3d971ca9f1
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@36232 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
349 lines
11 KiB
TeX
349 lines
11 KiB
TeX
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%% Name: file.tex
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%% Purpose: wxFile documentation
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%% Author: Vadim Zeitlin
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%% Modified by:
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%% Created: 14.01.02 (extracted from file.tex)
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%% RCS-ID: $Id$
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%% Copyright: (c) Vadim Zeitlin
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%% License: wxWindows license
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section{\class{wxFile}}\label{wxfile}
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A wxFile performs raw file I/O. This is a very small class designed to
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minimize the overhead of using it - in fact, there is hardly any overhead at
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all, but using it brings you automatic error checking and hides differences
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between platforms and compilers. wxFile also automatically closes the file in
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its destructor making it unnecessary to worry about forgetting to do it.
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wxFile is a wrapper around {\tt file descriptor.} - see also
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\helpref{wxFFile}{wxffile} for a wrapper around {\tt FILE} structure.
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{\tt wxFileOffset} is used by the wxFile functions which require offsets as
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parameter or return them. If the platform supports it, wxFileOffset if a typedef
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for a native 64 bit integer, else a 32 bit integer is used for wxFileOffset.
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\wxheading{Derived from}
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None.
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\wxheading{Include files}
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<wx/file.h>
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\wxheading{Constants}
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wx/file.h defines the following constants:
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\begin{verbatim}
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#define wxS_IRUSR 00400
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#define wxS_IWUSR 00200
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#define wxS_IXUSR 00100
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#define wxS_IRGRP 00040
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#define wxS_IWGRP 00020
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#define wxS_IXGRP 00010
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#define wxS_IROTH 00004
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#define wxS_IWOTH 00002
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#define wxS_IXOTH 00001
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// default mode for the new files: corresponds to umask 022
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#define wxS_DEFAULT (wxS_IRUSR | wxS_IWUSR | wxS_IRGRP | wxS_IWGRP | wxS_IROTH | wxS_IWOTH)
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\end{verbatim}
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These constants define the file access rights and are used with
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\helpref{wxFile::Create}{wxfilecreate} and \helpref{wxFile::Open}{wxfileopen}.
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The {\it OpenMode} enumeration defines the different modes for opening a file,
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it is defined inside wxFile class so its members should be specified with {\it wxFile::} scope
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resolution prefix. It is also used with \helpref{wxFile::Access}{wxfileaccess} function.
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\twocolwidtha{7cm}
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\begin{twocollist}\itemsep=0pt%
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\twocolitem{{\bf wxFile::read}}{Open file for reading or test if it can be opened for reading with Access()}
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\twocolitem{{\bf wxFile::write}}{Open file for writing deleting the contents of the file if it already exists
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or test if it can be opened for writing with Access()}
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\twocolitem{{\bf wxFile::read\_write}}{Open file for reading and writing; can not be used with Access()}
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\twocolitem{{\bf wxFile::write\_append}}{Open file for appending: the file is opened for writing, but the old
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contents of the file is not erased and the file pointer is initially placed at the end of the file;
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can not be used with Access(). This is the same as {\bf wxFile::write} if the
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file doesn't exist.}
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\twocolitem{{\bf wxFile::write\_excl}}{Open the file securely for writing (Uses O\_EXCL | O\_CREAT).
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Will fail if the file already exists, else create and open it atomically. Useful for opening temporary files without being vulnerable to race exploits.}
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\end{twocollist}
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Other constants defined elsewhere but used by wxFile functions are wxInvalidOffset which represents an
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invalid value of type {\it wxFileOffset} and is returned by functions returning {\it wxFileOffset} on error and the seek
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mode constants used with \helpref{Seek()}{wxfileseek}:
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\twocolwidtha{7cm}
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\begin{twocollist}\itemsep=0pt%
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\twocolitem{{\bf wxFromStart}}{Count offset from the start of the file}
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\twocolitem{{\bf wxFromCurrent}}{Count offset from the current position of the file pointer}
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\twocolitem{{\bf wxFromEnd}}{Count offset from the end of the file (backwards)}
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\end{twocollist}
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\latexignore{\rtfignore{\wxheading{Members}}}
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\membersection{wxFile::wxFile}\label{wxfilector}
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\func{}{wxFile}{\void}
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Default constructor.
