_W64 Annotation

I am compiling a open source library using Embarcadero RAD studio.

The library builds OK under VS2010. So I am keeping all the include/library paths the same as what is used in the VS2010 project.

The following are the VC++ Directories used in VS2010 as part of the project properties.

Executable Directories
Include Directories
Reference Directories
Library Directories
Source Directories
Exclude Directories

Out of the above I am only syncing Include and Library directories.

The directories refenced in the include section are:

$(VCInstallDir)include;
$(VCInstallDir)atlmfc\include;
$(WindowsSdkDir)include;
$(FrameworkSDKDir)\include;

I am not using atlmfc and .Net Framework. So I am just using VC include and SDK include. Similar set-up for library directories too.

Since I have included the SDK folder in the include path I was not expecting an error with the line below

typedef _W64 unsigned int   uintptr_t;

And yet when the build the library Embarcadero C++ builder throws the error below:

[BCC32 Error] vadefs.h(48): E2257 , expected

The file refered above I beleive is pulled into my build as an external dependency.

So my questions are, is _W64 a typedef? Where is it defined?

Why is my build giving the error above? Is there another include location I need to include to fix this error?