lua基础知识 | marstau's blog

编译

file:///D:/download/lua-5.3.5/lua-5.3.5/doc/readme.html

cygwin安装make gcc
make mingw

基础语法

table.nums

math.modf # 无法保证小数部分的精确度,如math.modf(279.001), 小数部分不一定是0.001

upvalueMore

local index;和local index

分号结尾不是必须的,只要后面没有句子即可。

lua for循环1,5,指的是1,2,3,4,5(包括5)More

Lua 缺省没有整数类型,除法一律按浮点数来算,因此不涉及商的取整问题More

取整More

1. 使用math.modf(x/y)此函数,第一参数返回整数部分,第二个参数返回小数部分:

t1,t2 = math.modf(30/10)

2. 使用math.floor(x),返回不大于x的最大整数

求余

a%b = a - math.floor(a/b)*b

求table元素数量

local testTable = {
    [1] = 0,
    [0] = 1,
}
print("testTable=",#testTable)

testTable=1

local testTable = {
    [1] = 0,
    [2] = 1,
}
print("testTable=",#testTable)

testTable=2Ish

垃圾回收More

自动内存管理,lua运行一个垃圾收集器来收集所有死对象.实现了一个增量标记-扫描收集器.使用这两个数字来控制垃圾收集循环:垃圾收集器间歇率和垃圾收集器步进倍率。这两个数字都用百分数为单位(值150代表1.5倍)

垃圾收集器间歇率:控制收集器需要在开启新的循环前要等待多久。 <100时,收集器开启新的循环前不会有等待. x >=100时,收集器等到总内存使用量达到之前的x/100倍时,才开始新的循环.

垃圾收集器步进倍率:控制收集器运作速度相对于内存分配速度的倍率。

`__call`

树形打印tableMore

function print_r ( t )  
    local print_r_cache={}
    local function sub_print_r(t,indent)
        if (print_r_cache[tostring(t)]) then
            print(indent.."*"..tostring(t))
        else
            print_r_cache[tostring(t)]=true
            if (type(t)=="table") then
                for pos,val in pairs(t) do
                    if (type(val)=="table") then
                        print(indent.."["..pos.."] => "..tostring(t).." {")
                        sub_print_r(val,indent..string.rep(" ",string.len(pos)+8))
                        print(indent..string.rep(" ",string.len(pos)+6).."}")
                    elseif (type(val)=="string") then
                        print(indent.."["..pos..'] => "'..val..'"')
                    else
                        print(indent.."["..pos.."] => "..tostring(val))
                    end
                end
            else
                print(indent..tostring(t))
            end
        end
    end
    if (type(t)=="table") then
        print(tostring(t).." {")
        sub_print_r(t,"  ")
        print("}")
    else
        sub_print_r(t,"  ")
    end
    print()
end

pairs和ipairsMore

pairs遍历table中的所有的key-vale 而ipairs会根据key的数值从1开始加1递增遍历对应的table[i]值

a = {[1] = "a1", [2] = "a2", [3] = "a3", [5] = "a4", [6] = "a5",}
for key, value in ipairs(a) do
  print(key, value)
end


结果：
1	a1
2	a2
3	a3

a = {[1] = "a1", [2] = "a2", [3] = "a3", [5] = "a4", [6] = "a5",}
for key, value in pairs(a) do
  print(key, value)
end
结果：
6	a5
2	a2
3	a3
1	a1
5	a4

table的使用

定义

local table1 = {}

才能使用

table1[1] = "abc";

lua模拟函数指针More

CacheManager._getInfo = {
    [1] = 
    {
        name = CacheManager._getName1,
        desc = CacheManager._getDesc1
    },
    [2] = 
    {
        name = CacheManager._getName2,
        desc = CacheManager._getDesc2
    },
}

function CacheManager:getDesc(type, id)
    return CacheManager._getInfo[type].desc(self, id)
end

function CacheManager:getName(type, id)
    return CacheManager._getInfo[type].name(self, id)
end

-- invoke
CacheManager c = CacheManager.new()
c:getName(2)
c:getDesc(1)

