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QTextCodec Class

The https:// class provides conversions between text encodings.

All functions in this class are https://.

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QTextCodec Class▲

  • Header: QTextCodec

  • qmake: QT += core

  • Inherited By:

  • Group: QTextCodec is part of i18n

Detailed Description▲

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:

 
Sélectionnez
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:

 
Sélectionnez
QString 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 https:// example for an application of https:// 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 https:// object for the codec and use this https:// for the whole decoding process, as shown below:

 
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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 https:// 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 https:// 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 https:// and implement the functions listed in the table below.

Function

Description

https://()

Returns the official name for the encoding. If the encoding is listed in the http://, the name should be the preferred MIME name for the encoding.

https://()

Returns a list of alternative names for the encoding. https:// provides a default implementation that returns an empty list. For example, "ISO-8859-1" has "latin1", "CP819", "IBM819", and "iso-ir-100" as aliases.

https://()

Return the MIB enum for the encoding if it is listed in the http://.

https://()

Converts an 8-bit character string to Unicode.

https://()

Converts a Unicode string to an 8-bit character string.

See Also▲

See also https://, https://, https://, https://

Member Type Documentation▲

 

enum QTextCodec::ConversionFlag▲

Constant

Value

Description

https://::DefaultConversion

0

No flag is set.

https://::ConvertInvalidToNull

0x80000000

If this flag is set, each invalid input character is output as a null character.

https://::IgnoreHeader

0x1

Ignore any Unicode byte-order mark and don't generate any.

Member Function Documentation▲

 

[protected] QTextCodec::QTextCodec()▲

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

[virtual protected] QTextCodec::~QTextCodec()▲

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

This function is not https://.

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

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

Standard aliases for codecs can be found in the http://.

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

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

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

This function is https://.

See Also▲

See also https://(), https://(), https://()

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

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

This function is https://.

See Also▲

See also https://(), https://()

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 function.

s contains the string being tested for encode-ability.

[since 5.10] bool QTextCodec::canEncode(QStringView s) const▲

This is an overloaded function.

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

This function was introduced in Qt 5.10.

[static, since 4.4] QTextCodec *QTextCodec::codecForHtml(const QByteArray &ba, QTextCodec *defaultCodec)▲

Tries to detect the encoding of the provided snippet of HTML in the given byte array, ba, by checking the BOM (Byte Order Mark) and the content-type meta header and returns a https:// 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.

See Also▲

See also https://()

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

This is an overloaded function.

Tries to detect the encoding of the provided snippet of HTML in the given byte array, ba, by checking the BOM (Byte Order Mark) and the content-type meta header and returns a https:// instance that is capable of decoding the html to unicode. If the codec cannot be detected, this overload returns a Latin-1 https://.

[static] QTextCodec *QTextCodec::codecForLocale()▲

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

The codec will be retrieved from ICU where that backend is in use, otherwise it may be obtained from an OS-specific API. In the latter case, the codec's name may be "System".

This function is https://.

See Also▲

See also https://()

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

Returns the https:// which matches the https:// mib.

This function is https://.

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

Searches all installed https:// 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.

This function is https://.

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

Searches all installed https:// 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.

[static, since 4.6] QTextCodec *QTextCodec::codecForUtfText(const QByteArray &ba, QTextCodec *defaultCodec)▲

Tries to detect the encoding of the provided snippet ba by using the BOM (Byte Order Mark) and returns a https:// instance that is capable of decoding the text to unicode. This function can detect one of the following codecs:

  • UTF-32 Little Endian

  • UTF-32 Big Endian

  • UTF-16 Little Endian

  • UTF-16 Big Endian

  • UTF-8

If the codec cannot be detected from the content provided, defaultCodec is returned.

This function was introduced in Qt 4.6.

See Also▲

See also https://()

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

This is an overloaded function.

Tries to detect the encoding of the provided snippet ba by using the BOM (Byte Order Mark) and returns a https:// instance that is capable of decoding the text to unicode. This function can detect one of the following codecs:

  • UTF-32 Little Endian

  • UTF-32 Big Endian

  • UTF-16 Little Endian

  • UTF-16 Big Endian

  • UTF-8

If the codec cannot be detected from the content provided, this overload returns a Latin-1 https://.

See Also▲

See also https://()

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

https:// 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 nullptr 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.

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

https:// 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 nullptr, 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.

[since 5.10] QByteArray QTextCodec::fromUnicode(QStringView str) const▲

This is an overloaded function.

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

This function was introduced in Qt 5.10.

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

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.

[since 4.7] QTextDecoder *QTextCodec::makeDecoder(QTextCodec::ConversionFlags flags = DefaultConversion) const▲

Creates a https:// with a specified flags to decode chunks of char * data to create chunks of Unicode data.

The caller is responsible for deleting the returned object.

This function was introduced in Qt 4.7.

[since 4.7] QTextEncoder *QTextCodec::makeEncoder(QTextCodec::ConversionFlags flags = DefaultConversion) const▲

Creates a https:// with a specified flags to encode chunks of Unicode data as char * data.

The caller is responsible for deleting the returned object.

This function was introduced in Qt 4.7.

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

Subclasses of https:// must reimplement this function. It returns the MIBenum (see http:// for more information). It is important that each https:// subclass returns the correct unique value for this function.

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

https:// 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 http:// this method should return the preferred mime name for the codec if defined, otherwise its name.

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

Set the codec to c; this will be returned by https://(). If c is nullptr, 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.

This function is not https://.

See Also▲

See also https://()

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 *chars) const▲

This is an overloaded function.

chars contains the source characters.

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

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.

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Ce document est disponible sous la licence https:// telle que publiée par la Free Software Foundation.