Lua与C++交互

1、Lua和C++交互

1、lua和c++交互机制是基于一个虚拟栈，C++和lua之间的所有数据交互都通过这个虚拟栈来完成，无论何时C++想从lua中调用一个值，被请求的值将会被压入栈，C++想要传递一个值给Lua，首选将整个值压栈，然后就可以在Lua中调用。
2、lua中提供正向和反向索引，区别在于证书永远是栈底，负数永远是栈顶。

2、基础练习

编译指令：g++ test.cpp -o test -llua -ldl

#include <iostream>  
#include <string.h>  
using namespace std;extern "C"
{
#include "lua.h"  
#include "lauxlib.h"  
#include "lualib.h"  
}// g++ test.cpp -o test  -llua -ldl
int main()
{//1.创建一个state  // luaL_newstate返回一个指向堆栈的指针lua_State *L = luaL_newstate();//2.入栈操作  lua_pushstring(L, "hello world");lua_pushnumber(L, 200);//3.取值操作  if (lua_isstring(L, 1)) {             //判断是否可以转为string  cout << lua_tostring(L, 1) << endl;  //转为string并返回  }if (lua_isnumber(L, 2)) {cout << lua_tonumber(L, 2) << endl;}//4.关闭state  lua_close(L);return 0;
}

2.1、加载Lua脚本并传递参数

编译指令：g++ test.cpp -o test -llua -ldl

函数说明：1、函数用于将Lua脚本加载到Lua虚拟机中并进行编译
luaL_loadbuffer(L,s,sz,n)lua_State *L：Lua状态对象，表示Lua虚拟机的运行实例。const char *buff：指向Lua脚本内容的字符串。size_t sz：Lua脚本内容的长度。const char *name：可选参数，用于给脚本设置一个名称，便于调试和错误消息的输出。返回值：不为0表示有错误2、函数用于调用Lua函数并处理其执行过程中可能发生的错误
lua_pcall(L,n,r,f)lua_State *L：Lua状态对象，表示Lua虚拟机的运行实例。int nargs：传递给Lua函数的参数数量。int nresults：期望的返回值数量。int errfunc：错误处理函数在调用栈中的索引。返回值：不为0表示有错误3、函数用于从全局环境中获取一个全局变量，并将其值压入Lua栈顶
int lua_getglobal(lua_State *L, const char *name)lua_State *L：Lua状态对象，表示Lua虚拟机的运行实例。const char *name：要获取的全局变量的名称。4、函数用于将一个数字（lua_Number类型）压入Lua栈顶
void lua_pushnumber(lua_State *L, lua_Number n)lua_State *L：Lua状态对象，表示Lua虚拟机的运行实例。lua_Number n：要压入栈的数字。

执行流程：
1、加载script脚本加载到lua虚拟机中
2、将脚本中的my_pow函数，压入到栈顶
3、压入my_pow需要的两个参数
4、执行脚本
5、获取脚本中的返回值

#include <cstdio>
#include <cstring>
#include <cmath>
#include <new>
extern "C" {#include <lua.h>#include <lualib.h>#include <lauxlib.h>
}char const *script = R"(
function hello()print('hello world')
endfunction my_pow(x,y)return x^y
end
)";char const *script_1 = R"(pkg.hello()
)";int main()
{/*加载脚本并传递参数*/// 创建lua虚拟机，创建虚拟栈lua_State *state = luaL_newstate();// 打开lua标准库，以便正常使用lua apiluaL_openlibs(state);{// 将lua脚本加载到虚拟机中，并编译auto rst = luaL_loadbuffer(state,script,strlen(script),"hello");// 判断是否加载成功if(rst !=0 ){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("load script faile:%s\n",msg);lua_pop(state,-1);}return -1;}// 执行加载并编译的Lua脚本if(lua_pcall(state,0,0,0)){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("load script faile:%s",msg);lua_pop(state,-1);}}// 从全局环境中获取一个my_pow函数压入到栈顶lua_getglobal(state,"my_pow");// 判断栈顶是不是一个函数，要是不是表示没有找到if(!lua_isfunction(state,-1)){printf("function  named my_pow not function\n");return -1;}// 将数字参数压入Lua栈中lua_pushnumber(state,2);lua_pushnumber(state,8);rst = lua_pcall(state,2,1,0);if(rst !=0 ){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("load script faile:%s\n",msg);lua_pop(state,-1);}return -1;}if(lua_isnumber(state,-1)){lua_Number val = lua_tonumber(state,-1);printf("%lf\n",val);}}lua_close(state);return 0;
}

