interface/wx/file.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        file.h
   3 // Purpose:     interface of wxTempFile, wxFile
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9
  10 /**
  11     We redefine these constants here because S_IREAD &c are _not_ standard.
  12     However, we do assume that the values correspond to the Unix umask bits.
  13 */
  14 enum wxPosixPermissions
  15 {
  16     /// standard Posix names for these permission flags
  17     //@{
  18     wxS_IRUSR = 00400,
  19     wxS_IWUSR = 00200,
  20     wxS_IXUSR = 00100,
  21
  22     wxS_IRGRP = 00040,
  23     wxS_IWGRP = 00020,
  24     wxS_IXGRP = 00010,
  25
  26     wxS_IROTH = 00004,
  27     wxS_IWOTH = 00002,
  28     wxS_IXOTH = 00001,
  29     //@}
  30
  31     /// longer but more readable synonims for the constants above
  32     //@{
  33     wxPOSIX_USER_READ = wxS_IRUSR,
  34     wxPOSIX_USER_WRITE = wxS_IWUSR,
  35     wxPOSIX_USER_EXECUTE = wxS_IXUSR,
  36
  37     wxPOSIX_GROUP_READ = wxS_IRGRP,
  38     wxPOSIX_GROUP_WRITE = wxS_IWGRP,
  39     wxPOSIX_GROUP_EXECUTE = wxS_IXGRP,
  40
  41     wxPOSIX_OTHERS_READ = wxS_IROTH,
  42     wxPOSIX_OTHERS_WRITE = wxS_IWOTH,
  43     wxPOSIX_OTHERS_EXECUTE = wxS_IXOTH,
  44     //@}
  45
  46     /// Default mode for the new files: allow reading/writing them to everybody but
  47     /// the effective file mode will be set after ANDing this value with umask and
  48     /// so won't include wxS_IW{GRP,OTH} for the default 022 umask value
  49     wxS_DEFAULT = (wxPOSIX_USER_READ | wxPOSIX_USER_WRITE | \
  50                    wxPOSIX_GROUP_READ | wxPOSIX_GROUP_WRITE | \
  51                    wxPOSIX_OTHERS_READ | wxPOSIX_OTHERS_WRITE),
  52
  53     /// Default mode for the new directories (see wxFileName::Mkdir): allow
  54     /// reading/writing/executing them to everybody, but just like wxS_DEFAULT
  55     /// the effective directory mode will be set after ANDing this value with umask
  56     wxS_DIR_DEFAULT = (wxPOSIX_USER_READ | wxPOSIX_USER_WRITE | wxPOSIX_USER_EXECUTE | \
  57                        wxPOSIX_GROUP_READ | wxPOSIX_GROUP_WRITE | wxPOSIX_GROUP_EXECUTE | \
  58                        wxPOSIX_OTHERS_READ | wxPOSIX_OTHERS_WRITE | wxPOSIX_OTHERS_EXECUTE)
  59 };
  60
  61
  62
  63 /**
  64     @class wxTempFile
  65
  66     wxTempFile provides a relatively safe way to replace the contents of the
  67     existing file. The name is explained by the fact that it may be also used as
  68     just a temporary file if you don't replace the old file contents.
  69
  70     Usually, when a program replaces the contents of some file it first opens it for
  71     writing, thus losing all of the old data and then starts recreating it.
  72     This approach is not very safe because during the regeneration of the file bad
  73     things may happen: the program may find that there is an internal error preventing
  74     it from completing file generation, the user may interrupt it (especially if file
  75     generation takes long time) and, finally, any other external interrupts (power
  76     supply failure or a disk error) will leave you without either the original file
  77     or the new one.
  78
  79     wxTempFile addresses this problem by creating a temporary file which is meant to
  80     replace the original file - but only after it is fully written. So, if the user
  81     interrupts the program during the file generation, the old file won't be lost.
  82     Also, if the program discovers itself that it doesn't want to replace the old
  83     file there is no problem - in fact, wxTempFile will @b not replace the old
  84     file by default, you should explicitly call wxTempFile::Commit() to do it.
