QTextCodec(3qt)QTextCodec(3qt)NAME
QTextCodec - Provides conversion between text encodings
#include <qtextcodec.h>
Inherited by QEucJpCodec, QEucKrCodec, QGbkCodec,
QJisCodec, QSjisCodec and QTsciiCodec.
Public Members
virtual ~QTextCodec ()
virtual const char* name () const
virtual int mibEnum () const
virtual QTextDecoder* makeDecoder () const
virtual QTextEncoder* makeEncoder () const
virtual QString toUnicode ( const char * chars, int len )
const
virtual QCString fromUnicode ( const QString & uc, int &
lenInOut ) const
QCString fromUnicode ( const QString & uc ) const
QString toUnicode ( const QByteArray &, int len ) const
QString toUnicode ( const QByteArray & ) const
QString toUnicode ( const char * chars ) const
virtual bool canEncode ( QChar ) const
virtual bool canEncode ( const QString & ) const
virtual int heuristicContentMatch ( const char * chars,
int len ) const
virtual int heuristicNameMatch ( const char * hint ) const
Static Public Members
QTextCodec* loadCharmap ( QIODevice * )
QTextCodec* loadCharmapFile ( QString filename )
QTextCodec* codecForMib ( int mib )
QTextCodec* codecForName ( const char * hint, int
accuracy=0 )
QTextCodec* codecForContent ( const char * chars, int len
)
QTextCodec* codecForIndex ( int i )
QTextCodec* codecForLocale ()
void deleteAllCodecs ()
const char* locale ()
Protected Members
QTextCodec ()
Static Protected Members
int simpleHeuristicNameMatch ( const char * name, const
char * hint )
DESCRIPTION
Provides conversion between text encodings.
By making objects of subclasses of QTextCodec, support for
new text encodings can be added to Qt.
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The abstract virtual functions describe the encoder to the
system and the coder is used as required in the different
text file formats supported QTextStream and, under X11 for
the locale-specific character input and output (under
Windows NT codecs are not needed for GUI I/O since the
system works with Unicode already, and Windows 95/98 has
built-in convertors for the 8-bit local encoding).
More recently created QTextCodec objects take precedence
over earlier ones.
To add support for another 8-bit encoding to Qt, make a
subclass or QTextCodec and implement at least the
following methods:
const char* name() const
Return the official name for the encoding.
int mibEnum() const
Return the MIB enum for the encoding if it is listed
in the IANA character-sets encoding file.
If the encoding is multi-byte then it will have "state";
that is, the interpretation of some bytes will be
dependent on some preceding bytes. For such an encoding,
you will need to implement
QTextDecoder* makeDecoder() const
Return a QTextDecoder that remembers incomplete
multibyte sequence prefixes or other required state.
If the encoding does not require state, you should
implement:
QString toUnicode(const char* chars, int len) const
Converts len characters from chars to Unicode.
The base QTextCodec class has default implementations of
the above two functions, but they are mutually recursive,
so you must re-implement at least one of them, or both for
improved efficiency.
For conversion from Unicode to 8-bit encodings, it is
rarely necessary to maintain state. However, two functions
similar to the two above are used for encoding:
QTextEncoder* makeEncoder() const
Return a QTextDecoder.
QCString fromUnicode(const QString& uc, int& lenInOut )
const;
Converts lenInOut characters (of type QChar) from the
start of the string uc, returning a QCString result,
and also returning the length of the result in
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lenInOut.
Again, these are mutually recursive so only one needs to
be implemented, or both if better efficiency is possible.
Finally, you must implement:
int heuristicContentMatch(const char* chars, int len)
const
Gives a value indicating how likely it is that len
characters from chars are in the encoding.
A good model for this function is the
QWindowsLocalCodec::heuristicContentMatch function found
in the Qt sources.
A QTextCodec subclass might have improved performance if
you also re-implement:
bool canEncode( QChar ) const
Test if a Unicode character can be encoded.
bool canEncode( const QString& ) const
Test if a string of Unicode characters can be encoded.
int heuristicNameMatch(const char* hint) const
Test if a possibly non-standard name is referring to
the codec.
MEMBER FUNCTION DOCUMENTATIONQTextCodec::QTextCodec () [protected]
Constructs a QTextCodec, making it of highest precedence.
The QTextCodec should always be constructed on the heap
(with new), and once constructed it becomes the
responsibility of Qt to delete it (which is done at
QApplication destruction).
