CODEWITHSUNDEEP
erlang
Holly
Holly

Reputation: 1976

Erlang string comparisons aren't working

I've been stumped just trying to compare two bits of data for hours.

This is essentially what i've written..

find_client(Search, [Client|Client_list])->
   {Name,Socket} = Client,
   io:fwrite("Name>~s<~n",[Name]),
   io:fwrite("Search>~s<~n",[Search]),
   case string:equal(Name,Search) of
      true->
         do_something;
      false->
         do_something_else
   end;
find_client(Search,[])->
   not_found.

The problem is that do_something_else is always returned even when i'm convinced they should be equal! io:fwrite prints out exactly the same thing to the console in my tests, ie- 

Name>name1<
Search>name1<

Before I tried string:equal I was trying to do my own pattern match but no matter the combination I couldn't seem to get it to work.

Am I missing something? I'd really appreciate a pait of fresh eyes or a suggestion for another way to try.

Upvotes: 1

Views: 1597

Answers (1)

YOUR ARGUMENT IS VALID
YOUR ARGUMENT IS VALID

Reputation: 2069

All of these print the same thing, because ~s formats iolists (and atoms!) the same way.

io:fwrite("~s~n", ["name"]),
io:fwrite("~s~n", [<<"name">>]),
io:fwrite("~s~n", [name]),
io:fwrite("~s~n", [[$n, $a, <<"m">>, "e"]]).

A better "what is this really?!" debug technique would be to use the ~p format string. Give it a try with the above examples.

The implementation of string:equal/2 isn't really any different than the =:= operator (it's a pattern match), so it's not going to return true for equivalent iolists that have different structure.

What you'll probably need to do is write a comparison function that can compare iolists, which is trivially done using iolist_to_binary/1.

iolist_equal(A, B) ->
    iolist_to_binary(A) =:= iolist_to_binary(B).

Upvotes: 8

Related Questions