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
 106         @warning
 107         You should use IsOpened() to verify that the constructor succeeded.
 108     */
 109     wxTempFile(const wxString& strName);
 110
 111     /**
 112         Destructor calls Discard() if temporary file is still open.
 113     */
 114     ~wxTempFile();
 115
 116     /**
 117         Validate changes: deletes the old file of name m_strName and renames the new
 118         file to the old name. Returns @true if both actions succeeded.
 119
 120         If @false is returned it may unfortunately mean two quite different things:
 121         either that the old file couldn't be deleted or that the new file
 122         couldn't be renamed to the old name.
 123     */
 124     bool Commit();
 125
 126     /**
 127         Discard changes: the old file contents are not changed, the temporary
 128         file is deleted.
 129     */
 130     void Discard();
 131
 132     /**
 133         Returns @true if the file was successfully opened.
 134     */
 135     bool IsOpened() const;
 136
 137     /**
 138         Returns the length of the file.
 139
 140         This method may return ::wxInvalidOffset if the length couldn't be
 141         determined or 0 even for non-empty files if the file is not seekable.
 142
 143         In general, the only way to determine if the file for which this function
 144         returns 0 is really empty or not is to try reading from it.
 145     */
 146     wxFileOffset Length() const;
 147
 148     /**
 149         Open the temporary file, returns @true on success, @false if an error
 150         occurred.
 151         @a strName is the name of file to be replaced. The temporary file is always
 152         created in the directory where @a strName is. In particular, if @a strName
 153         doesn't include the path, it is created in the current directory and the
 154         program should have write access to it for the function to succeed.
 155     */
 156     bool Open(const wxString& strName);
 157
 158     /**
 159         Seeks to the specified position.
 160     */
 161     wxFileOffset Seek(wxFileOffset ofs,
 162                       wxSeekMode mode = wxFromStart);
 163
 164     /**
 165         Returns the current position or ::wxInvalidOffset if file is not opened or
 166         if another error occurred.
 167     */
 168     wxFileOffset Tell() const;
 169
 170     /**
 171         Write to the file, return @true on success, @false on failure.
 172         The second argument is only meaningful in Unicode build of wxWidgets when
 173         @a conv is used to convert @a str to multibyte representation.
 174     */
 175     bool Write(const wxString& str,
 176                const wxMBConv& conv = wxConvUTF8);
 177 };
 178
 179
 180
 181 /**
 182     @class wxFile
 183
 184     A wxFile performs raw file I/O. This is a very small class designed to
 185     minimize the overhead of using it - in fact, there is hardly any overhead at
 186     all, but using it brings you automatic error checking and hides differences
 187     between platforms and compilers. wxFile also automatically closes the file in
 188     its destructor so you won't forget to do so.
 189     wxFile is a wrapper around @c file descriptor. - see also wxFFile for a
 190     wrapper around @c FILE structure.
 191
 192     ::wxFileOffset is used by the wxFile functions which require offsets as
 193     parameter or return them. If the platform supports it, wxFileOffset is a
 194     typedef for a native 64 bit integer, otherwise a 32 bit integer is used for
 195     ::wxFileOffset.
 196
 197     @library{wxbase}
 198     @category{file}
 199 */
 200 class wxFile
 201 {
 202 public:
 203
 204     /**
 205         The OpenMode enumeration defines the different modes for opening a file with wxFile.
 206         It is also used with wxFile::Access function.
 207     */
 208     enum OpenMode {
 209
 210         /** Open file for reading or test if it can be opened for reading with Access() */
 211         read,
 212
 213         /** Open file for writing deleting the contents of the file if it already exists
 214             or test if it can be opened for writing with Access(). */
 215         write,
 216
 217         /** Open file for reading and writing; can not be used with Access() */
 218         read_write,
 219
 220         /** Open file for appending: the file is opened for writing, but the old contents
 221             of the file are not erased and the file pointer is initially placed at the end
 222             of the file; can not be used with Access().
 223
 224             This is the same as OpenMode::write if the file doesn't exist.
 225         */
 226         write_append,
 227
 228         /**
 229             Open the file securely for writing (Uses O_EXCL | O_CREAT).
 230             Will fail if the file already exists, else create and open it atomically.
 231             Useful for opening temporary files without being vulnerable to race exploits.
 232         */
 233         write_excl
 234     };
 235
 236     /**
 237        Standard file descriptors
 238     */
 239     enum { fd_invalid = -1, fd_stdin, fd_stdout, fd_stderr };
 240
 241     /**
 242        Default constructor.
 243     */
 244     wxFile();
 245
 246     /**
 247         Opens a file with a filename.
 248
 249         @param filename
 250             The filename.
 251         @param mode
 252             The mode in which to open the file.
 253
 254         @warning
 255         You should use IsOpened() to verify that the constructor succeeded.
 256     */
 257     wxFile(const wxString& filename,
 258            wxFile::OpenMode mode = wxFile::read);
 259
 260     /**
 261         Associates the file with the given file descriptor, which has already been
 262         opened. See Attach() for the list of predefined descriptors.
 263
 264         @param fd
 265             An existing file descriptor.
 266     */
 267     wxFile(int fd);
 268
 269     /**
 270         Destructor will close the file.
 271         @note This destructor is not virtual so you should not use wxFile polymorphically.
