// This code demonstrates how to rewrite the 7th
        // image in a data cube with a new image.

        #include <iostream>
        #include "CFitsFile.h"

        using namespace std;
        using namespace arc;

        int main()
        {
            long naxes[ CFitsFile::NAXES_SIZE ] = { 0, 0, 0 };
            unsigned short *pBuf = NULL;
            unsigned short val = 0;

            try {
                CFitsFile cFits( "Image.fit" );

                cFits.GetParameters( naxes );

                //
                // Make sure there are at least 7 images
                // in the data cube.
                //
                if ( naxes[ CFitsFile::NAXES_NOF ] < 7 )
                {
                    cerr << "Error: Too few frames in data cube!" << endl;
                    exit( 1 );
                }

                //
                // Create new image data
                //
                pBuf = new unsigned short[ naxes[ CFitsFile::NAXES_ROW ] *
                                           naxes[ CFitsFile::NAXES_COL ] ];

                if ( pBuf == NULL )
                {
                    cerr << "Error: NULL image buffer!" << endl;
                    exit( 1 );
                }

                //
                // Fill the new buffer with a gradient image
                //
                for ( int r=0; r<naxes[ CFitsFile::NAXES_ROW ]; r++ )
                {
                    for ( int c=0; c<naxes[ CFitsFile::NAXES_COL ]; c++ )
                    {
                        pBuf[ c + r * naxes[ CFitsFile::NAXES_COL ] ] = val;
                    }

                    if ( val >= 65535 ) val = 0;
                    else val++;
                }

                //
                // Replace the 7th image ( zero based ) with
                // the new gradient image.
                //
                cFits.ReWrite3D( pBuf, 6 );

                delete[] pBuf;
            }
            catch ( std::exception &e )
            {
                cerr << "Exception Occurred: " << e.what() << endl;
                if ( pBuf != NULL ) delete[] pBuf;
            }
        }