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:     wxWindows 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 {\tt wxFileOffset} is used by the wxFile functions which require offsets as
  23 parameter or return them. If the platform supports it, wxFileOffset if a typedef
  24 for a native 64 bit integer, else a 32 bit integer is used for wxFileOffset.
  25
  26 \wxheading{Derived from}
  27
  28 None.
  29
  30 \wxheading{Include files}
  31
  32 <wx/file.h>
  33
  34 \wxheading{Constants}
  35
  36 wx/file.h defines the following constants:
  37
  38 \begin{verbatim}
  39 #define wxS_IRUSR 00400
  40 #define wxS_IWUSR 00200
  41 #define wxS_IXUSR 00100
  42
  43 #define wxS_IRGRP 00040
  44 #define wxS_IWGRP 00020
  45 #define wxS_IXGRP 00010
  46
  47 #define wxS_IROTH 00004
  48 #define wxS_IWOTH 00002
  49 #define wxS_IXOTH 00001
  50
  51 // default mode for the new files: corresponds to umask 022
  52 #define wxS_DEFAULT  (wxS_IRUSR | wxS_IWUSR | wxS_IRGRP | wxS_IWGRP | wxS_IROTH | wxS_IWOTH)
  53 \end{verbatim}
  54
  55 These constants define the file access rights and are used with
  56 \helpref{wxFile::Create}{wxfilecreate} and \helpref{wxFile::Open}{wxfileopen}.
  57
  58 The {\it OpenMode} enumeration defines the different modes for opening a file,
  59 it is defined inside wxFile class so its members should be specified with {\it wxFile::} scope
  60 resolution prefix. It is also used with \helpref{wxFile::Access}{wxfileaccess} function.
  61
  62 \twocolwidtha{7cm}
  63 \begin{twocollist}\itemsep=0pt%
  64 \twocolitem{{\bf wxFile::read}}{Open file for reading or test if it can be opened for reading with Access()}
  65 \twocolitem{{\bf wxFile::write}}{Open file for writing deleting the contents of the file if it already exists
  66 or test if it can be opened for writing with Access()}
  67 \twocolitem{{\bf wxFile::read\_write}}{Open file for reading and writing; can not be used with Access()}
  68 \twocolitem{{\bf wxFile::write\_append}}{Open file for appending: the file is opened for writing, but the old
  69 contents of the file is not erased and the file pointer is initially placed at the end of the file;
  70 can not be used with Access(). This is the same as {\bf wxFile::write} if the
  71 file doesn't exist.}
  72 \twocolitem{{\bf wxFile::write\_excl}}{Open the file securely for writing (Uses O\_EXCL | O\_CREAT).
  73 Will fail if the file already exists, else create and open it atomically.  Useful for opening temporary files without being vulnerable to race exploits.}
  74 \end{twocollist}
  75
  76 Other constants defined elsewhere but used by wxFile functions are wxInvalidOffset which represents an
  77 invalid value of type {\it wxFileOffset} and is returned by functions returning {\it wxFileOffset} on error and the seek
  78 mode constants used with \helpref{Seek()}{wxfileseek}:
  79
  80 \twocolwidtha{7cm}
  81 \begin{twocollist}\itemsep=0pt%
  82 \twocolitem{{\bf wxFromStart}}{Count offset from the start of the file}
  83 \twocolitem{{\bf wxFromCurrent}}{Count offset from the current position of the file pointer}
  84 \twocolitem{{\bf wxFromEnd}}{Count offset from the end of the file (backwards)}
  85 \end{twocollist}
  86
  87 \latexignore{\rtfignore{\wxheading{Members}}}
  88
  89
  90 \membersection{wxFile::wxFile}\label{wxfilector}
  91
  92 \func{}{wxFile}{\void}
  93
  94 Default constructor.
  95
  96 \func{}{wxFile}{\param{const char*}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}
  97
  98 Opens a file with the given mode. As there is no way to return whether the
  99 operation was successful or not from the constructor you should test the
 100 return value of \helpref{IsOpened}{wxfileisopened} to check that it didn't
 101 fail.