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\func{}{wxFile}{\param{const char*}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}
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Opens a file with the given mode. As there is no way to return whether the
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operation was successful or not from the constructor you should test the
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return value of \helpref{IsOpened}{wxfileisopened} to check that it didn't
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fail.
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\func{}{wxFile}{\param{int}{ fd}}
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Associates the file with the given file descriptor, which has already been opened.
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\wxheading{Parameters}
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\docparam{filename}{The filename.}
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\docparam{mode}{The mode in which to open the file. May be one of {\bf wxFile::read}, {\bf wxFile::write} and {\bf wxFile::read\_write}.}
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\docparam{fd}{An existing file descriptor (see \helpref{Attach()}{wxfileattach} for the list of predefined descriptors)}
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\membersection{wxFile::\destruct{wxFile}}\label{wxfiledtor}
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\func{}{\destruct{wxFile}}{\void}
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Destructor will close the file.
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{\bf NB:} it is not virtual so you should not use wxFile polymorphically.
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\membersection{wxFile::Access}\label{wxfileaccess}
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\func{static bool}{Access}{\param{const char *}{ name}, \param{OpenMode}{ mode}}
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This function verifies if we may access the given file in specified mode. Only
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values of wxFile::read or wxFile::write really make sense here.
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\membersection{wxFile::Attach}\label{wxfileattach}
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\func{void}{Attach}{\param{int}{ fd}}
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Attaches an existing file descriptor to the wxFile object. Example of predefined
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file descriptors are 0, 1 and 2 which correspond to stdin, stdout and stderr (and
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have symbolic names of {\bf wxFile::fd\_stdin}, {\bf wxFile::fd\_stdout} and {\bf wxFile::fd\_stderr}).
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The descriptor should be already opened and it will be closed by wxFile
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object.
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\membersection{wxFile::Close}\label{wxfileclose}
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\func{void}{Close}{\void}
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Closes the file.
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\membersection{wxFile::Create}\label{wxfilecreate}
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\func{bool}{Create}{\param{const char*}{ filename}, \param{bool}{ overwrite = false}, \param{int }{access = wxS\_DEFAULT}}
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Creates a file for writing. If the file already exists, setting {\bf overwrite} to true
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will ensure it is overwritten.
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\membersection{wxFile::Detach}\label{wxfiledetach}
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\func{void}{Detach}{\void}
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Get back a file descriptor from wxFile object - the caller is responsible for closing the file if this
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descriptor is opened. \helpref{IsOpened()}{wxfileisopened} will return false after call to Detach().
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\membersection{wxFile::fd}\label{wxfilefd}
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\constfunc{int}{fd}{\void}
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Returns the file descriptor associated with the file.
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\membersection{wxFile::Eof}\label{wxfileeof}
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\constfunc{bool}{Eof}{\void}
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Returns true if the end of the file has been reached.
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Note that the behaviour of the file pointer based class
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\helpref{wxFFile}{wxffile} is different as \helpref{wxFFile::Eof}{wxffileeof}
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will return true here only if an attempt has been made to read
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{\it past} the last byte of the file, while wxFile::Eof() will return true
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even before such attempt is made if the file pointer is at the last position
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in the file.
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Note also that this function doesn't work on unseekable file descriptors
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(examples include pipes, terminals and sockets under Unix) and an attempt to
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use it will result in an error message in such case. So, to read the entire
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file into memory, you should write a loop which uses
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\helpref{Read}{wxfileread} repeatedly and tests its return condition instead
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of using Eof() as this will not work for special files under Unix.
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\membersection{wxFile::Exists}\label{wxfileexists}
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\func{static bool}{Exists}{\param{const char*}{ filename}}
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Returns true if the given name specifies an existing regular file (not a
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directory or a link)
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\membersection{wxFile::Flush}\label{wxfileflush}
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\func{bool}{Flush}{\void}
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Flushes the file descriptor.
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Note that wxFile::Flush is not implemented on some Windows compilers
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due to a missing fsync function, which reduces the usefulness of this function
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(it can still be called but it will do nothing on unsupported compilers).
