Does it work? I have this in a plugin and I always see the "FALSE" message.
BOOL WINAPI InitializePlugin( VOID )
   Printf(L"QueryIsGUI returned %s\r\n", QueryIsGUI() ? L"TRUE" : L"FALSE");
Not sure why you're trying to use this; it's an obsolete function (since v8). It returns 1 if you're running the GUI command processor (i.e., TCMD 8.0) and 0 if you're running TCC or 4NT. And you're always running TCC.
No. I'm using it in TCMD. It's documented like this.
BOOL QueryIsGUI( void );
   Returns 1 if TCC is running inside a Take Command tab window
I meant I'm using in in TCC in a TCMD tab. I was looking at an older TakeCmd.h. Thanks for the clarification. I'm bringing 4AUTOTRAY up to date and I don't want it running when TCC is in a tab. But I figured out how to kill three birds with one stone.
BOOL WINAPI InitializePlugin( VOID )
   WCHAR szExpr[128] = L"%_PIPE %_TRANSIENT %_TCTAB";
   ExpandVariables(szExpr, 0);
   if ( lstrcmp(szExpr, L"0 0 0") )
      return TRUE;