com.trolltech.qt.core
Class QTextCodec

java.lang.Object
  com.trolltech.qt.internal.QSignalEmitterInternal
      com.trolltech.qt.QSignalEmitter
          com.trolltech.qt.QtJambiObject
              com.trolltech.qt.core.QTextCodec

All Implemented Interfaces:

QtJambiInterface

public abstract class QTextCodec
extends QtJambiObject

The QTextCodec class provides conversions between text encodings. 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 QTextCodec classes to help with converting non-Unicode formats to and from Unicode. You can also create your own codec classes.

The supported encodings are:

• Apple Roman
• Big5
• Big5-HKSCS
• CP949
• EUC-JP
• EUC-KR
• GB18030-0
• IBM 850
• IBM 866
• IBM 874
• ISO 2022-JP
• ISO 8859-1 to 10
• ISO 8859-13 to 16
• Iscii-Bng, Dev, Gjr, Knd, Mlm, Ori, Pnj, Tlg, and Tml
• JIS X 0201
• JIS X 0208
• KOI8-R
• KOI8-U
• MuleLao-1
• ROMAN8
• Shift-JIS
• TIS-620
• TSCII
• UTF-8
• UTF-16
• UTF-16BE
• UTF-16LE
• UTF-32
• UTF-32BE
• UTF-32LE
• Windows-1250 to 1258
• WINSAMI2

QTextCodecs 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 = new QByteArray("...");
        QTextCodec codec = QTextCodec.codecForName("KOI8-R");
        String 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:

        String string = new String("...");
        QTextCodec codec = QTextCodec.codecForName("KOI8-R");
        QByteArray encodedString = codec.fromUnicode(string);

To read or write files in various encodings, use QTextStream and its setCodec() function. See the Codecs example for an application of QTextCodec to file I/O.

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();

        String string = new String();
        while (new_data_available()) {
            QByteArray chunk = get_new_data();
            string += decoder.toUnicode(chunk);
        }

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

Support for new text encodings can be added to Qt by creating QTextCodec subclasses.

The pure virtual functions describe the encoder to the system and the coder is used as required in the different text file formats supported by QTextStream, and under X11, for the locale-specific character input and output.

To add support for another encoding to Qt, make a subclass of QTextCodec and implement the functions listed in the table below.

Function	Description
name()	Returns the official name for the encoding. If the encoding is listed in the IANA character-sets encoding file, the name should be the preferred MIME name for the encoding.
aliases()	Returns a list of alternative names for the encoding. QTextCodec provides a default implementation that returns an empty list. For example, "ISO-8859-1" has "latin1", "CP819", "IBM819", and "iso-ir-100" as aliases.
mibEnum()	Return the MIB enum for the encoding if it is listed in the IANA character-sets encoding file.
convertToUnicode()	Converts an 8-bit character string to Unicode.
convertFromUnicode()	Converts a Unicode string to an 8-bit character string.

You may find it more convenient to make your codec class available as a plugin; see How to Create Qt Plugins for details.

See also:

QTextStream, QTextDecoder, QTextEncoder, and Codecs Example.

Nested Class Summary

static class	QTextCodec.ConversionFlag
static class	QTextCodec.ConversionFlags

Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter

QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9

Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal

com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal

Field Summary

Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal

currentSender

Constructor Summary

protected

QTextCodec() Constructs a QTextCodec, and gives it the highest precedence.

