docs/latex/wx/file.tex

   1 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   2 %% Name:        file.tex
   3 %% Purpose:     wxFile documentation
   4 %% Author:      Vadim Zeitlin
   5 %% Modified by:
   6 %% Created:     14.01.02 (extracted from file.tex)
   7 %% RCS-ID:      $Id$
   8 %% Copyright:   (c) Vadim Zeitlin
   9 %% License:     wxWidgets license
  10 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  11
  12 \section{\class{wxFile}}\label{wxfile}
  13
  14 A wxFile performs raw file I/O. This is a very small class designed to
  15 minimize the overhead of using it - in fact, there is hardly any overhead at
  16 all, but using it brings you automatic error checking and hides differences
  17 between platforms and compilers. wxFile also automatically closes the file in
  18 its destructor making it unnecessary to worry about forgetting to do it.
  19 wxFile is a wrapper around {\tt file descriptor.} - see also
  20 \helpref{wxFFile}{wxffile} for a wrapper around {\tt FILE} structure.
  21
  22 \wxheading{Derived from}
  23
  24 None.
  25
  26 \wxheading{Include files}
  27
  28 <wx/file.h>
  29
  30 \wxheading{Constants}
  31
  32 wx/file.h defines the following constants:
  33
  34 \begin{verbatim}
  35 #define wxS_IRUSR 00400
  36 #define wxS_IWUSR 00200
  37 #define wxS_IXUSR 00100
  38
  39 #define wxS_IRGRP 00040
  40 #define wxS_IWGRP 00020
  41 #define wxS_IXGRP 00010
  42
  43 #define wxS_IROTH 00004
  44 #define wxS_IWOTH 00002
  45 #define wxS_IXOTH 00001
  46
  47 // default mode for the new files: corresponds to umask 022
  48 #define wxS_DEFAULT  (wxS_IRUSR | wxS_IWUSR | wxS_IRGRP | wxS_IWGRP | wxS_IROTH | wxS_IWOTH)
  49 \end{verbatim}
  50
  51 These constants define the file access rights and are used with
  52 \helpref{wxFile::Create}{wxfilecreate} and \helpref{wxFile::Open}{wxfileopen}.
  53
  54 The {\it OpenMode} enumeration defines the different modes for opening a file,
  55 it is defined inside wxFile class so its members should be specified with {\it wxFile::} scope
  56 resolution prefix. It is also used with \helpref{wxFile::Access}{wxfileaccess} function.
  57
  58 \twocolwidtha{7cm}
  59 \begin{twocollist}\itemsep=0pt%
  60 \twocolitem{{\bf wxFile::read}}{Open file for reading or test if it can be opened for reading with Access()}
  61 \twocolitem{{\bf wxFile::write}}{Open file for writing deleting the contents of the file if it already exists
  62 or test if it can be opened for writing with Access()}
  63 \twocolitem{{\bf wxFile::read\_write}}{Open file for reading and writing; can not be used with Access()}
  64 \twocolitem{{\bf wxFile::write\_append}}{Open file for appending: the file is opened for writing, but the old
  65 contents of the file is not erased and the file pointer is initially placed at the end of the file;
  66 can not be used with Access(). This is the same as {\bf wxFile::write} if the
  67 file doesn't exist.}
  68 \twocolitem{{\bf wxFile::write\_excl}}{Open the file securely for writing (Uses O\_EXCL | O\_CREAT).
  69 Will fail if the file already exists, else create and open it atomically.  Useful for opening temporary files without being vulnerable to race exploits.}
  70 \end{twocollist}
  71
  72 Other constants defined elsewhere but used by wxFile functions are wxInvalidOffset which represents an
  73 invalid value of type {\it off\_t} and is returned by functions returning {\it off\_t} on error and the seek
  74 mode constants used with \helpref{Seek()}{wxfileseek}:
  75
  76 \twocolwidtha{7cm}
  77 \begin{twocollist}\itemsep=0pt%
  78 \twocolitem{{\bf wxFromStart}}{Count offset from the start of the file}
  79 \twocolitem{{\bf wxFromCurrent}}{Count offset from the current position of the file pointer}
  80 \twocolitem{{\bf wxFromEnd}}{Count offset from the end of the file (backwards)}
  81 \end{twocollist}
  82
  83 \latexignore{\rtfignore{\wxheading{Members}}}
  84
  85 \membersection{wxFile::wxFile}\label{wxfileconstr}
  86
  87 \func{}{wxFile}{\void}
  88
  89 Default constructor.
  90
  91 \func{}{wxFile}{\param{const char*}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}
  92
  93 Opens a file with the given mode. As there is no way to return whether the
  94 operation was successful or not from the constructor you should test the
  95 return value of \helpref{IsOpened}{wxfileisopened} to check that it didn't
  96 fail.
