QFile(3qt)QFile(3qt)NAMEQFile - I/O device that operates on files
#include <qfile.h>
Inherits QIODevice.
Public Members
QFile ()
QFile ( const QString & name )
~QFile ()
QString name () const
void setName ( const QString & name )
typedef QCString ( * EncoderFn )( const QString &
fileName)
typedef QString ( * DecoderFn )( const QCString &
localfileName)
bool exists () const
bool remove ()
virtual bool open ( int )
bool open ( int, FILE * )
bool open ( int, int )
virtual void close ()
virtual void flush ()
virtual uint size () const
virtual int at () const
virtual bool at ( int )
virtual bool atEnd () const
virtual int readBlock ( char * data, uint len )
virtual int readLine ( char * data, uint maxlen )
int readLine ( QString &, uint maxlen )
virtual int getch ()
virtual int putch ( int )
virtual int ungetch ( int )
int handle () const
Static Public Members
QCString encodeName ( const QString & fileName )
QString decodeName ( const QCString & localFileName )
void setEncodingFunction ( EncoderFn )
void setDecodingFunction ( DecoderFn )
bool exists ( const QString & fileName )
bool remove ( const QString & fileName )
DESCRIPTION
The QFile class is an I/O device that operates on files.
QFile is an I/O device for reading and writing binary and
text files. A QFile may be used by itself (readBlock and
writeBlock) or by more conveniently using QDataStream or
QTextStream.
Here is a code fragment that uses QTextStream to read a
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text file line by line. It prints each line with a line
number.
QFile f("file.txt");
if ( f.open(IO_ReadOnly) ) { // file opened successfully
QTextStream t( &f ); // use a text stream
QString s;
int n = 1;
while ( !t.eof() ) { // until end of file...
s = t.readLine(); // line of text excluding '\n'
printf( "%3d: %s\n", n++, (const char *)s );
}
f.close();
}
The QFileInfo class holds detailed information about a
file, such as access permissions, file dates and file
types.
The QDir class manages directories and lists of file
names.
See also QDataStream and QTextStream.
Examples: xml/tagreader/tagreader.cpp xml/tagreader
MEMBER FUNCTION DOCUMENTATIONQFile::QFile ()
Constructs a QFile with no name.
QFile::QFile ( const QString & name )
Constructs a QFile with a file name name.
See also setName().
QFile::~QFile ()
Destructs a QFile. Calls close().
bool QFile::at ( int pos ) [virtual]
Sets the file index to pos. Returns TRUE if successful,
otherwise FALSE.
Example:
QFile f( "data.bin" );
f.open( IO_ReadOnly ); // index set to 0
f.at( 100 ); // set index to 100
f.at( f.at()+50 ); // set index to 150
f.at( f.size()-80 ); // set index to 80 before EOF
f.close();
Warning: The result is undefined if the file was opened
using the IO_Append specifier.
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See also size() and open().
Reimplemented from QIODevice.
int QFile::at () const [virtual]
Returns the file index.
See also size().
Reimplemented from QIODevice.
bool QFile::atEnd () const [virtual]
Returns TRUE if the end of file has been reached,
otherwise FALSE.
See also size().
Reimplemented from QIODevice.
void QFile::close () [virtual]
Closes an open file.
The file is not closed if it was opened with an existing
file handle. If the existing file handle is a FILE*, the
file is flushed. If the existing file handle is an int
file descriptor, nothing is done to the file.
Some "write-behind" filesystems may report an unspecified
error on closing the file. These errors only indicate that
something may have gone wrong since the previous open().
In such a case status() reports IO_UnspecifiedError after
close(), otherwise IO_Ok.
See also open() and flush().
Reimplemented from QIODevice.
QString QFile::decodeName ( const QCString & localFileName )
[static]
This does the reverse of QFile::encodeName().
See also setDecodingFunction().
QCString QFile::encodeName ( const QString & fileName ) [static]
When you use QFile, QFileInfo, and QDir to access the
filesystem with Qt, you can use Unicode filenames. On
Unix, these filenames are converted to an 8-bit encoding.
