what is 1UI64 type?

Question

I recently saw this 1UI64 type. I didnt get what kind of type is it. How can they use 1 before ?

Answer 1

It's not a type, it's a 64-bit constant integer of value 1.

Answer 2

In Microsoft C/C++ The I64 part of the expression is a suffix for integer constants that indicates the constant should be a 64-bit type:

• http://msdn.microsoft.com/en-us/library/2k2xf226.aspx

This is a Microsoft extension, even though the docs don't call that out.

A somewhat more portable way to specify such a constant might be to include <stdint.h> and use UINT64_C(1) - MSVC has stdint.h as of VS2010.

For versions prior to that you might consider the options provided in this SO question: C99 stdint.h header and MS Visual Studio