🔒 Locked

Array redimension

Started by Shadows Dec 30, 2001 at 2:59 PM 5 replies 2.1k views

Original Post

Shadows

Dec 30, 2001 at 2:59 PM

Just what it says how do I redimension an array? Regards //Shadows

MindWipe

152

MindWipe

Dec 30, 2001 at 3:17 PM

int array[100];

delete array;
array = new int[1000];

/MindWipe

"If it doesn''t fit, force it; if it breaks, it needed replacement anyway."

Brannon

Dec 30, 2001 at 7:04 PM

Just to be picky, MindWipe, that won''t work. You cant declare a static sized array (int array[100]), delete it, and then allocate new memory to it. You might be able to get away with allocating the new memory, but deleting it definitely wont work.

-Brannon

null_pointer

Dec 31, 2001 at 1:43 PM

C++''s standard vector class is great. I would also recommend using it unless you want to learn how to do this yourself. To redimension an array, you want to do something like this:

#include <algorithm>
 
using std::copy;
using std::swap;
 
int main()
{
  // p refers to the array that is to be resized
 
  int* p = new int[old_size];
 
  // redimension p to the new size while preserving old values
 
  int* temp = new int[new_size]; // allocate new space
  copy(p, p+old_size, temp);     // copy old elements over (optional)
  swap(p, temp);                 // swap the pointers, now p refers to the new array
  delete [] temp;                // deallocate old array
 
  // at some point, we need to deallocate memory for the array
 
  delete [] p;
 
  return 0;
}

null_pointer

Dec 31, 2001 at 1:53 PM

Remember that the example I gave you assumes that "new_size" is greater than or equal to "old_size." To wrap this code up into a function we do:

  
// This just makes "T" an alias for whatever type is really used

template <class T>
void redim(T*& array, int old_size, int new_size, bool preserve_old_elements = true)
{
  // allocate the new array

 
  T* temp = new T[new_size];
 
  // now copy the elements over, if desired

 
  if( preserve_old_elements )
  {
    // the number of elements to copy is either the old size or the new size, whichever is smaller

 
    const int elements_to_copy = min(old_size, new_size);
 
    // perform the actual copy

 
    copy(array, array + elements_to_copy, temp);
  }

  // swap the pointers, so that "array" now points to the new array


  swap(array, temp);
 
  // now we need to deallocate the old array

 
  delete [] temp;
}

Edited by - null_pointer on December 31, 2001 3:01:40 PM

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.