问题
In erlang, I want to format a string with integers in it and I want the result to be flattened. But I get this:
io_lib:format("sdfsdf ~B", [12312]).
[115,100,102,115,100,102,32,"12312"]
I can get the desired result by using the code below but it is really not elegant.
lists:flatten(io_lib:format("sdfsdf ~B", [12312])).
"sdfsdf 12312"
Is there a better formatting strings with integers in them, so that they are flat? Ideally, using only one function?
回答1:
You flatten a list using lists:flatten/1 as you've done in your example.
If you can accept a binary, list_to_binary/1 is quite efficient:
1> list_to_binary(io_lib:format("sdfsdf ~B", [12312])).
<<"sdfsdf 12312">>
However, question why you need a flat list in the first place. If it is just cosmetics, you don't need it. io:format/1,2,3 and most other port functions (gen_tcp etc) accept so called deep IO lists (nested lists with characters and binaries):
2> io:format([115,100,102,115,100,102,32,"12312"]).
sdfsdf 12312ok
回答2:
There is an efficiency reason that io_lib:format returns deep lists. Basically it saves a call to lists:flatten.
Ask yourself why you want the list flattened. If you are going to print the list or send it to a port or write it to a file, all those operations handle deep lists.
If you really need a flattened list for some reason, then just flatten it. Or you can create your own my_io_lib:format that returns flattened lists if you think it important.
(If you only want to flatten the list for debugging reasons then either print your strings with ~s, or create a flattener in an erlang module named user_default. Something like this:
-module(user_default).
-compile(export_all).
%% either this:
fl(String) ->
lists:flatten(String).
%% or this:
pp(String) ->
io:format("~s~n", [String]).
Then you can use fl/1 and print/1 in the Erlang shell (as long as user_default.beam is in your path of course).)
来源：https://stackoverflow.com/questions/6503289/how-to-format-a-flat-string-with-integers-in-it-in-erlang