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// custom error_category example
#include <iostream> // std::cout, std::endl
#include <system_error> // std::is_error_condition_enum, std::error_category,
// std::error_condition, std::error_code
#include <string> // std::string
// custom error conditions enum type:
enum class custom_errc { success=0, client_error, server_error, other };
namespace std {
template<> struct is_error_condition_enum<custom_errc> : public true_type {};
}
// custom category:
class custom_category_t : public std::error_category {
public:
virtual const char* name() const { return "custom"; }
virtual std::error_condition default_error_condition (int ev) const {
if ((ev>=200)&&(ev<300)) return std::error_condition(custom_errc::success);
else if ((ev>=400)&&(ev<500)) return std::error_condition(custom_errc::client_error);
else if ((ev>=500)&&(ev<600)) return std::error_condition(custom_errc::server_error);
else return std::error_condition(custom_errc::other);
}
virtual bool equivalent (const std::error_code& code, int condition) const {
return *this==code.category() &&
static_cast<int>(default_error_condition(code.value()).value())==condition;
}
virtual std::string message(int ev) const {
switch (ev) {
case 200: return "OK";
case 403: return "403 Forbidden";
case 404: return "404 Not Found";
case 500: return "500 Internal Server Error";
case 503: return "503 Service Unavailable";
default: return "Unknown error";
}
}
} custom_category;
// make_error_code overload to generate custom conditions:
std::error_condition make_error_condition (custom_errc e) {
return std::error_condition(static_cast<int>(e), custom_category);
}
int main()
{
// let's generate a 404:
std::error_code e (404, custom_category);
if (e == custom_errc::success) std::cout << "Success: " << e.message();
else if (e == custom_errc::client_error) std::cout << "Client Error: " << e.message();
else if (e == custom_errc::server_error) std::cout << "Server Error: " << e.message();
else std::cout << "Unknown";
std::cout << std::endl;
return 0;
}
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