 102
 103 \func{}{wxFile}{\param{int}{ fd}}
 104
 105 Associates the file with the given file descriptor, which has already been opened.
 106
 107 \wxheading{Parameters}
 108
 109 \docparam{filename}{The filename.}
 110
 111 \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}.}
 112
 113 \docparam{fd}{An existing file descriptor (see \helpref{Attach()}{wxfileattach} for the list of predefined descriptors)}
 114
 115
 116 \membersection{wxFile::\destruct{wxFile}}\label{wxfiledtor}
 117
 118 \func{}{\destruct{wxFile}}{\void}
 119
 120 Destructor will close the file.
 121
 122 {\bf NB:} it is not virtual so you should not use wxFile polymorphically.
 123
 124
 125 \membersection{wxFile::Access}\label{wxfileaccess}
 126
 127 \func{static bool}{Access}{\param{const char *}{ name}, \param{OpenMode}{ mode}}
 128
 129 This function verifies if we may access the given file in specified mode. Only
 130 values of wxFile::read or wxFile::write really make sense here.
 131
 132
 133 \membersection{wxFile::Attach}\label{wxfileattach}
 134
 135 \func{void}{Attach}{\param{int}{ fd}}
 136
 137 Attaches an existing file descriptor to the wxFile object. Example of predefined
 138 file descriptors are 0, 1 and 2 which correspond to stdin, stdout and stderr (and
 139 have symbolic names of {\bf wxFile::fd\_stdin}, {\bf wxFile::fd\_stdout} and {\bf wxFile::fd\_stderr}).
 140
 141 The descriptor should be already opened and it will be closed by wxFile
 142 object.
 143
 144
 145 \membersection{wxFile::Close}\label{wxfileclose}
 146
 147 \func{void}{Close}{\void}
 148
 149 Closes the file.
 150
 151
 152 \membersection{wxFile::Create}\label{wxfilecreate}
 153
 154 \func{bool}{Create}{\param{const char*}{ filename}, \param{bool}{ overwrite = false}, \param{int }{access = wxS\_DEFAULT}}
 155
 156 Creates a file for writing. If the file already exists, setting {\bf overwrite} to true
 157 will ensure it is overwritten.
 158
 159
 160 \membersection{wxFile::Detach}\label{wxfiledetach}
 161
 162 \func{void}{Detach}{\void}
 163
 164 Get back a file descriptor from wxFile object - the caller is responsible for closing the file if this
 165 descriptor is opened. \helpref{IsOpened()}{wxfileisopened} will return false after call to Detach().
 166
 167
 168 \membersection{wxFile::fd}\label{wxfilefd}
 169
 170 \constfunc{int}{fd}{\void}
 171
 172 Returns the file descriptor associated with the file.
 173
 174
 175 \membersection{wxFile::Eof}\label{wxfileeof}
 176
 177 \constfunc{bool}{Eof}{\void}
 178
 179 Returns true if the end of the file has been reached.
 180
 181 Note that the behaviour of the file pointer based class
 182 \helpref{wxFFile}{wxffile} is different as \helpref{wxFFile::Eof}{wxffileeof}
 183 will return true here only if an attempt has been made to read
 184 {\it past} the last byte of the file, while wxFile::Eof() will return true
 185 even before such attempt is made if the file pointer is at the last position
 186 in the file.
 187
 188 Note also that this function doesn't work on unseekable file descriptors
 189 (examples include pipes, terminals and sockets under Unix) and an attempt to
 190 use it will result in an error message in such case. So, to read the entire
 191 file into memory, you should write a loop which uses
 192 \helpref{Read}{wxfileread} repeatedly and tests its return condition instead
 193 of using Eof() as this will not work for special files under Unix.
 194
 195
 196 \membersection{wxFile::Exists}\label{wxfileexists}
 197
 198 \func{static bool}{Exists}{\param{const char*}{ filename}}
 199
 200 Returns true if the given name specifies an existing regular file (not a
 201 directory or a link)
 202
 203
 204 \membersection{wxFile::Flush}\label{wxfileflush}
 205
 206 \func{bool}{Flush}{\void}
 207
 208 Flushes the file descriptor.
 209
 210 Note that wxFile::Flush is not implemented on some Windows compilers
 211 due to a missing fsync function, which reduces the usefulness of this function
 212 (it can still be called but it will do nothing on unsupported compilers).
