坚强哥的代码记录

来源：互联网发布：在数组前面添加js 编辑：程序博客网时间：2024/04/25 18:39

转载自坚强的博客http://www.cnblogs.com/me-sa/archive/2012/05/22/erlang-code-snippet-2.html

整理了最近一段时间记录的Erlang代码片段,还有大量简短的代码都已经整理在官方文档的PDF中.从开始学习Erlang,写的测试代码都会整理到PDF中,从这个习惯中得益匪浅.可以在PDF上做批注,图形的工具我用的是:PDF-XChange Viewer

上一次代码片段整理:[Erlang 0043] Erlang Code Snippet

record 转 proplist

%% @spec record_to_proplist(Record, Fields) -> proplist()%% @doc calls record_to_proplist/3 with a default TypeKey of '__record'record_to_proplist(Record, Fields) ->    record_to_proplist(Record, Fields, '__record').%% @spec record_to_proplist(Record, Fields, TypeKey) -> proplist()%% @doc Return a proplist of the given Record with each field in the%%      Fields list set as a key with the corresponding value in the Record.%%      TypeKey is the key that is used to store the record type%%      Fields should be obtained by calling record_info(fields, record_type)%%      where record_type is the record type of Recordrecord_to_proplist(Record, Fields, TypeKey)  when tuple_size(Record) - 1 =:= length(Fields) ->    lists:zip([TypeKey | Fields], tuple_to_list(Record)).

测试代码:

Eshell V5.9 (abort with ^G)
1> rd(person,{name,id,age}).
person
2> mochiweb_util:record_to_proplist(#person{}, record_info(fields, person)).
[{'__record',person},
{name,undefined},
{id,undefined},
{age,undefined}]
3> mochiweb_util:record_to_proplist(#person{age=12,name=zen,id=2396}, record_info(fields, person)).
[{'__record',person},{name,zen},{id,2396},{age,12}]
4>

当然也可以这样:

Eshell V5.9  (abort with ^G)1> rd(person,{name,id,age,blog,addr}).person2> record_info(size,person).63> record_info(fields,person).[name,id,age,blog,addr]4>4> P=#person{name="zen",id=1234,age=28,blog="me_sa",addr="beijing"}.#person{name = "zen",id = 1234,age = 28,blog = "me_sa",        addr = "beijing"}5>  lists:zip(record_info(fields, person), tl(tuple_to_list(P))).[{name,"zen"},{id,1234},{age,28},{blog,"me_sa"},{addr,"beijing"}]6>  lists:zip(record_info(fields, person), tl(tuple_to_list(#person{}))).[{name,undefined},{id,undefined},{age,undefined},{blog,undefined},{addr,undefined}]7>  lists:zip(record_info(fields, person), tl(tuple_to_list(#person{age=23}))).[{name,undefined},{id,undefined},{age,23},{blog,undefined},{addr,undefined}]