Method Summary

java.util.List	aliases() Subclasses can return a number of aliases for the codec in question.
static java.util.List	availableCodecs() Returns the list of all available codecs, by name.
static java.util.List	availableMibs() Returns the list of MIBs for all available codecs.
boolean	canEncode(char arg__1) Returns true if the Unicode character ch can be fully encoded with this codec; otherwise returns false.
boolean	canEncode(java.lang.String arg__1) This is an overloaded member function, provided for convenience.
static QTextCodec	codecForCStrings() Returns the codec used by QString to convert to and from const char * and QByteArrays.
static QTextCodec	codecForHtml(QByteArray ba) This is an overloaded member function, provided for convenience.
static QTextCodec	codecForHtml(QByteArray ba, QTextCodec defaultCodec) Tries to detect the encoding of the provided snippet of html in the given byte array, ba, and returns a QTextCodec instance that is capable of decoding the html to unicode.
static QTextCodec	codecForLocale() Returns a pointer to the codec most suitable for this locale.
static QTextCodec	codecForMib(int mib) Returns the QTextCodec which matches the MIBenummib.
static QTextCodec	codecForName(QByteArray name) Searches all installed QTextCodec objects and returns the one which best matches name; the match is case-insensitive.
static QTextCodec	codecForName(java.lang.String name) Searches all installed QTextCodec objects and returns the one which best matches name; the match is case-insensitive.
protected abstract QByteArray	convertFromUnicode(char[] in, int length, QTextCodec_ConverterState state) QTextCodec subclasses must reimplement this function.
protected abstract java.lang.String	convertToUnicode(byte[] in, int length, QTextCodec_ConverterState state) QTextCodec subclasses must reimplement this function.
QByteArray	fromUnicode(java.lang.String uc) Converts str from Unicode to the encoding of this codec, and returns the result in a QByteArray.
QTextDecoder	makeDecoder() Creates a QTextDecoder which stores enough state to decode chunks of char * data to create chunks of Unicode data.
QTextEncoder	makeEncoder() Creates a QTextEncoder which stores enough state to encode chunks of Unicode data as char * data.
abstract int	mibEnum() Subclasses of QTextCodec must reimplement this function.
abstract QByteArray	name() QTextCodec subclasses must reimplement this function.
static void	setCodecForCStrings(QTextCodec c) Sets the codec used by QString to convert to and from const char * and QByteArrays.
static void	setCodecForLocale(QTextCodec c) Set the codec to c; this will be returned by codecForLocale().
java.lang.String	toUnicode(QByteArray arg__1) Converts a from the encoding of this codec to Unicode, and returns the result in a QString.

Methods inherited from class com.trolltech.qt.QtJambiObject

dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr

Methods inherited from class com.trolltech.qt.QSignalEmitter

blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread

Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal

__qt_signalInitialization

Methods inherited from class java.lang.Object

clone, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface com.trolltech.qt.QtJambiInterface

disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership

Constructor Detail

QTextCodec

protected QTextCodec()

Constructs a QTextCodec, and gives it the highest precedence. The QTextCodec should always be constructed on the heap (i.e. with new). Qt takes ownership and will delete it when the application terminates.

Method Detail

canEncode

public final boolean canEncode(char arg__1)

Returns true if the Unicode character ch can be fully encoded with this codec; otherwise returns false.

canEncode

public final boolean canEncode(java.lang.String arg__1)

This is an overloaded member function, provided for convenience.

s contains the string being tested for encode-ability.

fromUnicode

public final QByteArray fromUnicode(java.lang.String uc)

Converts str from Unicode to the encoding of this codec, and returns the result in a QByteArray.

makeDecoder

public final QTextDecoder makeDecoder()

Creates a QTextDecoder which stores enough state to decode chunks of char * data to create chunks of Unicode data.

The caller is responsible for deleting the returned object.

makeEncoder

public final QTextEncoder makeEncoder()

Creates a QTextEncoder which stores enough state to encode chunks of Unicode data as char * data.

The caller is responsible for deleting the returned object.

toUnicode

public final java.lang.String toUnicode(QByteArray arg__1)

Converts a from the encoding of this codec to Unicode, and returns the result in a QString.

aliases

public java.util.List aliases()

Subclasses can return a number of aliases for the codec in question.

Standard aliases for codecs can be found in the IANA character-sets encoding file.

convertFromUnicode

protected abstract QByteArray convertFromUnicode(char[] in,
                                                 int length,
                                                 QTextCodec_ConverterState state)

QTextCodec subclasses must reimplement this function.

