lua与C++相互调用

?在lua中是以函数指针的形式调用函数,并且所有的函数指针都必须满足如下此种类型:typedef int (*lua_CFunction) (lua_State *L);　　
也就是说,我们在C++中定义函数时必须以lua_State为参数,以int为返回值才能被Lua所调用。但是不要忘记了,我们的lua_State是支持栈的,所以通过栈可以传递无穷个参数,大小只受内存大小限制。而返回的int值也只是指返回值的个数真正的返回值都存储在lua_State的栈中。偶们通常的做法是做一个wrapper,把所有需要调用的函数都wrap一下,这样就可以调用任意的函数了。

lua和c/c++的数据交互通过"栈"进行,操作数据时，首先将数据拷贝到"栈"上，然后获取数据，栈中的每个数据通过索引值进行定位，索引值为正时表示相对于栈底的偏移索引，索引值为负时表示相对于栈顶的偏移索引，索引值以1或-1为起始值，因此栈顶索引值永远为-1,栈底索引值永远为1 。 "栈"相当于数据在lua和c/c++之间的中转地。每种数据都有相应的存取接口 。
数据入"栈"接口：
void? (lua_pushnil) (lua_State *L);
void? (lua_pushnumber) (lua_State *L,lua_Number n);
void? (lua_pushinteger) (lua_State *L,lua_Integer n);
void? (lua_pushlstring) (lua_State *L,const char *s,size_t l);
void? (lua_pushstring) (lua_State *L,const char *s);
void? (lua_pushboolean) (lua_State *L,int b);
void? (lua_pushcclosure) (lua_State *L,lua_CFunction fn,int n);

数据获取接口：
lua_Number????? (lua_tonumber) (lua_State *L,int idx);
lua_Integer???? (lua_tointeger) (lua_State *L,int idx);
int???????????? (lua_toboolean) (lua_State *L,int idx);
const char *??? (lua_tolstring) (lua_State *L,int idx,size_t *len);
lua_CFunction?? (lua_tocfunction) (lua_State *L,int idx);

"栈"操作接口：
int?? (lua_gettop) (lua_State *L);
void? (lua_settop) (lua_State *L,int idx);
void? (lua_pushvalue) (lua_State *L,int idx);
void? (lua_remove) (lua_State *L,int idx);
void? (lua_insert) (lua_State *L,int idx);
void? (lua_replace) (lua_State *L,int idx);
int?? (lua_checkstack) (lua_State *L,int sz);

lua中定义的变量和函数存放在一个全局table中，索引值为LUA_GLOBALSINDEX ，table相关操作接口：
void? (lua_gettable) (lua_State *L,int idx);
void? (lua_getfield) (lua_State *L,const char *k);
void? (lua_settable) (lua_State *L,int idx);
void? (lua_setfield) (lua_State *L,const char *k);

当"栈"中包含执行脚本需要的所有要素(函数名和参数)后，调用lua_pcall执行脚本：
int?? (lua_pcall) (lua_State *L,int nargs,int nresults,int errfunc);

以下是一些参考用例：
[PS]*************************************************************************
#include "stdafx.h"
#include <stdio.h>

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

/* Lua解释器指针 */

lua_State* L;

int main ( int argc,char *argv[] )
{
/* 初始化Lua */
L = lua_open();
?/* 载入Lua基本库 */
?luaL_openlibs(L);
?/* 运行脚本 */
?luaL_dofile(L,"Lua1.lua");
?/* 清除Lua */
?lua_close(L);
?/* 暂停 */
?printf( "Press enter to exit…" );

?getchar();

?return 0;
}
[PS]*************************************************************************
#include<iostream>
using namespace std;
#include<stdio.h>
extern "C" {
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
}
//#pragma comment(lib,"lua5.1.lib")
lua_State* L;
static int average(lua_State *L)
{
?//返回栈中元素的个数
?int n = lua_gettop(L);
?double sum = 0;
?int i;
?for (i = 1; i <= n; i++)
?{
??if (!lua_isnumber(L,i))
??{
???lua_pushstring(L,"Incorrect argument to 'average'");
???lua_error(L);
??}
??sum += lua_tonumber(L,i);
?}
?/* push the average */
?lua_pushnumber(L,sum / n);
?/* push the sum */
?lua_pushnumber(L,sum);

