Qt 5 encoding problems (UTF-8, Windows-1250, Windows-1251)

问题

All my source file are UTF-8 converted.

All my files Im opening are UTF-8.

My application is opening UTF-8 coded file which contains translated text for 3 languages: English, Polish and Russian and is saving the data to a file into 3 separate encoded blocks: Windows-1250 (English), Windows-1250 (Polish) and Windows-1251 (Russian) - yes that's right Im mixing encoding type inside one file which is then used by third-party device which know how to handle that.

Iv got a test program which worked flawlessly under Qt4 and now it stopped working (text is saved as ????????) when I moved to Qt5:

test_encoding.cpp

test_encoding::test_encoding(QWidget *parent) : QMainWindow(parent)
{
  ui.setupUi(this);

  QString d;
  QFile f(QDir::currentPath() + "/input.txt");
  if( f.open( QIODevice::ReadOnly | QIODevice::Text ) )
  {
    d = f.readAll();
    f.close();
  }

  QFile ff(QDir::currentPath() + "/output.txt");
  if( ff.open( QIODevice::WriteOnly | QIODevice::Text ) )
  {
    QTextStream t(&ff);
    auto cutf8 = QTextCodec::codecForName("UTF-8");
    auto cw50 = QTextCodec::codecForName("windows-1250");
    auto cw51 = QTextCodec::codecForName("windows-1251");

        // ____Block 1
    t.setCodec(cutf8);
    t << d << "\r\n";
    t << cutf8->fromUnicode(d) << "\r\n";
    t.flush();

        // ____Block 2
    t.setCodec(cw50);
    t << d << "\r\n";
    t << cw50->fromUnicode(d) << "\r\n";
    t.flush();

        // ____Block 3
    t.setCodec(cw51);
    t << d << "\r\n";
    t << cw51->fromUnicode(d) << "\r\n";
    t.flush();
  }
  ff.close();

  QCoreApplication::quit();
}

input.txt (UTF-8 without BOM)

Użytkownik niezalogowany

Not logged-in user

Не зарегистрированный

output.txt (multi code page blocks)

____Block 1:

Użytkownik niezalogowany

Not logged-in user

Не зарегистрированный

Użytkownik niezalogowany

Not logged-in user

Не зарегистрированный

____Block 2:

U࠹tkownik niezalogowany

Not logged-in user

?? ??????????????????

U?ytkownik niezalogowany

Not logged-in user

?? ??????????????????

____Block 3:

U࠹tkownik niezalogowany

Not logged-in user

?? ??????????????????

U?ytkownik niezalogowany

Not logged-in user

?? ??????????????????

It appears it is possible to save the text only to UTF-8 which is not suitable for me - i need to use code pages Windows-1251 and Windows-1250.

Is it possible in Qt5 to convert from UTF-8 to other code pages?

回答1:

There is a bug in Qt 5 which Iv reported to Qt: https://bugreports.qt.io/browse/QTBUG-42498

At the moment a workaround is to create a new QTextStream object every time you want to change the code page - after QTextStream::flush() has been executed it is NOT possible to change the code page with QTextStream::setCodec() - check description of the bug in the link above. The problem is in line 5 in the source of QIcuCodec::getConverter() - http://pastebin.com/2dEcCyET

So the code which does not work in Qt 5 (and did work in Qt 4.8.4) written this way:

QFile f;
QTextStream ts(&f);
ts.setCodec("Windows-1250");
ts << englishTranslationBlock();
ts << polishTranslationBlock();
ts.flush();
ts.setCodec("Windows-1251");
ts << russianTranslationBlock();
ts.flush();
f.close();

To work around the reported bug, the code must create a new QTextStream to allow the Codec to change. The code will work when written this way:

QFile f;
QTextStream* ts = new QTextStream(&f);
ts->setCodec("Windows-1250");
ts << englishTranslationBlock();
ts << polishTranslationBlock();
ts->flush();
delete ts;
ts = new QTextStream(&f);
ts->setCodec("Windows-1251");
ts << russianTranslationBlock();
ts->flush();
f.close();

来源：https://stackoverflow.com/questions/26803384/qt-5-encoding-problems-utf-8-windows-1250-windows-1251

标签

c++

utf-8

character-encoding

qt5

qt4.8