Destructors in C++

Key Takeaways

hey what's up guys my name is Aero and welcome back to my C++ series last time we talked about Constructors in C++ and what they are and how to use them definitely check out that video if you haven't already and today we're going to talk about their evil twin the destructor so similarly how a Constructor runs when you create a new instance of an object a Destructor runs when you destroy an object so anytime an object gets destroyed the destructor method will get called The Constructor is usually where you set variables up or do any kind of initialization that you need to do and similarly the destructor is where you unin ize anything that you might have to or clean any memory that you've used the destructure applies to both stack and Heap allocated objects so if you allocate an object using new when you call delete the destructor will get called if you just have a stack based object then when the scope ends the object will get deleted and thus the destructor will get called let's dive in and take a look at some examples so in the Constructor video we created this wonderful entity class which had multiple Constructors here let's go ahead and add a Destructor a Destructor begins with a tier and then the name of our class so basically the only difference between a construct and a Destructor in terms of Declaration and definition is the actual tier that you put at the front of the destructor that's how you know it's a Destructor in this case we just have a simple class with two members X and Y there is absolutely no clean up we need to do for memory here at all since these two floats are allocated in place with our class we're going to talk way more about memory allocation and all of that complicated stuff in the future so don't you worry but for an example let's go ahead and add a message which tells us that the object has been deleted so I might write something like destroyed entity and then for fun in our Constructor here I'm going to write constructed entity or I guess we should call it created since we called this destroyed and not destructed I'm going to get rid of this Constructor just so we don't get too confused I'll initialize X and Y to Z as well just so that we're not crazy I'll get rid of this as well now since this is stack allocated we will only see the destructure getting called when the main function exits which we're not really going to see because our program will close immediately after that so I'm going to just write a function here which will perform all of our entity operations I'll move all this code over here and I will call function now if I run my code just like this you should see created entity then our print function running which prints X and Y and then finally destroyed entity let's take a deeper look as to how this works I'm going to put a break point on line 28 here next to our entity and hit F5 currently I've got absolutely nothing in the console if I hit F10 here and look back you can see that my entity has been created I'm then going to hit F10 to print and you can see that my X and Y position gets printed and then finally the end of the scope is reached here we're about to jump back to line 34 which is our return address since this object was created on the stack it should get automatically destroyed when it goes out of scope which is right over here so if I hit F10 you can see that destroyed entity gets printed to the console because the destructor is called we jump back to our return address and everything is good so that is essentially what a Destructor is it's just a special function a special method which gets called when an object gets destroyed as for some real world examples as to why you would ever write a instructor well again if there is certain initialization code that you've called in the Constructor you will likely want to uninitialize or destroy all of that stuff in the destructor because if you don't you can get memory licks a good example of that is Heap allocated objects if you've allocated any kind of memory on the Heap manually then you need to manually clean it up if it was allocated throughout the usage of the entity or in the entity Constructor you're likely going to want to get rid of it in the destructor because when the destructor gets called that entity is gone you can also call the destructor manually not something that I see a lot of people doing rightly so it's a bit weird if you end up doing something like that the only reason I can really think of doing that is maybe if you've allocated using new however when you delete it you decide to use something like the free function and then you also want to call the destructor manually in that case I don't know not really use that often but you can do so by just calling e do entity like this as if it was any other function and that will actually call it instructor if I run this code which is innocent enough you can see that it destroys the entity twice seemingly we're not actually releasing any resources here so it doesn't crash it just prints this message twice again not something I would recommend or not something I I see often at all very very rarely I've seen something like this so yeah destructors sorted I'll see you guys next time goodbye you [Music] [Music]