QTextCodec Class

Qt uses Unicode to store, draw and manipulate strings. In many situations you may wish to deal with data that uses a different encoding. For example, most Japanese documents are still stored in Shift-JIS or ISO 2022-JP, while Russian users often have their documents in KOI8-R or Windows-1251.

Qt provides a set of https:// classes to help with converting non-Unicode formats to and from Unicode. You can also create your own codec classes.

The supported encodings are:

• https://

• https://

• CP949

• https://

• https://

• https://

• HP-ROMAN8

• IBM 850

• IBM 866

• IBM 874

• https://

• ISO 8859-1 to 10

• ISO 8859-13 to 16

• Iscii-Bng, Dev, Gjr, Knd, Mlm, Ori, Pnj, Tlg, and Tml

• KOI8-R

• KOI8-U

• Macintosh

• https://

• TIS-620

• https://

• UTF-8

• UTF-16

• UTF-16BE

• UTF-16LE

• UTF-32

• UTF-32BE

• UTF-32LE

• Windows-1250 to 1258

If Qt is compiled with ICU support enabled, most codecs supported by ICU will also be available to the application.

https://s can be used as follows to convert some locally encoded string to Unicode. Suppose you have some string encoded in Russian KOI8-R encoding, and want to convert it to Unicode. The simple way to do it is like this:

QByteArray encodedString = "...";
QTextCodec *codec = QTextCodec::codecForName("KOI8-R");
QString string = codec->toUnicode(encodedString);

After this, string holds the text converted to Unicode. Converting a string from Unicode to the local encoding is just as easy:

QString string = "...";
QTextCodec *codec = QTextCodec::codecForName("KOI8-R");
QByteArray encodedString = codec->fromUnicode(string);

Some care must be taken when trying to convert the data in chunks, for example, when receiving it over a network. In such cases it is possible that a multi-byte character will be split over two chunks. At best this might result in the loss of a character and at worst cause the entire conversion to fail.

The approach to use in these situations is to create a QTextDecoder object for the codec and use this QTextDecoder for the whole decoding process, as shown below:

QTextCodec *codec = QTextCodec::codecForName("Shift-JIS");
QTextDecoder *decoder = codec->makeDecoder();

QString string;
while (new_data_available()) {
    QByteArray chunk = get_new_data();
    string += decoder->toUnicode(chunk);
}
delete decoder;

The QTextDecoder object maintains state between chunks and therefore works correctly even if a multi-byte character is split between chunks.

Creating Your Own Codec Class▲

See Also▲