Question

Need for two dimensional array of objects that could be something like:

myContainer<myObject*> *a = new myArray<myObject*>( 20, 20 ); // passing int's as width & height 

later accessing values would be done with methods such as:

mylist<myObject*> getRow( int );
mylist<myObject*> getColumn( int );
mylist<myObject*> getDiagonalRow( int );

implementations of those could be something like:

myList<myObject*> myContainer::getRow( int a ){
    if( a < 0 && a>=this->height ) 
        return; 
    myList<myObject*> hlp;
    for( int i=0; i<this->width; i++)
        hlp.append( this->arr[a][i] );
    return hlp; // returns a copy. Could also be a pointer if created with new.
}

Other methods could follow similar lines, ie. creating a list object and filling it with what was requested.

My questions: Can anyone think of elegant way to create a container class I’m describing here. Which could for example avoid creating and filling of list-objects but still maintaining the abstraction and/or usability. Or please advice if I have missed something in STL etc. that has something like this.

Answer 1

STL has the valarray container which can be viewed as row and columns using slices, but you have to do it manually or wrap it into a wrapper class. Also the slices represents the values of the valarray (they are not a copy), but it is designed to be used with numbers and to be a bit optimized, it doesn’t have any iterator and cannot be grown. it’s doesn’t follow the usual STL container concept. but it can still be used as a quick and dirty workaround if you can’t use boost.

std::valarray<float> array(16);
// we can view it as a 4x4 matrix.
// this represents the first line
array[std::slice(0,4,1)];
// and the second column
array[std::slice(1,4,4)];
// you cannot use the sliced array directly. they don't
// have operator[], but they have operator=(valarray), and
// valarray has a constructor that takes sliced arrays as input.