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 \membersection{wxFile::wxFile}\label{wxfilector}
  90
  91 \func{}{wxFile}{\void}
  92
  93 Default constructor.
  94
  95 \func{}{wxFile}{\param{const char*}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}
  96
  97 Opens a file with the given mode. As there is no way to return whether the
  98 operation was successful or not from the constructor you should test the
  99 return value of \helpref{IsOpened}{wxfileisopened} to check that it didn't
 100 fail.
 101
 102 \func{}{wxFile}{\param{int}{ fd}}
 103
 104 Associates the file with the given file descriptor, which has already been opened.
 105
 106 \wxheading{Parameters}
 107
 108 \docparam{filename}{The filename.}
 109
 110 \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}.}
 111
 112 \docparam{fd}{An existing file descriptor (see \helpref{Attach()}{wxfileattach} for the list of predefined descriptors)}
 113
 114 \membersection{wxFile::\destruct{wxFile}}\label{wxfiledtor}
 115
 116 \func{}{\destruct{wxFile}}{\void}
 117
 118 Destructor will close the file.
 119
 120 {\bf NB:} it is not virtual so you should not use wxFile polymorphically.
 121
 122 \membersection{wxFile::Access}\label{wxfileaccess}
 123
 124 \func{static bool}{Access}{\param{const char *}{ name}, \param{OpenMode}{ mode}}
 125
 126 This function verifies if we may access the given file in specified mode. Only
 127 values of wxFile::read or wxFile::write really make sense here.
 128
 129 \membersection{wxFile::Attach}\label{wxfileattach}
 130
 131 \func{void}{Attach}{\param{int}{ fd}}
 132
 133 Attaches an existing file descriptor to the wxFile object. Example of predefined
 134 file descriptors are 0, 1 and 2 which correspond to stdin, stdout and stderr (and
 135 have symbolic names of {\bf wxFile::fd\_stdin}, {\bf wxFile::fd\_stdout} and {\bf wxFile::fd\_stderr}).
 136
 137 The descriptor should be already opened and it will be closed by wxFile
 138 object.
 139
 140 \membersection{wxFile::Close}\label{wxfileclose}
 141
 142 \func{void}{Close}{\void}
 143
 144 Closes the file.
 145
 146 \membersection{wxFile::Create}\label{wxfilecreate}
 147
 148 \func{bool}{Create}{\param{const char*}{ filename}, \param{bool}{ overwrite = false}, \param{int }{access = wxS\_DEFAULT}}
 149
 150 Creates a file for writing. If the file already exists, setting {\bf overwrite} to true
 151 will ensure it is overwritten.
 152
 153 \membersection{wxFile::Detach}\label{wxfiledetach}
 154
 155 \func{void}{Detach}{\void}
 156
 157 Get back a file descriptor from wxFile object - the caller is responsible for closing the file if this
 158 descriptor is opened. \helpref{IsOpened()}{wxfileisopened} will return false after call to Detach().
 159
 160 \membersection{wxFile::fd}\label{wxfilefd}
 161
 162 \constfunc{int}{fd}{\void}
 163
 164 Returns the file descriptor associated with the file.
 165
 166 \membersection{wxFile::Eof}\label{wxfileeof}
 167
 168 \constfunc{bool}{Eof}{\void}
 169
 170 Returns true if the end of the file has been reached.
 171
 172 Note that the behaviour of the file pointer based class
 173 \helpref{wxFFile}{wxffile} is different as \helpref{wxFFile::Eof}{wxffileeof}
 174 will return true here only if an attempt has been made to read
 175 {\it past} the last byte of the file, while wxFile::Eof() will return true
 176 even before such attempt is made if the file pointer is at the last position
 177 in the file.
 178
 179 Note also that this function doesn't work on unseekable file descriptors
 180 (examples include pipes, terminals and sockets under Unix) and an attempt to
 181 use it will result in an error message in such case. So, to read the entire
 182 file into memory, you should write a loop which uses
 183 \helpref{Read}{wxfileread} repeatedly and tests its return condition instead
 184 of using Eof() as this will not work for special files under Unix.
 185
 186 \membersection{wxFile::Exists}\label{wxfileexists}
 187
 188 \func{static bool}{Exists}{\param{const char*}{ filename}}
 189
 190 Returns true if the given name specifies an existing regular file (not a
 191 directory or a link)
 192
 193 \membersection{wxFile::Flush}\label{wxfileflush}
 194
 195 \func{bool}{Flush}{\void}
 196
 197 Flushes the file descriptor.
 198
 199 Note that wxFile::Flush is not implemented on some Windows compilers
 200 due to a missing fsync function, which reduces the usefulness of this function
 201 (it can still be called but it will do nothing on unsupported compilers).
