Lua快速入门实例

2012-12-06 15:06:56

分类： Python/Ruby

注：以下例子选自LuaForWindows(LFW)组件QuickLuaTour，对其中做了一些主要的翻译并加上了个人的理解注释，没有安装过LFW的朋友可以一看，虽然例子很简单，但是对初学者快速入门会有所帮助。

关键词：Lua、Lua实例、QuickLuaTour、LFW、Lua入门

-- Example 1 --
First Program.

-- Classic hello program.

print("hello")

-------- Output ------

Hello

-- Example 2 --
Comments. 注释

--单行注释以双连字符“--”开头多行注释“—[[”以开始，以“]]”结束

-- Single line comments in Lua start with double hyphen.

--[[ Multiple line comments start

with double hyphen and two square brackets.

and end with two square brackets. ]]

-- And of course this example produces no

-- output, since it's all comments!

-------- Output ------

-- Example 3 --
Variables.

-- Variables hold values which have types, variables don't have types.

--变量的值拥有类型，变量没有类型

a=1

b="abc"

c={}

d=print

print(type(a))

print(type(b))

print(type(c))

print(type(d))

-------- Output ------

number

string

table

function

-- Example 4 --
Variable names. 变量命名

-- Variable names consist of letters, digits and underscores.

-- They cannot start with a digit.

-- 变量的名称由字母、数字、下划线组成，但是不能以数字开始

one_two_3 = 123 -- is valid varable name --合法命名

-- 1_two_3 is not a valid variable name. --以数字开始，不合法

-------- Output ------

-- Example 5 --
More Variable names.
--[[ 在Lua中以下划线”_”开始的参数命名通常代表特殊的值，如（“_VERSION”），所以尽量不用使用以下划线开始命名。当时通常单个“_”代表虚假的参数。注：这是Lua的一个语法，后面将讲到，如：local
_, x = string.find(s, p) ]]

-- The underscore is typically used to start special values

-- like _VERSION in Lua.

print(_VERSION)

-- So don't use variables that start with _,

-- but a single underscore _ is often used as a

-- dummy variable.

-------- Output ------

-- Example 6 --
Case Sensitive. 大小写敏感

-- Lua is case sensitive so all variable names & keywords

-- must be in correct case.

-- 在Lua中所有的变量和关键字都是大小写敏感的

ab=1

Ab=2

AB=3

print(ab,Ab,AB)

-------- Output ------

1 2 3

-- Example 7 --
Keywords. Lua关键字

--[[ Lua的关键字大家可以去参考“Lua
Reference Manual”，附：5.1版本的参考手册在线地址：http://www.lua.org/manual/5.1/index.html 变量命名的时候应避免使用关键字,应Lua是大小写敏感的，所以“and”是关键字，但“AND”不是是合法的命名，尽管如此，建议大家尽量不要用关键词(各种大小写版本)]]

-- Lua reserved words are: and, break, do, else, elseif,

-- end, false, for, function, if, in, local, nil, not, or,

-- repeat, return, then, true, until, while.

-- Keywords cannot be used for variable names,

-- 'and' is a keyword, but AND is not, so it is a legal variable name.

AND=3

print(AND)

-------- Output ------

3

-- Example 8 --
Strings.

--[[字符串可以用双引号（“”）也可以用单引号（‘’），类似于JavaScript语法，对于多行字符串，使用“[[
]]”括起来 ]]

a="single 'quoted' string and double \"quoted\" string inside"

b='single \'quoted\' string and double "quoted" string inside'

c= [[ multiple line

with 'single'

and "double" quoted strings inside.]]

print(a)

print(b)

print(c)

-------- Output ------

single 'quoted' string and double "quoted" string inside

single 'quoted' string and double "quoted" string inside

multiple line

with 'single'

and "double" quoted strings inside.

-- Example 9 --
Assignments. 赋值

--[[可以一次对多个变量赋值，规则：如果等号（“=”）右边多了，则舍弃，左边多了，则赋值为空（nil） ]]

-- Multiple assignments are valid.

