qfile.3qt

linux下GUI编程工具qt的在线连接帮助手册

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
.PP
Returns TRUE if this file exists; otherwise returns FALSE.
.PP
See also name().
.SH "void QFile::flush ()\fC [virtual]\fR"
Flushes the file buffer to the disk.
.PP
close() also flushes the file buffer.
.PP
Reimplemented from QIODevice.
.SH "int QFile::getch ()\fC [virtual]\fR"
Reads a single byte/character from the file.
.PP
Returns the byte/character read, or -1 if the end of the file has been reached.
.PP
See also putch() and ungetch().
.PP
Reimplemented from QIODevice.
.SH "int QFile::handle () const"
Returns the file handle of the file.
.PP
This is a small positive integer, suitable for use with C library functions such as fdopen() and fcntl(), as well as with QSocketNotifier.
.PP
If the file is not open or there is an error, handle() returns -1.
.PP
See also QSocketNotifier.
.SH "QString QFile::name () const"
Returns the name set by setName().
.PP
See also setName() and QFileInfo::fileName().
.SH "bool QFile::open ( int m )\fC [virtual]\fR"
Opens the file specified by the file name currently set, using the mode \fIm\fR. Returns TRUE if successful, otherwise FALSE.
.PP

.PP
The mode parameter \fIm\fR must be a combination of the following flags:
.TP
IO_Raw specified raw (non-buffered) file access.
.TP
IO_ReadOnly opens the file in read-only mode.
.TP
IO_WriteOnly opens the file in write-only mode (and truncates).
.TP
IO_ReadWrite opens the file in read/write mode, equivalent to \fC(IO_ReadOnly | IO_WriteOnly)\fR.
.TP
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.
.TP
IO_Truncate truncates the file.
.TP
IO_Translate enables carriage returns and linefeed translation for text files under MS-DOS, Windows and OS/2.
.PP
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.
.PP
\fBImportant:\fR 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.
.PP
\fBWarning:\fR 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.
.PP
If the file does not exist and IO_WriteOnly or IO_ReadWrite is specified, it is created.
.PP
Example:
.PP
.nf
.br
    QFile f1( "/tmp/data.bin" );
.br
    QFile f2( "readme.txt" );
.br
    f1.open( IO_Raw | IO_ReadWrite | IO_Append );
.br
    f2.open( IO_ReadOnly | IO_Translate );
.br
.fi
.PP
See also name(), close(), isOpen() and flush().
.PP
Examples:
.)l action/application.cpp, application/application.cpp, helpviewer/helpwindow.cpp, mdi/application.cpp, qdir/qdir.cpp, qwerty/qwerty.cpp and xml/outliner/outlinetree.cpp.
.PP
Reimplemented from QIODevice.
.SH "bool QFile::open ( int m, FILE * f )"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
.PP
Opens a file in the mode \fIm\fR using an existing file handle \fIf\fR. Returns TRUE if successful, otherwise FALSE.
.PP
Example:
.PP
.nf
.br
    #include <stdio.h>
.br
.br
    void printError( const char* msg )
.br
    {
.br
        QFile f;
.br
        f.open( IO_WriteOnly, stderr );
.br
        f.writeBlock( msg, qstrlen(msg) );      // write to stderr
.br
        f.close();
.br
    }
.br
.fi
.PP
When a QFile is opened using this function, close() does not actually close the file, only flushes it.
.PP
\fBWarning:\fR If \fIf\fR is \fCstdin\fR, \fCstdout\fR, \fCstderr\fR, you may not be able to seek. See QIODevice::isSequentialAccess() for more information.
.PP
See also close().
.SH "bool QFile::open ( int m, int f )"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
.PP
Opens a file in the mode \fIm\fR using an existing file descriptor \fIf\fR. Returns TRUE if successful, otherwise FALSE.
.PP
When a QFile is opened using this function, close() does not actually close the file.
.PP
The QFile that is opened using this function, is automatically set to be in raw mode; this means that the file input/output functions are slow. If you run into performance issues, you should try to use one of the other open functions.
.PP
\fBWarning:\fR If \fIf\fR is one of 0 (stdin), 1 (stdout) or 2 (stderr), you may not be able to seek. size() is set to \fCINT_MAX\fR (in limits.h).
.PP
See also close().
.SH "int QFile::putch ( int ch )\fC [virtual]\fR"
Writes the character \fIch\fR to the file.
.PP
Returns \fIch\fR, or -1 if some error occurred.
.PP
See also getch() and ungetch().
.PP
Reimplemented from QIODevice.
.SH "QByteArray QIODevice::readAll ()\fC [virtual]\fR"
This convenience function returns all of the remaining data in the device.
.SH "Q_LONG QFile::readBlock ( char * p, Q_ULONG len )\fC [virtual]\fR"
