变量混乱

Question

I must read more elements P in a function. Is it better to create pElem every time in a loop?

dataStr *  process(char *start, char *stop, GTree* tree)
{
  while ( (cp != NULL) && ( cp   < nextI))
  {
      //I malloc inside of getPElem function
      pElem * p = getPElem(cp, dateP, s);
      free(p);
  }
}

Or should I better initialize once P-element and reuse it every time?

dataStr *  process(char *start, char *stop, GTree* tree)
{
  pElem * p = malloc(sizeof(p));
  while ( (cp != NULL) && ( cp   < nextI))
  {
      fillPElem(p, cp, dateP, s);

  }
  free(p);
}

If one element would be better, should I malloc it one outside the function (function "process" is called in a loop too):

dataStr *  process(char *start, char *stop, GTree* tree, pElem * p )
{

  while ( (cp != NULL) && ( cp   < nextI))
  {

       fillPElem(p, cp, dateP, s);

  }      
}

Or every time inside the function like in the second example?

Answer 1

If you don't need the pElems to live longer than the enclosing scope, there's no need to dynamically allocate at all:

dataStr *  process(char *start, char *stop, GTree* tree)
{
  pElem p;
  while ( (cp != NULL) && ( cp   < nextI))
  {
      fillPElem(&p, cp, dateP, s);

  }
}

(yes, I know that none of cp, nextI etc. are defined - I just copied from the question).