-- var1,var2=var3,var4

a,b,c,d,e = 1, 2, "three", "four", 5

print(a,b,c,d,e)

-------- Output ------

1 2 three four 5

-- Example 10 --
More Assignments.

-- Multiple assignments allows one line to swap two variables.

-- 表达式 a,b=b,a表示a和b的值交换

print(a,b)

a,b=b,a

print(a,b)

-------- Output ------

1 2

2 1

-- Example 11 --
Numbers.

-- Multiple assignment showing different number formats.

-- Two dots (..) are used to concatenate strings (or a

-- string and a number). – 在Lua中两点“..”表示字符串连接，对应其他语言中的“+”连接

a,b,c,d,e = 1, 1.123, 1E9, -123, .0008

print("a="..a, "b="..b, "c="..c, "d="..d, "e="..e)

-------- Output ------

a=1 b=1.123 c=1000000000 d=-123 e=0.0008

-- Example 12 --
More Output.

-- More writing output. –多种输出方式或写法

print "Hello from Lua!" -- 不带括号

print("Hello from Lua!") -- 带括号，两者等价

-------- Output ------

Hello from Lua!

Hello from Lua!

--[[什么时候可以省略括号? 这是以种特殊的情况，只有当函数的参数只有一个，而且这个参数是字面上的字符串串（a
literal string:即直接传字符串，而不是值为字符串的参数变量）或者蚕食是table结构。这两种情况才可以省略圆括号]]

-- Example 14 --
Tables.

-- 表结构在Lua中特别常见，可以存储任何类型，很灵活。非常类似于JS中的一个对象。

-- Simple table creation.

a={} -- {} creates an empty table

b={1,2,3} -- creates a table containing numbers 1,2,3

c={"a","b","c"} -- creates a table containing strings a,b,c

print(a,b,c) -- tables don't print directly, we'll get back to this!!

-------- Output ------

table: 00410A58 table: 00410E90 table: 00410FB8

-- Example 15 --
More Tables.

-- Lua中表结构和JS中的对象一样可以随时增加或删除（直接赋值nil）属性。

--[[ 读取有多种方式，可以用点“.”的方式，也可以用索引index,不过在Lua有点特殊，首先索引是从一开始，其次index=1并不一定是第一个元素值，比如下面的address[1]=nil，而不是“Wyman
Street”,具体的以后在讲]]

-- Associate index style.

address={}
-- empty address

address.Street="Wyman Street"

address.StreetNumber=360

address.AptNumber="2a"

address.City="Watertown"

address.State="Vermont"

address.Country="USA"

print(address.StreetNumber, address["AptNumber"])

-------- Output ------

360 2a

-- Example 16 --
if statement. if语句

-- Lua中的语句块语法有点类似VB都是以end结束

-- Simple if.

a=1

if a==1 then

print ("a is one")

end

-------- Output ------

a is one

-- Example 17 --
if else statement.

b="happy"

if b=="sad" then

print("b is sad")

else

print("b is not sad")

end

-------- Output ------

b is not sad

-- Example 18 --
if elseif else statement

-- 需要注意的是“elseif” 是连在一起的，这个和C#的 else
if 不同

c=3

if c==1 then

print("c is 1")

elseif c==2 then

print("c is 2")

else

print("c isn't 1 or 2, c is "..tostring(c))

end

-------- Output ------

c isn't 1 or 2, c is 3

-- Example 19 --
Conditional assignment. 条件语句

-- value = test and x or y

--注：value
= test and x or y 等价于我们平时写的三元运算符（“？:”)的效果 value=
test?x:y

a=1

b=(a==1) and "one" or "not one"

print(b)

-- is equivalent to

a=1

if a==1 then

b = "one"

else

b = "not one"

end

print(b)

-------- Output ------

one

one

-- Example 20 --
while statement.

-- while语句

a=1

while a~=5 do -- Lua uses ~= to mean not equal

a=a+1

io.write(a.." ")

end

-------- Output ------

2 3 4 5

-- Example 21 --
repeat until statement.

a=0

repeat

a=a+1

print(a)

until a==5

-------- Output ------

1

2

3

4

5

-- Example 22 --
for statement.

