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 is a typedef
  24 for a native 64 bit integer, otherwise 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{Library}
  35
  36 \helpref{wxBase}{librarieslist}
  37
  38 \wxheading{Constants}
  39
  40 wx/file.h defines the following constants:
  41
  42 \begin{verbatim}
  43 #define wxS_IRUSR 00400
  44 #define wxS_IWUSR 00200
  45 #define wxS_IXUSR 00100
  46
  47 #define wxS_IRGRP 00040
  48 #define wxS_IWGRP 00020
  49 #define wxS_IXGRP 00010
  50
  51 #define wxS_IROTH 00004
  52 #define wxS_IWOTH 00002
  53 #define wxS_IXOTH 00001
  54
  55 // default mode for the new files: corresponds to umask 022
  56 #define wxS_DEFAULT  (wxS_IRUSR | wxS_IWUSR | wxS_IRGRP | wxS_IWGRP | wxS_IROTH | wxS_IWOTH)
  57 \end{verbatim}
  58
  59 These constants define the file access rights and are used with
  60 \helpref{wxFile::Create}{wxfilecreate} and \helpref{wxFile::Open}{wxfileopen}.
  61
  62 The {\it OpenMode} enumeration defines the different modes for opening a file,
  63 it is defined inside wxFile class so its members should be specified with {\it wxFile::} scope
  64 resolution prefix. It is also used with \helpref{wxFile::Access}{wxfileaccess} function.
  65
  66 \twocolwidtha{7cm}
  67 \begin{twocollist}\itemsep=0pt%
  68 \twocolitem{{\bf wxFile::read}}{Open file for reading or test if it can be opened for reading with Access()}
  69 \twocolitem{{\bf wxFile::write}}{Open file for writing deleting the contents of the file if it already exists
  70 or test if it can be opened for writing with Access()}
  71 \twocolitem{{\bf wxFile::read\_write}}{Open file for reading and writing; can not be used with Access()}
  72 \twocolitem{{\bf wxFile::write\_append}}{Open file for appending: the file is opened for writing, but the old
  73 contents of the file is not erased and the file pointer is initially placed at the end of the file;
  74 can not be used with Access(). This is the same as {\bf wxFile::write} if the
  75 file doesn't exist.}
  76 \twocolitem{{\bf wxFile::write\_excl}}{Open the file securely for writing (Uses O\_EXCL | O\_CREAT).
  77 Will fail if the file already exists, else create and open it atomically.  Useful for opening temporary files without being vulnerable to race exploits.}
  78 \end{twocollist}
  79
  80 Other constants defined elsewhere but used by wxFile functions are wxInvalidOffset which represents an
  81 invalid value of type {\it wxFileOffset} and is returned by functions returning {\it wxFileOffset} on error and the seek
  82 mode constants used with \helpref{Seek()}{wxfileseek}:
  83
  84 \twocolwidtha{7cm}
  85 \begin{twocollist}\itemsep=0pt%
  86 \twocolitem{{\bf wxFromStart}}{Count offset from the start of the file}
  87 \twocolitem{{\bf wxFromCurrent}}{Count offset from the current position of the file pointer}
  88 \twocolitem{{\bf wxFromEnd}}{Count offset from the end of the file (backwards)}
  89 \end{twocollist}
  90
  91 \latexignore{\rtfignore{\wxheading{Members}}}
  92
  93
  94 \membersection{wxFile::wxFile}\label{wxfilector}
  95
  96 \func{}{wxFile}{\void}
  97
  98 Default constructor.
  99
 100 \func{}{wxFile}{\param{const wxString\&}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}
 101
 102 Opens a file with the given mode. As there is no way to return whether the
 103 operation was successful or not from the constructor you should test the
 104 return value of \helpref{IsOpened}{wxfileisopened} to check that it didn't
 105 fail.
 106
 107 \func{}{wxFile}{\param{int}{ fd}}
 108
 109 Associates the file with the given file descriptor, which has already been opened.
 110
 111 \wxheading{Parameters}
 112
 113 \docparam{filename}{The filename.}
 114
 115 \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}.}
 116
 117 \docparam{fd}{An existing file descriptor (see \helpref{Attach()}{wxfileattach} for the list of predefined descriptors)}
 118
 119
 120 \membersection{wxFile::\destruct{wxFile}}\label{wxfiledtor}
 121
 122 \func{}{\destruct{wxFile}}{\void}
 123
 124 Destructor will close the file.
 125
 126 {\bf NB:} it is not virtual so you should not use wxFile polymorphically.
 127
 128
 129 \membersection{wxFile::Access}\label{wxfileaccess}
 130
 131 \func{static bool}{Access}{\param{const wxString\&}{ name}, \param{OpenMode}{ mode}}
 132
 133 This function verifies if we may access the given file in specified mode. Only
 134 values of wxFile::read or wxFile::write really make sense here.
 135
 136
 137 \membersection{wxFile::Attach}\label{wxfileattach}
 138
 139 \func{void}{Attach}{\param{int}{ fd}}
 140
 141 Attaches an existing file descriptor to the wxFile object. Example of predefined
 142 file descriptors are 0, 1 and 2 which correspond to stdin, stdout and stderr (and
 143 have symbolic names of {\bf wxFile::fd\_stdin}, {\bf wxFile::fd\_stdout} and {\bf wxFile::fd\_stderr}).
 144
 145 The descriptor should be already opened and it will be closed by wxFile
 146 object.
 147
 148
 149 \membersection{wxFile::Close}\label{wxfileclose}
 150
 151 \func{void}{Close}{\void}
 152
 153 Closes the file.
 154
 155
 156 \membersection{wxFile::Create}\label{wxfilecreate}
 157
 158 \func{bool}{Create}{\param{const wxString\&}{ filename}, \param{bool}{ overwrite = false}, \param{int }{access = wxS\_DEFAULT}}
 159
 160 Creates a file for writing. If the file already exists, setting {\bf overwrite} to true
 161 will ensure it is overwritten.
 162
 163
 164 \membersection{wxFile::Detach}\label{wxfiledetach}
 165
 166 \func{void}{Detach}{\void}
 167
 168 Get back a file descriptor from wxFile object - the caller is responsible for closing the file if this
 169 descriptor is opened. \helpref{IsOpened()}{wxfileisopened} will return false after call to Detach().
 170
 171
 172 \membersection{wxFile::fd}\label{wxfilefd}
 173
 174 \constfunc{int}{fd}{\void}
 175
 176 Returns the file descriptor associated with the file.
 177
 178
 179 \membersection{wxFile::Eof}\label{wxfileeof}
 180
 181 \constfunc{bool}{Eof}{\void}
 182
 183 Returns true if the end of the file has been reached.
 184
 185 Note that the behaviour of the file pointer based class
 186 \helpref{wxFFile}{wxffile} is different as \helpref{wxFFile::Eof}{wxffileeof}
 187 will return true here only if an attempt has been made to read
 188 {\it past} the last byte of the file, while wxFile::Eof() will return true
 189 even before such attempt is made if the file pointer is at the last position
 190 in the file.
 191
 192 Note also that this function doesn't work on unseekable file descriptors
 193 (examples include pipes, terminals and sockets under Unix) and an attempt to
 194 use it will result in an error message in such case. So, to read the entire
 195 file into memory, you should write a loop which uses
 196 \helpref{Read}{wxfileread} repeatedly and tests its return condition instead
 197 of using Eof() as this will not work for special files under Unix.
 198
 199
 200 \membersection{wxFile::Exists}\label{wxfileexists}
 201
 202 \func{static bool}{Exists}{\param{const wxString\&}{ filename}}
 203
 204 Returns true if the given name specifies an existing regular file (not a
 205 directory or a link)
 206
 207
 208 \membersection{wxFile::Flush}\label{wxfileflush}
 209
 210 \func{bool}{Flush}{\void}
 211
 212 Flushes the file descriptor.
 213
 214 Note that wxFile::Flush is not implemented on some Windows compilers
 215 due to a missing fsync function, which reduces the usefulness of this function
 216 (it can still be called but it will do nothing on unsupported compilers).