2.2、加载脚本到stable（包）

编译命令： g++ main.cpp -o main -llua -ldl

#include <cstdio>
#include <cstring>
#include <cmath>
#include <new>
extern "C" {#include <lua.h>#include <lualib.h>#include <lauxlib.h>
}
char const *script = R"(
function hello()print('hello world')
endfunction my_pow(x,y)return x^y
end
)";/*   _G = {"helloworld" = function print("hello world")}_G = {"pkg" = {"helloworld" = function print("hello world")}}pkg.helloworld()
*/char const *script_1 = R"(pkg.hello()
)";int main()
{/*加载脚本到stable（包）1、生成chunk push到栈顶2、创建table，设置给_G表，_G["pkg"] = {}3、给这个table设置元表，元表继承_G的访问域(__index)4、执行code chunk*/lua_State *state = luaL_newstate();luaL_openlibs(state);{auto rst = luaL_loadbuffer(state,script,strlen(script),"helloworld");if(rst != 0){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("load script faile:%s\n",msg);lua_pop(state,1);}return -1;}// 取出_G表lua_getglobal(state,"_G");if(lua_istable(state,-1)){  // chunk _Glua_newtable(state);    // 创建表 chunk _G new_stablelua_pushstring(state,"pkg"); // chunk _G new_stable pkglua_pushvalue(state,-2); // chunk _G new_stable pkg new_stablelua_rawset(state,-4);   // chunk _G new_stablechar const *upvalueName = lua_setupvalue(state,-3,1); // chunk _Glua_newtable(state);    // chunk _G metastablelua_pushstring(state,"__index");    // chunk _G metastable "__index"lua_pushvalue(state,-3); // chunk _G metastable "__index" _Glua_rawset(state,-3);   // chunk _G metastablelua_pushstring(state,"pkg");lua_rawget(state,-3);   // chunk _G metastable "pkg"(table)lua_pushvalue(state,-2);    // chunk _G metastable pkg(table) metastablelua_setmetatable(state,-2); // chunk _G metastable pkg(stable)lua_pop(state,3);   // chunk}// 执行chunkif(lua_pcall(state,0,0,0)){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("call function chunk failed:%s\n",msg);lua_pop(state,1);}}// 加载script_1rst = luaL_loadbuffer(state,script_1,strlen(script_1),"script_1");if(rst != 0){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("load script failed:%s\n",msg);lua_pop(state,1);}return -1;}if(lua_pcall(state,0,0,0)){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("call function chunk failed:%s\n",msg);lua_pop(state,1);}}lua_close(state);}return 0;
}

2.3、Lua调用c语言接口

#include <cstdio>
#include <cstring>
#include <cmath>
#include <new>
extern "C" {#include <lua.h>#include <lualib.h>#include <lauxlib.h>
}int pow_from_c(lua_State *L)
{int param_count = lua_gettop(L);if(param_count != 2)return 0;if(lua_isinteger(L,1) && lua_isinteger(L,2)){auto x = lua_tointeger(L,1);auto y = lua_tointeger(L,2);int rst = (int)pow(x,y);lua_pushinteger(L,rst);return 1;}return 0;
}char const *script_2 = R"(local val = pow_from_c(2,3)print(val)
)";
int main()
{// lua调用c语言接口lua_State *state = luaL_newstate();luaL_openlibs(state);{/*"_G" = {"pow_from_c" = pow_from_c}*/lua_getglobal(state,"_G");lua_pushstring(state,"pow_from_c");lua_pushcclosure(state,pow_from_c,0);    // _G "pow_from_c"; closurelua_rawset(state,-3);   // _Glua_pop(state,1);   // _G}auto rst = luaL_loadbuffer(state,script_2,strlen(script_2),"script_2");if(rst != 0){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("load script faile:%s\n",msg);lua_pop(state,1);}return -1;}if(lua_pcall(state,0,0,0)){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("call function chunk failed:%s\n",msg);lua_pop(state,1);}}lua_close(state);return 0;
}

