Linking a windows app in gfortran

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@andrew_4619,

Welcome, glad you have joined here in addition to the Intel forum!

From your comments, it appears you have Windows SDK installed and perhaps also Microsoft Windows C / C++ compiler via Microsoft Visual Studio application. Is that correct? If yes, a quick workaround you can use is the “command prompt” shortcuts made available via the Visual Studio installer. You likely know of them via Start → Programs and the folder for Visual Studio 201X. You can pick one of the prompts corresponding to your target platform, say 'x64 Native Tools Command Prompt for VS 201X". Will that be an option? If yes, things can be made much simpler by using the Microsoft Linker ‘link.exe’.

The usual libraries needed are ‘libcmt.lib’ and perhaps ‘user32.lib’.

Here’s a ‘Hello World’ example built with gfortran and Microsoft linker:

module IWinAPI_m

   use, intrinsic :: iso_c_binding, only : c_char, c_null_char, c_int, c_ptr, C_NULL => c_null_ptr, c_loc

   interface
      function MessageBox(hWnd, lpText, lpCaption, uType) result(RetVal) &
          bind(C, name="MessageBoxA")
      !DIR$ ATTRIBUTES STDCALL :: MessageBox

      ! Microsoft Windows API function prototype
      ! https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-messagebox
      ! int MessageBox( HWND hWnd, LPCTSTR lpText, LPCTSTR lpCaption, UINT uType);

         import :: c_ptr, c_int

         ! Argument List
         type(c_ptr), intent(in), value    :: HWnd
         type(c_ptr), intent(in), value    :: lpText
         type(c_ptr), intent(in), value    :: lpCaption
         integer(c_int), intent(in), value :: uType
         !.. Function result
         integer(kind=c_int) :: RetVal

      !GCC$ ATTRIBUTES STDCALL :: MessageBox
      end function MessageBox
   end interface

   ! Mnemonics
   type :: MsgBoxFlags
      integer(c_int) :: ABORTRETRYIGNORE  = int(Z"00000002", kind=c_int)
      integer(c_int) :: CANCELTRYCONTINUE = int(Z"00000006", kind=c_int)
      integer(c_int) :: HELP              = int(Z"00004000", kind=c_int)
      integer(c_int) :: OK                = int(Z"00000000", kind=c_int)
      integer(c_int) :: OKCANCEL          = int(Z"00000001", kind=c_int)
      integer(c_int) :: RETRYCANCEL       = int(Z"00000005", kind=c_int)
      integer(c_int) :: YESNO             = int(Z"00000004", kind=c_int)
      integer(c_int) :: YESNOCANCEL       = int(Z"00000003", kind=c_int)
      integer(c_int) :: ICONEXCLAMATION   = int(Z"00000030", kind=c_int)
   end type
   type(MsgBoxFlags), parameter, public :: MB = MsgBoxFlags()

contains

   function WinMain( hInstance, hPrevInstance, lpCmdLine, nShowCmd ) result(RetVal) &
             bind(C, name="WinMain")
   !DIR$ ATTRIBUTES STDCALL :: WinMain
   !GCC$ ATTRIBUTES STDCALL :: WinMain

   ! the entry point for any Windows program
   ! https://docs.microsoft.com/en-us/windows/win32/learnwin32/winmain--the-application-entry-point
   ! int WINAPI WinMain(HINSTANCE hInstance,
   !                    HINSTANCE hPrevInstance,
   !                    LPSTR lpCmdLine,
   !                    int nShowCmd)

         ! Argument List
         type(c_ptr), intent(in), value :: hInstance
         type(c_ptr), intent(in), value :: hPrevInstance
         character(kind=c_char, len=1), intent(in) :: lpCmdLine(*)
         integer(c_int), intent(in), value         :: nShowCmd
         !.. Function result
         integer(kind=c_int) :: RetVal

      ! Local variables
      integer(c_int) :: uType
      character(kind=c_char,len=:), allocatable, target :: Text
      character(kind=c_char,len=:), allocatable, target :: Caption

      Caption = c_char_"Fortran WinMain Function" // c_null_char
      Text = c_char_"Hello World!" // c_null_char
      uType = ior( MB%ICONEXCLAMATION, MB%OK)

      RetVal = MessageBox( C_NULL, c_loc(Text), c_loc(Caption), uType )

      return

   end function WinMain

end module IWinAPI_m

Compilation and link steps:

** Visual Studio 2019 Developer Command Prompt v16.6.4
** Copyright (c) 2020 Microsoft Corporation

[vcvarsall.bat] Environment initialized for: ‘x64’

C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional>cd\temp

C:\Temp>gfortran -c -std=f2018 p.f90

C:\Temp>link p.o libcmt.lib user32.lib /subsystem:windows /out:p.exe
Microsoft (R) Incremental Linker Version 14.26.28806.0
Copyright (C) Microsoft Corporation. All rights reserved.

C:\Temp>p.exe

C:\Temp>

Here’s the program output:
p