interface/wx/file.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        file.h
   3 // Purpose:     interface of wxTempFile
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10     @class wxTempFile
  11
  12     wxTempFile provides a relatively safe way to replace the contents of the
  13     existing file. The name is explained by the fact that it may be also used as
  14     just a temporary file if you don't replace the old file contents.
  15
  16     Usually, when a program replaces the contents of some file it first opens it for
  17     writing, thus losing all of the old data and then starts recreating it. This
  18     approach is not very safe because during the regeneration of the file bad things
  19     may happen: the program may find that there is an internal error preventing it
  20     from completing file generation, the user may interrupt it (especially if file
  21     generation takes long time) and, finally, any other external interrupts (power
  22     supply failure or a disk error) will leave you without either the original file
  23     or the new one.
  24
  25     wxTempFile addresses this problem by creating a temporary file which is meant to
  26     replace the original file - but only after it is fully written. So, if the user
  27     interrupts the program during the file generation, the old file won't be lost.
  28     Also, if the program discovers itself that it doesn't want to replace the old
  29     file there is no problem - in fact, wxTempFile will @b not replace the old
  30     file by default, you should explicitly call wxTempFile::Commit
  31     to do it. Calling wxTempFile::Discard explicitly discards any
  32     modifications: it closes and deletes the temporary file and leaves the original
  33     file unchanged. If you don't call neither of Commit() and Discard(), the
  34     destructor will call Discard() automatically.
  35
  36     To summarize: if you want to replace another file, create an instance of
  37     wxTempFile passing the name of the file to be replaced to the constructor (you
  38     may also use default constructor and pass the file name to
  39     wxTempFile::Open). Then you can wxTempFile::write
  40     to wxTempFile using wxFile-like functions and later call
  41     Commit() to replace the old file (and close this one) or call Discard() to
  42     cancel
  43     the modifications.
  44
  45     @library{wxbase}
  46     @category{file}
  47 */
  48 class wxTempFile
  49 {
  50 public:
  51     /**
  52         Associates wxTempFile with the file to be replaced and opens it. You should use
  53         IsOpened() to verify if the constructor succeeded.
  54     */
  55     wxTempFile(const wxString& strName);
  56
  57     /**
  58         Destructor calls Discard() if temporary file
  59         is still opened.
  60     */
  61     ~wxTempFile();
  62
  63     /**
  64         Validate changes: deletes the old file of name m_strName and renames the new
  65         file to the old name. Returns @true if both actions succeeded. If @false is
  66         returned it may unfortunately mean two quite different things: either that
  67         either the old file couldn't be deleted or that the new file couldn't be renamed
  68         to the old name.
  69     */
  70     bool Commit();
  71
  72     /**
  73         Discard changes: the old file contents is not changed, temporary file is
  74         deleted.
  75     */
  76     void Discard();
  77
  78     /**
  79         Returns @true if the file was successfully opened.
  80     */
  81     bool IsOpened() const;
  82
  83     /**
  84         Returns the length of the file.
  85     */
  86     wxFileOffset Length() const;
  87
  88     /**
  89         Open the temporary file, returns @true on success, @false if an error
  90         occurred.
  91         @a strName is the name of file to be replaced. The temporary file is always
  92         created in the directory where @a strName is. In particular, if
  93         @a strName doesn't include the path, it is created in the current directory
  94         and the program should have write access to it for the function to succeed.
  95     */
  96     bool Open(const wxString& strName);
  97
  98     /**
  99         Seeks to the specified position.
 100     */
 101     wxFileOffset Seek(wxFileOffset ofs,
 102                       wxSeekMode mode = wxFromStart);
 103
 104     /**
 105         Returns the current position or wxInvalidOffset if file is not opened or if
 106         another
 107         error occurred.
 108     */
 109     wxFileOffset Tell() const;
 110
 111     /**
 112         Write to the file, return @true on success, @false on failure.
 113         The second argument is only meaningful in Unicode build of wxWidgets when
 114         @a conv is used to convert @a str to multibyte representation.
 115     */
 116     bool Write(const wxString& str,
 117                const wxMBConv& conv = wxConvUTF8);
 118 };
 119
 120
 121
 122 /**
 123     @class wxFile
 124
 125     A wxFile performs raw file I/O. This is a very small class designed to
 126     minimize the overhead of using it - in fact, there is hardly any overhead at
 127     all, but using it brings you automatic error checking and hides differences
 128     between platforms and compilers. wxFile also automatically closes the file in
 129     its destructor making it unnecessary to worry about forgetting to do it.
 130     wxFile is a wrapper around @c file descriptor. - see also
 131     wxFFile for a wrapper around @c FILE structure.
 132
 133     @c wxFileOffset is used by the wxFile functions which require offsets as
 134     parameter or return them. If the platform supports it, wxFileOffset is a typedef
 135     for a native 64 bit integer, otherwise a 32 bit integer is used for
 136     wxFileOffset.
 137
 138     @library{wxbase}
 139     @category{file}
 140 */
 141 class wxFile
 142 {
 143 public:
 144     //@{
 145     /**
 146         Associates the file with the given file descriptor, which has already been
 147         opened.
 148
 149         @param filename
 150             The filename.
 151         @param mode
 152             The mode in which to open the file. May be one of read(), write() and
 153         wxFile::read_write.
