string conversion, format functions

[Chris Pressey]

On Wed, 23 Apr 2003 16:52:45 -0400 (EDT)
HP Wei <hp@REDACTED> wrote:

> I have a string "123" and want to convert it to an integer
> or float, and vice versa.
> 
> In python, I go to the string module and
> there are string.atoi(), string.atof(), and str(number).
> So, by habit, I went to string module doc in Erlang
> I could not find the counterparts of these functions. Where are they ?

They're BIFs (Built In Functions); they can also be found in the module
'erlang':

  list_to_integer(String)
  list_to_float(String)
  integer_to_list(Integer)
  etc.

btw, there is no integer_to_float; use coercion (Integer + 0.0 works)

Also, converting the string "123" into a float will fail.

> -------------------------
> B = 3.
> 
> I want to form a string "0003".  
>   ** Can io:format generate such a printout ? 

Hmmm... good question!  If it can, it's not documented.  (Why is there
no formatting code for integers in io:format?)

I tried

17> io:fwrite("~5.1.0f~n", [3 + 0.0]).
003.0
ok
18> io:fwrite("~5.0.0f", [3 + 0.0]).
** exited: {format,[{io,format,[<0.21.0>,"~5.0.0f",[3.00000]]},
                    {erl_eval,expr,3},
                    {erl_eval,exprs,4},
                    {shell,eval_loop,2}]} **

I also tried

20> io:fwrite("~5.0.0p~n", [3]).
3
ok

No luck...

>   ** Can it be redirected to a string ?

Yes, see io_lib:format/2.

>   ** If not, how do folks in Erlang world do this padding?

I guess the best way right now is:

23> string:right(integer_to_list(3), 4, $0).
"0003"

> thanks,  
> hp

Hope that helps,
-Chris