Lua userdata详解

userdata

Q：什么是 userdata ？
A：分为两类，full userdata 和 light userdata。Lua使用他们来表示C中的类型。

Q：两种”userdata”的区别？
A：

例子一 light userdata

#include <stdio.h>  
#include <string>
#include <iostream>
using namespace std;
extern "C" {
#include "lua.h"  
#include "lualib.h"  
#include "lauxlib.h"  
}
typedef struct
{
    int x;
    int y;
    int z;
}TData;
static int getAttribute(lua_State* L)
{
    TData *data = (TData*)lua_touserdata(L, 1);
    std::string attribute = luaL_checkstring(L, 2);
    int result = 0;
    if (attribute == "x")
    {
        result = data->x;
    }
    else if (attribute == "y")
    {
        result = data->y;
    }
    else
    {
        result = data->z;
    }
    lua_pushnumber(L, result);
    return 1;
}
static  luaL_Reg dataLib[] = {
    { "__index", getAttribute },
    { NULL, NULL }
};
void getMetaTable(lua_State* L, luaL_Reg* methods)
{
    lua_pushlightuserdata(L, methods);
    lua_gettable(L, LUA_REGISTRYINDEX);
    if (lua_isnil(L, -1)) {
        /* not found */
        lua_pop(L, 1);
        lua_newtable(L);
        luaL_setfuncs(L, methods, 0);
        lua_pushlightuserdata(L, methods);
        lua_pushvalue(L, -2);
        lua_settable(L, LUA_REGISTRYINDEX);
    }
}
int main()
{
    const char* filename = "test.lua";
    lua_State *lua = luaL_newstate();
    if (lua == NULL)
    {
        fprintf(stderr, "open lua failed");
        return -1;
    }
    luaL_openlibs(lua);
    TData input = { 123, 231, 321 };
    lua_pushlightuserdata(lua, &input);
    getMetaTable(lua, dataLib);
    lua_setmetatable(lua, -2);
    lua_setglobal(lua, "input");
    if (luaL_dofile(lua, filename))
    {
        //luaL_error(lua, "load file %s failed", filename);
    }
    lua_getglobal(lua, "data");
    int output = lua_tointeger(lua, -1);
    std::cout << output << std::endl;
    return 0;
}

lua文件

data = input.x;
print(data)

例子二 full userdata

//#include <string.h>  

extern "C" {
    #include "lua.h"  
    #include "lauxlib.h"  
    #include "lualib.h"  
}

#include <iostream>  
using namespace std;

static struct StudentTag
{
    char *strName; // 学生姓名
    char *strNum; // 学号
    int iSex; // 学生性别
    int iAge; // 学生年龄
}T;

static int Student(lua_State *L)
{
    size_t iBytes = sizeof(struct StudentTag);
    struct StudentTag *pStudent;
    pStudent = (struct StudentTag *)lua_newuserdata(L, iBytes);

     //设置元表
    luaL_getmetatable(L, "Student");
    lua_setmetatable(L, -2);

    //lua_pushnumber(L, 123);

    return 1; // 新的userdata已经在栈上了
}

static int GetName(lua_State *L)
{
    struct StudentTag *pStudent = (struct StudentTag *)luaL_checkudata(L, 1, "Student");
    lua_pushstring(L, pStudent->strName);
    return 1;
}

static int SetName(lua_State *L)
{
    // 第一个参数是userdata
    struct StudentTag *pStudent = (struct StudentTag *)luaL_checkudata(L, 1, "Student");

    // 第二个参数是一个字符串
    const char *pName = luaL_checkstring(L, 2);
    luaL_argcheck(L, pName != NULL && pName != "", 2, "Wrong Parameter");

    pStudent->strName =(char*) pName;
    return 0;
}

static int GetAge(lua_State *L)
{
    struct StudentTag *pStudent = (struct StudentTag *)luaL_checkudata(L, 1, "Student");
    lua_pushinteger(L, pStudent->iAge);
    return 1;
}

static int SetAge(lua_State *L)
{
    struct StudentTag *pStudent = (struct StudentTag *)luaL_checkudata(L, 1, "Student");

    int iAge = luaL_checkinteger(L, 2);
    luaL_argcheck(L, iAge >= 6 && iAge <= 100, 2, "Wrong Parameter");
    pStudent->iAge = iAge;
    return 0;
}

static int GetSex(lua_State *L)
{
    // 这里由你来补充
    return 1;
}

static int SetSex(lua_State *L)
{
    // 这里由你来补充
    return 0;
}

static int GetNum(lua_State *L)
{
    // 这里由你来补充
    return 1;
}

static int SetNum(lua_State *L)
{
    // 这里由你来补充
    return 0;
}

static  luaL_Reg arrayFunc_meta[] =
{
    { "getName", GetName },
    { "setName", SetName },
    { "getAge", GetAge },
    { "setAge", SetAge },
    { "getSex", GetSex },
    { "setSex", SetSex },
    { "getNum", GetNum },
    { "setNum", SetNum },
    { NULL, NULL }
};

static luaL_Reg arrayFunc[] =
{
    { "new", Student},
    { NULL, NULL }
};

extern "C"  _declspec(dllexport) int luaopen_mytestlib(lua_State *L)
{
    // 创建一个新的元表
    luaL_newmetatable(L, "Student");
    // 元表.__index = 元表
    lua_pushvalue(L, -1);
    lua_setfield(L, -2, "__index");
    luaL_setfuncs(L, arrayFunc_meta, 0);
    luaL_newlib(L, arrayFunc);
    lua_pushvalue(L, -1);
    lua_setglobal(L, "Sdudent"); /* the module name */
    return 1;
}

lua 文件

require "mytestlib"

local objStudent = Sdudent.new()

objStudent:setName("果冻")
local strName = objStudent:getName()
print(strName )

for k,v in pairs(getmetatable(objStudent)) do
    print(tostring(k),tostring(v))
end

参考

http://blog.csdn.net/mydriverc2/article/details/51007803
http://blog.csdn.net/rain_qingtian/article/details/44781183