Freeing other variable types in C

Question

C does not have garbage collection, hence whenever we allocate memory using malloc/calloc/realloc, we need to manually free it after its use is over. How are variables of other data types like int, char etc. handled by C? How is the memory allocated to those variables released?

Answer 1

That depends. If you allocate any of those data types with malloc/calloc/realloc you will still need to free them.

On the other side, if a variable is declared inside a function, they are called automatic variables and whenever that function ends they'll be automatically collected.

The point here is not the data type per se, is the storage location. malloc/calloc/realloc allocate memory in the heap whereas automatic variables (variables declared inside functions) are allocated in the stack.

The heap is completely managed by the programmer, while the stack works in a way that when a function ends, the stack frame is shrink and every variable occupying that frame will be automatically overwritten when another function is called.

To grasp a better feeling of these, take a look at the memory layout of a C program. Other useful references might be free(3) man page and Wikipedia page for Automatic variables.

Hope this helps!

Answer 2

Resources (such as memory) have nothing to do with variables. You never have to think about variables. You only have to think about the resource itself, and you need to manage the lifetime of the resource. There are function calls that acquire a resource (such as malloc) and give you a handle for the resource (such as a void pointer), and you have to call another function (such as free) later on with that handle to release the resource.

Memory is only one example, C standard I/O-files work the same way, as do mutexes, sockets, window handles, etc. (In C++, add "dynamically allocated object" to the list.) But the central concept is that of the resource, the thing that needs acquiring and releasing. Variables have nothing to do with it except for the trivial fact that you can use variables to store the resource handles.