How Does Allocated Memory Get Freed In C++?

Question

Let's say I have a header file, armorshop.h, containing a class definition, along with a corresponding .cpp for this header file.

My question is:

1. How does allocated memory get freed in c++?
2. Will allocatedmemory1, allocatedmemory2, allocatedmemory3, or allocatedmemory4 ever be freed on its own in each of these scenarios?
3. Will these aformentioned allocatedmemories be redefined and cause an error in each of these scenarios?
4. Do variables and classes, etc defined inside of a class definition get freed when they are not being used, and redefined when they are used again? Or do they get defined once and use up resources while not being used?

Thanks

//scenario 1
//armorshop.h
#ifndef __SFML__armorshop__
#define __SFML__armorshop__


class armorshop : public entity
{
public:

};

int allocatedmemory1;
sf::FloatRect allocatedmemory2;
class armorshop allocatedmemory3;
std::vector<armorshop> allocatedmemory4;

#endif

(question 3 clarification in relation to scenario 1:) If I #include "armorshop.h" multiple times will this cause an error

//scenario 2
//armorshop.cpp
int allocatedmemory1;
sf::FloatRect allocatedmemory2;
class armorshop allocatedmemory3;
std::vector<armorshop> allocatedmemory4;

Answer 1

1. How does allocated memory get freed in c++?

How memory is freed, depends on the implementation, and how the memory was allocated in the first place.

2. Will allocatedmemory1, allocatedmemory2, allocatedmemory3, or allocatedmemory4 ever be freed on its own in each of these scenarios?

All of those variables have static storage duration. Objects with static storage duration are deallocated after main has returned.

Whether global variables were defined in a header file that is included in a source file (scenario 1), or the globals were defined in a source file directly (scenario 2), makes no difference to when the variables are "freed".

4. Do variables and ... get freed when they are not being used

Nothing is "freed" based on whether they are used or not.

Do ... classes ... get freed

Classes are not "freed".

If I #include "armorshop.h" multiple times will this cause an error

armorshop.h defines global variables. Including the header in multiple source files will cause each source file to define those same variables. That violates the one definition rule. You should hardly ever define global variables in a header.

PS. __SFML__armorshop__ is a reserved identifier, because it contains two consecutive underscores. Defining it in your code makes your program ill-formed.

Answer 2

This is a two-part question.

The first part, is that if the globally-scoped objects get declared in a header file in this fashion, and this header file gets included from multiple translation units, this is undefined behavior, and will typically result in duplicate symbol declaration errors during the link phase. A recently-adopted addition to the forthcoming C++17 allows globally-scoped objects to be declared as inline , permitting them to be declared in multiple translation units, as defined behavior.

For the second part, the globally-scoped objects get declared in a single translation unit, the globally-scoped objects get constructed at some point before main() is invoked, and they get destroyed, or deallocated, at some point after main() returns. The relative order in which statically-scoped objects in different translation units get constructed or destroyed is not specified. Only the relative order in which statically-scoped objects in the same translation unit get constructed, or destroyed, is specified.