Question

I know that if I don’t free allocated memory with delete/free I’d end up with memory leaks. My question is: if my program gets terminated, does the operating system free the memory for me even if I didn’t?

Answer 1

Whether the memory leaks or not depends on the Operating system. In case of most operating systems once the process in which your program runs exits the OS simply reclaims back the memory it allocated to the process.

There is another important aspect to it. new results in calling of the class constructor and delete results in call to an destructor. So if you called new and never called delete then in addition to the so called memory leak which may/may not exist after the program exit there is an additional condition that if the destructor of the particular class invokes some code which has side effects then it results in Undefined Behavior.

So the answer is it depends, You may possibly have:

• A memory leak(depending on the OS behavior)
• An undefined behavior(depending on whether code in destructor has side effects)

C++11 Standard 3.8 Object lifetime:
Para 4:

A program may end the lifetime of any object by reusing the storage which the object occupies or by explicitly calling the destructor for an object of a class type with a non-trivial destructor. For an object of a class type with a non-trivial destructor, the program is not required to call the destructor explicitly before the storage
which the object occupies is reused or released; however, if there is no explicit call to the destructor or if a delete-expression (5.3.5) is not used to release the storage, the destructor shall not be implicitly called and any program that depends on the side effects produced by the destructor has undefined behavior.