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[wxWidgets.git] / docs / latex / wx / file.tex

\section{\class{wxFile}}\label{wxfile}

A wxFile performs raw file I/O. This is a very small class designed to
minimize the overhead of using it - in fact, there is hardly any overhead at
all, but using it brings you automatic error checking and hides differences
between platforms and compilers.

\wxheading{Derived from}

None.

\wxheading{Include files}

<wx/file.h>

\wxheading{Constants}

wx/file.h defines the following constants:

{\small
\begin{verbatim}
#define wxS_IRUSR 00400
#define wxS_IWUSR 00200
#define wxS_IXUSR 00100

#define wxS_IRGRP 00040
#define wxS_IWGRP 00020
#define wxS_IXGRP 00010

#define wxS_IROTH 00004
#define wxS_IWOTH 00002
#define wxS_IXOTH 00001

// default mode for the new files: corresponds to umask 022
#define wxS_DEFAULT  (wxS_IRUSR | wxS_IWUSR | wxS_IRGRP | wxS_IWGRP | wxS_IROTH | wxS_IWOTH)
\end{verbatim}
}

These constants define the file access rights and are used with 
\helpref{wxFile::Create}{wxfilecreate} and \helpref{wxFile::Open}{wxfileopen}.

The {\it OpenMode} enumeration defines the different modes for opening a file,
it's defined inside wxFile class so its members should be specified with {\it wxFile::} scope
resolution prefix. It is also used with \helpref{wxFile::Access}{wxfileaccess} function.

\twocolwidtha{7cm}
\begin{twocollist}\itemsep=0pt%
\twocolitem{{\bf wxFile::read}}{Open file for reading or test if it can be opened for reading with Access()}
\twocolitem{{\bf wxFile::write}}{Open file for writing deleting the contents of the file if it already exists
or test if it can be opened for writing with Access()}
\twocolitem{{\bf wxFile::read\_write}}{Open file for reading and writing; can not be used with Access()}
\twocolitem{{\bf wxFile::write\_append}}{Open file for appending: the file is opened for writing, but the old
contents of the file is not erased and the file pointer is initially placed at the end of the file;
can not be used with Access()}
\end{twocollist}

Other constants defined elsewhere but used by wxFile functions are wxInvalidOffset which represents an
invalid value of type {\it off\_t} and is returned by functions returning {\it off\_t} on error and the seek
mode constants used with \helpref{Seek()}{wxfileseek}:

\twocolwidtha{7cm}
\begin{twocollist}\itemsep=0pt%
\twocolitem{{\bf wxFromStart}}{Count offset from the start of the file}
\twocolitem{{\bf wxFromCurrent}}{Count offset from the current position of the file pointer}
\twocolitem{{\bf wxFromEnd}}{Count offset from the end of the file (backwards)}
\end{twocollist}

\latexignore{\rtfignore{\wxheading{Members}}}

\membersection{wxFile::wxFile}\label{wxfileconstr}

\func{}{wxFile}{\void}

Default constructor.

\func{}{wxFile}{\param{const char*}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}

Opens a file with the given mode. As there is no way to return whether the
operation was successful or not from the constructor you should test the
return value of \helpref{IsOpened}{wxfileisopened} to check that it didn't
fail.

\func{}{wxFile}{\param{int}{ fd}}

Opens a file with the given file descriptor, which has already been opened.

\wxheading{Parameters}

\docparam{filename}{The filename.}

\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}.}

\docparam{fd}{An existing file descriptor (see \helpref{Attach()}{wxfileattach} for the list of predefined descriptors)}

\membersection{wxFile::\destruct{wxFile}}

\func{}{\destruct{wxFile}}{\void}

Destructor will close the file.

NB: it is not virtual so you should {\it not} derive from wxFile!

\membersection{wxFile::Access}\label{wxfileaccess}

\func{static bool}{Access}{\param{const char *}{ name}, \param{OpenMode}{ mode}}

This function verifies if we may access the given file in specified mode. Only
values of wxFile::read or wxFile::write really make sense here.

\membersection{wxFile::Attach}\label{wxfileattach}

\func{void}{Attach}{\param{int}{ fd}}

Attaches an existing file descriptor to the wxFile object. Example of predefined
file descriptors are 0, 1 and 2 which correspond to stdin, stdout and stderr (and
have symbolic names of wxFile::fd\_stdin, wxFile::fd\_stdout and wxFile::fd\_stderr).