Reads at most \fIlen\fR bytes from the file into \fIp\fR and returns the number of bytes actually read.
.PP
Returns -1 if a serious error occurred.
.PP
\fBWarning:\fR 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.
.PP
See also writeBlock().
.PP
Example: qwerty/qwerty.cpp.
.PP
Reimplemented from QIODevice.
.SH "Q_LONG QFile::readLine ( char * p, Q_ULONG maxlen )\fC [virtual]\fR"
Reads a line of text.
.PP
Reads bytes from the file into the char* \fIp\fR, until end-of-line or \fImaxlen\fR bytes have been read, whichever occurs first. Returns the number of bytes read, or -1 if there was an error. The terminating newline is not stripped.
.PP
This function is efficient only for buffered files. Avoid readLine() for files that have been opened with the IO_Raw flag.
.PP
See also readBlock() and QTextStream::readLine().
.PP
Reimplemented from QIODevice.
.SH "Q_LONG QFile::readLine ( QString & s, Q_ULONG maxlen )"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
.PP
Reads a line of text.
.PP
Reads bytes from the file into string \fIs\fR, until end-of-line or \fImaxlen\fR bytes have been read, whichever occurs first. Returns the number of bytes read, or -1 if there was an error.g. end of file. The terminating newline is not stripped.
.PP
This function is efficient only for buffered files. Avoid readLine() for files that have been opened with the IO_Raw flag.
.PP
Note that the string is read as plain Latin1 bytes, not Unicode.
.PP
See also readBlock() and QTextStream::readLine().
.SH "bool QFile::remove ()"
Removes the file specified by the file name currently set. Returns TRUE if successful; otherwise returns FALSE.
.PP
The file is closed before it is removed.
.SH "bool QFile::remove ( const QString & fileName )\fC [static]\fR"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
.PP
Removes the file \fIfileName\fR. Returns TRUE if successful, otherwise FALSE.
.SH "void QFile::setDecodingFunction ( DecoderFn f )\fC [static]\fR"
Sets the function for decoding 8-bit file names to \fIf\fR. The default uses the locale-specific 8-bit encoding.
.PP
See also encodeName() and decodeName().
.SH "void QFile::setEncodingFunction ( EncoderFn f )\fC [static]\fR"
Sets the function for encoding Unicode file names to \fIf\fR. The default encodes in the locale-specific 8-bit encoding.
.PP
See also encodeName().
.SH "void QFile::setName ( const QString & name )"
Sets the name of the file to \fIname\fR. The name may have no path, a relative path or an absolute absolute directory path.
.PP
Do not call this function if the file has already been opened.
.PP
If the file name has no path or a relative path, the path used will be whatever the application's current directory path is \fIat the time of the open()\fR call.
.PP
Example:
.PP
.nf
.br
     QFile f;
.br
     QDir::setCurrent( "/tmp" );
.br
     f.setName( "readme.txt" );
.br
     QDir::setCurrent( "/home" );
.br
     f.open( IO_ReadOnly );        // opens "/home/readme.txt" under Unix
.br
.fi
.PP
Note that the directory separator "/" works for all operating systems supported by Qt.
.PP
See also name(), QFileInfo and QDir.
.SH "Offset QFile::size () const\fC [virtual]\fR"
Returns the file size.
.PP
See also at().
.PP
Reimplemented from QIODevice.
.SH "int QFile::ungetch ( int ch )\fC [virtual]\fR"
Puts the character \fIch\fR back into the file and decrements the index if it is not zero.
.PP
This function is normally called to "undo" a getch() operation.
.PP
Returns \fIch\fR, or -1 if some error occurred.
.PP
See also getch() and putch().
.PP
Reimplemented from QIODevice.

.SH "SEE ALSO"
.BR http://doc.trolltech.com/qfile.html
.BR http://www.trolltech.com/faq/tech.html
.SH COPYRIGHT
Copyright 1992-2001 Trolltech AS, http://www.trolltech.com.  See the
license file included in the distribution for a complete license
statement.
.SH AUTHOR
Generated automatically from the source code.
.SH BUGS
If you find a bug in Qt, please report it as described in
.BR http://doc.trolltech.com/bughowto.html .
Good bug reports help us to help you. Thank you.
.P
The definitive Qt documentation is provided in HTML format; it is
located at $QTDIR/doc/html and can be read using Qt Assistant or with
a web browser. This man page is provided as a convenience for those
users who prefer man pages, although this format is not officially
supported by Trolltech. 
.P
If you find errors in this manual page, please report them to
.BR [e-mail] .
Please include the name of the manual page (qfile.3qt) and the Qt
version (3.0.0).