QTextCodec Class Reference
[QtCore module]

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.

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.

Member Type Documentation

enum QTextCodec::ConversionFlag
flags QTextCodec::ConversionFlags

The ConversionFlags type is a typedef for QFlags<ConversionFlag>. It stores an OR combination of ConversionFlag values.

Member Function Documentation

QTextCodec::QTextCodec ()   [protected]

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.

Warning: This function is not reentrant.

QTextCodec::~QTextCodec ()   [virtual protected]

Destroys the QTextCodec. Note that you should not delete codecs yourself: once created they become Qt's responsibility.

Warning: This function is not reentrant.

QList<QByteArray> QTextCodec::aliases () const   [virtual]

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.

QList<QByteArray> QTextCodec::availableCodecs ()   [static]

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().

QList<int> QTextCodec::availableMibs ()   [static]

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

See also availableCodecs() and mibEnum().

bool QTextCodec::canEncode ( QChar ch ) const

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

bool QTextCodec::canEncode ( const QString & s ) const

This is an overloaded member function, provided for convenience.

s contains the string being tested for encode-ability.

QTextCodec * QTextCodec::codecForCStrings ()   [static]

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().

QTextCodec * QTextCodec::codecForHtml ( const QByteArray & ba, QTextCodec * defaultCodec )   [static]

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.

This function was introduced in Qt 4.4.

QTextCodec * QTextCodec::codecForHtml ( const QByteArray & ba )   [static]

This is an overloaded member function, provided for convenience.

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

QTextCodec * QTextCodec::codecForLocale ()   [static]

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().

QTextCodec * QTextCodec::codecForMib ( int mib )   [static]

Returns the QTextCodec which matches the MIBenum mib.

QTextCodec * QTextCodec::codecForName ( const QByteArray & name )   [static]

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.

QTextCodec * QTextCodec::codecForName ( const char * name )   [static]

This is an overloaded member function, provided for convenience.

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.

QTextCodec * QTextCodec::codecForTr ()   [static]

Returns the codec used by QObject::tr() on its argument. If this function returns 0 (the default), tr() assumes Latin-1.

See also setCodecForTr().

QByteArray QTextCodec::convertFromUnicode ( const QChar * input, int number, ConverterState * state ) const   [pure virtual protected]

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.

QString QTextCodec::convertToUnicode ( const char * chars, int len, ConverterState * state ) const   [pure virtual protected]

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.

QByteArray QTextCodec::fromUnicode ( const QString & str ) const

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

QByteArray QTextCodec::fromUnicode ( const QChar * input, int number, ConverterState * state = 0 ) const

This is an overloaded member function, provided for convenience.

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

The state of the convertor used is updated.

QTextDecoder * QTextCodec::makeDecoder () const

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.

QTextEncoder * QTextCodec::makeEncoder () const

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.

int QTextCodec::mibEnum () const   [pure virtual]

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

QByteArray QTextCodec::name () const   [pure virtual]

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.

void QTextCodec::setCodecForCStrings ( QTextCodec * codec )   [static]

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().

Warning: This function is not reentrant.

See also codecForCStrings() and setCodecForTr().

void QTextCodec::setCodecForLocale ( QTextCodec * c )   [static]

Set the codec to c; this will be returned by codecForLocale(). If 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().

void QTextCodec::setCodecForTr ( QTextCodec * c )   [static]

Sets the codec used by QObject::tr() on its argument to c. If c is 0 (the default), tr() assumes Latin-1.

If the literal quoted text in the program is not in the Latin-1 encoding, this function can be used to set the appropriate encoding. For example, software developed by Korean programmers might use eucKR for all the text in the program, in which case the main() function might look like this:

 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);
     QTextCodec::setCodecForTr(QTextCodec::codecForName("eucKR"));
     ...
 }

Note that this is not the way to select the encoding that the user has chosen. For example, to convert an application containing literal English strings to Korean, all that is needed is for the English strings to be passed through tr() and for translation files to be loaded. For details of internationalization, see Internationalization with Qt.

Warning: This function is not reentrant.

See also codecForTr() and setCodecForCStrings().

QString QTextCodec::toUnicode ( const QByteArray & a ) const

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

QString QTextCodec::toUnicode ( const char * input, int size, ConverterState * state = 0 ) const

This is an overloaded member function, provided for convenience.

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

The state of the convertor used is updated.

QString QTextCodec::toUnicode ( const char * chars ) const

This is an overloaded member function, provided for convenience.

chars contains the source characters.