DOCERR: Win32 APIs Callable from a QuickWin Application (118814)

MORE INFORMATION

To call a Win32 API, you must create a proper INTERFACE TO statement and link with the proper import library.

You can determine the proper INTERFACE TO statement by reading the "Win32 Programmer's Reference". The STDCALL attribute is required for the function declaration.

The sample code below calls the MessageBox() API, contained in the import library, USER32.LIB, which is already linked into the program for a QuickWin application by default. The first parameter of MessageBox() is a window handle or 0 (NULL). You must use 0, because the window handle is not available in a QuickWin application.

NOTE: When you pass a string to an API, make sure that you use the C convention, so that the string is NULL terminated. See page 53 of the "Programmer's Guide" for a discussion of C strings.

Sample Code

C Compile options needed: /MW

      INTERFACE TO FUNCTION
     +MESSAGEBOX  (hwnd, text, title, icon)
      INTEGER*4 MESSAGEBOX [STDCALL, ALIAS:'_MessageBoxA@16']
      INTEGER*4 hwnd [VALUE]
      CHARACTER*(*) text [REFERENCE]
      CHARACTER*(*) title [REFERENCE]
      INTEGER*4 icon [VALUE]
      END

      CHARACTER text*34, title*21

      text = 'This API was called from FORTRAN.'C
      title = 'QuickWin Application'C

      PRINT*, "Enter any character to continue: "
      READ(*, '(A)')

      i = MESSAGEBOX(0, text, title, 1)

      PRINT*, "MessageBox called"

      END