Reputation: 865
I know strings in Erlang can be costly to use. So how do I convert "5"
to 5
?
Is there anything like io:format("~p",[5])
that would return a formatted string instead of printing to a stream?
Upvotes: 63
Views: 55522
Reputation: 65054
The following is probably not the neatest way, but it works:
1> lists:flatten(io_lib:format("~p", [35365])).
"35365"
EDIT: I've found that the following function comes in useful:
%% string_format/2
%% Like io:format except it returns the evaluated string rather than write
%% it to standard output.
%% Parameters:
%% 1. format string similar to that used by io:format.
%% 2. list of values to supply to format string.
%% Returns:
%% Formatted string.
string_format(Pattern, Values) ->
lists:flatten(io_lib:format(Pattern, Values)).
EDIT 2 (in response to comments): the above function came from a small program I wrote a while back to learn Erlang. I was looking for a string-formatting function and found the behaviour of io_lib:format/2
within erl
counter-intuitive, for example:
1> io_lib:format("2 + 2 = ~p", [2+2]).
[50,32,43,32,50,32,61,32,"4"]
At the time, I was unaware of the 'auto-flattening' behaviour of output devices mentioned by @archaelus and so concluded that the above behaviour wasn't what I wanted.
This evening, I went back to this program and replaced calls to the string_format
function above with io_lib:format
. The only problems this caused were a few EUnit tests that failed because they were expecting a flattened string. These were easily fixed.
I agree with @gleber and @womble that using this function is overkill for converting an integer to a string. If that's all you need, use integer_to_list/1
. KISS!
Upvotes: 17
Reputation: 6274
As an aside if you ever need to deal with the string representation of floats you should look at the work that Bob Ippolito has done on mochinum.
Upvotes: 4
Reputation: 12426
There's also integer_to_list/1
, which does exactly what you want, without the ugliness.
Upvotes: 156