CODEWITHSUNDEEP
cpointersstructfree
Yiannis
Yiannis

Reputation: 950

Does the struct get freed this way in C?

I have the following struct which I use to implement a priority queue

struct q_element
{
    //Declaration of struct members
    int element;
    int priority;
    struct q_element *next_element;
};

and I use a pointer to a struct 'cur' to start from the first item in the queue

struct q_element* cur = start_element;

and keep moving until I find the one I want to delete from list.

while (cur->priority!=max_priority)
    cur = cur->next_element;

Does the following line of code actually free the struct? Because 'cur' is a pointer to the struct I wasn't completely sure.

free(cur);

Upvotes: 1

Views: 85

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726499

You need to pass a pointer to free, so free(cur) is the way to go, assuming that the struct itself has been allocated using malloc/calloc/realloc. Specifically, if you allocated your curr in the automatic memory (i.e. on the stack) you are not supposed to call free on it.

It looks like q_element is part of a linked list. Freeing the struct itself will not free other structs pointed to by it, so if you'd like to free the struct along with its tail, you need to write a loop.

Finally, when you free memory pointed to by some pointer in your program, it is a very good idea to assign NULL to the pointer that you freed to avoid accidental double-freeing and undefined behavior on accessing freed memory.

Upvotes: 3

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