Why does SHFileOperation have internal error codes for DVD?

erangi asks why the SHFileOperation function has internal error codes DE_DEST_IS_DVD and DE_SRC_IS_DVD if DVDs hadn't been invented at the time it was first written a long time ago.

As my colleague Christopher Davis explained, the SHFileOperation function originally came from the old File Manager of Windows 3.0, code which was written before Win32 error codes were invented. File Manager error codes and Win32 error codes had a common starting point (the MS-DOS error codes), but evolved under divergent paths. When no suitable MS-DOS error code existed for a situation that might arise during file copying, the File Manager folks invented an error code for it. Meanwhile, when no suitable MS-DOS error code existed for a situation that might arise in Win32, the Win32 folks invented an error code for it. That the two sets of error codes would come up with different meanings for the same numerical value is to be expected, since in both cases, the number was "available for use."

Okay, so when the DVD error codes were added, why weren't they added to winerror.h to make them official instead of adding them to the internal error list?

Well, for one, these are internal error codes (which happen to be exposed to applications in an accidental way). Why bother making official error codes for things which were meant to be internal anyway?

"Dear kernel team, please add this error code to winerror.h."

Okay, how should we document it?

"Oh, it's not documented."

Then why the heck do you need it in winerror.h?

Second, there may be considerations that are not immediately obvious from the raw list of internal error codes. For example, I noticed that there is one error code called ERRORONDEST which is "or"d with other error codes. The case of DE_ROOTDIR | ERRORONDEST is specifically called out, but it's highly likely that the more general case applies. For example, DE_FILENAMETOOLONG | ERRORONDEST probably means that a file name on the destination was too long. If the file copy engine were to switch entirely to Win32 error codes, all the uses of internal error codes would have to broken up into two parts, one for the Win32 error code and another for the boolean that specifies whether the Win32 error code applies to the source or destination. This means changing all the functions which pass or return internal error codes, which can get particularly tricky if you were passing the error code as a parameter to SendMessage or PostMessage or some other function where you've already used up all the bits of expressiveness. (You'd have to put the information into a structure and then worry about keeping track of whose job it is to free that structure.)

Third, there's the principle of proportionate response: Sure, the person who wanted to add DVD handling to the file copy engine could have torn apart and rewritten the way error codes are handled inside the copy engine. But would that have been a proportionate response to a request to add DVD error handling to the copy engine? "Here you go, I added DVD error handling, and I completely redesigned the way errors are handled."

It's like asking someone to come fix a broken light switch and discovering that they rewired your house while they were there. Maybe they did a good job, or maybe they accidentally introduced a short circuit somewhere in a little-used closet. It's even more exciting when they don't even tell you that they rewired your house. You test the light switch, it works, and you thank them for a job well done. Then two months later, you visit that closet, turn on the light switch, and all the outlets on the second floor explode.

Now, the principle of proportionate response is not a law of the universe. It's just a principle, and sometimes principles need to be broken. For example, the principle of proportionate response also results in a frog being boiled alive. Sometimes you just have to get out of the pot. But apparently this was not one of those times.

Chris did point out that the new Vista copy engine returns HRESULTs rather than goofy internal undocumented error codes, so at least things are better now. The frog has been taken out of the pot.

Sidebar: It was only after I had written up this message that I realized that erangi had already asked this question at the bottom of the original blog entry. If I had known that, I wouldn't have bothered writing up this entry, because I don't like it when people ask the same question in multiple places, especially since my response is based is purely speculation, guesswork that you too could have performed.

Comments (12)
  1. Yuhong Bao says:

    When were the DVD error codes added, BTW?

  2. Jared says:

    I admit I’m old, feeble minded, dense, and only working on one cup of coffee…  but I read the stream of consciousness blog entry twice and the answer to the original question didn’t jump out at me.

    Q. Why is there an error code in an ancient package that presupposes prophetic vision?

    A. The code was added during modernization of said package, and didn’t exist on day 1.

    I assume that’s what Raymond is saying?

    PS:  Lesson on how to write prophetic literature.

    1.  Invent "wise old sage" living before your time.
    2.  Write document credited to WOS documenting history from then to now.

    3.  Insert comment about how wonderful a prophet WOS has been, getting everything right so far in the document.

    4.  Add your predictions for the future, riding on WOS’s coat tails for accuracy.

    Result is an instant "infallible" source.

  3. asf says:

    Any hope of the shellrevealed blog returning?

    [I had nothing to do with the running of that site. -Raymond]
  4. 640k says:

    90s called and want their return codes back.

    Use exceptions please.

    [Is that a proportionate response? -Raymond]
  5. Leo Davidson says:


    "Use exceptions please."

    Just one look at CloseHandle (among several hundred other things) is all you need to know that Win32 isn’t an exception-safe API and never could be. Making it use exceptions, except for truly exceptional circumstances, would be insane.

    If you want exceptions then that’s fair enough but use a wrapper/framework (e.g. .Net).

  6. Ken Hagan says:

    The 90s called and want their silver bullet back.

    Witticisms aside, if you are talking about Win32 exceptions, please note that they are not separate classes arranged in a nice hierarchy within your chosen programming language. There is only one "class" of Win32 exception, and its principal discriminant is an HRESULT.

  7. Nick says:

    640k: People with attitudes like yours make me sigh.  Besides, don’t you have an open source project you should be contributing to?

  8. JamesNT says:

    Mr. Chen,

    Regarding your sidebar – thank you for writing this post, anyway.  You just helped me solve a small problem by pointing me in a the right direction.


  9. Yuhong Bao says:

    "Any hope of the shellrevealed blog returning?"

    Luckily, many of the info that was once there is now documented elsewhere. For example, the error codes once documented there is now documented on the MSDN page for SHFileOperation.

  10. Joe says:

    Why bother with those error codes at all? Does DE_SRC_IS_DVD give you some information that DE_SRC_IS_CDROM doesn’t? Seems it would have been better to redefine DE_SRC_IS_CDROM to mean ‘The source is a read-only optical disk, possibly unformatted’.

    That way, SHFileOperation would be able to give sensible error codes for writeable DVDs (there’s a DE_SRC_IS_CDRECORD but not DE_SRC_IS_DVDRECORD) and would be able to handle Bluray disks.

  11. GWO says:

    @Nick : Congratulations – you managed to follow up a ill-thought-out, petty and small minded comment with a pettier and smaller minded one.  Well played.

  12. Mike Dimmick says:

    @Jared: Microsoft would have known much earlier than 1997 that there would be a successor to CD-ROM for video playback and data storage. The two competitors were announced officially at the end of 1994, and the merged spec in mid- to late 1995.

    The current documentation does say "These error codes are subject to change and have historically done so." (my emphasis). You may find that non-DVD-supporting versions of Windows used 0x83 for some other purpose.

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