QTextCodec Class

The QTextCodec class provides conversions between text encodings. 更多...

Header: #include <QTextCodec>
CMake: find_package(Qt6 COMPONENTS Core5Compat REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Core5Compat)
qmake: QT += core5compat

注意: 此类的所有函数 可重入 .

注意: 这些函数也是 thread-safe :

公共类型

公共函数

virtual QList<QByteArray> aliases () const
bool canEncode (QChar ch ) const
bool canEncode (const QString & s ) const
bool canEncode (QStringView s ) const
QByteArray fromUnicode (const QString & str ) const
QByteArray fromUnicode (QStringView str ) const
QByteArray fromUnicode (const QChar * input , int number , QTextCodec::ConverterState * state = nullptr) const
QTextDecoder * makeDecoder (QTextCodec::ConversionFlags flags = DefaultConversion) const
QTextEncoder * makeEncoder (QTextCodec::ConversionFlags flags = DefaultConversion) const
virtual int mibEnum () const = 0
virtual QByteArray name () const = 0
QString toUnicode (const QByteArray & a ) const
QString toUnicode (const char * chars ) const
QString toUnicode (const char * input , int size , QTextCodec::ConverterState * state = nullptr) const

静态公共成员

QList<QByteArray> availableCodecs ()
QList<int> availableMibs ()
QTextCodec * codecForHtml (const QByteArray & ba , QTextCodec * defaultCodec )
QTextCodec * codecForHtml (const QByteArray & ba )
QTextCodec * codecForLocale ()
QTextCodec * codecForMib (int mib )
QTextCodec * codecForName (const QByteArray & name )
QTextCodec * codecForName (const char * name )
QTextCodec * codecForUtfText (const QByteArray & ba , QTextCodec * defaultCodec )
QTextCodec * codecForUtfText (const QByteArray & ba )
void setCodecForLocale (QTextCodec * c )

保护函数

QTextCodec ()
virtual ~QTextCodec ()
virtual QByteArray convertFromUnicode (const QChar * input , int number , QTextCodec::ConverterState * state ) const = 0
virtual QString convertToUnicode (const char * chars , int len , QTextCodec::ConverterState * state ) const = 0

详细描述

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:

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

QTextCodec 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;
							

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 描述
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.

另请参阅 QTextStream , QTextDecoder ,和 QTextEncoder .

成员类型文档编制

[alias] QTextCodec:: ConversionFlags

常量 描述
DefaultConversion No flag is set.
ConvertInvalidToNull If this flag is set, each invalid input character is output as a null character.
IgnoreHeader Ignore any Unicode byte-order mark and don't generate any.

[alias] QTextCodec:: ConverterState

成员函数文档编制

[protected] QTextCodec:: 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.

[virtual protected] QTextCodec:: ~QTextCodec ()

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

警告: 此函数不 可重入 .

[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 IANA character-sets encoding file .

[static] QList < QByteArray > QTextCodec:: 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.

注意: 此函数是 thread-safe .

另请参阅 availableMibs (), name (),和 aliases ().

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

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

注意: 此函数是 thread-safe .

另请参阅 availableCodecs () 和 mibEnum ().

bool QTextCodec:: canEncode ( QChar ch ) const

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

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

这是重载函数。

s contains the string being tested for encode-ability.

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

这是重载函数。

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

该函数在 Qt 5.10 引入。

[static] 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 QTextCodec instance that is capable of decoding the html to unicode. If the codec cannot be detected from the content provided, defaultCodec 被返回。

另请参阅 codecForUtfText ().

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

这是重载函数。

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 QTextCodec instance that is capable of decoding the html to unicode. If the codec cannot be detected, this overload returns a Latin-1 QTextCodec .

[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".

注意: 此函数是 thread-safe .

另请参阅 setCodecForLocale ().

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

返回 QTextCodec which matches the MIBenum mib .

注意: 此函数是 thread-safe .

[static] QTextCodec *QTextCodec:: codecForName (const 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.

注意: 此函数是 thread-safe .

[static] QTextCodec *QTextCodec:: codecForName (const char * 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.

[static] 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 QTextCodec 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 被返回。

另请参阅 codecForHtml ().

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

这是重载函数。

Tries to detect the encoding of the provided snippet ba by using the BOM (Byte Order Mark) and returns a QTextCodec 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 QTextCodec .

另请参阅 codecForHtml ().

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

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 可以是 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

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 可以是 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

转换 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

这是重载函数。

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

该函数在 Qt 5.10 引入。

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 .

state of the convertor used is updated.

QTextDecoder *QTextCodec:: makeDecoder ( QTextCodec::ConversionFlags flags = DefaultConversion) const

创建 QTextDecoder 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.

QTextEncoder *QTextCodec:: makeEncoder ( QTextCodec::ConversionFlags flags = DefaultConversion) const

创建 QTextEncoder with a specified flags to encode chunks of Unicode data as char * data.

The caller is responsible for deleting the returned object.

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

子类化的 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.

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

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.

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

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

警告: 此函数不 可重入 .

另请参阅 codecForLocale ().

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

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

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

这是重载函数。

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 .

state of the convertor used is updated.