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Thread: How to pass and get unicode strings from external dll

  1. #1
    Join Date
    Mar 2014
    Qt products
    Unix/X11 Windows Android

    Default How to pass and get unicode strings from external dll

    I have a very old working dll.
    It has a function that takes in a unicode string.
    It does some processing.
    Prepares another string and returns the prepared unicode string.

    I have used this dll successfully in other projects. (Including in a firefox extension using js-ctype).

    Now I want to use the same dll in my current QT project. (I am new to QT)

    I have done some googling and have tried some ways; however could not successfully do what I wanted to do.

    Here is my function in the working dll

    DECLDIR TCHAR * process_string ( TCHAR * wList)
    wstring outStr(L"{");
    //does some processing and prepares outStr
    ...... etc....

    TCHAR buff [10000] = L"";

    wcscpy ( buff, L"");
    wcscat ( buff, outStr.c_str());
    return buff;

    here is my header file

    #if defined DLL_EXPORT
    #define DECLDIR __declspec(dllexport)
    #define DECLDIR __declspec(dllimport)

    // Specify "C" linkage to get rid of C++ name mangeling
    extern "C"
    DECLDIR TCHAR * process_string ( TCHAR * wlist);


    I request you to guide me or give me some pointers so that I can use the above dll in my QT project

    Thanks in advance.

  2. #2
    Join Date
    Mar 2009
    Brisbane, Australia
    Thanked 1,610 Times in 1,537 Posts
    Qt products
    Qt4 Qt5
    Unix/X11 Windows
    Wiki edits

    Default Re: How to pass and get unicode strings from external dll

    It strikes me that that function only works by accident rather than design. It is returning a pointer to a destroyed stack array.

    Anyway, QString has functions QString fromUtf16()/QString::utf16() and QString::fromWCharArray()/QString::toWCharArray() for dealing with these strings.

    Include your header (may require INCLUDEPATH variable), link your library into your project (LIBS variable) and use the QString functions.

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