Comparing two arrays

Nelly · #1 16-Jun-2004, 04:15

Hello guys,
I am using Visual C++ 6.0.

I have a vector of array. Each element of the vector contains an array [25].
I have a button on my dialog window which call a save function to to save the array in the vector.
I want to add a function to check the changes made to the array and pop up a message if the user forget to save changes.

I want save a copy of the array at the start and use that array to check for any changes made. That is, compare the copy and the main array.

Code:

bool savechanges()
{
 //making a copy of the vector
for (int i  = 0; i < Feat.size(); i++)
{
    FaceCopy   = Feat[i];
}

//call the function to add update the vector element, ie, the array
addFeatures();
	

for (int j  = 0; j < CFF.Feat.size(); j++) 
{
    FaceFeat = Feat[j];

}
// ckecking using the FrameNo ans index
if (Feat[j].FrameNo = Feat[i].FrameNo)
{
     //if there is no change don't call the pop dialog
     if (FaceCopy == FaceFeat)
         {
	return false;
           }
        else 
            //call the Save popup dialog to save the changes
            if (FaceCopy != FaceFeat)
            {
	  /**Call the Apply pop-up dialog box the allow users to
	  save changes to the vector*/
	  CSaveDlg Sav;
				
	   if(Sav.DoModal()== IDOK)
	    {
	        /**Save array to the vector*/
	         OnSave();
	     }
		
                }
            }
return true;
	
}

But unfortunately I get the following error messages:

error C2678: binary '==' : no operator defined which takes a left-hand operand of type 'struct Face' (or there is no acceptable conversion)

error C2678: binary '!=' : no operator defined which takes a left-hand operand of type 'struct Face' (or there is no acceptable conversion)

I have included the following header

Code:

#include <iostream>
using namesapae std;
#include <vector>
#include <algorithm>
#include <math>
#include <cstring>

Can anyone please advise on what I'm doing wrong.

Thank you very in advance...

sho · #2 16-Jun-2004, 05:15

Well, i think your problem is here:
if (FaceCopy == FaceFeat)
and if (FaceCopy != FaceFeat)
specifically in the comparations "FaceCopy == FaceFeat", "FaceCopy != FaceFeat"...

Its because you cant compare two different arrays or structures like that, you would have to do comparison comparind their elements one by one...

The "==" operator doesnt accepts structures or arrays because they may contain many elements and it only compares between pairs of simple elements... so thats why the compiler says:

error C2678: binary '==' : no operator defined which takes a left-hand operand of type 'struct Face' (or there is no acceptable conversion)

error C2678: binary '!=' : no operator defined which takes a left-hand operand of type 'struct Face' (or there is no acceptable conversion)

Garth Farley · #3 16-Jun-2004, 05:38

You're not making copies or comparing them properly. Your copy loop:

CPP / C++ / C Code:

 //making a copy of the vector
for (int i  = 0; i < Feat.size(); i++)
{
    FaceCopy   = Feat[i];
}

is flawed. All this is doing is:
FaceCopy = Feat[0];
FaceCopy = Feat[1];
FaceCopy = Feat[2];
FaceCopy = Feat[3];
...
i.e. it's overwriting whatever value is placed in FaceCopy. So all it ends up with the last value in the object Feat.

Similarily for the second loop. Also then after, are you sure you wish to use the iterative indices i & j outside the scope of their loops?

Whatever types FaceCopy & FaceFeat are, there is no comparison operators defined. Are they objects? If so you can create them as follows (C++ only):

CPP / C++ / C Code:

bool Feat::operator==(const Feat&, const Feat&){
      if( identical - check each element of the array) return true;
      else return false;
}

If you're sticking to C and structs, you'll have to loop through each member of the struct explicitly.
GF

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