.列表操作
lists:foreach
(fun(X) -> io:format("E=~p~n",[X]) end, [1,2,3]).
lists:duplicate
(10, 16#f). % [15,15,15,15,15,15,15,15,15,15]
"abc-123" -> "abc"
no_vsn(Name) -> lists:takewhile
(fun($-)->false;(_)-> true end,Name).
"abc-123" -> "123"
vsn(Name) ->
case lists:dropwhile
(fun($-)->false;(_)->true end,Name) of
[_Sep|Vsn] -> Vsn;
_ -> "0"
end.
取偶数
EvenN = lists:filter
(fun (N) -> N rem 2 == 0 end, lists:seq
(1,100))
lists:foldl
(fun(F, Last) -> F(Last) end, foo(), [fun whee/1, fun bar/1])
将URL中的空格换成+
UW = lists:map
(fun($ )->$+;(C)->C end,Words)
判断是否为空格
is_nb_space(X) ->
lists:member
(X, [$\s, $\t]).
>Data = [{"apple", "red"}, {"banana", "yellow"}, {"pear", "white"}].
>lists:keymember
("pear",1,Data).
true
>lists:keydelete
("banana",1,Data).
[{"apple","red"},{"pear","white"}]
>lists:keyreplace
("apple",1,Data,{"tomato", "red"}).
[{"tomato","red"},{"banana","yellow"},{"pear","white"}]
> rd(user,{id,name}). %% 用户记录
> lists:keysearch
("wang", #user.name, [#user{id=1,name="li"}, #user{id=2,name="wang"}]).
> {value,#user{id = 2,name = "wang"}}
.二进制操作
-define(BYTE, 8/unsigned-big-integer).
<<C:2/unit
:?BYTE>> 意思就是取两个单位，每单位8bits。
unit的默认值取决于type，如果type是integer或者float，则为1，binary为8。
<<C:4/binary, _/binary>>
意思就是取4个单位，每单位8比特，总共4*8比特
1>A = <<1:32/little,1:8/little>>. %低位在前
<<1,0,0,0,1>>
2> B = <<1:32/big,1:8/big>>. %高位在前
<<0,0,0,1,1>>
.位操作
O2 = ((C1 band
16#03) bsl
4) bor
(C2 bsr
4).
. 文件操作
Destination = filename:join
([code:root_dir(), "include", no_vsn( New_lib )]),
file:make_dir
(Destination),
lists:foreach( fun(File) ->
FileName = lists:last(string:tokens(File,"/\\")),
file:copy
(File, filename:join([Destination,FileName]))
end,
filelib:wildcard
(filename:join([Source,"*"])) ).
remove(Path, File) ->
Desc = filename:join([Path,File]),
case filelib:is_dir
(Desc) of
true ->
case file:list_dir
(Desc) of
{ok,Sub} -> lists:foreach(fun(S) -> remove(Desc,S) end,Sub);
{error,Reason} -> io:format("error: ~p~n",[Reason])
end,
file:del_dir
(Desc);
false ->
file:delete
(Desc)
end.
uncompress(Archive) ->
case file:read_file
(Archive) of
{ok,Tgz} ->
Tar = zlib:gunzip(Tgz),
erl_tar:extract({binary,Tar},[{cwd,code:lib_dir
()}]);
Error ->
Error
end.
file:write_file("test.txt", "12 13 14 15 16 17 18").
{ok, Bin
} = file:read_file
(File
),
Rules = string:tokens
(erlang:binary_to_list
(Bin), "\n").
case file:open(File, [write]) of
{ok, FD} ->
%io:put_chars(FD, Text), <-- ERROR
ok = file:close(FD),
file:write_file(File, unicode:characters_to_binary(Text)); <-- HACK
{error, R} ->
R1 = file:format_error(R),
report("could not write file '~s': ~s.", [File, R1]),
exit(error)
end.
或
file:open(File, [write, {encoding, utf8}])
.日期,时间操作
{{Y,M,D},{H,M,S}} = calendar:local_time
().
calendar:day_of_the_week
(2009,2,24).
next_day({Y, M, D}) ->
Day1 = calendar:date_to_gregorian_days
(Y, M, D),
calendar:gregorian_days_to_date
(Day1 + 1).