 202
 203 \membersection{wxFile::GetKind}\label{wxfilegetfilekind}
 204
 205 \constfunc{wxFileKind}{GetKind}{\void}
 206
 207 Returns the type of the file. Possible return values are:
 208
 209 \begin{verbatim}
 210 enum wxFileKind
 211 {
 212   wxFILE_KIND_UNKNOWN,
 213   wxFILE_KIND_DISK,     // a file supporting seeking to arbitrary offsets
 214   wxFILE_KIND_TERMINAL, // a tty
 215   wxFILE_KIND_PIPE      // a pipe
 216 };
 217
 218 \end{verbatim}
 219
 220 \membersection{wxFile::IsOpened}\label{wxfileisopened}
 221
 222 \constfunc{bool}{IsOpened}{\void}
 223
 224 Returns true if the file has been opened.
 225
 226 \membersection{wxFile::Length}\label{wxfilelength}
 227
 228 \constfunc{wxFileOffset}{Length}{\void}
 229
 230 Returns the length of the file.
 231
 232 \membersection{wxFile::Open}\label{wxfileopen}
 233
 234 \func{bool}{Open}{\param{const char*}{ filename}, \param{wxFile::OpenMode}{ mode = wxFile::read}}
 235
 236 Opens the file, returning true if successful.
 237
 238 \wxheading{Parameters}
 239
 240 \docparam{filename}{The filename.}
 241
 242 \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}.}
 243
 244 \membersection{wxFile::Read}\label{wxfileread}
 245
 246 \func{size\_t}{Read}{\param{void*}{ buffer}, \param{size\_t}{ count}}
 247
 248 Reads the specified number of bytes into a buffer, returning the actual number read.
 249
 250 \wxheading{Parameters}
 251
 252 \docparam{buffer}{A buffer to receive the data.}
 253
 254 \docparam{count}{The number of bytes to read.}
 255
 256 \wxheading{Return value}
 257
 258 The number of bytes read, or the symbol {\bf wxInvalidOffset} (-1) if there was an error.
 259
 260 \membersection{wxFile::Seek}\label{wxfileseek}
 261
 262 \func{wxFileOffset}{Seek}{\param{wxFileOffset }{ofs}, \param{wxSeekMode }{mode = wxFromStart}}
 263
 264 Seeks to the specified position.
 265
 266 \wxheading{Parameters}
 267
 268 \docparam{ofs}{Offset to seek to.}
 269
 270 \docparam{mode}{One of {\bf wxFromStart}, {\bf wxFromEnd}, {\bf wxFromCurrent}.}
 271
 272 \wxheading{Return value}
 273
 274 The actual offset position achieved, or wxInvalidOffset on failure.
 275
 276 \membersection{wxFile::SeekEnd}\label{wxfileseekend}
 277
 278 \func{wxFileOffset}{SeekEnd}{\param{wxFileOffset }{ofs = 0}}
 279
 280 Moves the file pointer to the specified number of bytes before the end of the file.
 281
 282 \wxheading{Parameters}
 283
 284 \docparam{ofs}{Number of bytes before the end of the file.}
 285
 286 \wxheading{Return value}
 287
 288 The actual offset position achieved, or wxInvalidOffset on failure.
 289
 290 \membersection{wxFile::Tell}\label{wxfiletell}
 291
 292 \constfunc{wxFileOffset}{Tell}{\void}
 293
 294 Returns the current position or wxInvalidOffset if file is not opened or if another
 295 error occurred.
 296
 297 \membersection{wxFile::Write}\label{wxfilewrite}
 298
 299 \func{size\_t}{Write}{\param{const void*}{ buffer}, \param{wxFileOffset}{ count}}
 300
 301 Writes the specified number of bytes from a buffer.
 302
 303 \wxheading{Parameters}
 304
 305 \docparam{buffer}{A buffer containing the data.}
 306
 307 \docparam{count}{The number of bytes to write.}
 308
 309 \wxheading{Return value}
 310
 311 the number of bytes actually written
 312
 313 \membersection{wxFile::Write}\label{wxfilewrites}
 314
 315 \func{bool}{Write}{\param{const wxString\& }{s}, \param{wxMBConv\&}{ conv = wxConvUTF8}}
 316
 317 Writes the contents of the string to the file, returns true on success.
 318
 319 The second argument is only meaningful in Unicode build of wxWidgets when
 320 {\it conv} is used to convert {\it s} to multibyte representation.
 321
 322 Note that this method only works with {\tt NUL}-terminated strings, if you want
 323 to write data with embedded {\tt NUL}s to the file you should use the other
 324 \helpref{Write() overload}{wxfilewrite}.
 325