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\membersection{wxFile::GetKind}\label{wxfilegetfilekind}
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\constfunc{wxFileKind}{GetKind}{\void}
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Returns the type of the file. Possible return values are:
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\begin{verbatim}
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enum wxFileKind
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{
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wxFILE_KIND_UNKNOWN,
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wxFILE_KIND_DISK, // a file supporting seeking to arbitrary offsets
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wxFILE_KIND_TERMINAL, // a tty
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wxFILE_KIND_PIPE // a pipe
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};
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\end{verbatim}
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\membersection{wxFile::IsOpened}\label{wxfileisopened}
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\constfunc{bool}{IsOpened}{\void}
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Returns true if the file has been opened.
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\membersection{wxFile::Length}\label{wxfilelength}
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\constfunc{wxFileOffset}{Length}{\void}
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Returns the length of the file.
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\membersection{wxFile::Open}\label{wxfileopen}
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\func{bool}{Open}{\param{const char*}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}
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Opens the file, returning true if successful.
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\wxheading{Parameters}
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\docparam{filename}{The filename.}
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\docparam{mode}{The mode in which to open the file. May be one of {\bf wxFile::read}, {\bf wxFile::write} and {\bf wxFile::read\_write}.}
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\membersection{wxFile::Read}\label{wxfileread}
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\func{size\_t}{Read}{\param{void*}{ buffer}, \param{size\_t}{ count}}
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Reads the specified number of bytes into a buffer, returning the actual number read.
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\wxheading{Parameters}
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\docparam{buffer}{A buffer to receive the data.}
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\docparam{count}{The number of bytes to read.}
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\wxheading{Return value}
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The number of bytes read, or the symbol {\bf wxInvalidOffset} (-1) if there was an error.
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\membersection{wxFile::Seek}\label{wxfileseek}
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\func{wxFileOffset}{Seek}{\param{wxFileOffset }{ofs}, \param{wxSeekMode }{mode = wxFromStart}}
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Seeks to the specified position.
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\wxheading{Parameters}
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\docparam{ofs}{Offset to seek to.}
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\docparam{mode}{One of {\bf wxFromStart}, {\bf wxFromEnd}, {\bf wxFromCurrent}.}
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\wxheading{Return value}
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The actual offset position achieved, or wxInvalidOffset on failure.
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\membersection{wxFile::SeekEnd}\label{wxfileseekend}
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\func{wxFileOffset}{SeekEnd}{\param{wxFileOffset }{ofs = 0}}
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Moves the file pointer to the specified number of bytes relative to the end of
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the file. For example, \texttt{SeekEnd($-5$)} would position the pointer $5$
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bytes before the end.
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\wxheading{Parameters}
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\docparam{ofs}{Number of bytes before the end of the file.}
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\wxheading{Return value}
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The actual offset position achieved, or wxInvalidOffset on failure.
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\membersection{wxFile::Tell}\label{wxfiletell}
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\constfunc{wxFileOffset}{Tell}{\void}
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Returns the current position or wxInvalidOffset if file is not opened or if another
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error occurred.
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\membersection{wxFile::Write}\label{wxfilewrite}
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\func{size\_t}{Write}{\param{const void*}{ buffer}, \param{size\_t}{ count}}
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Writes the specified number of bytes from a buffer.
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\wxheading{Parameters}
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\docparam{buffer}{A buffer containing the data.}
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\docparam{count}{The number of bytes to write.}
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\wxheading{Return value}
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the number of bytes actually written
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\membersection{wxFile::Write}\label{wxfilewrites}
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\func{bool}{Write}{\param{const wxString\& }{s}, \param{wxMBConv\&}{ conv = wxConvUTF8}}
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Writes the contents of the string to the file, returns true on success.
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The second argument is only meaningful in Unicode build of wxWidgets when
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{\it conv} is used to convert {\it s} to multibyte representation.
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Note that this method only works with {\tt NUL}-terminated strings, if you want
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to write data with embedded {\tt NUL}s to the file you should use the other
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\helpref{Write() overload}{wxfilewrite}.
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