c++ overload operator ++

Question

For a school project I have to implement a sensor class in c++ which has a private property active (boolean) which indicates if the sensor is active or not. I have to overload the ++ operator in such way that if the operator ++ is used the property active will be set to true.

I implemented the following (sensor.cpp):

Sensor::Sensor(int id, std::string vendor) : _id(id), _vendor(vendor) { std::cout << "Sensor created with id: " << Sensor::getId() << std::endl; _status = false; } bool Sensor::getStatus() { return _status; } void Sensor::setStatus(bool status) { _status = status; } Sensor& Sensor::operator++() { Sensor result = *this; this->setStatus(true); return result; }

main.cpp:

int main(int argc, char *argv[]) { Sensor * sensor = new Sensor(1, "sample vendor"); sensor->setStatus(false); sensor++; std::cout << "status: " << sensor->getStatus() << std::endl; }

I noticed that the program stops executing (finishes) with the last method to be executed the sensor->setStatus(false); in main.cpp but no error is shown in my terminal nor did my compiler complain.

Does someone has an idea what i did wrong and how I can correct it so that the status is set to true?

Thanks in advance

The right tool to solve such problems is your debugger. You should step through your code line-by-line before asking on Stack Overflow. For more help, please read How to debug small programs (by Eric Lippert). At a minimum, you should [edit] your question to include a Minimal, Complete, and Verifiable example that reproduces your problem, along with the observations you made in the debugger. — πάντα ῥεῖ
– πάντα ῥεῖ, Commented Nov 6, 2016 at 21:10
Quite a few mistakes. Better read this. Also, ++ on a boolean doesn't make much sense. — juanchopanza
– juanchopanza, Commented Nov 6, 2016 at 21:11
Sensor result = *this; should be Sensor &result = *this; to avoid returning reference to a temporary (better: return *this; directly), even if you don't use it. Also you're using an incrementation operator to do something else. Not good. — Jean-François Fabre
– Jean-François Fabre ♦, Commented Nov 6, 2016 at 21:11

Dietrich Epp · Accepted Answer · 2016-11-06 21:13:29Z

Since sensor is a pointer, sensor++ increments the pointer not the object. Easiest solution is to just not use a pointer in the first place.

int main() { Sensor sensor{1, "sample vendor"}; sensor.setStatus(false); sensor++; std::cout << "status: " << sensor.getStatus() << std::endl; }

Another solution is to use (*sensor)++...

int main() { std::unique_ptr<Sensor> sensor = std::make_unique<Sensor>(1, "sample vendor"); sensor->setStatus(false); (*sensor)++; std::cout << "status: " << sensor->getStatus() << std::endl; }

Another error in your code is here:

Sensor& Sensor::operator++() { // You don't want to do this... it creates a copy! Sensor result = *this; this->setStatus(true); // This is a dangling reference! return result; }

Use this instead:

Sensor& Sensor::operator++() { this->setStatus(true); return *this; }

C++ is a great language, it enables people to make creative bugs.
check that one: stackoverflow.com/questions/40427771/…. Creative as hell.

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