Re-sizing an array with a loop

Question

I am trying to re-size my array when calling grow() if my current array is to small to continue adding values to the front or back.

void Vector::grow(void)
{
    // Double the capacity
  capacity_ = (capacity_) ? capacity_ * 2 : 1;

  int *temp = new int[capacity_];

  for(unsigned int i = 0; i < size_; i++)
    temp[i] = array_[i];

  array_ = temp;
  ++allocs_;
}

The array_ is part of the private variables in the class .h file

private:
  int *array_;        // The dynamically allocated array
  unsigned size_;     // The number of elements in the array
  unsigned capacity_; // The allocated size of the array
  unsigned allocs_;   // Number of allocations (resizes)

I am getting some problems where I am leaking memory according to Valgrind: Invalid read of size 4 Address 0x59ff044 is 0 bytes after a block of size 4 alloc'd

Answer 1

The problem is you never free the old memory.

for(unsigned int i = 0; i < size_; i++)
   temp[i] = array_[i];

array_ = temp;

should be:

for(unsigned int i = 0; i < size_; i++){
    temp[i] = array_[i];
}

delete[] array_;
array_ = temp;

You could also likely use memcopy instead of the for-loop.

Answer 2

If you allocate memory you have to free it, or it will leak.

int *temp = new int[capacity_];

for(unsigned int i = 0; i < size_; i++)
    temp[i] = array_[i];

delete [] array_;  // this leaks if you don't free it.

array_ = temp;
++allocs_;