  97
  98 \func{}{wxFile}{\param{int}{ fd}}
  99
 100 Associates the file with the given file descriptor, which has already been opened.
 101
 102 \wxheading{Parameters}
 103
 104 \docparam{filename}{The filename.}
 105
 106 \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}.}
 107
 108 \docparam{fd}{An existing file descriptor (see \helpref{Attach()}{wxfileattach} for the list of predefined descriptors)}
 109
 110 \membersection{wxFile::\destruct{wxFile}}
 111
 112 \func{}{\destruct{wxFile}}{\void}
 113
 114 Destructor will close the file.
 115
 116 {\bf NB:} it is not virtual so you should not use wxFile polymorphically.
 117
 118 \membersection{wxFile::Access}\label{wxfileaccess}
 119
 120 \func{static bool}{Access}{\param{const char *}{ name}, \param{OpenMode}{ mode}}
 121
 122 This function verifies if we may access the given file in specified mode. Only
 123 values of wxFile::read or wxFile::write really make sense here.
 124
 125 \membersection{wxFile::Attach}\label{wxfileattach}
 126
 127 \func{void}{Attach}{\param{int}{ fd}}
 128
 129 Attaches an existing file descriptor to the wxFile object. Example of predefined
 130 file descriptors are 0, 1 and 2 which correspond to stdin, stdout and stderr (and
 131 have symbolic names of {\bf wxFile::fd\_stdin}, {\bf wxFile::fd\_stdout} and {\bf wxFile::fd\_stderr}).
 132
 133 The descriptor should be already opened and it will be closed by wxFile
 134 object.
 135
 136 \membersection{wxFile::Close}\label{wxfileclose}
 137
 138 \func{void}{Close}{\void}
 139
 140 Closes the file.
 141
 142 \membersection{wxFile::Create}\label{wxfilecreate}
 143
 144 \func{bool}{Create}{\param{const char*}{ filename}, \param{bool}{ overwrite = false}, \param{int }{access = wxS\_DEFAULT}}
 145
 146 Creates a file for writing. If the file already exists, setting {\bf overwrite} to true
 147 will ensure it is overwritten.
 148
 149 \membersection{wxFile::Detach}\label{wxfiledetach}
 150
 151 \func{void}{Detach}{\void}
 152
 153 Get back a file descriptor from wxFile object - the caller is responsible for closing the file if this
 154 descriptor is opened. \helpref{IsOpened()}{wxfileisopened} will return false after call to Detach().
 155
 156 \membersection{wxFile::fd}\label{wxfilefd}
 157
 158 \constfunc{int}{fd}{\void}
 159
 160 Returns the file descriptor associated with the file.
 161
 162 \membersection{wxFile::Eof}\label{wxfileeof}
 163
 164 \constfunc{bool}{Eof}{\void}
 165
 166 Returns true if the end of the file has been reached.
 167
 168 Note that the behaviour of the file pointer based class
 169 \helpref{wxFFile}{wxffile} is different as \helpref{wxFFile::Eof}{wxffileeof}
 170 will return true here only if an attempt has been made to read
 171 {\it past} the last byte of the file, while wxFile::Eof() will return true
 172 even before such attempt is made if the file pointer is at the last position
 173 in the file.
 174
 175 Note also that this function doesn't work on unseekable file descriptors
 176 (examples include pipes, terminals and sockets under Unix) and an attempt to
 177 use it will result in an error message in such case. So, to read the entire
 178 file into memory, you should write a loop which uses
 179 \helpref{Read}{wxfileread} repeatedly and tests its return condition instead
 180 of using Eof() as this will not work for special files under Unix.
