How do I pass a data type to a resource (.rc) file in Win32 C++?

Question

I'd like to center a dialog box in my Win32 application, but am having trouble passing constants to my resource.rc file. I make the following declaration in resource.h :

const int SCREENX = GetSystemMetrics(SM_CXSCREEN);

However, when I replace 100 with SCREENX in my .rc file (below) and build, I get: error RC2108: expected numerical dialog constant .

#include <windows.h>
#include "resource.h"
#include "afxres.h"

// I'd like to replace "100" with "GetSystemMetrics(SM_CXSCREEN)"
ID_ABOUT DIALOG DISCARDABLE  100, 0, 237, 87
STYLE DS_MODALFRAME | WS_POPUP | WS_CAPTION | WS_SYSMENU
CAPTION "About"
FONT 10, "MS Sans Serif"

BEGIN
    GROUPBOX "Contact", IDC_CONTACT, 7, 43, 98, 39, WS_CHILD | WS_VISIBLE
    LTEXT    "My info", IDC_CONTACT, 16, 53, 85, 25, WS_CHILD | WS_VISIBLE
END

Neither can I use GetSystemMetrics(SM_CXSCREEN) directly in the desired location (same error).

I'd think it would be routine to pass data types to .rc , so I must be missing something basic here. (Resource files are giving me no end of headaches.) Thank you!

Answer 1

A resource file is compiled into a bunch of static data that is stored in your executable. For example, a dialog resource might be compiled into a DLGTEMPLATE structure.

In other words, everything in a compiled resource is a constant.

GetSystemMetrics(SM_CXSCREEN) is not a constant. It evaluates to the current screen width in pixels at run-time.

As the other answer says, to center your dialog use the DS_CENTER style or handle WM_INITDIALOG .

Answer 2

To center a Dialog on the screen, just OR the DS_CENTER style to the other window style for the dialog.

If you want to use GetSystemMetrics, do this in WM_INITDIALOG and position the dialog there.

A resource file is just a script.