 213
 214
 215 \membersection{wxFile::GetKind}\label{wxfilegetfilekind}
 216
 217 \constfunc{wxFileKind}{GetKind}{\void}
 218
 219 Returns the type of the file. Possible return values are:
 220
 221 \begin{verbatim}
 222 enum wxFileKind
 223 {
 224   wxFILE_KIND_UNKNOWN,
 225   wxFILE_KIND_DISK,     // a file supporting seeking to arbitrary offsets
 226   wxFILE_KIND_TERMINAL, // a tty
 227   wxFILE_KIND_PIPE      // a pipe
 228 };
 229
 230 \end{verbatim}
 231
 232
 233 \membersection{wxFile::IsOpened}\label{wxfileisopened}
 234
 235 \constfunc{bool}{IsOpened}{\void}
 236
 237 Returns true if the file has been opened.
 238
 239
 240 \membersection{wxFile::Length}\label{wxfilelength}
 241
 242 \constfunc{wxFileOffset}{Length}{\void}
 243
 244 Returns the length of the file.
 245
 246
 247 \membersection{wxFile::Open}\label{wxfileopen}
 248
 249 \func{bool}{Open}{\param{const char*}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}
 250
 251 Opens the file, returning true if successful.
 252
 253 \wxheading{Parameters}
 254
 255 \docparam{filename}{The filename.}
 256
 257 \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}.}
 258
 259
 260 \membersection{wxFile::Read}\label{wxfileread}
 261
 262 \func{size\_t}{Read}{\param{void*}{ buffer}, \param{size\_t}{ count}}
 263
 264 Reads the specified number of bytes into a buffer, returning the actual number read.
 265
 266 \wxheading{Parameters}
 267
 268 \docparam{buffer}{A buffer to receive the data.}
 269
 270 \docparam{count}{The number of bytes to read.}
 271
 272 \wxheading{Return value}
 273
 274 The number of bytes read, or the symbol {\bf wxInvalidOffset} (-1) if there was an error.
 275
 276
 277 \membersection{wxFile::Seek}\label{wxfileseek}
 278
 279 \func{wxFileOffset}{Seek}{\param{wxFileOffset }{ofs}, \param{wxSeekMode }{mode = wxFromStart}}
 280
 281 Seeks to the specified position.
 282
 283 \wxheading{Parameters}
 284
 285 \docparam{ofs}{Offset to seek to.}
 286
 287 \docparam{mode}{One of {\bf wxFromStart}, {\bf wxFromEnd}, {\bf wxFromCurrent}.}
 288
 289 \wxheading{Return value}
 290
 291 The actual offset position achieved, or wxInvalidOffset on failure.
 292
 293
 294 \membersection{wxFile::SeekEnd}\label{wxfileseekend}
 295
 296 \func{wxFileOffset}{SeekEnd}{\param{wxFileOffset }{ofs = 0}}
 297
 298 Moves the file pointer to the specified number of bytes relative to the end of
 299 the file. For example, \texttt{SeekEnd($-5$)} would position the pointer $5$
 300 bytes before the end.
 301
 302 \wxheading{Parameters}
 303
 304 \docparam{ofs}{Number of bytes before the end of the file.}
 305
 306 \wxheading{Return value}
 307
 308 The actual offset position achieved, or wxInvalidOffset on failure.
 309
 310
 311 \membersection{wxFile::Tell}\label{wxfiletell}
 312
 313 \constfunc{wxFileOffset}{Tell}{\void}
 314
 315 Returns the current position or wxInvalidOffset if file is not opened or if another
 316 error occurred.
 317
 318
 319 \membersection{wxFile::Write}\label{wxfilewrite}
 320
 321 \func{size\_t}{Write}{\param{const void*}{ buffer}, \param{size\_t}{ count}}
 322
 323 Writes the specified number of bytes from a buffer.
 324
 325 \wxheading{Parameters}
 326
 327 \docparam{buffer}{A buffer containing the data.}
 328
 329 \docparam{count}{The number of bytes to write.}
 330
 331 \wxheading{Return value}
 332
 333 the number of bytes actually written
 334
 335
 336 \membersection{wxFile::Write}\label{wxfilewrites}
 337
 338 \func{bool}{Write}{\param{const wxString\& }{s}, \param{wxMBConv\&}{ conv = wxConvUTF8}}
 339
 340 Writes the contents of the string to the file, returns true on success.
 341
 342 The second argument is only meaningful in Unicode build of wxWidgets when
 343 {\it conv} is used to convert {\it s} to multibyte representation.
 344
 345 Note that this method only works with {\tt NUL}-terminated strings, if you want
 346 to write data with embedded {\tt NUL}s to the file you should use the other
 347 \helpref{Write() overload}{wxfilewrite}.
 348