  85     Calling wxTempFile::Discard() explicitly discards any modifications: it
  86     closes and deletes the temporary file and leaves the original file unchanged.
  87     If you call neither Commit() nor Discard(), the destructor will
  88     call Discard() automatically.
  89
  90     To summarize: if you want to replace another file, create an instance of
  91     wxTempFile passing the name of the file to be replaced to the constructor.
  92     (You may also use default constructor and pass the file name to wxTempFile::Open.)
  93     Then you can write to wxTempFile using wxFile-like functions and later call
  94     wxTempFile::Commit() to replace the old file (and close this one) or call
  95     wxTempFile::Discard() to cancel the modifications.
  96
  97     @library{wxbase}
  98     @category{file}
  99 */
 100 class wxTempFile
 101 {
 102 public:
 103     /**
 104         Associates wxTempFile with the file to be replaced and opens it.
 105         You should use IsOpened() to verify that the constructor succeeded.
 106     */
 107     wxTempFile(const wxString& strName);
 108
 109     /**
 110         Destructor calls Discard() if temporary file is still open.
 111     */
 112     ~wxTempFile();
 113
 114     /**
 115         Validate changes: deletes the old file of name m_strName and renames the new
 116         file to the old name. Returns @true if both actions succeeded.
 117
 118         If @false is returned it may unfortunately mean two quite different things:
 119         either that the old file couldn't be deleted or that the new file
 120         couldn't be renamed to the old name.
 121     */
 122     bool Commit();
 123
 124     /**
 125         Discard changes: the old file contents are not changed, the temporary
 126         file is deleted.
 127     */
 128     void Discard();
 129
 130     /**
 131         Returns @true if the file was successfully opened.
 132     */
 133     bool IsOpened() const;
 134
 135     /**
 136         Returns the length of the file.
 137
 138         This method may return wxInvalidOffset if the length couldn't be
 139         determined or 0 even for non-empty files if the file is not seekable.
 140
 141         In general, the only way to determine if the file for which this function
 142         returns 0 is really empty or not is to try reading from it.
 143     */
 144     wxFileOffset Length() const;
 145
 146     /**
 147         Open the temporary file, returns @true on success, @false if an error
 148         occurred.
 149         @a strName is the name of file to be replaced. The temporary file is always
 150         created in the directory where @a strName is. In particular, if @a strName
 151         doesn't include the path, it is created in the current directory and the
 152         program should have write access to it for the function to succeed.
 153     */
 154     bool Open(const wxString& strName);
 155
 156     /**
 157         Seeks to the specified position.
 158     */
 159     wxFileOffset Seek(wxFileOffset ofs,
 160                       wxSeekMode mode = wxFromStart);
 161
 162     /**
 163         Returns the current position or wxInvalidOffset if file is not opened or
 164         if another error occurred.
 165     */
 166     wxFileOffset Tell() const;
 167
 168     /**
 169         Write to the file, return @true on success, @false on failure.
 170         The second argument is only meaningful in Unicode build of wxWidgets when
 171         @a conv is used to convert @a str to multibyte representation.
 172     */
 173     bool Write(const wxString& str,
 174                const wxMBConv& conv = wxConvUTF8);
 175 };
 176
 177
 178
 179 /**
 180     @class wxFile
 181
 182     A wxFile performs raw file I/O. This is a very small class designed to
 183     minimize the overhead of using it - in fact, there is hardly any overhead at
 184     all, but using it brings you automatic error checking and hides differences
 185     between platforms and compilers. wxFile also automatically closes the file in
 186     its destructor so you won't forget to do so.
 187     wxFile is a wrapper around @c file descriptor. - see also wxFFile for a
 188     wrapper around @c FILE structure.
 189
 190     ::wxFileOffset is used by the wxFile functions which require offsets as
 191     parameter or return them. If the platform supports it, wxFileOffset is a
 192     typedef for a native 64 bit integer, otherwise a 32 bit integer is used for
 193     ::wxFileOffset.