record proplists 转换

地址: https://github.com/hio/erlang-record_info/blob/master/src/record_info.erl

% ----------------------------------------------------------------------------% record_info.% ----------------------------------------------------------------------------% Copyright 2011 YAMASHINA Hio. All rights reserved.% License: BSD (2-clause)% -----------------------------------------------------------------------------module(record_info).-export([version/0]).-export([version_string/0]).-export([record_list/1]).-export([field_list/2]).-export([default_value/3]).-export([record_to_proplist/2]).-export([proplist_to_record/3]).% private.-export([parse_transform/2]).-type proplist() :: [{atom(), any()}].-type a_record() :: tuple().-type record_name() :: atom().-type field_name()  :: atom().-spec version() -> {non_neg_integer(),non_neg_integer(),non_neg_integer(),non_neg_integer()}.version() ->  {0,3,0,0}.-spec version_string() -> string().version_string() ->  {Major,Minor,Patch,Build} = version(),  lists:flatten(io_lib:format("~p.~p.~p.~p", [Major,Minor,Patch,Build])).-spec record_list(    Module :: module()  ) -> [record_name()].record_list(Module) ->  Module:record_info(list).-spec field_list(    RecordName :: record_name(),    Module     :: module()  ) -> [field_name()].field_list(RecordName, Module) ->  Module:record_info({keys, RecordName}).-spec default_value(    Key        :: field_name(),    RecordName :: record_name(),    Module     :: module()  ) -> any().default_value(Key, RecordName, Module) ->  Module:record_info({value, RecordName, Key}).-spec parse_transform(    Forms :: [erl_parse:abstract_form()],    Opts  :: [compile:option()]  ) -> [erl_parse:abstract_form()].parse_transform(Form, Opts) ->  record_info_transform:parse_transform(Form, Opts).-spec record_to_proplist(    Record :: a_record(),    Module :: module()  ) -> proplist().record_to_proplist(Record, Module) ->  [RecordName | Values] = tuple_to_list(Record),  Keys = field_list(RecordName, Module),  lists:zip(Keys, Values).-spec proplist_to_record(    List       :: proplist(),    RecordName :: record_name(),    Module     :: module()  ) -> a_record().proplist_to_record(List, RecordName, Module) ->  Keys = field_list(RecordName, Module),  Values = [    case proplists:lookup(Key, List) of      {_, Value} ->        Value;      none ->        default_value(Key, RecordName, Module);      Any ->        erlang:error({badarg, Any}, [List, Module, RecordName])    end    || Key <- Keys  ],  list_to_tuple([RecordName | Values]).% ----------------------------------------------------------------------------% End of File.% ----------------------------------------------------------------------------

保证应用程序已经启动

%% @spec ensure_started(App::atom()) -> ok%% @doc Start the given App if it has not been started already.ensure_started(App) ->    case application:start(App) of        ok ->            ok;        {error, {already_started, App}} ->            ok    end.

解析IP地址是否支持IP V6

%%判断是否支持IPV6ipv6_supported() ->    case (catch inet:getaddr("localhost", inet6)) of        {ok, _Addr} ->            true;        {error, _} ->            false    end. 6> inet_parse:address("192.168.0.1").{ok,{192,168,0,1}}

整形幂运算

%% @spec int_pow(X::integer(), N::integer()) -> Y::integer()%% @doc  Moderately efficient way to exponentiate integers.%%       int_pow(10, 2) = 100.int_pow(_X, 0) ->    1;int_pow(X, N) when N > 0 ->    int_pow(X, N, 1). int_pow(X, N, R) when N < 2 ->    R * X;int_pow(X, N, R) ->    int_pow(X * X, N bsr 1, case N band 1 of 1 -> R * X; 0 -> R end).

测试代码:

2> math:pow(2,3).
8.0
3> test:int_pow(2,3).
8

向上取整

%% @spec int_ceil(F::float()) -> integer()%% @doc  Return the ceiling of F as an integer. The ceiling is defined as%%       F when F == trunc(F);%%       trunc(F) when F &lt; 0;%%       trunc(F) + 1 when F &gt; 0.int_ceil(X) ->    T = trunc(X),    case (X - T) of        Pos when Pos > 0 -> T + 1;        _ -> T    end.

在Erlang Shell中生成随机字符串

2> F=fun(Len, AllowedChars) ->    lists:foldl(fun(_, Acc) -> [lists:nth(random:uniform(length(AllowedChars)),  AllowedChars)]  ++ Acc  end, [], lists:seq(1, Len)) end.#Fun<erl_eval.12.111823515>3> F(4,"0123456789abcdefghijklmnopqrstuvwxyz")."iyqf"4> F(4,"0123456789abcdefghijklmnopqrstuvwxyz")."owlb"5> F(4,"0123456789abcdefghijklmnopqrstuvwxyz")."75lh"6> F(4,"0123456789abcdefghijklmnopqrstuvwxyz")."7k5p"7> F(4,"0123456789abcdefghijklmnopqrstuvwxyz")."k0fg"

产生GUID

random_token() ->    Term = term_to_binary({node(), make_ref()}),    Digest = erlang:md5(Term),    binary_to_hex(Digest).binary_to_hex(Bin) when is_binary(Bin) ->    [oct_to_hex(N) || <<N:4>> <= Bin].oct_to_hex(0) -> $0;oct_to_hex(1) -> $1;oct_to_hex(2) -> $2;oct_to_hex(3) -> $3;oct_to_hex(4) -> $4;oct_to_hex(5) -> $5;oct_to_hex(6) -> $6;oct_to_hex(7) -> $7;oct_to_hex(8) -> $8;oct_to_hex(9) -> $9;oct_to_hex(10) -> $a;oct_to_hex(11) -> $b;oct_to_hex(12) -> $c;oct_to_hex(13) -> $d;oct_to_hex(14) -> $e;oct_to_hex(15) -> $f.

