• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 601
  • Last Modified:

Array copying

I am working on a project using different sorting algorithms.  The original unsorted array must be used by each sorting algorithm.  My question is, how is the best way to pass the array into a function but have it return to the original array when the function is done?  Should I just pass a copy of the original?  A code example would be very helpful.  Thanks,

Ant_Dogg
0
Ant_Dogg
Asked:
Ant_Dogg
1 Solution
 
monkesdbCommented:
STL is simplest


#include <algorithm>


MyObj myArray[NUM_ELEMENTS];
// fill myArray with values.

MyObj cpyArray[NUM_ELEMENTS];

copy(myArray, myArray + NUM_ELEMENTS, cpyArray);


then cpyArray is a copy of myArray which you can pass to your sorting algorithm.

MyObj can be any class which has a copy constructor, any of the primitives like int, double, etc. will be fine.
0
 
bcladdCommented:
Where is this being assigned? You should take a look at two other questions here:

    http://www.experts-exchange.com/Programming/Programming_Languages/Cplusplus/Q_20782423.html
    http://www.experts-exchange.com/Programming/Programming_Languages/Cplusplus/Q_20786730.html

Both pertain to sorting a an array containing strings or integers and counting the number of comparisons and timing the results.  Sounds a lot like another student doing the same work. Take a look for discussion of approach and some code; you will want to actually write your own code for reasons of academic honesty.

Hope this helps, -bcl
0
 
freewellCommented:
Declare your original unsorted input array as a constant parameter of your sorting function, which means the function will not change the input array. Create a temporary working array in your function to manipulate the array, so that the implementaion of your sorting is transperent to outside world.

int MySort(const int Data[],int nElement)
{
//      Data[0] = 1; // This is not allowed.

      int *m_Data = new int[nElement];
      memcpy(m_Data,Data,nElement);

// your algorithms here

      delete [] m_Data;
      return 0;
}
0
Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

 
freewellCommented:
I think the memcpy function should allocate the actual size of array

memcpy(m_Data,Data,nElement * sizeof(int));
0
 
rendaduiyanCommented:
The best way is to use STL function sort.
template<class RandomAccessIterator>
   void sort(
      RandomAccessIterator _First,
      RandomAccessIterator _Last
   );
It doesnot need a copy of original array.
0
 
bcladdCommented:
rendaduiyan-

Using the STL is, of course, the right answer if the goal is solely to have the array end up in sorted order. The original poster mentions that the project is for comparing different sorting algorithms. With STL sort you get a sort with certain performance bounds but with any given STL implementation you get one sort (okay, you get one general sort and one list<>::sort). The question asked was how to present the same test data to multiple sorts. The choices are reading the file multiple times (loading each array from a persistent copy of the data) or read the file once into a "cached" copy of the contents and then copy the in-memory version of the array (or seed a pseudo-random number generator with a know value and generate the "random" contents of the array before each sort but this is really close to reading it from the file).

0
 
grg99Commented:
The easiest way is to put the array in a struct.  C can copy structs with the assignment operator, so it's as simple as:

typedef struct foo { int TheArray[1000] }  EasyCopyArrayType;

 
EasyCopyArrayType   Main, Copy;

for( i= .... )   Main.TheArray[i] = rand( 9999 );


Copy = Main;

SortByInsertion( Copy );

Copy = Main;

SortByInsertion( Copy );

... etc...

0
 
Ant_DoggAuthor Commented:
>>typedef struct foo { int TheArray[1000] }  EasyCopyArrayType;

That sounds like it will work for me.  But what is the foo there for if it isn't used when calling the structure? Would this work just the same?

typedef struct {int Array[1000]} EasyArrayCopy;
EasyArrayCopy Main, Copy;

Ant_Dogg
0

Featured Post

Free Tool: Subnet Calculator

The subnet calculator helps you design networks by taking an IP address and network mask and returning information such as network, broadcast address, and host range.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Tackle projects and never again get stuck behind a technical roadblock.
Join Now