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Overriding QDir::homePath()

  • Other programmers and I wish to bypass QDir::homePath() in order to portabilize programs. The big question is what's the default of QDir::homePath()? Hint: it's not %homepath% - see "the documentation":

    Also see these links:

  • Take a look at the sources: qfilesystemengine*.cpp files.

    On the other hand, this method is already portable so what do you wanna do with it?

  • I did and didn't understand a thing. It's not portable at all because it does something weird and only upon failure uses environment variables.

    Please explain what it does (something with tokens).

  • Have you tested this method on different kinds of OS'? What is it returning on Windows/Linux/MacOSX?

  • From doc :

    bq. Under Windows this function will return the directory of the current user's profile. Typically, this is:
    C:/Documents and Settings/Username

    bq. Under non-Windows operating systems the HOME environment variable is used if it exists, otherwise the path returned by the rootPath().

  • On Windows, the user directory is searched in the following order, the first method that returns a valid[1] path is used:

    • The value returned by GetUserProfileDirectoryW Windows API call
    • The value of USERPROFILE environment variable
    • The value of HOMEDRIVE + HOMEPATH environment variables
    • The value of HOME environment variable
    • The value of SystemDrive environment variable (no check for existence)
    • "C:/" (hard coded as last resort, no check for existence)

    fn1. valid means the method returns a value and the directory denoted by that value does exist

  • [quote author="Volker" date="1332108047"]

    • The value returned by GetUserProfileDirectoryW Windows API call[/quote]
      So my question is how does GetUserProfileDirectoryW work. Had I understood it, maybe I could have bypassed it.

  • I don't know the internals. Thats Windows API and I avoid digging into that wherever I can :-) Some Google search may get you more details. Usually that method returns "C:/Documents and Settings/USER" on Win2k/XP and "C:/Users/USER" on Vista/Win7.

  • Just to let me get this right: you want to modify the behaviour of an existing binary, you are not a developer who wants to modify its own sourcecode or application.

    Well, I guess you are left with four options then, in the order of work and stress involved

    • recompile the binary not using QDir::homePath() or
    • file a bug report or a merge request which modifies the behaviour of QDir::homePath() in a way that <code>%USERPROFILE%</code> takes precedence over GetUserProfileDirectoryW or
    • distribute the binary with a patched set of the Qt libraries which modify the behaviour of QDir::homePath() or
    • hook GetUserProfileDirectoryW directly to modify its behaviour.

    I'm not quite sure as of right now but I tend to say that <code>%USERPROFILE%</code> and <code>%HOME%</code> should take precedence over GetUserProfileDirectoryW just to cover cases like yours (where you want to temporarily redirect the home directory) and to get a more consistent cross-platform behaviour.

  • Would you be kind enough to submit that bug report? I don't seem to find such an option anywhere.

    Had I understood GetUserProfileDirectoryW, I could have somehow bypassed it without actually modifying the code.

  • Regarding the text in your bugreport:

    bq. Various standalone portable softwares could have been forced to become portable, if only they hadn't stored their data in a path that involves QDir::homePath().

    A sane Qt application doesn't use homePath() for that, but calls QDesktopServices::storageLocation() with, for example, QDesktopServices::DataLocation as argument. These methods do not use homePath() under the hood (or only as a last resort), but call SHGetFolderPath() on Windows, which is native Windows API again.

  • The OP links to at least 2 programs that do this. Well, if their authors knew what they were doing, they would have accepted an "/ini=" command line parameter in the first place.

    But what advantage does SHGetFolderPath() offer? Can it easily be bypassed?


    bq. Deprecated

  • Deprecated for Vista and up, but Qt also runs on XP, where the replacement function does not exist yet.

  • Please answer:

    bq. But what advantage does SHGetFolderPath() offer? Can it easily be bypassed?

  • [quote author="lwcorp" date="1337853314"]Please answer:

    bq. But what advantage does SHGetFolderPath() offer? Can it easily be bypassed?[/quote]

    Advantage: it is official API, although deprecated. But as Andre already mentioned, as long as Qt is running on XP, one will have to use it, as the replacement isn't there.

    Bypassing: I don't know, as I never had a need to do this.

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