 194
 195     @library{wxbase}
 196     @category{file}
 197 */
 198 class wxFile
 199 {
 200 public:
 201
 202     /**
 203         The OpenMode enumeration defines the different modes for opening a file with wxFile.
 204         It is also used with wxFile::Access function.
 205     */
 206     enum OpenMode {
 207
 208         /** Open file for reading or test if it can be opened for reading with Access() */
 209         read,
 210
 211         /** Open file for writing deleting the contents of the file if it already exists
 212             or test if it can be opened for writing with Access(). */
 213         write,
 214
 215         /** Open file for reading and writing; can not be used with Access() */
 216         read_write,
 217
 218         /** Open file for appending: the file is opened for writing, but the old contents
 219             of the file are not erased and the file pointer is initially placed at the end
 220             of the file; can not be used with Access().
 221
 222             This is the same as OpenMode::write if the file doesn't exist.
 223         */
 224         write_append,
 225
 226         /**
 227             Open the file securely for writing (Uses O_EXCL | O_CREAT).
 228             Will fail if the file already exists, else create and open it atomically.
 229             Useful for opening temporary files without being vulnerable to race exploits.
 230         */
 231         write_excl
 232     };
 233
 234     /**
 235        Standard file descriptors
 236     */
 237     enum { fd_invalid = -1, fd_stdin, fd_stdout, fd_stderr };
 238
 239     /**
 240        Default constructor.
 241     */
 242     wxFile();
 243
 244     /**
 245         Opens a file with a filename.
 246
 247         @param filename
 248             The filename.
 249         @param mode
 250             The mode in which to open the file.
 251     */
 252     wxFile(const wxString& filename,
 253            wxFile::OpenMode mode = wxFile::read);
 254
 255     /**
 256         Associates the file with the given file descriptor, which has already been
 257         opened. See Attach() for the list of predefined descriptors.
 258
 259         @param fd
 260             An existing file descriptor.
 261     */
 262     wxFile(int fd);
 263
 264     /**
 265         Destructor will close the file.
 266         @note This destructor is not virtual so you should not use wxFile polymorphically.
 267     */
 268     ~wxFile();
 269
 270     /**
 271         This function verifies if we may access the given file in specified mode.
 272         Only values of @c wxFile::read or @c wxFile::write really make sense here.
 273     */
 274     static bool Access(const wxString& name, wxFile::OpenMode mode);
 275
 276     /**
 277         Attaches an existing file descriptor to the wxFile object.
 278         Examples of predefined file descriptors are 0, 1 and 2 which correspond to
 279         stdin, stdout and stderr (and have symbolic names of @c wxFile::fd_stdin,
 280         @c wxFile::fd_stdout and @c wxFile::fd_stderr).
 281
 282         The descriptor should be already opened and it will be closed by wxFile
 283         object.
 284     */
 285     void Attach(int fd);
 286
 287     /**
 288         Closes the file.
 289     */
 290     bool Close();
 291
 292     /**
 293         Creates a file for writing.
 294
 295         If the file already exists, setting @b overwrite to @true will ensure
 296         it is overwritten.
 297
 298         @a access may be an OR combination of the ::wxPosixPermissions enumeration
 299         values.
 300     */
 301     bool Create(const wxString& filename,
 302                 bool overwrite = false,
 303                 int access = wxS_DEFAULT);
 304
 305     /**
 306         Get back a file descriptor from wxFile object - the caller is responsible for
 307         closing the file if this descriptor is opened.
 308         IsOpened() will return @false after call to Detach().
 309     */
 310     void Detach();
 311
 312     /**
 313         Returns @true if the end of the file has been reached.
 314         Note that the behaviour of the file pointer-based class wxFFile is
 315         different as wxFFile::Eof() will return @true here only if an
 316         attempt has been made to read @b past the last byte of the file, while
 317         wxFile::Eof() will return @true even before such attempt is made if the
 318         file pointer is at the last position in the file.
