C Memory Management

Question

I\'ve always heard that in C you have to really watch how you manage memory. And I\'m still beginning to learn C, but thus far, I have not had to do any memory managing rela

Answer 1

(I'm writing because I feel the answers so far aren't quite on the mark.)

The reason you have to memory management worth mentioning is when you have a problem / solution that requires you to create complex structures. (If your programs crash if you allocate to much space on the stack at once, that's a bug.) Typically, the first data structure you'll need to learn is some kind of list. Here's a single linked one, off the top of my head:

typedef struct listelem { struct listelem *next; void *data;} listelem;

listelem * create(void * data)
{
   listelem *p = calloc(1, sizeof(listelem));
   if(p) p->data = data;
   return p;
}

listelem * delete(listelem * p)
{
   listelem next = p->next;
   free(p);
   return next;
}

void deleteall(listelem * p)
{
  while(p) p = delete(p);
}

void foreach(listelem * p, void (*fun)(void *data) )
{
  for( ; p != NULL; p = p->next) fun(p->data);
}

listelem * merge(listelem *p, listelem *q)
{
  while(p != NULL && p->next != NULL) p = p->next;
  if(p) {
    p->next = q;
    return p;
  } else
    return q;
}

Naturally, you'd like a few other functions, but basically, this is what you need memory management for. I should point out that there are a number tricks that are possible with "manual" memory management, e.g.,

• Using the fact that malloc is guaranteed (by the language standard) to return a pointer divisible by 4,
• allocating extra space for some sinister purpose of your own,
• creating memory pools..

Get a good debugger... Good luck!