In Microsoft Studio, what could be happening is that your solution target is set up for a Win32 project, which is the default (even on a 64-bit OS).
Make sure that your active solution target is set for X64. This is selected from the MS Studio Configuration Manager within the IDE. If you do not have an x64 target, that just means that your MS Studio has never been used for that type of project, and you have to create one in the Configuration Manager->New tab.
The image below shows a proper Debug/x64 project in the MS Studio status bar.
