为什么它返回垃圾值

Question

我有一个非常简单的自定义 error_category ，如下所示。我只是想用“例外”来封装它。因此我为它编写了一个自定义异常类。但是当我运行代码时，我得到垃圾值（每次运行它都会得到不同的值。）。由于错误代码是在异常类中全局定义的，所以应该不会有问题。这是什么原因呢？

#include <string>
#include <system_error>
#include <iostream>
#include <stdexcept>


enum class FlightsErrc {
  // no 0
  NonexistentLocations = 10, // requested airport doesn't exist
  DatesInThePast,            // booking flight for yesterday
  InvertedDates,             // returning before departure
  NoFlightsFound       = 20, // did not find any combination
  ProtocolViolation    = 30, // e.g., bad XML
  ConnectionError,           // could not connect to server
  ResourceError,             // service run short of resources
  Timeout,                   // did not respond in time
};

class FlightsErrorCategory : public std::error_category {
public:
    const char* name() const noexcept override { return "FlightsError"; }
    std::string message(int ev) const override {
        switch (static_cast<FlightsErrc>(ev)) {
            case FlightsErrc::NonexistentLocations: return "Nonexistent locations";
            case FlightsErrc::DatesInThePast:       return "Dates are in the past";
            case FlightsErrc::InvertedDates:        return "Inverted dates";
            case FlightsErrc::NoFlightsFound:       return "No flights found";
            case FlightsErrc::ProtocolViolation:    return "Protocol violation";
            case FlightsErrc::ConnectionError:      return "Connection error";
            case FlightsErrc::ResourceError:        return "Resource error";
            case FlightsErrc::Timeout:             return "Timeout occurred";
            default: return "Unknown Flights error";
        }
    }
};

inline const std::error_category& flights_error_category() {
    static FlightsErrorCategory instance;
    return instance;
}

namespace std {
    template <> struct is_error_code_enum<FlightsErrc> : true_type {};
}

std::error_code make_error_code(FlightsErrc e) {
    return {static_cast<int>(e), flights_error_category()};
}

class FlightsException : public std::exception {
public:
    explicit FlightsException(const std::error_code& ec)
        : errorCode(ec) {}

    const char* what() const noexcept override {
        return errorCode.message().c_str();
    }

    std::error_code code() const noexcept { return errorCode; }

private:
    std::error_code errorCode;
};


void flightsServiceFunction(bool simulateError) {
    if (simulateError) {
        throw FlightsException(FlightsErrc::ConnectionError);
    }
}

int main() {
    try {
        flightsServiceFunction(true);
    } catch (const FlightsException& ex) {
        std::cout << "FlightException: " << ex.what() << "\n";
    } catch (const std::exception& ex) {
        std::cerr << "General Exception: " << ex.what() << std::endl;
    }

    return 0;
}

Answer 1

您遇到了 Heap use after free 错误，

message

返回的临时字符串在您从

what

返回之前被销毁。

您的

what

需要返回

std::string

。