三目运算More

a and b or c

这里有个问题，就是当b是nil的时候会返回c的值

(a and {b} or {c})[1]

switch模拟More

local key = 1  
local switch = {  
    [1] = function()  
        print("switch:"..1)  
    end,  
    [2] = function()  
        print("switch:"..2)  
    end,  
    ["test"] = function()  
        print("switch:test")  
    end,  
}  
  
local fSwitch = switch[key] --switch func  
  
if fSwitch then --key exists  
    local result = fSwitch() --do func  
else
     --key not found
end  

1001 转中文一千零一

local CHS_NUMBER = {
    [0] = "零",
    [1] = "一",
    [2] = "二",
    [3] = "三",
    [4] = "四",
    [5] = "五",
    [6] = "六",
    [7] = "七",
    [8] = "八",
    [9] = "九",
    [10] = "十",
    [11] = "百",
    [12] = "千",
    [13] = "万",
}

-- 最大支持 < 10 0000
function getCHSNumberString(number)
    local bitIdx = 1

    local str = ""

    while number > 0 do
        local red = number%10

        number = math.floor(number/10)
        local zero = self:getString(self.CHS_NUMBER[0])
        if red == 0 then
            if not string.find(str, zero) and str ~= "" then
                str = zero..str
            end
        else
            if bitIdx > 1 then
                str = self:getString(self.CHS_NUMBER[bitIdx + 8])..str
            end

            if number > 0 or bitIdx ~= 2 or red ~= 1 then
                str = self:getString(self.CHS_NUMBER[red])..str
            end
        end

        bitIdx = bitIdx + 1
    end

    return str
end

获取utf8字符串长度

function getUTF8Len(str)
    local len  = string.len(str)
    local left = len
    local cnt  = 0
    local arr  = {0, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc}
    while left ~= 0 do
        local tmp = string.byte(str, -left)
        local i   = #arr
        while arr[i] do
            if tmp >= arr[i] then
                left = left - i
                break
            end
            i = i - 1
        end
        cnt = cnt + 1
    end
    return cnt
end

table为空

function isTableEmpty(t)
    if not t then
        return true
    end

    return next(t) == nil
end

重新加载More

使用package.loaded和require

function S:reload()
    local loadedTable = package.loaded
    for k,v in pairs(loadedTable) do
        local subStr = string.sub(k, 1, 4)
        if subStr == "app." then
            loadedTable[k] = nil
        end
    end

    for k,v in pairs(globalTable) do
        if not string.find(k, "Manager") and not string.find(k, "getClass") and not globalTable[k].init then
            globalTable[k] = nil
        end
    end
end

string.unpackMore

返回不定参数

local args = {func(self, params)}
local res = false
if args[1] == result_code then
    res = true
end
return res, unpack(args)

生成随机字符串数组

local totalCount = 5
local strLen = 12

local strs = "abcdefghijklmnopqrstuvwxyz"
local array = {}
for curCount = 1, totalCount do
    local tmpStrArray = {}
    for i = 1, strLen do
        local randValue = math.random(1, #strs)
        tmpStrArray[#tmpStrArray + 1] = string.sub(strs, randValue, randValue)
    end
    local str = table.concat(tmpStrArray,'')
    array[str] = str
end

Output:

jfbprlvargtw,
etlkdnmmcvwo,
ncjsadcwciqq,
mjulafvktjys,
muktlsfjctao,

正则使用

local res
local rate
local tmpS
self._description1 = string.gsub(row.description1, "%[(.-)%]", function (s)
    tmpS = {}
    string.gsub(s, "(%d+)", function(s2)
        tmpS[#tmpS + 1] = s2
    end)

    res = skillContent[tonumber(tmpS[1])]
    rate = tmpS[2] and tonumber(tmpS[2])
    if rate and rate > 0 then
        res = res / rate
    end
    return res
end)