 272     */
 273     ~wxFile();
 274
 275     /**
 276         This function verifies if we may access the given file in specified mode.
 277         Only values of @c wxFile::read or @c wxFile::write really make sense here.
 278     */
 279     static bool Access(const wxString& name, wxFile::OpenMode mode);
 280
 281     /**
 282         Attaches an existing file descriptor to the wxFile object.
 283         Examples of predefined file descriptors are 0, 1 and 2 which correspond to
 284         stdin, stdout and stderr (and have symbolic names of @c wxFile::fd_stdin,
 285         @c wxFile::fd_stdout and @c wxFile::fd_stderr).
 286
 287         The descriptor should be already opened and it will be closed by wxFile
 288         object.
 289     */
 290     void Attach(int fd);
 291
 292     /**
 293         Closes the file.
 294     */
 295     bool Close();
 296
 297     /**
 298         Creates a file for writing.
 299
 300         If the file already exists, setting @b overwrite to @true will ensure
 301         it is overwritten.
 302
 303         @a access may be an OR combination of the ::wxPosixPermissions enumeration
 304         values.
 305     */
 306     bool Create(const wxString& filename,
 307                 bool overwrite = false,
 308                 int access = wxS_DEFAULT);
 309
 310     /**
 311         Get back a file descriptor from wxFile object - the caller is responsible for
 312         closing the file if this descriptor is opened.
 313         IsOpened() will return @false after call to Detach().
 314     */
 315     void Detach();
 316
 317     /**
 318         Returns @true if the end of the file has been reached.
 319         Note that the behaviour of the file pointer-based class wxFFile is
 320         different as wxFFile::Eof() will return @true here only if an
 321         attempt has been made to read @b past the last byte of the file, while
 322         wxFile::Eof() will return @true even before such attempt is made if the
 323         file pointer is at the last position in the file.
 324
 325         Note also that this function doesn't work on unseekable file descriptors
 326         (examples include pipes, terminals and sockets under Unix) and an attempt to
 327         use it will result in an error message.
 328
 329         So, to read the entire file into memory, you should write a loop which uses
 330         Read() repeatedly and tests its return condition instead of using Eof()
 331         as this will not work for special files under Unix.
 332     */
 333     bool Eof() const;
 334
 335     /**
 336         Returns @true if the given name specifies an existing regular file
 337         (not a directory or a link).
 338     */
 339     static bool Exists(const wxString& filename);
 340
 341     /**
 342         Flushes the file descriptor.
 343
 344         Note that Flush() is not implemented on some Windows compilers due to a
 345         missing fsync function, which reduces the usefulness of this function
 346         (it can still be called but it will do nothing on unsupported compilers).
 347     */
 348     bool Flush();
 349
 350     /**
 351         Returns the type of the file.
 352     */
 353     wxFileKind GetKind() const;
 354
 355     /**
 356         Returns @true if the file has been opened.
 357     */
 358     bool IsOpened() const;
 359
 360     /**
 361         Returns the length of the file.
 362     */
 363     wxFileOffset Length() const;
 364
 365     /**
 366         Opens the file, returning @true if successful.
 367
 368         @param filename
 369             The filename.
 370         @param mode
 371             The mode in which to open the file.
 372         @param access
 373             An OR-combination of ::wxPosixPermissions enumeration values.
 374     */
 375     bool Open(const wxString& filename, wxFile::OpenMode mode = wxFile::read,
 376               int access = wxS_DEFAULT);
 377
 378     /**
 379         Reads from the file into a memory buffer.
 380
 381         @param buffer
 382            Buffer to write in
 383         @param count
 384            Bytes to read
 385
 386         @return The number of bytes read, or the symbol ::wxInvalidOffset.
 387     */
 388     ssize_t Read(void* buffer, size_t count);
 389
 390     /**
 391         Seeks to the specified position.
 392
 393         @param ofs
 394             Offset to seek to.
 395         @param mode
 396             One of wxFromStart, wxFromEnd, wxFromCurrent.
 397
 398         @return The actual offset position achieved, or ::wxInvalidOffset on
 399                 failure.
 400     */
 401     wxFileOffset Seek(wxFileOffset ofs,
 402                       wxSeekMode mode = wxFromStart);
 403
 404     /**
 405         Moves the file pointer to the specified number of bytes relative to the
 406         end of the file. For example, @c SeekEnd(-5) would position the pointer 5
 407         bytes before the end.
 408
 409         @param ofs
 410             Number of bytes before the end of the file.
 411
 412         @return The actual offset position achieved, or ::wxInvalidOffset on
 413                 failure.
 414     */
 415     wxFileOffset SeekEnd(wxFileOffset ofs = 0);
 416
 417     /**
 418         Returns the current position or ::wxInvalidOffset if file is not opened or
 419         if another error occurred.
 420     */
 421     wxFileOffset Tell() const;
 422
 423     /**
 424        Write data to the file (descriptor).
 425
 426        @param buffer
 427           Buffer from which to read data
 428        @param count
 429          Number of bytes to write
 430
 431        @return The number of bytes written.
 432     */
 433     size_t Write(const void *buffer, size_t count);
 434
 435     /**
 436         Writes the contents of the string to the file, returns @true on success.
 437         The second argument is only meaningful in Unicode build of wxWidgets when
 438         @a conv is used to convert @a s to a multibyte representation.
 439
 440         Note that this method only works with @c NUL-terminated strings, if you want
 441         to write data with embedded @c NULs to the file you should use the other
 442         Write() overload.
 443     */
 444     bool Write(const wxString& s, const wxMBConv& conv = wxConvUTF8);
 445
 446     /**
 447         Returns the file descriptor associated with the file.
 448     */
 449     int fd() const;
 450 };
 451