[Erlang脚印 0008] string 常用函数
参考文档：http://www.erlang.org/erldoc?q=string%3Bright&x=-967&y=-384
string类型，经常用到，所有练习一下：
3> string:len("fan"). %% 字符串长度
3
4> string:len("你的").
2
5> string:len("fan你的中国").
7
6> string:equal("an","aa"). %%字符串比较
false
7> string:equal("an", "an").
true
8> string:equal("an", 'an').
false
9> string:concat("fan", "zhongguo"). %% 字符串添加
"fanzhongguo"
10> string:concat("fan", '中国 ').
* 1: illegal atom
10> string:concat("fan", '中国').
* 1: illegal atom
10> strign:concat("fan", "中国").
** exception error: undefined function strign:concat/2
11> string:concat("fan", "中国").
[102,97,110,20013,22269]
12> string:concat("fan","china").
"fanchina"
13> string:chr("fan","a"). %% 返回字符串指定字符的位置 ， 从左边查找
** exception error: no function clause matching string:chr("fan","a") (string.erl, line 97)
14> string:chr("fan",'a').
** exception error: no function clause matching string:chr("fan",a) (string.erl, line 97)
15> string:chr("fan",$a).
2
16> string:chr("fanan",$a).
2
17> strign:rchr("fanan",$a).
** exception error: undefined function strign:rchr/2
18> string:rchr("fanan", $a). %% 返回字符串指定字符串的位置， 从右边查找
4
19> string:str("fanan","a").
2
20> string:str("fanan", "an").
2
21> string:rstr("fanan", "an").
4
22> string:span("abcdef", "b").
0
23> string:span("ab cdef", "b").
0
24> string:substr("abcdef",2).
"bcdef"
25> string:substr("abcdef",2,6). %% 截取字符串，从指定位置或长度
"bcdef"
26> string:substr("abcdef",2,16).
"bcdef"
27> tokens("abcdef","a").
** exception error: undefined shell command tokens/2
28> string:tokens("abcdefabc ","b").
["a","cdefa","c "]
29> string:tokens("abcdefabc", "bc"). %% 将字符串转化为list，按照指定字符或字符串
["a","defa"]
30> string:tokens("abcdefabc", "ab").
["cdef","c"]
31> string:join(["ab","c","def"],""). %% 将list，连接成字符串
"abcdef"
32> string:join(["ab","c","def"], "--").
"ab--c--def"
33> string:chars("a", 5).
** exception error: no function clause matching string:chars("a",0,["a","a","a","a","a"]) (string.erl, line 256)
34> string:chars($a, 5).
"aaaaa"
35> string:chars('a', 5).
** exception error: no function clause matching string:chars(a,0,[a,a,a,a,a]) (string.erl, line 256)
36> string:chars("ab",5).
** exception error: no function clause matching string:chars("ab",0,["ab","ab","ab","ab","ab"]) (string.erl, line 256)
37> string:chars($a,6,"bbcc"). %%给字符串固定长度，添加字符串
"aaaaaabbcc"
38> string:copies("abcdefabcdef", 5).
"abcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdef"
39> string:copies("中国", 6).
[20013,22269,20013,22269,20013,22269,20013,22269,20013,
22269,20013,22269]
40> string:words("abcdef"). %% 字符串中以空格分开的字符的数量
1
41> string:words("abcdef, ab").
2
42> string:words("abcdef ab").
2
43> string:words("abcdef ab, haa").
3
44> string:words("abcdef ab, haa",a).
** exception error: no function clause matching string:words("abcdef ab, haa",a) (string.erl, line 291)
45> string:words("abcdef ab, haa","a").
** exception error: no function clause matching string:words("abcdef ab, haa","a") (string.erl, line 291)
46> string:words("abcdef ab, haa",$a).
2
47> string:words("abcdef ab haa", $a).
2
48> string:words(" Hello old boy !", $o).
4
49> string:words(" Hello old boy !", $l).
3
50> string:sub_word("abcdef ab haa",2).
"ab"
51> string:sub_word("abcdef ab haa",6).
[]
52> string:sub_word("abcdef ab haa",3).
"haa"
53> string:sub_word("abcdef ab haa",0).
** exception error: no function clause matching string:s_word("abcdef ab haa",0,32,1,[]) (string.erl, line 321)
54> string:sub_word("abcdef ab haa",1).
"abcdef"
55> string:sub_word("abcdef ab haa", 2, $a).
"b h"
56> string:sub_word("abcdef ab haa", 1, $a).
"bcdef "
57> string:strip(" abcdef "). %% 字符串进行裁剪
"abcdef"
58> string:strip(" abcdef ", left).
"abcdef "
59> stringstrip(" abcdef ", right).
** exception error: undefined shell command stringstrip/2
60> strign:strip(" abcdef ", right).
** exception error: undefined function strign:strip/2
61> string:strip(" abcdef ", right).
" abcdef"
62> string:strip(" abcdef ", both).
"abcdef"
63> string;strip("abcdeff", $f).
* 1: syntax error before: '.'
63> string:strip("abcdeff", $f).
** exception error: no function clause matching string:strip("abcdeff",102) (string.erl, line 340)
64> string:strip("abcdeff", 'f').
** exception error: no function clause matching string:strip("abcdeff",f) (string.erl, line 340)
65> string:strip("abcdeff", "f").
** exception error: no function clause matching string:strip("abcdeff","f") (string.erl, line 340)
66> string:strip("abcdeff",both, "f").
** exception error: no function clause matching string:strip_left("abcdeff","f") (string.erl, line 356)
in function string:strip/3 (string.erl, line 354)
67> string:strip("abcdeff",both, $f).
"abcde"
68> string:left("abcdeff", 2).
"ab"
69> string:left("abcdeff", 2, $s).
"ab"
70> string:left("abcdeff", 20, $s).
"abcdeffsssssssssssss"
71> string:right("abcdeff", 2).
"ff"
72> string:right("abcdeff", 20, $s).
"sssssssssssssabcdeff"
73> string:centre("abcdeff", 2).
"cd"
74> string:centre("abcdeff", 5).
"bcdef"
75> string:centre("abcdeff", 1).
"d"
76> string:centre("abcdeffg", 1).
"d"
77> string:centre("abcdeffg", 2).
"de"
78> string:centre("abcdeffg ijklmndeffa", 2, $d).
"ij"
79> string:centre("abcdeffg ijklmndeffa", 2, $a).
"ij"
80> string:centre("abcdeffg ijklmndeffa", 2, $f).
"ij"
81> string:stu_string("abcdeffg", 1).
** exception error: undefined function string:stu_string/2
82> string:sub_string("abcdeffg", 2).
"bcdeffg"
83> string:sub_string("abcdeffg", 2,3). %% 获取子字符串，并且指定开始，和结束位置
"bc"
84> string:sub_string("abcdeffg", 2,9).
"bcdeffg"
85> string:to_float("abcdeffg").
{error,no_float}
86> string:to_float("20"). %% 字符串转化为浮点形
{error,no_float}
87> string:to_float("20.0").
{20.0,[]}
88> string:to_integer("20").
{20,[]}
89> string:to_integer("20.0").
{20,".0"}
90> string:to_integer("20.3").
{20,".3"}
91> string:to_lower("abcdefg"). %% 字符串大小写转化
"abcdefg"
92> string:to_upper("abcdef").
"ABCDEF"
93> string:to_upper("20").
"20"
94> string:to_upper($a).
65
95> string:to_upper($A).
65
96>