.字符串操作
count_chars(String, Char) ->
length
([X || X <- String, X == Char]).
格式化字符串, 像C语言的sscanf()
Cmd = io_lib:format
(\"cd ~s/include; rm ~s; ln -s ../lib/~s/include ~s\", [code:root_dir(), no_vsn( New_lib ), New_lib, no_vsn( New_lib )]),
os:cmd(Cmd);
PN = [erlang:list_to_integer(N) || N <- string:tokens
( vsn( Package_that_might_be_newer ), "." )],
packages_from_html(Html,Packages) ->
case string:str
(Html,"class=\"package\"") of
0 -> Packages;
Start ->
Sub = string:sub_string(Html,Start),
T1 = string:sub_string(Sub,string:chr(Sub,$>)+1),
PName = string:sub_string
(T1,1,string:chr(T1,$<)-1),
T2 = string:sub_string(T1,string:str(T1,"<i>")+3),
Descr = string:sub_string(T2,1,string:str(T2,"</i>")-1),
packages_from_html(T2,[{PName,Descr}|Packages])
end.
当使用Erlang程序与其它语言程序通讯时，可能需要把一个字符串转换成为Erlang的Term，可以这样实现
{ok, Tokens, _} = erl_scan:string(String),
{ok, Term} = erl_parse:parse_term(Tokens).
注意这里的String需要以句号结尾。
例如在erlang shell下：
> {ok, Tokens, _} = erl_scan:string("{1, {2}, [3]}.").
> {ok, {X, Y, Z}} = erl_parse:parse_term(Tokens).
.ETS/DETS操作
E = ets:new
(my_code, [public, set]),
ets:match_delete
(E,'_'),
ets:insert
(E, {num_files, 0}),
ets:insert(E, {num_bytes, 0}).
%% T = ets:new(?MODULE, [{write_concurrency, true}]).
{ok,?MODULE}=dets:open_file
(?MODULE,[{type,set},{file,"fcnum.dets"}]),
dets:insert(?MODULE, {1, [1,2,3,4,5,6,7]}),
dets:insert(?MODULE, {1, [7,6,5,4,3,2,1]}),
dets:close
(?MODULE).
>Table = ets:new(foobar, [set, public]).
>ets:tab2list
(Table).
[]
> ets:insert(Table, {1}).
true
> ets:insert(Table, {2}).
true
> ets:tab2list(Table).
[{1},{2}]
. mnesia操作
$erl -mnesia dir '"/home/sw2wolf/data"' -s mnesia start
-record(hitNum, {
oid,
hitnum
}).
% 在指定节点创建schema用数据表
install( Nodes ) when is_list( Nodes ) ->
mnesia:stop(),
mnesia:delete_schema
( Nodes ),
catch ( mnesia:create_schema
( Nodes ) ),
mnesia:start(),
case mnesia:create_table
( hitNum, [
{ disc_copies, Nodes },
{ type, set },
{ attributes, record_info( fields, hitNum) }
] ) of
{ atomic, ok } -> ok;
_Any ->
io:format( "create table error!~n")
end,
mnesia:stop(),
ok.
%增加记录
add_hitnum(HitNums) ->
F = fun() ->
lists:foreach( fun mnesia:write/
1, HitNums)
end,
mnesia:transaction
( F ).
%查寻
qry_hitnum() ->
Q = qlc:q( [X || X <- mnesia:table
(hitNum)] ),
F = fun() -> qlc:e( Q ) end,
{ atomic, Val } = mnesia:transaction
( F ),
lists:sort(Val).
动态改变Mnesia
表结构:
-record
(old, {key, val}).
-record
(new, {key, val, extra}).
Transformer =
fun
(X) ->
#new{key = X#old.key, val = X#old.val, extra = 42}
end
,
{atomic, ok} = mnesia
:transform_table
(foo, Transformer, record_info
(fields, new)).
例外处理
try
catch
_:_ -> ignore
end
.
嵌套记录
-record(name, {first = "Robert", last = "Ericsson"}).
-record(person, {name = #name{}, phone}). demo() -> P = #person{name= #name{first="Robert",last="Virding"}, phone=123},
First = (P#person.name)#name.first.