 319
 320         Note also that this function doesn't work on unseekable file descriptors
 321         (examples include pipes, terminals and sockets under Unix) and an attempt to
 322         use it will result in an error message.
 323
 324         So, to read the entire file into memory, you should write a loop which uses
 325         Read() repeatedly and tests its return condition instead of using Eof()
 326         as this will not work for special files under Unix.
 327     */
 328     bool Eof() const;
 329
 330     /**
 331         Returns @true if the given name specifies an existing regular file
 332         (not a directory or a link).
 333     */
 334     static bool Exists(const wxString& filename);
 335
 336     /**
 337         Flushes the file descriptor.
 338
 339         Note that Flush() is not implemented on some Windows compilers due to a
 340         missing fsync function, which reduces the usefulness of this function
 341         (it can still be called but it will do nothing on unsupported compilers).
 342     */
 343     bool Flush();
 344
 345     /**
 346         Returns the type of the file.
 347     */
 348     wxFileKind GetKind() const;
 349
 350     /**
 351         Returns @true if the file has been opened.
 352     */
 353     bool IsOpened() const;
 354
 355     /**
 356         Returns the length of the file.
 357     */
 358     wxFileOffset Length() const;
 359
 360     /**
 361         Opens the file, returning @true if successful.
 362
 363         @param filename
 364             The filename.
 365         @param mode
 366             The mode in which to open the file.
 367         @param access
 368             An OR-combination of wxPosixPermissions enumeration values.
 369     */
 370     bool Open(const wxString& filename, wxFile::OpenMode mode = wxFile::read,
 371               int access = wxS_DEFAULT);
 372
 373     /**
 374         Reads from the file into a memory buffer.
 375
 376         @param buffer
 377            Buffer to write in
 378         @param count
 379            Bytes to read
 380
 381         @return The number of bytes read, or the symbol wxInvalidOffset.
 382     */
 383     ssize_t Read(void* buffer, size_t count);
 384
 385     /**
 386         Seeks to the specified position.
 387
 388         @param ofs
 389             Offset to seek to.
 390         @param mode
 391             One of wxFromStart, wxFromEnd, wxFromCurrent.
 392
 393         @return The actual offset position achieved, or wxInvalidOffset on
 394                 failure.
 395     */
 396     wxFileOffset Seek(wxFileOffset ofs,
 397                       wxSeekMode mode = wxFromStart);
 398
 399     /**
 400         Moves the file pointer to the specified number of bytes relative to the
 401         end of the file. For example, @c SeekEnd(-5) would position the pointer 5
 402         bytes before the end.
 403
 404         @param ofs
 405             Number of bytes before the end of the file.
 406
 407         @return The actual offset position achieved, or wxInvalidOffset on
 408                 failure.
 409     */
 410     wxFileOffset SeekEnd(wxFileOffset ofs = 0);
 411
 412     /**
 413         Returns the current position or wxInvalidOffset if file is not opened or
 414         if another error occurred.
 415     */
 416     wxFileOffset Tell() const;
 417
 418     /**
 419        Write data to the file (descriptor).
 420
 421        @param buffer
 422           Buffer from which to read data
 423        @param count
 424          Number of bytes to write
 425
 426        @return The number of bytes written.
 427     */
 428     size_t Write(const void *buffer, size_t count);
 429
 430     /**
 431         Writes the contents of the string to the file, returns @true on success.
 432         The second argument is only meaningful in Unicode build of wxWidgets when
 433         @a conv is used to convert @a s to a multibyte representation.
 434
 435         Note that this method only works with @c NUL-terminated strings, if you want
 436         to write data with embedded @c NULs to the file you should use the other
 437         Write() overload.
 438     */
 439     bool Write(const wxString& s, const wxMBConv& conv = wxConvUTF8);
 440
 441     /**
 442         Returns the file descriptor associated with the file.
 443     */
 444     int fd() const;
 445 };
 446