 181
 182 \membersection{wxFile::Exists}\label{wxfileexists}
 183
 184 \func{static bool}{Exists}{\param{const char*}{ filename}}
 185
 186 Returns true if the given name specifies an existing regular file (not a
 187 directory or a link)
 188
 189 \membersection{wxFile::Flush}\label{wxfileflush}
 190
 191 \func{bool}{Flush}{\void}
 192
 193 Flushes the file descriptor.
 194
 195 Note that wxFile::Flush is not implemented on some Windows compilers
 196 due to a missing fsync function, which reduces the usefulness of this function
 197 (it can still be called but it will do nothing on unsupported compilers).
 198
 199 \membersection{wxFile::IsOpened}\label{wxfileisopened}
 200
 201 \constfunc{bool}{IsOpened}{\void}
 202
 203 Returns true if the file has been opened.
 204
 205 \membersection{wxFile::Length}\label{wxfilelength}
 206
 207 \constfunc{off\_t}{Length}{\void}
 208
 209 Returns the length of the file.
 210
 211 \membersection{wxFile::Open}\label{wxfileopen}
 212
 213 \func{bool}{Open}{\param{const char*}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}
 214
 215 Opens the file, returning true if successful.
 216
 217 \wxheading{Parameters}
 218
 219 \docparam{filename}{The filename.}
 220
 221 \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}.}
 222
 223 \membersection{wxFile::Read}\label{wxfileread}
 224
 225 \func{off\_t}{Read}{\param{void*}{ buffer}, \param{off\_t}{ count}}
 226
 227 Reads the specified number of bytes into a buffer, returning the actual number read.
 228
 229 \wxheading{Parameters}
 230
 231 \docparam{buffer}{A buffer to receive the data.}
 232
 233 \docparam{count}{The number of bytes to read.}
 234
 235 \wxheading{Return value}
 236
 237 The number of bytes read, or the symbol {\bf wxInvalidOffset} (-1) if there was an error.
 238
 239 \membersection{wxFile::Seek}\label{wxfileseek}
 240
 241 \func{off\_t}{Seek}{\param{off\_t }{ofs}, \param{wxSeekMode }{mode = wxFromStart}}
 242
 243 Seeks to the specified position.
 244
 245 \wxheading{Parameters}
 246
 247 \docparam{ofs}{Offset to seek to.}
 248
 249 \docparam{mode}{One of {\bf wxFromStart}, {\bf wxFromEnd}, {\bf wxFromCurrent}.}
 250
 251 \wxheading{Return value}
 252
 253 The actual offset position achieved, or wxInvalidOffset on failure.
 254
 255 \membersection{wxFile::SeekEnd}\label{wxfileseekend}
 256
 257 \func{off\_t}{SeekEnd}{\param{off\_t }{ofs = 0}}
 258
 259 Moves the file pointer to the specified number of bytes before the end of the file.
 260
 261 \wxheading{Parameters}
 262
 263 \docparam{ofs}{Number of bytes before the end of the file.}
 264
 265 \wxheading{Return value}
 266
 267 The actual offset position achieved, or wxInvalidOffset on failure.
 268
 269 \membersection{wxFile::Tell}\label{wxfiletell}
 270
 271 \constfunc{off\_t}{Tell}{\void}
 272
 273 Returns the current position or wxInvalidOffset if file is not opened or if another
 274 error occurred.
 275
 276 \membersection{wxFile::Write}\label{wxfilewrite}
 277
 278 \func{size\_t}{Write}{\param{const void*}{ buffer}, \param{off\_t}{ count}}
 279
 280 Writes the specified number of bytes from a buffer.
 281
 282 \wxheading{Parameters}
 283
 284 \docparam{buffer}{A buffer containing the data.}
 285
 286 \docparam{count}{The number of bytes to write.}
 287
 288 \wxheading{Return value}
 289
 290 the number of bytes actually written
 291
 292 \membersection{wxFile::Write}\label{wxfilewrites}
 293
 294 \func{bool}{Write}{\param{const wxString\& }{s}, \param{wxMBConv\&}{ conv = wxConvUTF8}}
 295
 296 Writes the contents of the string to the file, returns true on success.
 297
 298 The second argument is only meaningful in Unicode build of wxWidgets when
 299 {\it conv} is used to convert {\it s} to multibyte representation.
 300
 301 Note that this method only works with {\tt NUL}-terminated strings, if you want
 302 to write data with embedded {\tt NUL}s to the file you should use the other
 303 \helpref{Write() overload}{wxfilewrite}.
 304