generate random clues for a sudoku game

I'm trying to implement a sudoku game in Qt using C++. I want to set random hints in the game.But unfortunately my random hints are repeating row wise,column wise and 3x3 grid wise. So how do i set clues/hints in sudoku game? Screenshot of the UI is displayed below.Pleasemy sudoku grid

Please suggest a way to maintain the randomness throughout thw whole grid