TITLE: Placement new operator



PROBLEM: hrook@cantor.math.uwaterloo.ca (Harvey Rook)

How can I turn a specific piece of memory into an object? i.e supose i have

class X 
	{
	....
	};

char y[255];

X *px;


and I know that sizeof(X) < 255. How can I turn *px into a
valid X such that px==y? I know this is could be considered
bad style, but I'm curious.



RESPONSE: gs4t@virginia.edu (Gnanasekaran Swaminathan), 23 Feb 93

px = new (y) X;

I don't think it is a bad style as long you know what you are doing.
An appropriate placement operator new is also used to make a call
to a constructor which is not otherwise possible. For example,

 X x;
 x.X ("string"); // error
 x.~X ();
 new (&x) X("string"); // ok. same effect as x.X ("string")