FAQ

性能优化

lua invalid key to next

tbl["key1"] = true
for k, v in pairs(tbl) do
    tbl["key2"] = nil
end

改为

tbl["key1"] = true
for k, v in pairs(tbl) do
    if tbl["key2"] then
        tbl["key2"] = nil
    end
end

table.sort栈溢出

table.sort(list, function(a, b)
    return true -- 改为 return false即可。
end)

string.split

function split(input, delimiter)
    input = tostring(input)
    delimiter = tostring(delimiter)
    if (delimiter=='') then return false end
    local pos,arr = 0, {}
    -- for each divider found
    for st,sp in function() return string.find(input, delimiter, pos, true) end do
        table.insert(arr, string.sub(input, pos, st - 1))
        pos = sp + 1
    end
    table.insert(arr, string.sub(input, pos))
    return arr
end

string.gsub

lua中的string.gsub第二个参数可以使用匹配模式，并且模式串里面带中括号。那么表示会“捕捉”括号括起来的模式匹配到的字符串。

字符串太长安卓会导致连接不成功(1002个字符, luajit编译)

url = url .. "&extra4=" .. string.urlencode(self._attachURL)

洗牌

function shuffle(t)
    local tblLen = #t
    while(tblLen > 0)
    do
        local idx = math.random(tblLen)
        t[tblLen], t[idx] = t[idx], t[tblLen]
        tblLen = tblLen - 1
    end
    return t
end

 
local testTbl = {1, 2, 3, 4, 5, 6, 7, 8, 9}
local retTbl = shuffle(testTbl)
for k, v in ipairs(retTbl) do
    print(k, v)    
end

math.floor的坑

math.floor(34.5/0.75)可能会产生两种结果
math.floor(34.5*1.34) = 46
math.floor(34.5*1.33) = 45
1/0.75的结果是不确定的1.33333334或者1.3333333

local per = -9000
local v = 30
math.floor(v * (1 + per/10000)) = 2

万分比运算:
math.floor(v * (10000 + per)/10000) = 3

捕获异常

xpcall(function(a, b)
end, function(err, level)
    event_err_handle(err)
end, a, b)

asset

asset执行了之后的代码是不会执行的

内存泄漏More

内存不断增长More

每帧执行如下语句内存会不断分配

local t = {3, 4}

class高效率省内存实现

ClassType = {
    class = 1,
    instance = 2,
}

function class(classname, super)
    assert(type(classname) == "string" and #classname > 0)
    local cls
    
    if super then
        cls = {}
        setmetatable(cls, {__index = super})
        cls.super = super
    else
        cls = {ctor = function() end, dtor = false}
    end

    cls.__cname = classname
    cls.__ctype = ClassType.class
    cls.__index = cls

    cls.new = function(...)
        local obj = setmetatable({}, cls)
        obj.__cls = cls
        obj.__ctype = ClassType.instance
        obj:ctor(...)
        return obj
    end

    cls.delete = function(self)
        local curSuper = self.__cls
        while curSuper ~= nil do    
            local dtor = rawget(curSuper, "dtor")
            if dtor then
                dtor(self)
            end
            curSuper = curSuper.super
        end
    end
    
    return cls
end

一个坑：

-- TestClass.lua
local TestClass = class("TestClass")
TestClass.Tbl = {}
return TestClass

local t1 = TestClass.new()
t1.Tbl[#t1.Tbl + 1] = 3

local t2 = TestClass.new()
t2.Tbl[#t2.Tbl + 1] = 4

此时 #t2.Tbl == 2

全局变量管理More

检测全局变量：

if device.isStandalone then
    local __global_mt = {
        __newindex = function(t, k, v)
            if not _G[k] then
               print(debug.traceback("attempt to write an new global variable=" .. k, 2))
            end

            rawset(t, k, v)
        end
    }

    setmetatable(_G, __global_mt)
end

class的ctor中执行 `= self`赋值操作获取部分变量出问题

function WorldBaseActor:ctor()
    WorldCachingSingleton.WorldActorMap[self:getActorIdx()] = self
end

ctor会修改元表,执行完子类和父类的ctor,self的指针已经修改

lua profile各含义More

currentTime 总时间
self 总时间

`_ENV`More

`0` `-0`处理More

math.atan(-1.0, -0.0)
math.atan(-1.0, 0.0)
得到两个值

0计算的精度问题导致0存在正负号,解决方式:
math.atan(x + 0, y + 0)

Reference

Lua表存储优化, excel表压缩存储

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`__call`

1001 转中文一千零一

class的ctor中执行 `= self`赋值操作获取部分变量出问题

`_ENV`More

`0` `-0`处理More