Basic Malloc/Free

Question

If I have a snippit of my program like this:

struct Node *node;
while(...){
    node = malloc(100);
    //do stuff with node
}

This means that every time I loop through the while loop I newly allocate 100 bytes that is pointed to by the node pointer right?

If this is true, then how do I free up all the memory that I have made with all the loops if I only have a pointer left pointing to the last malloc that happened?

Thanks!

Answer 1

Please allocate exactly the size you need: malloc(sizeof *node); -- if you move to a 64-bit platform that doubles the size of all your members, your old 96-byte structure might take 192 bytes in the new environment.

If you don't have any pointers to any of the struct Nodes you have created, then I don't think you should be allocating them with malloc(3) in the first place. malloc(3) is best if your application requires the data to persist outside the calling scope of the current function. I expect that you could re-write your function like this:

struct Node node;
while(...){
    //do stuff with node
}

or

while(...){
    struct Node node;
    //do stuff with node
}

depending if you want access to the last node (the first version) or not (the second version).

Of course, if you actually need those structures outside this piece of code, then you need to store references to them somewhere. Add them to a global list keeping track of struct Node objects, or add each one to the next pointer of the previous struct Node, or add each one to a corresponding struct User that refers to them, whatever is best for your application.