 154         @param fd
 155             An existing file descriptor (see Attach() for the list of predefined
 156         descriptors)
 157     */
 158     wxFile();
 159     wxFile(const wxString& filename,
 160            wxFile::OpenMode mode = wxFile::read);
 161     wxFile(int fd);
 162     //@}
 163
 164     /**
 165         Destructor will close the file.
 166         @note it is not virtual so you should not use wxFile polymorphically.
 167     */
 168     ~wxFile();
 169
 170     /**
 171         This function verifies if we may access the given file in specified mode. Only
 172         values of read() or write() really make sense here.
 173     */
 174     static bool Access(const wxString& name, OpenMode mode);
 175
 176     /**
 177         Attaches an existing file descriptor to the wxFile object. Example of predefined
 178         file descriptors are 0, 1 and 2 which correspond to stdin, stdout and stderr
 179         (and
 180         have symbolic names of @b wxFile::fd_stdin, @b wxFile::fd_stdout and @b
 181         wxFile::fd_stderr).
 182         The descriptor should be already opened and it will be closed by wxFile
 183         object.
 184     */
 185     void Attach(int fd);
 186
 187     /**
 188         Closes the file.
 189     */
 190     void Close();
 191
 192     /**
 193         Creates a file for writing. If the file already exists, setting @b overwrite to
 194         @true
 195         will ensure it is overwritten.
 196     */
 197     bool Create(const wxString& filename, bool overwrite = false,
 198                 int access = wxS_DEFAULT);
 199
 200     /**
 201         Get back a file descriptor from wxFile object - the caller is responsible for
 202         closing the file if this
 203         descriptor is opened. IsOpened() will return @false after call to Detach().
 204     */
 205     void Detach();
 206
 207     /**
 208         Returns @true if the end of the file has been reached.
 209         Note that the behaviour of the file pointer based class
 210         wxFFile is different as wxFFile::Eof
 211         will return @true here only if an attempt has been made to read
 212         @e past the last byte of the file, while wxFile::Eof() will return @true
 213         even before such attempt is made if the file pointer is at the last position
 214         in the file.
 215         Note also that this function doesn't work on unseekable file descriptors
 216         (examples include pipes, terminals and sockets under Unix) and an attempt to
 217         use it will result in an error message in such case. So, to read the entire
 218         file into memory, you should write a loop which uses
 219         Read() repeatedly and tests its return condition instead
 220         of using Eof() as this will not work for special files under Unix.
 221     */
 222     bool Eof() const;
 223
 224     /**
 225         Returns @true if the given name specifies an existing regular file (not a
 226         directory or a link)
 227     */
 228     static bool Exists(const wxString& filename);
 229
 230     /**
 231         Flushes the file descriptor.
 232         Note that Flush() is not implemented on some Windows compilers
 233         due to a missing fsync function, which reduces the usefulness of this function
 234         (it can still be called but it will do nothing on unsupported compilers).
 235     */
 236     bool Flush();
 237
 238     /**
 239         Returns the type of the file. Possible return values are:
 240     */
 241     wxFileKind GetKind() const;
 242
 243     /**
 244         Returns @true if the file has been opened.
 245     */
 246     bool IsOpened() const;
 247
 248     /**
 249         Returns the length of the file.
 250     */
 251     wxFileOffset Length() const;
 252
 253     /**
 254         Opens the file, returning @true if successful.
 255
 256         @param filename
 257             The filename.
 258         @param mode
 259             The mode in which to open the file. May be one of read(), write() and
 260         wxFile::read_write.
 261     */
 262     bool Open(const wxString& filename,
 263               wxFile::OpenMode mode = wxFile::read);
 264
 265     //@{
 266     /**
 267         if there was an error.
 268     */
 269     size_t Read(void* buffer, size_t count);
 270     Parameters Return value
 271     The number of bytes read, or the symbol wxInvalidOffset();
 272     //@}
 273
 274     /**
 275         Seeks to the specified position.
 276
 277         @param ofs
 278             Offset to seek to.
 279         @param mode
 280             One of wxFromStart, wxFromEnd, wxFromCurrent.
 281
 282         @return The actual offset position achieved, or wxInvalidOffset on
 283                  failure.
 284     */
 285     wxFileOffset Seek(wxFileOffset ofs,
 286                       wxSeekMode mode = wxFromStart);
 287
 288     /**
 289         Moves the file pointer to the specified number of bytes relative to the end of
 290         the file. For example, @c SeekEnd(-5) would position the pointer 5
 291         bytes before the end.
 292
 293         @param ofs
 294             Number of bytes before the end of the file.
 295
 296         @return The actual offset position achieved, or wxInvalidOffset on
 297                  failure.
 298     */
 299     wxFileOffset SeekEnd(wxFileOffset ofs = 0);
 300
 301     /**
 302         Returns the current position or wxInvalidOffset if file is not opened or if
 303         another
 304         error occurred.
 305     */
 306     wxFileOffset Tell() const;
 307
 308     /**
 309         Writes the contents of the string to the file, returns @true on success.
 310         The second argument is only meaningful in Unicode build of wxWidgets when
 311         @a conv is used to convert @a s to multibyte representation.
 312         Note that this method only works with @c NUL-terminated strings, if you want
 313         to write data with embedded @c NULs to the file you should use the other
 314         @ref write() "Write() overload".
 315     */
 316     bool Write(const wxString& s, const wxMBConv& conv = wxConvUTF8);
 317
 318     /**
 319         Returns the file descriptor associated with the file.
 320     */
 321     int fd() const;
 322 };
 323