Corona中文站

这个库提供了字符串处理的通用函数，例如查找和提取子字符串，以及模式匹配。当在lua中索引一个字符串时，第一个字符是从1开始的（而不象C那样从0开始）。索引号可以是附属，用来从后向前索引。例如，最后一个字符的位置就是－1，以此类推。

这个string库把所有的函数放在一个table（string）里。它允许你为字符串设置元表，__index字段指向string table。因此，你可以以面向对象的风格来使用字符串函数。例如，string.byte(s, i)也可以写成 s:byte(i)。

这个string库假定为一字节字符编码。

string.byte (s [, i [, j]])

返回内部字符的数字码 s[i], s[i+1], ..., s[j]。默认值i＝1；而j默认值为i。

注意数字码，不一定是跨平台兼容的。

string.char (...)

接收0个或更多个整数。返回一个长度等于参数个数的字符串，每个字符对应其每个参数。

string.find (s, pattern [, init [, plain]])

在字符串s中使用第一个 pattern来匹配。如果找到一个匹配，则返回其开始和结束的索引号。否则，返回nil。第三，可选的参数init标明要从哪里开始搜索；它默认值是1，并且可以为负。第四个可选参数 plain，如果是false，将关闭模式匹配机制，所以这个函数只是一个纯“子字符串查找”，没有字符被作为模式中的特殊符号。如果有plain参数，那么init参数也必须给出。

如果模式匹配成功，被匹配到的值也会被返回，在前两个返回值之后。

string.format (formatstring, ...)

返回一个字符串的格式化版本。格式字符串formatstring允许和标准C函数一样的规则。唯一的不同是，选项／ 和修改器*，I，L，n，p和h不会被支持，以及有增加一个q选项。这个q选项很神奇，它通过Lua解释起安全的回读一个包含格式符的字符串。这个字符串被两个单引号包围，其中的所有的双引号，换行，嵌入0，反斜杠，都被正确分析出来。例如：

1
string.format('%q', 'a string with "quotes" and \n new line')


将产生如下字符串:

1

2
"a string with \"quotes\" and \

new line"


选项 c, d, E, e, f, g, G, i, o, u, X, 和 x ，都是对应一个数字做为参数，只有q对应一个字符串。

这个函数不接受嵌入\0的字符串值，除非用q选项。

string.gmatch (s, pattern)

返回一个迭代器函数，每次它被调用，就返回从s字符串中按照pattern模式，下一次捕获的内容。如果pattern指定不捕获，那么每次调用都会产生整个match内容。

下面是一个例子：

1

2

3

4
s = "hello world from Lua"

for w in string.gmatch(s, "%a+") do

print(w)

end


将会在s字符串中迭代所有的单词，每行打印一个。下一个例子从给定字符串中，搜集所有key＝value的pair 到一个table里：

1

2

3

4

5
t = {}

s = "from=world, to=Lua"

for k, v in string.gmatch(s, "(%w+)=(%w+)") do

t[k] = v

end


在这个函数里，不会在pattern开头使用“^”作为一个锚点，因为这样阻止迭代。

string.gsub (s, pattern, repl [, n])

Returns a copy of s in which all (or the first n, if given) occurrences of the pattern have been replaced by a replacement string specified by repl, which can be a string, a table, or a function. gsub also returns, as its second value, the total number of matches that occurred.

If repl is a string, then its value is used for replacement. The character % works as an escape character: any sequence in repl of the form %n, with n between 1 and 9, stands for the value of the n-th captured substring (see below). The sequence %0 stands for the whole match. The sequence %% stands for a single %.

If repl is a table, then the table is queried for every match, using the first capture as the key; if the pattern specifies no captures, then the whole match is used as the key.

If repl is a function, then this function is called every time a match occurs, with all captured substrings passed as arguments, in order; if the pattern specifies no captures, then the whole match is passed as a sole argument.

If the value returned by the table query or by the function call is a string or a number, then it is used as the replacement string; otherwise, if it is false or nil, then there is no replacement (that is, the original match is kept in the string).

