Re: binary files

[John Belmonte <jvb@...>]

Ignacio Castaño wrote:
> Hi,
>
> I just noticed there aren't any functions for reading/writting binary files
> in the lua standard library, I would like to suggest the addition of them.
> Something like:
>
> fh:readb( "pattern", [num] )
> fh:writeb( "pattern", ... )
>
> where pattern would be something like: "ub", "sd", "df" for unsigned byte,
> signed dword and double float.

I've had the experience of roughly implementing something like this for Lua.

Instead of directly reading and writing to files, you will want to be 
more general and operate on Lua strings, since they can hold binary 
data.  There are several issues to complicate things.  For example, the 
pattern syntax must be flexible enough to contain byte ordering and 
alignment info.  See Perl's pack/unpack 
(http://www.perldoc.com/perl5.6/pod/func/pack.html).

Lua has limited data types, and so in the end is not so well suited for 
working with binary data.  For example, with the standard double 
numbers, you cannot work with 64-bit integers.  Furthermore some users 
set the number type to float, and then they can't even work with 32-bit 
integers.

If something like this is put into a library, obviously that library 
will have to offer binary operations also.  Otherwise you have no way to 
look at flags and file headers, for example.

-John


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