global variable to be used by different classes

[deathmoon]

How to make classes to use the global variable which resides in main.cpp?
I have a project with multiple files, for my problem now I have a main.cpp, Tiles.hpp and .cpp, and Player.hpp and .cpp..
the global variable is an instance of class Tiles
Tiles boardTiles
which is a data structure that stores colour and number in a linked list form.
I want to make Player class access to the boardTiles, I want to take value of the nodes from the boardTiles and copy into each player's rack, which is a composition of Tiles class too.

The method defined for copying the value to players' rack is shown below. This method is inside Player.cpp

void Player::playerGetTiles()
{
    for(int i=0;i<14;++i)
    {
        COLOUR c = boardTiles.getTailColour();
        int n = boardTiles.getTailNumber();
        rack.push_back(c,n);
        boardTiles.pop_back();
    }

}

[Moschops]

In cpp files that need to know about the global variable that is created in some other cpp file, define the global variable with extern on the front

extern Tiles boardTiles;