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<  Erlang  ~  Printing binary stuff in base 16.
wolfgke
Posted: Sun Dec 02, 2007 6:51 pm Reply with quote
User Joined: 16 Sep 2007 Posts: 16
An example:

Code:
FooBar= <<255:8, 0:24>>.
io:format("~w~n", [FooBar]).


In this example the binary type is printed in base 10. Since such code is mainly used for debugging purposes it would be very useful to get the output in base 16.

So could please anybody help me. For numbers I can use

Code:
io:format("~.16B~n", [FooBar]).


But this does not work for the binary type.

I also know I could convert the binary stuff to a number and print this - but is there a way to avoid this?

So please help me.
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francesco
Posted: Sun Dec 02, 2007 10:25 pm Reply with quote
User Joined: 07 Jul 2006 Posts: 249 Location: London
Quote:
But this does not work for the binary type.

I also know I could convert the binary stuff to a number and print this - but is there a way to avoid this?


The Erlang way would be to extract the integer from the binary and print it. If it is for debug purposes, why not... I would do something like this:

Code:
40> Bin = <<1,2,3,4,5>>.         
<<1,2,3,4,5>>
41> <<Int:24, Rest/binary>> = Bin.
<<1,2,3,4,5>>
42> io:format("~.16b~n", [Int]). 
10203
ok
43> Int.
66051
44>


Not as fun as having to write your own conversion functions as was custom in the good old days

Code:
to_hex(Int) ->
    to_hex(Int, []).

to_hex(0, Buff) -> Buff;
to_hex(Int, Buff) ->
    to_hex(Int div 16, [to_char(Int rem 16)|Buff]).



to_char(Int) when Int > 9 -> Int rem 10 + $A;
to_char(Int)              -> Int + $0.


Smile

Francesco
--
http://www.erlang-consulting.com
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wolfgke
Posted: Mon Dec 03, 2007 3:37 pm Reply with quote
User Joined: 16 Sep 2007 Posts: 16
The reason why I want to avoid converting it to a number is endianness. It is an Erlang conversation of some rather ugly C code which depends a lot on little endian.

When I simply convert the binary to a number I always have to think whether the "wrong" byte oder is as it should or not - very error-prone I think.

The solution which I will probably take is letting some very nasty but little parts as a C function and call them by Erlang.
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