The descriptor should be already opened and it will be closed by wxFile
object.

\membersection{wxFile::Close}\label{wxfileclose}

\func{void}{Close}{\void}

Closes the file.

\membersection{wxFile::Create}\label{wxfilecreate}

\func{bool}{Create}{\param{const char*}{ filename}, \param{bool}{ overwrite = FALSE}, \param{int }{access = wxS\_DEFAULT}}

Creates a file for writing. If the file already exists, setting {\bf overwrite} to TRUE
will ensure it is overwritten.

\membersection{wxFile::Detach}\label{wxfiledetach}

\func{void}{Detach}{\void}

Get back a file descriptor from wxFile object - the caller is responsible for closing the file if this
descriptor is opened. \helpref{IsOpened()}{wxfileisopened} will return FALSE after call to Detach().

\membersection{wxFile::fd}\label{wxfilefd}

\constfunc{int}{fd}{\void}

Returns the file descriptor associated with the file.

\membersection{wxFile::Eof}\label{wxfileeof}

\constfunc{bool}{Eof}{\void}

Returns TRUE if the end of the file has been reached.

\membersection{wxFile::Exists}\label{wxfileexists}

\func{static bool}{Exists}{\param{const char*}{ filename}}

Returns TRUE if the given name specifies an existing regular file.

\membersection{wxFile::Flush}\label{wxfileflush}

\func{bool}{Flush}{\void}

Flushes the file descriptor.

Note that wxFile::Flush is not implemented on some Windows compilers
due to a missing fsync function, which reduces the usefulness of this function
(it can still be called but it will do nothing on unsupported compilers).

\membersection{wxFile::IsOpened}\label{wxfileisopened}

\constfunc{bool}{IsOpened}{\void}

Returns TRUE if the file has been opened.

\membersection{wxFile::Length}\label{wxfilelength}

\constfunc{off\_t}{Length}{\void}

Returns the length of the file.

\membersection{wxFile::Open}\label{wxfileopen}

\func{bool}{Open}{\param{const char*}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}

Opens the file, returning TRUE if successful.

\wxheading{Parameters}

\docparam{filename}{The filename.}

\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}.}

\membersection{wxFile::Read}\label{wxfileread}

\func{off\_t}{Read}{\param{void*}{ buffer}, \param{off\_t}{ count}}

Reads the specified number of bytes into a buffer, returning the actual number read.

\wxheading{Parameters}

\docparam{buffer}{A buffer to receive the data.}

\docparam{count}{The number of bytes to read.}

\wxheading{Return value}

The number of bytes read, or the symbol {\bf wxInvalidOffset} (-1) if there was an error.

\membersection{wxFile::Seek}\label{wxfileseek}

\func{off\_t}{Seek}{\param{off\_t }{ofs}, \param{wxFile::SeekMode }{mode = wxFile::FromStart}}

Seeks to the specified position.

\wxheading{Parameters}

\docparam{ofs}{Offset to seek to.}

\docparam{mode}{One of {\bf wxFile::FromStart}, {\bf wxFile::FromEnd}, {\bf wxFile::FromCurrent}.}

\wxheading{Return value}

The actual offset position achieved, or wxInvalidOffset on failure.

\membersection{wxFile::SeekEnd}\label{wxfileseekend}

\func{off\_t}{SeekEnd}{\param{off\_t }{ofs = 0}}

Moves the file pointer to the specified number of bytes before the end of the file.

\wxheading{Parameters}

\docparam{ofs}{Number of bytes before the end of the file.}

\wxheading{Return value}

The actual offset position achieved, or wxInvalidOffset on failure.

\membersection{wxFile::Tell}\label{wxfiletell}

\constfunc{off\_t}{Tell}{\void}

Returns the current position or wxInvalidOffset if file is not opened or if another
error occured.

\membersection{wxFile::Write}\label{wxfilewrite}

\func{bool}{Write}{\param{const void*}{ buffer}, \param{off\_t}{ count}}

Writes the specified number of bytes from a buffer.

\wxheading{Parameters}

\docparam{buffer}{A buffer containing the data.}

\docparam{count}{The number of bytes to write.}

\wxheading{Return value}

TRUE if the operation was successful.

\membersection{wxFile::Write}\label{wxfilewrites}

\func{bool}{Write}{\param{const wxString\& }{s}}

Writes the contents of the string to the file, returns TRUE on success.