Passing Other Types by Reference

It’s not just objects that can be passed by reference. All the other types we’ve seen can, too. For example, to swap two integers, we could write something like:

void Swap ( double &dX, double &dY )

{

double dTemp = dX;

dX = dY;

dY = dTemp;

}

We would call this function in the usual way:

double dX = 0;

double dY = 100;

Max.SetPos ( dX, dY );

Swap ( dX, dY );

Max.GoesTo ( dX, dY, 5 );

When people start passing things like integers by reference, they often try to use an expression as a reference argument. For example:

double dX = 0;

double dY = 100;

Swap ( dX, dY + 1 ); // WRONG!!

This is not legal because the expression dY + 1 is not a variable – it does not occupy a location that the reference can refer to. It is a little tricky to figure out exactly what kinds of expressions can be passed by reference. For now a good rule of thumb is that reference arguments have to be variables.