2.4、Lua实现面向对象

local anial_matestable = {__index = {walk = function (self)print(self,"我是walk")end,eat = function (self)print(self,"eat.")end,},__newindex = function (object,key,value)print("assigned "..value.."named "..key.."but not really")end,
}function newobject()local objs = {name = "xxxx"}setmetatable(objs,anial_matestable)return objs
endlocal obj = newobject()
obj.eat()
obj.walk()
obj.name = "abc"
obj.id = 0

2.5、向脚本中注册c++的类

#include <cstdio>
#include <cstring>
#include <cmath>
#include <new>
extern "C" {#include <lua.h>#include <lualib.h>#include <lauxlib.h>
}
char const *script_3 = R"(local obj_1 = create_game_object(1);local obj_2 = create_game_object(1);local obj_3 = create_game_object(2);local rst1 = obj_1:equal(obj_2)local rst2 = obj_1:equal(obj_3)print(rst1,";",rst2)print(""..obj_1:id())
)";class GameObject{
private:u_int32_t _id;
public:static size_t registy_value;
public:GameObject(u_int32_t id):_id(id){}u_int32_t id()const{return _id;}bool equal(GameObject *obj){return _id == obj->id();}
};
size_t GameObject::registy_value = 0;int GameObject_equal(lua_State *state){int arg_count = lua_gettop(state);if(arg_count!=2){return 0;}if(lua_isuserdata(state,1) && lua_isuserdata(state,2)){void *userdata_self = lua_touserdata(state,1);void *userdata_that = lua_touserdata(state,2);GameObject *obj1 = (GameObject*)userdata_self;GameObject *obj2 = (GameObject*)userdata_that;auto rst = obj1->equal(obj2);lua_pushboolean(state,rst);return 1;}return 0;
}int GameObject_id(lua_State* state){GameObject *this_obj = (GameObject*)lua_touserdata(state,1);auto rst = this_obj->id();lua_pushinteger(state,rst);return 1;
}int create_game_object(lua_State* state){auto id = lua_tointeger(state,1);void *p = lua_newuserdata(state,sizeof(GameObject));GameObject *obj = new(p)GameObject(id);lua_rawgetp(state,LUA_REGISTRYINDEX,&GameObject::registy_value);lua_setmetatable(state,-2);return 1;
}int main()
{// 怎么向脚本中注册c++的类// 使用userdata/*userdata:{metadata:{__index = {equal = function(){},id = function(){},}}}*/lua_State *state = luaL_newstate();luaL_openlibs(state);{lua_getglobal(state,"_G");lua_pushstring(state,"create_game_object");lua_pushcclosure(state,create_game_object,0);lua_rawset(state,-3);lua_pop(state,1);lua_newtable(state);lua_pushstring(state,"__index");lua_newtable(state);lua_pushstring(state,"equal");lua_pushcclosure(state,GameObject_equal,0);lua_rawset(state,-3);lua_pushstring(state,"id");lua_pushcclosure(state,GameObject_id,0);lua_rawset(state,-3);lua_rawset(state,-3);lua_rawsetp(state,LUA_REGISTRYINDEX,&GameObject::registy_value);auto rst = luaL_loadbuffer(state,script_3,strlen(script_3),"oop");if(rst != 0){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("load script failed:%s\n",msg);lua_pop(state,1);}return -1;}// 执行if(lua_pcall(state,0,0,0)){if(lua_isstring(state,-1)){auto msg = lua_tostring(state,-1);printf("load script failed:%s\n",msg);lua_pop(state,1);}}}lua_close(state);return 0;
}