartError& e) {
24        std::cout << "cannot checkout: " << e.what() << "\n";
25    }
26    return 0;
27}