??/* return the number of results */
?return 2;
}

int main (int argc,char*argv[])
{
?/* initialize Lua */
?L = lua_open();
?/* load Lua libraries */
?luaL_openlibs(L);
?/* register our function */
?lua_register(L,"average",average);
?/* run the script */
?luaL_dofile(L,"e15.lua");

??lua_getglobal(L,"avg");
cout<<"avg is:"<<lua_tointeger(L,-1)<<endl;
?lua_pop(L,1);
?lua_getglobal(L,"sum");
?cout<<"sum is:"<<lua_tointeger(L,-1)<<endl;
?/* cleanup Lua */
?lua_close(L);

??return 0;
}

//程序中：
//*lua_gettop()的作用是返回栈顶元素的序号. 由于Lua的栈是从1开始编号的,所以栈顶元素的序号也相当于栈中的元素个数. 在这里,栈中元素的个数就
是传入的参数个数。
//* for循环计算所有传入参数的总和. 这里用到了数值转换lua_tonumber()。
//* 然后偶们用lua_pushnumber()把平均值和总和push到栈中。
//* 最后,偶们返回2,表示有两个返回值(这里不能错，push了几个就是返回几，否则外部按照你返回的值取值会出错)。
//* 虽然在C++中定义了average()函数,但Lua程序并不知道,所以需要在main函数中加入
//? lua_register(L,average);
//　这行的作用就是注册函数后告诉e15.lua有average()这样一个函数.
//* 这个程序可以存成cpp也可以存成c,如果以.c为扩展名就不需要加extern "C"
//编译的方法偶们上次说过了,方法相同.
//e15.lua执行的方法只能用上例中的C++中执行,而不能用命令行方式执行.*/

lua脚本为:
avg,sum = average(10,20,30,40,50)
print("The average is ",avg)
print("The sum is ",sum)
[PS]*************************************************************************
/* A simple Lua interpreter. */
#include <stdio.h>
extern "C" {
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
}
#include <stdio.h>
extern "C" { // 这是个C++程序,所以要extern "C",
?// 因为lua的头文件都是C格式的
#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"
}
#pragma comment(lib,"lua5.1.lib")
/* the Lua interpreter */
lua_State* L;
int luaadd ( int x,int y )
{
?int sum;
?/* the function name */
?lua_getglobal(L,"add");??int nTop = lua_gettop(L); //得到栈的元素个数。栈顶的位置。
?/* the first argument */
?lua_pushnumber(L,x);???nTop = lua_gettop(L);
?/* the second argument */
?lua_pushnumber(L,y);???nTop = lua_gettop(L);
?/* call the function with 2
?arguments,return 1 result */
lua_call(L,2,1);???nTop = lua_gettop(L);
?/* get the result */
?sum = (int)lua_tonumber(L,-1);???????? nTop = lua_gettop(L);
?/*清掉返回值*/
?lua_pop(L,1);????nTop = lua_gettop(L);
?/*取出脚本中的变量z的值*/
?lua_getglobal(L,"z");???nTop = lua_gettop(L);
?int z = (int)lua_tonumber(L,1);??????? nTop = lua_gettop(L);
?lua_pop(L,1);????nTop = lua_gettop(L);
?//没调通
?/*lua_pushnumber(L,4);???nTop = lua_gettop(L);
?lua_setglobal(L,"r");???nTop = lua_gettop(L);
?int r = (int)lua_tonumber(L,1);??????? nTop = lua_gettop(L);*/

?return sum;
}

int main ( int argc,char *argv[] )
{
?int sum;
?/* initialize Lua */
?L = lua_open();
?/* load Lua base libraries */
?//lua_baselibopen(L);
?/* load the script */
?luaL_dofile(L,"e12.lua");
?/* call the add function */
?sum = luaadd( 10,15 );
?/* print the result */
?printf( "The sum is %d",sum );
?/* cleanup Lua */
?lua_close(L);

?return 0;
}

程序说明:

main中过程偶们上次已经说过了,所以这次只说说luaadd的过程

首先用lua_getglobal()把add函数压栈

然后用lua_pushnumber()依次把x,y压栈

然后调用lua_call(),并且告诉程序偶们有两个参数一个返回值

接着偶们从栈顶取回返回值,用lua_tonumber()

