c - crash when free pointer to function

Question

I have the following struct

typedef struct test {
    int                                 action;
    void                                *data;
    void (*function)(int, void*);
} test;

int execute_func(void(*function)(int a, void *d), int action, void *data)
{
    struct test             *todo;

    todo = calloc (1,sizeof(struct test));
    if (todo == NULL)
    {
        return -1;
    }
    todo->action = action;
    todo->data = data;
    todo->function = function;
    todo->function(todo->action, todo->data);
    return 0;
}

After executing the function, i want to free the allocated structure usinf the following:

if(todo != NULL)
{
    if(todo->data != NULL)
    {
        free(todo->data);
    }
    if(todo->function != NULL)
    {
        free(todo->function); //Cause a crash
    }
    free(todo);
}

but i get a crash.

Answer 1

You only can free memory that have been allocated with malloc. So, you can't free function. A function pointer stores address from static memory.

if(todo != NULL)
{
    if(todo->data != NULL)
    {
        free(todo->data);
    }
    free(todo);
}

Also, same remark for data: you have to free it only and only if memory pointed by data have been dynamically allocated with malloc.

And to a more generic point of view, only free dynamically allocated memory if you are owner of it.

To answer of one of OP comments, when you use calloc to your structure, you allocate memory for structure only: an int and two pointer. You don't have allocated memory for function nor for memory pointed by data. To avoid memory leak, you just have to free memory from your structure, ie an int and two pointer (and not for pointed memory, because you don't know how they had been allocated)