If you want to do your own file I/O on Unix, you should
convert the filename using this function. On Windows NT,
Unicode filenames are supported directly in the filesystem
and this function should be avoided. On Windows 95, non-
Latin1 locales are not supported at this time.
By default, this function converts to the local 8-bit
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encoding determined by the user's locale. This is
sufficient for filenames that the user chooses. Filenames
hard-coded into the application should only use 7-bit
ASCII filename characters.
The conversion scheme can be changed using
setEncodingFunction(). This might be useful if you wish to
give the user an option to store in filenames in UTF-8,
etc., but beware that such filenames would probably then
be unrecognizable when seen by other programs.
See also decodeName().
bool QFile::exists () const
Returns TRUE if this file exists, otherwise FALSE.
See also name().
bool QFile::exists ( const QString & fileName ) [static]
Returns TRUE if the file given by fileName exists,
otherwise FALSE.
void QFile::flush () [virtual]
Flushes the file buffer to the disk.
close() also flushes the file buffer.
Reimplemented from QIODevice.
int QFile::getch () [virtual]
Reads a single byte/character from the file.
Returns the byte/character read, or -1 if the end of the
file has been reached.
See also putch() and ungetch().
Reimplemented from QIODevice.
int QFile::handle () const
Returns the file handle of the file.
This is a small positive integer, suitable for use with C
library functions such as fdopen() and fcntl(), as well as
with QSocketNotifier.
If the file is not open or there is an error, handle()
returns -1.
See also QSocketNotifier.
QString QFile::name () const
Returns the name set by setName().
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See also setName() and QFileInfo::fileName().
bool QFile::open ( int m ) [virtual]
Opens the file specified by the file name currently set,
using the mode m. Returns TRUE if successful, otherwise
FALSE.
The mode parameter m must be a combination of the
following flags:
IO_Raw specified raw (non-buffered) file access.
IO_ReadOnly opens the file in read-only mode.
IO_WriteOnly opens the file in write-only mode (and
truncates).
IO_ReadWrite opens the file in read/write mode, equivalent
to (IO_ReadOnly|IO_WriteOnly).
IO_Append opens the file in append mode. This mode is very
useful when you want to write something to a log file. The
file index is set to the end of the file. Note that the
result is undefined if you position the file index
manually using at() in append mode.
IO_Truncate truncates the file.
IO_Translate enables carriage returns and linefeed
translation for text files under MS-DOS, Windows and OS/2.
The raw access mode is best when I/O is block-operated
using 4kB block size or greater. Buffered access works
better when reading small portions of data at a time.
Important: When working with buffered files, data may not
be written to the file at once. Call flush to make sure
the data is really written.
Warning: We have experienced problems with some C
libraries when a buffered file is opened for both reading
and writing. If a read operation takes place immediately
after a write operation, the read buffer contains garbage
data. Worse, the same garbage is written to the file.
Calling flush() before readBlock() solved this problem.
If the file does not exist and IO_WriteOnly or
IO_ReadWrite is specified, it is created.
Example:
QFile f1( "/tmp/data.bin" );
QFile f2( "readme.txt" );
f1.open( IO_Raw | IO_ReadWrite | IO_Append );
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f2.open( IO_ReadOnly | IO_Translate );
See also name(), close(), isOpen() and flush().
Reimplemented from QIODevice.
bool QFile::open ( int m, FILE * f )
Opens a file in the mode m using an existing file handle
f. Returns TRUE if successful, otherwise FALSE.
Example:
#include <stdio.h>
void printError( const char* msg )
{
QFile f;
f.open( IO_WriteOnly, stderr );
f.writeBlock( msg, qstrlen(msg) ); // write to stderr
f.close();
}
When a QFile is opened using this function, close() does
not actually close the file, only flushes it.
Warning: If f is stdin, stdout, stderr, you may not be
able to seek. See QIODevice::isSequentialAccess() for more
information.
See also close().
bool QFile::open ( int m, int f )
Opens a file in the mode m using an existing file
descriptor f. Returns TRUE if successful, otherwise FALSE.