Here are some examples:

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20
x = string.gsub("hello world", "(%w+)", "%1 %1")

--> x="hello hello world world"



x = string.gsub("hello world", "%w+", "%0 %0", 1)

--> x="hello hello world"



x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")

--> x="world hello Lua from"



x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)

--> x="home = /home/roberto, user = roberto"



x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)

return loadstring(s)()

end)

--> x="4+5 = 9"



local t = {name="lua", version="5.1"}

x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)

--> x="lua-5.1.tar.gz"


string.len (s)

Receives a string and returns its length. The empty string "" has length 0. Embedded zeros are counted, so "a\000bc\000" has length 5.

string.lower (s)

Receives a string and returns a copy of this string with all uppercase letters changed to lowercase. All other characters are left unchanged. The definition of what an uppercase letter is depends on the current locale.

string.match (s, pattern [, init])

Looks for the first match of pattern in the string s. If it finds one, then match returns the captures from the pattern; otherwise it returns nil. If pattern specifies no captures, then the whole match is returned. A third, optional numerical argument init specifies where to start the search; its default value is 1 and can be negative.

string.rep (s, n)

Returns a string that is the concatenation of n copies of the string s.

string.reverse (s)

Returns a string that is the string s reversed.

string.sub (s, i [, j])

Returns the substring of s that starts at i and continues until j; i and j can be negative. If j is absent, then it is assumed to be equal to -1 (which is the same as the string length). In particular, the call string.sub(s,1,j) returns a prefix of s with length j, and string.sub(s, -i) returns a suffix of s with length i.

string.upper (s)

Receives a string and returns a copy of this string with all lowercase letters changed to uppercase. All other characters are left unchanged. The definition of what a lowercase letter is depends on the current locale.

Patterns

Character Class:

A character class is used to represent a set of characters. The following combinations are allowed in describing a character class: x: (where x is not one of the magic characters ^$()%.[]*+-?) represents the character x itself.

.: (a dot) represents all characters.

%a: represents all letters.

%c: represents all control characters.

%d: represents all digits.

%l: represents all lowercase letters.

%p: represents all punctuation characters.

%s: represents all space characters.

%u: represents all uppercase letters.

%w: represents all alphanumeric characters.

%x: represents all hexadecimal digits.

%z: represents the character with representation 0.

%x: (where x is any non-alphanumeric character) represents the character x. This is the standard way to escape the magic characters. Any punctuation character (even the non magic) can be preceded by a '%' when used to represent itself in a pattern.

[set]: represents the class which is the union of all characters in set. A range of characters can be specified by separating the end characters of the range with a '-'. All classes %x described above can also be used as components in set. All other characters in set represent themselves. For example, [%w_] (or [_%w]) represents all alphanumeric characters plus the underscore, [0-7] represents the octal digits, and [0-7%l%-] represents the octal digits plus the lowercase letters plus the '-' character. The interaction between ranges and classes is not defined. Therefore, patterns like [%a-z] or [a-%%] have no meaning.

[^set]: represents the complement of set, where set is interpreted as above.

For all classes represented by single letters (%a, %c, etc.), the corresponding uppercase letter represents the complement of the class. For instance, %S represents all non-space characters.

The definitions of letter, space, and other character groups depend on the current locale. In particular, the class [a-z] may not be equivalent to %l.

Pattern Item:

A pattern item can be

• a single character class, which matches any single character in the class;

• a single character class followed by '*', which matches 0 or more repetitions of characters in the class. These repetition items will always match the longest possible sequence;

• a single character class followed by '+', which matches 1 or more repetitions of characters in the class. These repetition items will always match the longest possible sequence;

• a single character class followed by '-', which also matches 0 or more repetitions of characters in the class. Unlike '*', these repetition items will always match the shortest possible sequence;

• a single character class followed by '?', which matches 0 or 1 occurrence of a character in the class;

• %n, for n between 1 and 9; such item matches a substring equal to the n-th captured string (see below);

• %bxy, where x and y are two distinct characters; such item matches strings that start with x, end with y, and where the x and y are balanced. This means that, if one reads the string from left to right, counting +1 for an x and -1 for a y, the ending y is the first y where the count reaches 0. For instance, the item %b() matches expressions with balanced parentheses.

Pattern:

A pattern is a sequence of pattern items. A '^' at the beginning of a pattern anchors the match at the beginning of the subject string. A '$' at the end of a pattern anchors the match at the end of the subject string. At other positions, '^' and '$' have no special meaning and represent themselves.

Captures:

A pattern can contain sub-patterns enclosed in parentheses; they describe captures. When a match succeeds, the substrings of the subject string that match captures are stored (captured) for future use. Captures are numbered according to their left parentheses. For instance, in the pattern "(a*(.)%w(%s*))", the part of the string matching "a*(.)%w(%s*)" is stored as the first capture (and therefore has number 1); the character matching "." is captured with number 2, and the part matching "%s*" has number 3.

As a special case, the empty capture () captures the current string position (a number). For instance, if we apply the pattern "()aa()" on the string "flaaap", there will be two captures: 3 and 5.

A pattern cannot contain embedded zeros. Use %z instead.