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Thread: Passing to a console application (managed via QProcess) UTF-8 encoded parameters

  1. #1
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    Default Passing to a console application (managed via QProcess) UTF-8 encoded parameters

    Hi guys,

    I'm playing now with QProcess and external console applications. The console application is accepting image file name as a command line parameter. The problem is that image file names may be weird and contain Unicode symbols (umlauts, greek symbols) wich are not included into ASCII or Local 8 Bit encoding on my computer.

    I use the following code for launching console utility:

    Qt Code:
    1. QProcess process_exiflist;
    2. QStringList exiflist_params;
    3. exiflist_params << "/o";
    4. exiflist_params << "a";
    5. exiflist_params << fileName;
    6. process_exiflist.start(utils_exiflist_exe, exiflist_params);
    To copy to clipboard, switch view to plain text mode 

    The problem occurs when QProcess passes file name to the console application. Qt libs performs conversion of QString into char* (which is normal) and this char* contains locally encoded file name. But local encoding does not contain some Unicode symbols and console application can not find the file specified

    The ideal solution would be to make console application to understand UTF-8 encoded command line parameters. Let's suppose I have such an application. The question is: how to make QProcess to encode QString into UTF-8 rather that in Local encoding.

    Thanks

  2. #2
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    Default Re: Passing to a console application (managed via QProcess) UTF-8 encoded parameters

    Qt Code:
    1. exiflist_params << QString::fromLocal8Bit(fileName);
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    Save yourself some pain. Learn C++ before learning Qt.

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    Default Re: Passing to a console application (managed via QProcess) UTF-8 encoded parameters

    Nop, this is not the case

    fileName variable is a QString (not a ByteArray), i.e. fileName is Unicode (not a Local8Bit encoded)

    The problem is that fileName QString is converted by QProcess to QByteArray (== char*)(as I suppose with using toLocal8Bit() method) and then passed it to the console application. But I'd like fileName to be converted to UTF-8

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    Default Re: Passing to a console application (managed via QProcess) UTF-8 encoded parameters

    Did you try QString::toUtf8() ?
    Save yourself some pain. Learn C++ before learning Qt.

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    Default Re: Passing to a console application (managed via QProcess) UTF-8 encoded parameters

    I thought about

    Qt Code:
    1. exiflist_params << fileName.toUtf8();
    To copy to clipboard, switch view to plain text mode 

    but this is wrong since fileName.toUtf8() gives QByteArray which will be used for creating QString (costructor QString::QString ( const QByteArray & ba )) which will be inserted into exiflist_params. This cunstructror constructs QString assuming that QByteArray contains ASCII encoded data. This I think just like

    Qt Code:
    1. exiflist_params << QString::fromAscii(fileName.toUtf8());
    To copy to clipboard, switch view to plain text mode 

    It seems to be weird and does not work

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    Default Re: Passing to a console application (managed via QProcess) UTF-8 encoded parameters

    On Mac OS X, QProcess uses UTF-8 for command line arguments. On Windows and Unix, it calls QString::toLocal8Bit(). If your file system uses UTF-8, just make sure your applications run the UTF-8 locale too (a good idea, in general). So fex, export LANG=en_US.UTF-8, and then launch your app. QProcess will then use UTF-8 for the arguments.
    Bitto / Andreas Aardal Hanssen - andreas dot aardal dot hanssen at nokia
    Nokia Software Manager, Qt Development

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    Question Re: Passing to a console application (managed via QProcess) UTF-8 encoded parameters

    I'm having the same issue - trying to write a German umlaut (ü) to QProcess but it doesn't work.

    toLatin1() gets me "?", toUtf8() and toLocal8Bit() get me random symbols.

    I didn't manage to understand from this thread how to address this. I'm running on Windows 7. Is there a way to set QProcess to handle UTF-8?

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    Default Re: Passing to a console application (managed via QProcess) UTF-8 encoded parameters

    I do not think there is a way to change QProcess' behaviour, which unfortunately abstracts arguments as Unicode strings instead of plain NULL-terminated byte sequences. Here are two suggestions for working around the problem, in unspecified order of ugliness:
    1. Call QTextCodec::​setCodecForLocale() to set an UTF-8 codec, so that when QProcess calls QString::toLocal8Bit() to serialize the arguments, UTF-8 will be used. Unfortunately, this means changing an application-wide setting to solve a local issue.
    2. Preprocess the arguments before adding them to the QProcess' argument list: QString::fromLocal8Bit(fileName.toUtf8()). Something may get lost in translation.

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    Default Re: Passing to a console application (managed via QProcess) UTF-8 encoded parameters

    Thank you for your reply!

    After some thinking I figured I really could skip the whole cmd.exe usage and do something else. But I hope this thread is helpful to other users.

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