Opens a file according to mode.
Opens a file according to mode, which may contain any of the flags:
`r' - open file for reading.
`w' - open file for writing, overwriting any existing data.
`p' - open file in packed mode. Data will be compressed as it is
written to the file, and automatically uncompressed during read
operations. Files created in this mode will produce garbage if
they are read without this flag being set.
`!' - open file for writing in normal, unpacked mode, but add the
value F_NOPACK_MAGIC to the start of the file, so that it can
later be opened in packed mode and Allegro will automatically
detect that the data does not need to be decompressed.
Instead of these flags, one of the constants F_READ, F_WRITE,
F_READ_PACKED, F_WRITE_PACKED or F_WRITE_NOPACK may be used as the mode
The packfile functions also understand several "magic" filenames that are
used for special purposes. These are:
`#' - read data that has been appended to your executable file with
the exedat utility, as if it was a regular independent disk file.
`filename.dat#object_name' - open a specific object from a datafile,
and read from it as if it was a regular file. You can treat nested
datafiles exactly like a normal directory structure, for example
you could open `filename.dat#graphics/level1/mapdata'.
`#object_name' - combination of the above, reading an object from a
datafile that has been appended onto your executable.
With these special filenames, the contents of a datafile object or
appended file can be read in an identical way to a normal disk file, so
any of the file access functions in Allegro (eg. load_pcx() and
set_config_file()) can be used to read from them. Note that you can't
write to these special files, though: the fake file is read only. Also,
you must save your datafile uncompressed or with per-object compression
if you are planning on loading individual objects from it (otherwise
there will be an excessive amount of seeking when it is read).
Finally, be aware that the special Allegro object types aren't the same
format as the files you import the data from. When you import data like
bitmaps or samples into the grabber, they are converted into a special
Allegro-specific format, but the `#' marker file syntax reads the objects
as raw binary chunks. This means that if, for example, you want to use
load_pcx() to read an image from a datafile, you should import it as a
binary block rather than as a BITMAP object.
input_file = pack_fopen("scores.dat", "rp");
abort_on_error("Couldn't read `scores.dat'!");
On success, pack_fopen() returns a pointer to a PACKFILE structure, and on
error it returns NULL and stores an error code in `errno'. An attempt to
read a normal file in packed mode will cause `errno' to be set to EDOM.