-- for语句有两种变体，一种叫 Numeric
for ,一种叫 Generic
for 就是例23中的for…in结构

--[[ Numeric for 的语法为：

for var=exp1,exp2,exp3 do something end

等价于C#中的：for(int
i=exp1; i<=exp2; i+=exp3) { something }

]]

-- Numeric iteration form.

-- Count from 1 to 4 by 1.

for a=1,4 do io.write(a) end

print()

-- Count from 1 to 6 by 3.

for a=1,6,3 do io.write(a) end

-------- Output ------

1234

14

-- Example 23 --
More for statement.

-- for语句的Generic
for变体

-- Sequential iteration form.

for key,value in pairs({1,2,3,4}) do print(key, value) end

-------- Output ------

1 1

2 2

3 3

4 4

-- Example 24 --
Printing tables.

-- 用简单的方式遍历table结构，并输出

-- Simple way to print tables.

a={1,2,3,4,"five","elephant", "mouse"}

for i,v in pairs(a) do print(i,v) end

-------- Output ------

1 1

2 2

3 3

4 4

5 five

6 elephant

7 mouse

-- Example 25 --
break statement.

-- break is used to exit a loop.

-- break关键字用于跳出循环，当然return也可以，不过有区别

a=0

while true do

a=a+1

if a==10 then

break

end

end

print(a)

-------- Output ------

10

-- Example 26 --
Functions.

-- 最简单的函数调用

-- Define a function without parameters or return value.

function myFirstLuaFunction()

print("My first lua function was called")

end

-- Call myFirstLuaFunction.

myFirstLuaFunction()

-------- Output ------

My first lua function was called

-- Example 27 --
More functions.

--[[ 带返回值的函数调用，大家注意a=mySecondLuaFunction("string")带了一个参数，但是mySecondLuaFunction定义并没有带参数，这个在Lua比较松，会直接忽略，即使你多写几个也没关系。]]

-- Define a function with a return value.

function mySecondLuaFunction()

return "string from my second function"

end

-- Call function returning a value.

a=mySecondLuaFunction("string")

print(a)

-------- Output ------

string from my second function

-- Example 28 --
More functions.

--[[ 使用函数返回值对多个变量赋值，规则和多参数赋值一样，如果函数返回值多了，则抛弃，少了则少的赋值为nil ]]

-- Define function with multiple parameters and multiple return values.

function myFirstLuaFunctionWithMultipleReturnValues(a,b,c)

return a,b,c,"My first lua function with multiple return values", 1, true

end

a,b,c,d,e,f = myFirstLuaFunctionWithMultipleReturnValues(1,2,"three")

print(a,b,c,d,e,f)

-------- Output ------

1 2 three My first lua function with multiple return values

1 true

-- Example 29 --
Variable scoping and functions. 变量作用域

--[[ 在Lua中，默认声明的变量为全局变量，以local 为修饰符的为局部变量，局部变量只在所属的语句块内有效]]

-- All variables are global in scope by default.

b="global"

-- To make local variables you must put the keyword 'local' in front.

function myfunc()

local b=" local variable"

a="global variable"

print(a,b)

end

myfunc()

print(a,b)

-------- Output ------

global variable local variable

global variable global

-- Example 30 --
Formatted printing. 字符串格式

--[[ 字符串格式大家可以去参考Lua参考手册“Lua
Reference Manual”http://www.lua.org/manual/5.1/index.html 这里重点说明一下在这些例子中第一次见到三个点“…”的作用，在Lua中在函数的参数列表中，表示参数的格式是可变不固定的，当这个函数在被调用时，函数的所有参数都被存储在一个名为arg的表结构中，同时arg还有一个n属性，代表实际传人的可变参数的个数，那么可以通过arg来访问所有的可变参数了，细节的以后再讲]]

-- An implementation of printf.

function printf(fmt, ...)

io.write(string.format(fmt, ...))

end

printf("Hello %s from %s on %s\n",

os.getenv"USER" or "there", _VERSION, os.date())

-------- Output ------

Hello there from Lua 5.1 on 08/11/11 16:48:19

-- Example 31 --[[

Standard Libraries

Lua has standard built-in libraries for common operations in

math, string, table, input/output & operating system facilities.

