Question

我试图通过interviewstreet学习erlang。我现在只是学习这门语言所以我什么都不知道。我想知道如何从stdin读取并写入stdout。

我想写一个简单的程序，写下＆＃34; Hello World！＆＃34; stdin收到的次数。

所以使用stdin输入：

写入stdout：

Hello World!
Hello World!
Hello World!
Hello World!
Hello World!
Hello World!

理想情况下，我会一次读取stdin一行（即使在这种情况下它只是一位数），所以我想我会使用get_line。这就是我现在所知道的全部。

感谢

由于

Answer 1

这是另一种解决方案，可能更具功能性。

#!/usr/bin/env escript

main(_) ->
    %% Directly reads the number of hellos as a decimal
    {ok, [X]} = io:fread("How many Hellos?> ", "~d"),
    %% Write X hellos
    hello(X).

%% Do nothing when there is no hello to write
hello(N) when N =< 0 -> ok;
%% Else, write a 'Hello World!', and then write (n-1) hellos
hello(N) ->
   io:fwrite("Hello World!~n"),
   hello(N - 1).

Answer 2

这是我的镜头。我已经使用了escript，因此它可以从命令行运行，但它可以很容易地放入模块中：

#!/usr/bin/env escript

main(_Args) ->
    % Read a line from stdin, strip dos&unix newlines
    % This can also be done with io:get_line/2 using the atom 'standard_io' as the
    % first argument.
    Line = io:get_line("Enter num:"), 
    LineWithoutNL = string:strip(string:strip(Line, both, 13), both, 10),

    % Try to transform the string read into an unsigned int
    {ok, [Num], _} = io_lib:fread("~u", LineWithoutNL),

    % Using a list comprehension we can print the string for each one of the
    % elements generated in a sequence, that goes from 1 to Num.
    [ io:format("Hello world!~n") || _ <- lists:seq(1, Num) ].

如果您不想使用列表推导，这是对最后一行代码的类似方法，使用list：foreach和相同的序列：

    % Create a sequence, from 1 to Num, and call a fun to write to stdout
    % for each one of the items in the sequence.
    lists:foreach(
        fun(_Iteration) ->
            io:format("Hello world!~n")
        end,
        lists:seq(1,Num)
    ).

Answer 3

% Enter your code here. Read input from STDIN. Print output to STDOUT 
% Your class should be named solution

-module(solution).
-export([main/0, input/0, print_hello/1]).

main() ->
    print_hello(input()).

print_hello(0) ->io:format("");
print_hello(N) ->
    io:format("Hello World~n"),
    print_hello(N-1).
input()->
    {ok,[N]} = io:fread("","~d"),
N.

Erlang读stdin写stdout

3 个答案: