CODEWITHSUNDEEP
c++exceptioncustom-exceptions
Alex Netkachov
Alex Netkachov

Reputation: 13522

C++ Exceptions with message

I'm not sure that my custom exception approach is correct. What I want to do is to throw exceptions with custom messages but it seems that I created a memory leak...

class LoadException: public std::exception {
private:
    const char* message;
public:
    LoadException(const std::string message);
    virtual const char* what() const throw();
};


LoadException::LoadException(const std::string message) {
    char* characters = new char[message.size() + 1];
    std::copy(message.begin(), message.end(), characters);
    characters[message.size()] = '\0';
    this->message = characters;
}

I use it as follows:

void array_type_guard(Local<Value> obj, const std::string path) {
    if (!obj->IsArray()) {
        throw LoadException(path + " is not an array");
    }
}

try {
    objects = load_objects();
} catch (std::exception& e) {
    ThrowException(Exception::TypeError(String::New(e.what())));
    return scope.Close(Undefined());
}

I afraid that the array created in constructor is never deleted. But I'm not sure how to delete it - should I add destructor or maybe use completely different approach?

Update:

I've actually tried to use the string class as follows:

class LoadException: public std::exception {
private:
    const char* msg;
public:
    LoadException(const std::string message);
    virtual const char* what() const throw();
};

LoadException::LoadException(const std::string message) {
    msg = message.c_str();
}

const char* LoadException::what() const throw() {
    return msg;
}

But cannot get the error message then - some random output is displayed when I print the "what()".

Upvotes: 17

Views: 43008

Answers (3)

NG.
NG.

Reputation: 22904

You can take advantage of std:string

class LoadException: public std::exception {
private:
    std::string message_;
public:
    explicit LoadException(const std::string& message);
    const char* what() const noexcept override {
        return message_.c_str();
    }
};


LoadException::LoadException(const std::string& message) : message_(message) {
    
}

Then the C++ scoping will take care of cleaning things up for you

Upvotes: 24

kometen
kometen

Reputation: 7792

In the constructor I have

Printer::Printer(boost::asio::io_service& io, unsigned int interval) {
    if (interval < 1) {
        throw std::runtime_error("Interval can't be less than one second");
    }
}

And when creating the object

try {
    Printer p{io, 0};
} catch (std::exception& e) {
    std::cerr << e.what() << std::endl;
}

the program will exit with the message thrown.

Upvotes: 2

MonoThreaded
MonoThreaded

Reputation: 12033

How about
throw std::runtime_error("My very own message");

Upvotes: 40

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