免费的函数指针数组

Question

If an array of function pointers is statically allocated, do I still need to free() it? Lets say I have this code:

typedef void (*test_ptr)(void);

int main(void) 
{
    test_ptr test[3];
    test[0] = a;
    test[1] = b;
    test[2] = c;
}

So, when I would be done with it, would I have to free all the pointers, maybe like so:

for(int i = 0; i < 3; i++) {
    free(test[i]);
}

Or is it automatically de-allocated when function ends, like other arrays?

Answer 1

Absolutely not!

An array allocated like that is located on the stack, and free will fail horribly if you try it.

As an aside, the array you show is not "static". I think you mean "local", or even "auto" (although that can be confused with a C++ concept).

Aside no. 2: allocation on the stack means that you should not allocate large arrays this way. The stack typically has limited capacity, so anything large should be allocated via malloc .

Answer 2

So, when I would be done with it, would I have to free all the pointers

No. You must not because free(ptr) is used only when pointer ptr is previously returned by any of malloc family functions.
Passing free a pointer to any other object (like a variable or array element) causes undefined behaviour .

C11: 7.22.3.3 The free function:

[...] If ptr is a null pointer, no action occurs. Otherwise, if the argument does not match a pointer earlier returned by a memory management function, or if the space has been deallocated by a call to free or realloc , the behavior is undefined .

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Or is it automatically de-allocated when function ends, like other arrays?

Yes. It will no longer exist once its enclosing function returns.

Answer 3

Automatic local variables like the ones in your case are destroyed as soon as the function in which they are created gets over. In your case, they will be destroyed when the main() function gets over.

So you don't have to explicitly free() those variables.

Answer 4

Does that code own the pointed-to-object, and was it allocated with one of the allocation-functions corresponding to free ( malloc realloc calloc )?

If so, free it at the end.

If not, desist.

You are clearly in the second case...