External Libraries

Numerous other libraries have been created: sockets, XML, profiling,

logging, unittests, GUI toolkits, web frameworks, and many more.

]]

-------- Output ------

-- Example 32 --
Standard Libraries - math. Lua中标准的数学函数

--[[详细请参考Lua参考手册“Lua
Reference Manual” http://www.lua.org/manual/5.1/index.html ]]

-- Math functions:

-- math.abs, math.acos, math.asin, math.atan, math.atan2,

-- math.ceil, math.cos, math.cosh, math.deg, math.exp, math.floor,

-- math.fmod, math.frexp, math.huge, math.ldexp, math.log, math.log10,

-- math.max, math.min, math.modf, math.pi, math.pow, math.rad,

-- math.random, math.randomseed, math.sin, math.sinh, math.sqrt,

-- math.tan, math.tanh

print(math.sqrt(9),
math.pi)

-------- Output ------

3 3.1415926535898

-- Example 33 --
Standard Libraries - string. Lua中string类库

-- String functions:

-- string.byte, string.char, string.dump, string.find, string.format,

-- string.gfind, string.gsub, string.len, string.lower, string.match,

-- string.rep, string.reverse, string.sub, string.upper

print(string.upper("lower"),string.rep("a",5),string.find("abcde", "cd"))

-------- Output ------

LOWER aaaaa 3 4

-- Example 34 --
Standard Libraries - table. Lua中的table类库

-- Table functions:

-- table.concat, table.insert, table.maxn, table.remove, table.sort

a={2}

table.insert(a,3);

table.insert(a,4);

table.sort(a,function(v1,v2) return v1 > v2 end)

for i,v in ipairs(a) do print(i,v) end

-------- Output ------

1 4

2 3

3 2

-- Example 35 --
Standard Libraries - input/output. 输入输出

--[[其中：io.write函数和print函数的功能相同都是输出显示，只是io.write输出后不换行]]

-- IO functions:

-- io.close , io.flush, io.input, io.lines, io.open, io.output, io.popen,

-- io.read, io.stderr, io.stdin, io.stdout, io.tmpfile, io.type, io.write,

-- file:close, file:flush, file:lines ,file:read,

-- file:seek, file:setvbuf, file:write

print(io.open("file doesn't exist", "r"))

-------- Output ------

nil file doesn't exist: No such file or directory 2

-- Example 36 --
Standard Libraries - operating system facilities. 操作系统中类库

-- OS functions:

-- os.clock, os.date, os.difftime, os.execute, os.exit, os.getenv,

-- os.remove, os.rename, os.setlocale, os.time, os.tmpname

print(os.date())

-------- Output ------

08/11/11 17:07:30

-- Example 37 --
External Libraries. 扩展类库

-- Lua has support for external modules using the 'require' function

-- INFO: A dialog will popup but it could get hidden behind the console.

require( "iuplua" )

ml = iup.multiline

{

expand="YES",

value="Quit this multiline edit app to continue Tutorial!",

border="YES"

}

dlg = iup.dialog{ml; title="IupMultiline", size="QUARTERxQUARTER",}

dlg:show()

print("Exit GUI app to continue!")

iup.MainLoop()

-------- Output ------

-- Example 38 --[[

-- 后续学习lua-users
wiki

To learn more about Lua scripting see

Lua Tutorials: http://lua-users.org/wiki/TutorialDirectory

"Programming in Lua" Book: http://www.inf.puc-rio.br/~roberto/pil2/

Lua 5.1 Reference Manual:

Start/Programs/Lua/Documentation/Lua 5.1 Reference Manual

Examples: Start/Programs/Lua/Examples

]]