When a QFile is opened using this function, close() does
not actually close the file.
Warning: If f is one of 0 (stdin), 1 (stdout) or 2
(stderr), you may not be able to seek. size() is set to
INT_MAX (in limits.h).
See also close().
int QFile::putch ( int ch ) [virtual]
Writes the character ch to the file.
Returns ch, or -1 if some error occurred.
See also getch() and ungetch().
Reimplemented from QIODevice.
int QFile::readBlock ( char * p, uint len ) [virtual]
Reads at most len bytes from the file into p and returns
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the number of bytes actually read.
Returns -1 if a serious error occurred.
Warning: We have experienced problems with some C
libraries when a buffered file is opened for both reading
and writing. If a read operation takes place immediately
after a write operation, the read buffer contains garbage
data. Worse, the same garbage is written to the file.
Calling flush() before readBlock() solved this problem.
See also writeBlock().
Reimplemented from QIODevice.
int QFile::readLine ( QString & s, uint maxlen )
Reads a line of text.
Reads bytes from the file until end-of-line is reached, or
up to maxlen bytes, and returns the number of bytes read,
or -1 in case of error. The terminating newline is not
stripped.
This function is efficient only for buffered files. Avoid
readLine() for files that have been opened with the IO_Raw
flag.
Note that the string is read as plain Latin1 bytes, not
Unicode.
See also readBlock() and QTextStream::readLine().
int QFile::readLine ( char * p, uint maxlen ) [virtual]
Reads a line of text.
Reads bytes from the file until end-of-line is reached, or
up to maxlen bytes, and returns the number of bytes read,
or -1 in case of error. The terminating newline is not
stripped.
This function is efficient only for buffered files. Avoid
readLine() for files that have been opened with the IO_Raw
flag.
See also readBlock() and QTextStream::readLine().
Reimplemented from QIODevice.
bool QFile::remove ()
Removes the file specified by the file name currently set.
Returns TRUE if successful, otherwise FALSE.
The file is closed before it is removed.
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Removes the file fileName. Returns TRUE if successful,
otherwise FALSE.
void QFile::setDecodingFunction ( DecoderFn f ) [static]
Sets the function for decoding 8-bit filenames. The
default uses the locale-specific 8-bit encoding.
See also encodeName() and decodeName().
void QFile::setEncodingFunction ( EncoderFn f ) [static]
Sets the function for encoding Unicode filenames. The
default encodes in the locale-specific 8-bit encoding.
See also encodeName().
void QFile::setName ( const QString & name )
Sets the name of the file. The name can include an
absolute directory path or it can be a name or a path
relative to the current directory.
Do not call this function if the file has already been
opened.
Note that if the name is relative QFile does not associate
it with the current directory. If you change directory
before calling open(), open uses the new current
directory.
Example:
QFile f;
QDir::setCurrent( "/tmp" );
f.setName( "readme.txt" );
QDir::setCurrent( "/home" );
f.open( IO_ReadOnly ); // opens "/home/readme.txt" under UNIX
Also note that the directory separator '/' works for all
operating systems supported by Qt.
See also name(), QFileInfo and QDir.
uint QFile::size () const [virtual]
Returns the file size.
See also at().
Reimplemented from QIODevice.
int QFile::ungetch ( int ch ) [virtual]
Puts the character ch back into the file and decrements
the index if it is not zero.
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operation.
Returns ch, or -1 if some error occurred.
See also getch() and putch().
Reimplemented from QIODevice.
int QFile::writeBlock ( const QByteArray & data )
Reimplemented for internal reasons; the API is not
affected.
int QFile::writeBlock ( const char * p, uint len ) [virtual]
Reimplemented for internal reasons; the API is not
affected.
Writes len bytes from p to the file and returns the number
of bytes actually written.
Returns -1 if a serious error occurred.
Warning: When working with buffered files, data may not be
written to the file at once. Call flush() to make sure the
data is really written.
See also readBlock().
Reimplemented from QIODevice.
SEE ALSO
http://doc.trolltech.com/qfile.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 (qfile.3qt) and
the Qt version (2.3.1).
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