Converts the first number of characters from the input array from Unicode to the encoding of the subclass, and returns the result in a QByteArray.

state can be 0 in which case the conversion is stateless and default conversion rules should be used. If state is not 0, the codec should save the state after the conversion in state, and adjust the remainingChars and invalidChars members of the struct.

convertToUnicode

protected abstract java.lang.String convertToUnicode(byte[] in,
                                                     int length,
                                                     QTextCodec_ConverterState state)

QTextCodec subclasses must reimplement this function.

Converts the first len characters of chars from the encoding of the subclass to Unicode, and returns the result in a QString.

state can be 0, in which case the conversion is stateless and default conversion rules should be used. If state is not 0, the codec should save the state after the conversion in state, and adjust the remainingChars and invalidChars members of the struct.

mibEnum

public abstract int mibEnum()

Subclasses of QTextCodec must reimplement this function. It returns the MIBenum (see IANA character-sets encoding file for more information). It is important that each QTextCodec subclass returns the correct unique value for this function.

name

public abstract QByteArray name()

QTextCodec subclasses must reimplement this function. It returns the name of the encoding supported by the subclass.

If the codec is registered as a character set in the IANA character-sets encoding file this method should return the preferred mime name for the codec if defined, otherwise its name.

availableCodecs

public static java.util.List availableCodecs()

Returns the list of all available codecs, by name. Call QTextCodec::codecForName() to obtain the QTextCodec for the name.

The list may contain many mentions of the same codec if the codec has aliases.

See also:

availableMibs(), name(), and aliases().

availableMibs

public static java.util.List availableMibs()

Returns the list of MIBs for all available codecs. Call QTextCodec::codecForMib() to obtain the QTextCodec for the MIB.

See also:

availableCodecs(), and mibEnum().

codecForCStrings

public static QTextCodec codecForCStrings()

Returns the codec used by QString to convert to and from const char * and QByteArrays. If this function returns 0 (the default), QString assumes Latin-1.

See also:

setCodecForCStrings().

codecForHtml

public static QTextCodec codecForHtml(QByteArray ba)

This is an overloaded member function, provided for convenience.

If the codec cannot be detected, this overload returns a Latin-1 QTextCodec.

codecForHtml

public static QTextCodec codecForHtml(QByteArray ba,
                                      QTextCodec defaultCodec)

Tries to detect the encoding of the provided snippet of html in the given byte array, ba, and returns a QTextCodec instance that is capable of decoding the html to unicode. If the codec cannot be detected from the content provided, defaultCodec is returned.

codecForLocale

public static QTextCodec codecForLocale()

Returns a pointer to the codec most suitable for this locale.

On Windows, the codec will be based on a system locale. On Unix systems, starting with Qt 4.2, the codec will be using the iconv library. Note that in both cases the codec's name will be "System".

See also:

setCodecForLocale().

codecForMib

public static QTextCodec codecForMib(int mib)

Returns the QTextCodec which matches the MIBenummib.

codecForName

public static QTextCodec codecForName(QByteArray name)

Searches all installed QTextCodec objects and returns the one which best matches name; the match is case-insensitive. Returns 0 if no codec matching the name name could be found.

setCodecForCStrings

public static void setCodecForCStrings(QTextCodec c)

Sets the codec used by QString to convert to and from const char * and QByteArrays. If the codec is 0 (the default), QString assumes Latin-1.

Warning: Some codecs do not preserve the characters in the ASCII range (0x00 to 0x7F). For example, the Japanese Shift-JIS encoding maps the backslash character (0x5A) to the Yen character. To avoid undesirable side-effects, we recommend avoiding such codecs with setCodecsForCString().

See also:

codecForCStrings(), and setCodecForTr().

setCodecForLocale

public static void setCodecForLocale(QTextCodec c)

Set the codec to c; this will be returned by codecForLocale(). If c is a null pointer, the codec is reset to the default.

This might be needed for some applications that want to use their own mechanism for setting the locale.

Setting this codec is not supported on DOS based Windows.

See also:

codecForLocale().

codecForName

public static QTextCodec codecForName(java.lang.String name)

Searches all installed QTextCodec objects and returns the one which best matches name; the match is case-insensitive. Returns 0 if no codec matching the name \a name could be found.