Dynamic Array

[Chris]

can someone teach me how to create a dynamic array in C/C++/VC++ Juz like what we use in VB ReDim

regards,

[kedaman]

Dynamic arrays must be allocated on the heap, which means you need to use pointers, new and delete[]

The pointer is used to store the position where the array is allocated, new [datatypename] allocates data and returns a pointer to it for instance

int* a= new int[3];

allocates and array of 3 integers and stores the pointer in a.
then you use a as if it was an array;

a[2]=4;
cout << a[2] << endl;

and when you're done with the array you need to delete it, because since it's not on the stack, it won't be automatically deleted either.

delete[] a;

[Sc0rp]

Note that if you wish to resize the array you need to copy its contents to a temporary array, delete[] the array, reallocate the memory for it with the new size and copy the contents of the temporary array to the newly allocated memory.

[Chris]

is there a way I can copy a array or structure with size 50 at one go instead of loop through each element?

[Sc0rp]

You could do something like:

int* theArray = new int[50];
int* tempArray;

// fill the array with something.....

int newSize = 70;

tempArray = theArray;
theArray = new int[newSize];

for (int i = 0; i < newSize; i++)
    theArray[i] = tempArray[i];

delete [] tempArray; 

This should work. I don't think there is a way out of looping.

[Sc0rp]

Found a way without looping!

#include <iostream>
using namespace std;

int main()
{
    int newSize;
    int curSize = 50;
    int* theArray = new int[curSize];
    int* tempArray;

    // fill the array with something.....

    newSize = 70;

    tempArray = theArray;
    theArray = new int[newSize];

    memcpy(theArray, tempArray, curSize * sizeof(int));
    newSize = curSize;

    delete [] tempArray;
    return 0;
} 

[Destined Soul]

I guess that could be called without looping, but if you look at a lower level, every value has to be copied.

Does anyone know if memcpy actually faster than an element by element copy?

Destined

[Sc0rp]

No, atually it's the exact same speed because what memcpy does is loop and copy.

[Megatron]

If you want something similar to ReDim Preserve, then you could use a vector.

#include <iostream>
#include <vector>
using namespace std;

int main()
{
	// Creates an array of integers (replace int with
	// the type of data you want to use)
	vector<int> var;

	// myval = amount to resize to
	var.resize(myval);

	// Element = element you want to change
	var[element] = 343 
	return 0;
}

[kedaman]

A vector is freaking 16 bytes