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creallocalloc

Is this use of realloc correct?

Original question

Can I use realloc() function like the following code:

int *ptr, i, num=5;

for (i=0; i<num; i++)
  void *nptr = realloc (ptr, (i+1) * sizeof(int) );
Solution

  • no, you should initialize ptr at the beginning and then assign the new value

    int *ptr = 0;

for (unsigned i=0; i<5; i++) {
  void *nptr = realloc (ptr, (i+1) * sizeof(int) );
  if (nptr) ptr = nptr;
  else abort();
}

    Otherwise at the first call you could pass some random value to realloc. And the memory that you allocate in subsequent calls would simply be lost.