QTextCodec 类

QTextCodec 类提供文本编码之间的转换。 更多...

头: #include <QTextCodec>
qmake: QT += core

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

struct ConverterState
enum ConversionFlag { DefaultConversion, ConvertInvalidToNull, IgnoreHeader }
flags ConversionFlags

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 使用 Unicode 存储、绘制及操纵字符串。在很多状况下,可能希望处理使用不同编码的数据。例如,大多数日语文档仍然存储在 Shift-JIS 或 ISO 2022-JP,而俄罗斯用户经常将其文档存储在 KOI8-R 或 Windows-1251。

Qt 提供了一组 QTextCodec 类,以帮助转换非 Unicode 格式到和来自 Unicode。还可以创建自己的编解码器类。

支持的编码:

若启用 ICU 支持编译 Qt,则 ICU 支持的大多数编解码器也可用于应用程序。

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);
					

To read or write files in various encodings, use QTextStream 及其 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();
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.

创建自己的编解码器类

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.

函数 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 , QTextEncoder ,和 文本编解码器范例 .

成员类型文档编制

enum QTextCodec:: ConversionFlag
flags QTextCodec:: ConversionFlags

常量 描述
QTextCodec::DefaultConversion 0 No flag is set.
QTextCodec::ConvertInvalidToNull 0x80000000 If this flag is set, each invalid input character is output as a null character.
QTextCodec::IgnoreHeader 0x1 Ignore any Unicode byte-order mark and don't generate any.

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

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 .

[虚拟] 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.

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。

该函数在 Qt 4.4 引入。

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。

该函数在 Qt 4.6 引入。

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 子类必须重实现此函数。

转换第一 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 子类必须重实现此函数。

转换第一 len 字符的 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 .

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

转换第一 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 ( 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.

该函数在 Qt 4.7 引入。

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.

该函数在 Qt 4.7 引入。

[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

转换第一 size 字符来自 input from the encoding of this codec to Unicode, and returns the result in a QString .

The state of the convertor used is updated.