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Array redimension

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int array[100];

delete array;
array = new int[1000];

/MindWipe

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

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Guest Anonymous Poster
You free the old array and allocate memory for the new one. It''s slow but also the only way, since arrays are located in the memory as a continuous sequence.
  
for (i=0;i<old_height;i++) delete array[i];
delete array;
array = new char *[new_height];
for (int i=0;i<new_height;i++) array[i] = new char [new_width];

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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

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Guest Anonymous Poster
I suggest using std::vector. Don''t let the name fool you; it is basically a fancy array.

  
#include <vector> //note: no .h
using namespace std;


vector<int> vi; //vector of ints

vector<string> vs; //vector of strings (look up std::string)


vi.push_back(5); //puts five onto the end

if(vi.size()==1) cout<<"one"; //prints one

int i = 2 * vi[0]; //i equals 10;

vi[0]=3; //change the 5 to a 3

vi.pop_back();//takes the last element off


//if you #include <algorithm> this sorts your vector:
sort(vi.begin(),vi.end());



As with arrays you have to be careful, don''t try to assign or access out of bounds.

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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;
}

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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

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