how to get the device handler from volume name?

I build a program that directly interact with USB( In my case, volume is 'G')

So CreateFile,ReadFile,WriteFile must be used to build my program...

But volume name is resolved by users, So it should be variables....

HANDLE WINAPI CreateFile(
  _In_      LPCTSTR lpFileName,
  _In_      DWORD dwDesiredAccess,
  _In_      DWORD dwShareMode,
  _In_opt_  LPSECURITY_ATTRIBUTES lpSecurityAttributes,
  _In_      DWORD dwCreationDisposition,
  _In_      DWORD dwFlagsAndAttributes,
  _In_opt_  HANDLE hTemplateFile
);
 onyl 'lpFileName' wasn't resolved 
If you can give me some advice, tip, any help, please tell me somethings