 217
 218
 219 \membersection{wxFile::GetKind}\label{wxfilegetfilekind}
 220
 221 \constfunc{wxFileKind}{GetKind}{\void}
 222
 223 Returns the type of the file. Possible return values are:
 224
 225 \begin{verbatim}
 226 enum wxFileKind
 227 {
 228   wxFILE_KIND_UNKNOWN,
 229   wxFILE_KIND_DISK,     // a file supporting seeking to arbitrary offsets
 230   wxFILE_KIND_TERMINAL, // a tty
 231   wxFILE_KIND_PIPE      // a pipe
 232 };
 233
 234 \end{verbatim}
 235
 236
 237 \membersection{wxFile::IsOpened}\label{wxfileisopened}
 238
 239 \constfunc{bool}{IsOpened}{\void}
 240
 241 Returns true if the file has been opened.
 242
 243
 244 \membersection{wxFile::Length}\label{wxfilelength}
 245
 246 \constfunc{wxFileOffset}{Length}{\void}
 247
 248 Returns the length of the file.
 249
 250
 251 \membersection{wxFile::Open}\label{wxfileopen}
 252
 253 \func{bool}{Open}{\param{const wxString\&}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}
 254
 255 Opens the file, returning true if successful.
 256
 257 \wxheading{Parameters}
 258
 259 \docparam{filename}{The filename.}
 260
 261 \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}.}
 262
 263
 264 \membersection{wxFile::Read}\label{wxfileread}
 265
 266 \func{size\_t}{Read}{\param{void*}{ buffer}, \param{size\_t}{ count}}
 267
 268 Reads the specified number of bytes into a buffer, returning the actual number read.
 269
 270 \wxheading{Parameters}
 271
 272 \docparam{buffer}{A buffer to receive the data.}
 273
 274 \docparam{count}{The number of bytes to read.}
 275
 276 \wxheading{Return value}
 277
 278 The number of bytes read, or the symbol {\bf wxInvalidOffset} (-1) if there was an error.
 279
 280
 281 \membersection{wxFile::Seek}\label{wxfileseek}
 282
 283 \func{wxFileOffset}{Seek}{\param{wxFileOffset }{ofs}, \param{wxSeekMode }{mode = wxFromStart}}
 284
 285 Seeks to the specified position.
 286
 287 \wxheading{Parameters}
 288
 289 \docparam{ofs}{Offset to seek to.}
 290
 291 \docparam{mode}{One of {\bf wxFromStart}, {\bf wxFromEnd}, {\bf wxFromCurrent}.}
 292
 293 \wxheading{Return value}
 294
 295 The actual offset position achieved, or wxInvalidOffset on failure.
 296
 297
 298 \membersection{wxFile::SeekEnd}\label{wxfileseekend}
 299
 300 \func{wxFileOffset}{SeekEnd}{\param{wxFileOffset }{ofs = 0}}
 301
 302 Moves the file pointer to the specified number of bytes relative to the end of
 303 the file. For example, \texttt{SeekEnd($-5$)} would position the pointer $5$
 304 bytes before the end.
 305
 306 \wxheading{Parameters}
 307
 308 \docparam{ofs}{Number of bytes before the end of the file.}
 309
 310 \wxheading{Return value}
 311
 312 The actual offset position achieved, or wxInvalidOffset on failure.
 313
 314
 315 \membersection{wxFile::Tell}\label{wxfiletell}
 316
 317 \constfunc{wxFileOffset}{Tell}{\void}
 318
 319 Returns the current position or wxInvalidOffset if file is not opened or if another
 320 error occurred.
 321
 322
 323 \membersection{wxFile::Write}\label{wxfilewrite}
 324
 325 \func{size\_t}{Write}{\param{const void*}{ buffer}, \param{size\_t}{ count}}
 326
 327 Writes the specified number of bytes from a buffer.
 328
 329 \wxheading{Parameters}
 330
 331 \docparam{buffer}{A buffer containing the data.}
 332
 333 \docparam{count}{The number of bytes to write.}
 334
 335 \wxheading{Return value}
 336
 337 the number of bytes actually written
 338
 339
 340 \membersection{wxFile::Write}\label{wxfilewrites}
 341
 342 \func{bool}{Write}{\param{const wxString\& }{s}, \param{const wxMBConv\&}{ conv = wxConvUTF8}}
 343
 344 Writes the contents of the string to the file, returns true on success.
 345
 346 The second argument is only meaningful in Unicode build of wxWidgets when
 347 {\it conv} is used to convert {\it s} to multibyte representation.
 348
 349 Note that this method only works with {\tt NUL}-terminated strings, if you want
 350 to write data with embedded {\tt NUL}s to the file you should use the other
 351 \helpref{Write() overload}{wxfilewrite}.
 352