I'm writing a UI for my program using opengl with SDL in a combination of Lua and C++
What I need now is some library that will allow me to call a function that presents the user with a file select dialog for opening/saving a file. But if the OS offers native functionality for such a dialog, then I want to use that dialog (eg Window's GetOpenFileName).
The only platforms I need to support are Windows and Linux, but I want to be able to still use most of the SDL & openGL code I've already written.
What options are available?
In my opinion, wxWidgets is the open source, battle tested, mature, cross platform, cross language, free, open source, GUI library. Beside wxWidgets, there are also many other such cross platform libraries, such as:
... and more.
You will most likely find you're looking for in the AbiWord source code. Look for "FileOpen" inside the src directory:
./af/xap/cocoa/xap_CocoaDlg_FileOpenSaveAs.cpp
./af/xap/cocoa/xap_CocoaDlg_FileOpenSaveAs.h
./af/xap/cocoa/xap_CocoaFileOpen_Views.nib
./af/xap/cocoa/xap_CocoaFileOpen_Views.nib/classes.nib
./af/xap/cocoa/xap_CocoaFileOpen_Views.nib/info.nib
./af/xap/cocoa/xap_CocoaFileOpen_Views.nib/keyedobjects.nib
./af/xap/gtk/xap_UnixDlg_FileOpenSaveAs.cpp
./af/xap/gtk/xap_UnixDlg_FileOpenSaveAs.h
./af/xap/win/xap_Win32Dlg_FileOpenSaveAs.cpp
./af/xap/win/xap_Win32Dlg_FileOpenSaveAs.h
./af/xap/xp/xap_Dlg_FileOpenSaveAs.cpp
./af/xap/xp/xap_Dlg_FileOpenSaveAs.h
The Windows version does indeed use GetOpenFileName().
Of course, as Andre points out while downvoting a valid alternative answer, there's also Qt, as you already know. Refer to raj's answer for a link.