Converting Win16 C code to Win32

Question

In general, what needs to be done to convert a 16 bit Windows program to Win32? I'm sure I'm not the only person to inherit a codebase and be stunned to find 16-bit code lurking in the corners.

The code in question is C.

Answer 1

1. The meanings of wParam and lParam have changed in many places. I strongly encourage you to be paranoid and convert as much as possible to use message crackers. They will save you no end of headaches. If there is only one piece of advice I could give you, this would be it.
2. As long as you're using message crackers, also enable STRICT. It'll help you catch the Win16 code base using int where it should be using HWND, HANDLE, or something else. Converting these will greatly help with #9 on this list.
3. hPrevInstance is useless. Make sure it's not used.
4. Make sure you're using Unicode-friendly calls. That doesn't mean you need to convert everything to TCHARs, but means you better replace OpenFile, _lopen, and _lcreat with CreateFile, to name the obvious
5. LibMain is now DllMain, and the entire library format and export conventions are different
6. Win16 had no VMM. GlobalAlloc, LocalAlloc, GlobalFree, and LocalFree should be replaced with more modern equivalents. When done, clean up calls to LocalLock, LocalUnlock and friends; they're now useless. Not that I can imagine your app doing this, but make sure you don't depend on WM_COMPACTING while you're there.
7. Win16 also had no memory protection. Make sure you're not using SendMessage or PostMessage to send pointers to out-of-process windows. You'll need to switch to a more modern IPC mechanism, such as pipes or memory-mapped files.
8. Win16 also lacked preemptive multitasking. If you wanted a quick answer from another window, it was totally cool to call SendMessage and wait for the message to be processed. That may be a bad idea now. Consider whether PostMessage isn't a better option.
9. Pointer and integer sizes change. Remember to check carefully anywhere you're reading or writing data to disk—especially if they're Win16 structures. You'll need to manually redo them to handle the shorter values. Again, the least painful way to deal with this will be to use message crackers where possible. Otherwise, you'll need to manually hunt down and convert int to DWORD and so on where applicable.
10. Finally, when you've nailed the obvious, consider enabling 64-bit compilation checks. A lot of the issues faced with going from 16 to 32 bits are the same as going from 32 to 64, and Visual C++ is actually pretty smart these days. Not only will you catch some lingering issues; you'll get yourself ready for your eventual Win64 migration, too.

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EDIT: As @ChrisN points out, the official guide for porting Win16 apps to Win32 is available archived, and both fleshes out and adds to my points above.

Answer 2

Apart from getting your build environment right, Here are few specifics you will need to address:

1. structs containing ints will need to change to short or widen from 16 to 32 bits. If you change the size of the structure and this is loaded/saved to disk you will need write data file upgrade code.

2. Per window data is often stored with the window handle using GWL_USERDATA. If you widen some of the data to 32 bits, your offsets will change.

3. POINT & SIZE structures are 64 bits in Win32. In Win16 they were 32 bits and could be returned as a DWORD (caller would split return value into two 16 bit values). This no longer works in Win32 (i.e. Win32 does not return 64 bit results) and the functions were changed to accept a pointers to store the return values. You will need to edit all of these. APIs like GetTextExtent are affected by this. This same issue also applies to some Windows messages.

4. The use of INI files is discouraged in Win32 in favour of the registry. While the INI file functions still work you will need to be careful with Vista issues. 16 bit programs often stored their INI file in the Windows system directory.

This is just a few of the issues I can recall. It has been over a decade since I did any Win32 porting. Once you get into it it is quite quick. Each codebase will have its own "feel" when it comes to porting which you will get used to. You will probably even find a few bugs along the way.

Answer 3

There was a definitive guide in the article Porting 16-Bit Code to 32-Bit Windows on MSDN.

Answer 4

The original win32 sdk had a tool that scanned source code and flagged lines that needed to be changed, but I can't remember the name of the tool.

When I've had to do this in the past, I've used a brute force technique - i.e.: 1 - update makefiles or build environment to use 32 bit compiler and linker. Optionally, just create a new project in your IDE (I use Visual Studio), and add the files manually.

2 - build

3 - fix errors

4 - repeat 2&3 until done

The pain of the process depends on the application you are migrating. I've converted 10,000 line programs in an hour, and 75,000 line programs in less than a week. I've also had some small utilities that I just gave up on and rewrote (mostly) from scratch.