测试代码:

1> test:random_token().
"db6f50cc40d54e338b0362c05d1b0295"
2> test:random_token().
"98b784e379dee8fa68ff863ba6c02cff"
3> test:random_token().
"7bc7db7cbab45025adaa02e28cc3972d"
4> test:random_token().
"0f794a8aed063184393bc5bb883f53bf"
5> test:random_token().
"4e18f2879d8d05e86445082bf4a46f19"

YA生成随机字符串

-define(SAFE_CHARS, {$a, $b, $c, $d, $e, $f, $g, $h, $i, $j, $k, $l, $m,                     $n, $o, $p, $q, $r, $s, $t, $u, $v, $w, $x, $y, $z,                     $A, $B, $C, $D, $E, $F, $G, $H, $I, $J, $K, $L, $M,                     $N, $O, $P, $Q, $R, $S, $T, $U, $V, $W, $X, $Y, $Z,                     $0, $1, $2, $3, $4, $5, $6, $7, $8, $9, $_}).rngchars(0) ->    "";rngchars(N) ->    [rngchar() | rngchars(N - 1)].rngchar() ->    rngchar(crypto:rand_uniform(0, tuple_size(?SAFE_CHARS))).rngchar(C) ->    element(1 + C, ?SAFE_CHARS).

测试代码:

10> test:rngchars(6).
"vlrLnt"
11> test:rngchars(6).
"y_fvQ_"
12> test:rngchars(6).
"VpOg8w"
13> test:rngchars(6).
"YzTnps"

2012-07-14更新

移除首尾空格
1> string:strip(" hi this is erlang ! ").
"hi this is erlang !"
格式化输出补零
7> io:format("~8..0B~n", [42]).
00000042
13> io:format("~10B~n", [73]).
73
ok
格式化右侧Padding
8> io:format("~-6B~n", [1024]).
1024
ok
9> io_lib:format("~-6B~n", [1024]).
[["1024",32,32],"\n"]
浮点数格式化输出
11> io:format("~.2f~n", [1/3]).
0.33
ok
12> 1/3.
0.3333333333333333
13>
移除List重复的元素
15> lists:usort([18, 16, 17, 18, 16, 19, 14, 17, 19, 18]).
[14,16,17,18,19]

处理XML

解析处理XML

<shopping>   <item name="bread" quantity="3" price="2.50"/>   <item name="milk" quantity="2" price="3.50"/> </shopping>

打印输出总金额: $14.50

-include_lib("xmerl/include/xmerl.hrl").-export([get_total/1]).get_total(ShoppingList) ->        {XmlElt, _} = xmerl_scan:string(ShoppingList),        Items = xmerl_xpath:string("/shopping/item", XmlElt),        Total = lists:foldl(fun(Item, Tot) ->                                [#xmlAttribute{value = PriceString}] = xmerl_xpath:string("/item/@price", Item),                                {Price, _} = string:to_float(PriceString),                                [#xmlAttribute{value = QuantityString}] = xmerl_xpath:string("/item/@quantity", Item),                                {Quantity, _} = string:to_integer(QuantityString),                                Tot + Price*Quantity                        end,                0, Items),        io:format("$~.2f~n", [Total]).

Erlang 动态创建XML
Given the following CSV:

bread,3,2.50
milk,2,3.50

Produce the equivalent information in XML, e.g.:

<shopping>   <item name="bread" quantity="3" price="2.50" />   <item name="milk" quantity="2" price="3.50" /> </shopping>

to_xml(ShoppingList) ->        Items = lists:map(fun(L) ->                                [Name, Quantity, Price] = string:tokens(L, ","),                                {item, [{name, Name}, {quantity, Quantity}, {price, Price}], []}                end, string:tokens(ShoppingList, "\n")),        xmerl:export_simple([{shopping, [], Items}], xmerl_xml).

好代码,一次擦肩而过可能就再也见不到了哦