QTextCodec::~QTextCodec () [virtual]
Destructs the QTextCodec. Note that you should not delete
codecs yourself - once created they become the
responsibility of Qt to delete.
bool QTextCodec::canEncode ( QChar ch ) const [virtual]
Returns TRUE if the unicode character ch can be fully
encoded with this codec. The default implementation tests
if the result of toUnicode(fromUnicode(ch)) is the
original ch. Subclasses may be able to improve the
efficiency.
bool QTextCodec::canEncode ( const QString & s ) const [virtual]
Returns TRUE if the unicode string s can be fully encoded
with this codec. The default implementation tests if the
result of toUnicode(fromUnicode(s)) is the original s.
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Subclasses may be able to improve the efficiency.
QTextCodec* QTextCodec::codecForContent ( const char * chars, int
len ) [static]
Searches all installed QTextCodec objects, returning the
one which most recognizes the given content. May return 0.
Note that this is often a poor choice, since character
encodings often use most of the available character
sequences, and so only by linguistic analysis could a true
match be made.
See also heuristicContentMatch().
QTextCodec* QTextCodec::codecForIndex ( int i ) [static]
Returns the QTextCodec i places from the more recently
inserted, or NULL if there is no such QTextCodec. Thus,
codecForIndex(0) returns the most recently created
QTextCodec.
QTextCodec* QTextCodec::codecForLocale () [static]
Returns a pointer to the codec most suitable for this
locale.
QTextCodec* QTextCodec::codecForMib ( int mib ) [static]
Returns the QTextCodec which matches the MIBenum mib.
QTextCodec* QTextCodec::codecForName ( const char * hint, int
accuracy=0 ) [static]
Searches all installed QTextCodec objects, returning the
one which best matches given name. Returns NULL if no
codec has a match closeness above accuracy.
See also heuristicNameMatch().
void QTextCodec::deleteAllCodecs () [static]
Deletes all the created codecs.
Warning: Do not call this function.
QApplication calls this just before exiting, to delete any
QTextCodec objects that may be lying around. Since various
other classes hold pointers to QTextCodec objects, it is
not safe to call this function earlier.
If you are using the utility classes (like QString) but
not using QApplication, calling this function at the very
end of your application can be helpful to chasing down
memory leaks, as QTextCodec objects will not show up.
QCString QTextCodec::fromUnicode ( const QString & uc, int &
lenInOut ) const [virtual]
Subclasses of QTextCodec must reimplement either this
function or makeEncoder(). It converts the first lenInOut
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characters of uc from Unicode to the encoding of the
subclass. If lenInOut is negative or too large, the length
of uc is used instead.
The value returned is the property of the caller, which is
responsible for deleting it with "delete []". The length
of the resulting Unicode character sequence is returned in
lenInOut.
The default implementation makes an encoder with
makeEncoder() and converts the input with that. Note that
the default makeEncoder() implementation makes an encoder
that simply calls this function, hence subclasses must
reimplement one function or the other to avoid infinite
recursion.
Reimplemented in QEucJpCodec, QGbkCodec, QEucKrCodec,
QSjisCodec, QJisCodec and QTsciiCodec.
QCString QTextCodec::fromUnicode ( const QString & uc ) const
This is an overloaded member function, provided for
convenience. It differs from the above function only in
what argument(s) it accepts.
int QTextCodec::heuristicContentMatch ( const char * chars, int
len ) const [virtual]
Subclasses of QTextCodec must reimplement this function.
It examines the first len bytes of chars and returns a
value indicating how likely it is that the string is a
prefix of text encoded in the encoding of the subclass.
Any negative return value indicates that the text is
detectably not in the encoding (eg. it contains undefined
characters). A return value of 0 indicates that the text
should be decoded with this codec rather than as ASCII,
but there is no particular evidence. The value should
range up to len. Thus, most decoders will return -1, 0, or
-len.
The characters are not null terminated.
See also codecForContent().
Reimplemented in QEucJpCodec, QJisCodec, QGbkCodec,
QEucKrCodec, QSjisCodec and QTsciiCodec.
int QTextCodec::heuristicNameMatch ( const char * hint ) const
[virtual]
Returns a value indicating how likely this decoder is for
decoding some format that has the given name.
A good match returns a positive number around the length
of the string. A bad match is negative.
The default implementation calls
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QTextCodec(3qt)QTextCodec(3qt)simpleHeuristicNameMatch() with the name of the codec.
Reimplemented in QGbkCodec, QJisCodec, QEucKrCodec,
QSjisCodec, QEucJpCodec and QTsciiCodec.
QTextCodec* QTextCodec::loadCharmap ( QIODevice * iod ) [static]
Reads a POSIX2 charmap definition from iod. The parser
recognizes the following lines:
<code_set_name> name
<escape_char> character
% alias alias
CHARMAP
<token> /xhexbyte <Uunicode> ...
<token> /ddecbyte <Uunicode> ...
<token> /octbyte <Uunicode> ...
<token> /any/any... <Uunicode> ...
END CHARMAP
The resulting QTextCodec is returned (and also added to
the global list of codecs). The name() of the result is
taken from the code_set_name.
Note that a codec constructed in this way uses much more
memory and is slower than a hand-written QTextCodec
subclass, since tables in code are in memory shared by all
applications simultaneously using Qt.
See also loadCharmapFile().
QTextCodec* QTextCodec::loadCharmapFile ( QString filename )
[static]
A convenience function for loadCharmap().
const char* QTextCodec::locale () [static]
Returns a string representing the current language.
QTextDecoder* QTextCodec::makeDecoder () const [virtual]
Creates a QTextDecoder which stores enough state to decode
chunks of char* data to create chunks of Unicode data. The
default implementation creates a stateless decoder, which
is sufficient for only the simplest encodings where each
byte corresponds to exactly one Unicode character.
The caller is responsible for deleting the returned
object.
Reimplemented in QEucKrCodec, QEucJpCodec, QJisCodec,
QSjisCodec and QGbkCodec.
QTextEncoder* QTextCodec::makeEncoder () const [virtual]
Creates a QTextEncoder which stores enough state to encode
chunks of Unicode data as char* data. The default
implementation creates a stateless encoder, which is
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sufficient for only the simplest encodings where each
Unicode character corresponds to exactly one char.
The caller is responsible for deleting the returned
object.
int QTextCodec::mibEnum () const [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 return the correct unique value
for this function.
const char* QTextCodec::name () const [virtual]
Subclasses of QTextCodec must reimplement this function.
It returns the name of the encoding supported by the
subclass. When choosing a name for an encoding, consider
these points:
On X11, heuristicNameMatch( const char * hint ) is used to
test if a the QTextCodec can convert between Unicode and
the encoding of a font with encoding hint, such as
"iso8859-1" for Latin-1 fonts," koi8-r" for Russian KOI8
fonts. The default algorithm of heuristicNameMatch() uses
name().
Some applications may use this function to present
encodings to the end user.
Reimplemented in QJisCodec, QEucJpCodec, QEucKrCodec,
QGbkCodec, QTsciiCodec and QSjisCodec.
int QTextCodec::simpleHeuristicNameMatch ( const char * name,
const char * hint ) [static protected]
A simple utility function for heuristicNameMatch() - it
does some very minor character-skipping so that almost-
exact matches score high.
QString QTextCodec::toUnicode ( const char * chars, int len )
const [virtual]
Subclasses of QTextCodec must reimplement this function or
makeDecoder(). It converts the first len characters of
chars to Unicode.
The default implementation makes a decoder with
makeDecoder() and converts the input with that. Note that
the default makeDecoder() implementation makes a decoder
that simply calls this function, hence subclasses must
reimplement one function or the other to avoid infinite
recursion.
Reimplemented in QEucJpCodec, QEucKrCodec, QJisCodec,
QSjisCodec, QGbkCodec and QTsciiCodec.
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QTextCodec(3qt)QTextCodec(3qt)QString QTextCodec::toUnicode ( const QByteArray & a ) const
This is an overloaded member function, provided for
convenience. It differs from the above function only in
what argument(s) it accepts.
QString QTextCodec::toUnicode ( const QByteArray & a, int len )
const
This is an overloaded member function, provided for
convenience. It differs from the above function only in
what argument(s) it accepts.
QString QTextCodec::toUnicode ( const char * chars ) const
This is an overloaded member function, provided for
convenience. It differs from the above function only in
what argument(s) it accepts.
SEE ALSO
http://doc.trolltech.com/qtextcodec.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2001 Trolltech AS,
http://www.trolltech.com. See the license file included
in the distribution for a complete license statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports
make our job much simpler. Thank you.
In case of content or formattting problems with this
manual page, please report them to qt-bugs@trolltech.com.
Please include the name of the manual page
(qtextcodec.3qt) and the Qt version (2.3.1).
Trolltech AS 13 June 2001 8
