pack_fopen_chunk(3)             Allegro manual             pack_fopen_chunk(3)



NAME
       pack_fopen_chunk - Opens a sub-chunk of a file. Allegro game
       programming library.

SYNOPSIS
       #include <allegro.h>


       PACKFILE *pack_fopen_chunk(PACKFILE *f, int pack);

DESCRIPTION
       Opens a sub-chunk of a file. Chunks are primarily intended for use by
       the datafile code, but they may also be useful for your own file
       routines. A chunk provides a logical view of part of a file, which can
       be compressed as an individual entity and will automatically insert and
       check length counts to prevent reading past the end of the chunk. The
       PACKFILE parameter is a previously opened file, and `pack' is a boolean
       parameter which will turn compression on for the sub-chunk if it is
       non-zero.  Example:

          PACKFILE *output = pack_fopen("out.raw", "w!");
          ...
          /* Create a sub-chunk with compression. */
          output = pack_fopen(chunk(output, 1);
          if (!output)
             abort_on_error("Error saving data!");
          /* Write some data to the sub-chunk. */
          ...
          /* Close the sub-chunk, recovering parent file. */
          output = pack_fclose_chunk(output);

       The data written to the chunk will be prefixed with two length counts
       (32-bit, a.k.a. big-endian). For uncompressed chunks these will both be
       set to the size of the data in the chunk. For compressed chunks
       (created by setting the `pack' flag), the first length will be the raw
       size of the chunk, and the second will be the negative size of the
       uncompressed data.

       To read the chunk, use the following code:

          PACKFILE *input = pack_fopen("out.raw", "rp");
          ...
          input = pack_fopen_chunk(input, 1);
          /* Read data from the sub-chunk and close it. */
          ...
          input = pack_fclose_chunk(input);

       This sequence will read the length counts created when the chunk was
       written, and automatically decompress the contents of the chunk if it
       was compressed. The length will also be used to prevent reading past
       the end of the chunk (Allegro will return EOF if you attempt this), and
       to automatically skip past any unread chunk data when you call
       pack_fclose_chunk().

       Chunks can be nested inside each other by making repeated calls to
       pack_fopen_chunk(). When writing a file, the compression status is
       inherited from the parent file, so you only need to set the pack flag
       if the parent is not compressed but you want to pack the chunk data. If
       the parent file is already open in packed mode, setting the pack flag
       will result in data being compressed twice: once as it is written to
       the chunk, and again as the chunk passes it on to the parent file.

RETURN VALUE
       Returns a pointer to the sub-chunked PACKFILE, or NULL if there was
       some error (eg. you are using a custom PACKFILE vtable).


SEE ALSO
       pack_fclose_chunk(3), pack_fopen(3)



Allegro                          version 4.2.3             pack_fopen_chunk(3)
