[erlang-questions] Reading fixed structures from file

[Dave Smith]

On Sat, Mar 1, 2008 at 11:54 AM, Gleb Peregud <gleber.p@REDACTED> wrote:
> Hello.
>
>  I have one simple question regarding reading a fixed structure from files.
>
>  Let say i have a binary file filled with sequence of fixed length
>  structures. Each structure is of the form:
>
>  struct {
>   int32 key,
>   int64 adr,
>   char type
>  };
>
>  File was written at x86 platform, hence it is little-endian. I use R12B
>
>  Is the following way the best way to read whole file to the list:
>
>  scan_file(Binary) ->
>     scan_file(0, Binary, []).
>  scan_file(N, <<>>, List) ->
>     list:reverse(List);
>  scan_file(N, Binary, List) ->
>     <<
>      Key:4/little-integer-unit:8,
>      Adr:8/little-integer-unit:8,
>      Type:1/little-integer-unit:8,
>      Rest/binary
>      >> = Binary,
>     Obj = {N, Type, Adr, Key},
>     scan_file(N+1, Rest, [Obj | List]).
>
>  Code was not tested.

I'm pretty sure you code would be fine that way. Personally, I would
do something like:

scan_file(N, <<>>, List) ->
	lists:reverse(List);
scan_file(N, <<Key:32/little-integer, Addr:64/little-integer,
	           Type:8/little-integer, Rest/binary>>, List) ->
	scan_file(N+1, Rest, [{N, Type, Addr, Key} | List]).

I personally feel that reads a little clearer since it's in bits and
you don't have to do clever adjustments in your head when reading the
code.

My $0.02 (and with the dollar declining, worth less every day!) :)

D.