最后偶们用lua_pop()把返回值清掉

lua脚本为：
-- add two numbers
function add ( x,y )
return x + y + 2
end
?
z = 6
[PS]*************************************************************************
（func.lua）

--变量定义
width=1 ;
height=2 ;
--lua函数定义，实现加法
function sum(a,b)
??? return a+b ;
end
--lua函数定义，实现字符串相加
function mystrcat(a,b)
??? return a..b ;
end
--lua函数定义，通过调用c代码中的csum函数实现加法
function mysum(a,b)
??? return csum(a,b) ;
end

（test_lua.c）

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
//lua头文件
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>

#define err_exit(num,fmt,args)?
??? do{printf("[%s:%d]"fmt"n",__FILE__,__LINE__,##args);exit(num);} while(0)
#define err_return(num,##args);return(num);} while(0)

//lua中调用的c函数定义,实现加法
int csum(lua_State* l)
{
??? int a = lua_tointeger(l,1) ;
??? int b = lua_tointeger(l,2) ;
??? lua_pushinteger(l,a+b) ;
??? return 1 ;
}

int main(int argc,char** argv)
{
??? lua_State * l = luaL_newstate() ;??????? //创建lua运行环境
??? if ( l == NULL ) err_return(-1,"luaL_newstat() failed");
??? int ret = 0 ;
??? ret = luaL_loadfile(l,"func.lua") ;????? //加载lua脚本文件
??? if ( ret != 0 ) err_return(-1,"luaL_loadfile failed");
??? ret = lua_pcall(l,0) ;
??? if ( ret != 0 ) err_return(-1,"lua_pcall failed:%s",lua_tostring(l,-1)) ;

??? lua_getglobal(l,"width");????????????? //获取lua中定义的变量
??? lua_getglobal(l,"height");
??? printf("height:%ld width:%ldn",lua_tointeger(l,-1),-2)) ;
??? lua_pop(l,1) ;??????????????????????? //恢复lua的栈

??? int a = 11 ;
??? int b = 12 ;
??? lua_getglobal(l,"sum");?????????????? //调用lua中的函数sum
??? lua_pushinteger(l,a) ;
??? lua_pushinteger(l,b) ;
??? ret = lua_pcall(l,1,-1)) ;
??? printf("sum:%d + %d = %ldn",a,b,-1)) ;
??? lua_pop(l,1) ;

??? const char str1[] = "hello" ;
??? const char str2[] = "world" ;
??? lua_getglobal(l,"mystrcat");????????? //调用lua中的函数mystrcat
??? lua_pushstring(l,str1) ;
??? lua_pushstring(l,str2) ;
??? ret = lua_pcall(l,-1)) ;
??? printf("mystrcat:%s%s = %sn",str1,str2,1) ;

??? lua_pushcfunction(l,csum) ;???????? //注册在lua中使用的c函数
??? lua_setglobal(l,"csum") ;?????????? //绑定到lua中的名字csum

??? lua_getglobal(l,"mysum");?????????? //调用lua中的mysum函数，该函数调用本程序中定义的csum函数实现加法
??? lua_pushinteger(l,-1)) ;
??? printf("mysum:%d + %d = %ldn",1) ;

??? lua_close(l) ;???????????????????? //释放lua运行环境
??? return 0 ;
}
[PS]*************************************************************************
下面的代码演示了在C++和lua脚本之间传递数据。
首先在C++中创建一个table，添加元素，然后放置到lua的全局表中。在lua脚本中可以使用C++创建的这个表。
然后在脚本中创建一个表，以脚本返回值的方式返回给C++，在C++中可以读取表中的值。

例子代码需要一个args.lua的lua文件，要手工创建，我把它放到了C盘根目录下。

// cpplua.cpp : Defines the entry point for the console application.??
?
#include "stdafx.h"??
?
extern "C"?
{??
#include <lua.h>??
#include <lauxlib.h>??
#include <lualib.h>??
}??
#include <iostream>??
?
/* args.lua文件的内容
io.write( "[lua] These args were passed into the script from Cn" );

for i=1,table.getn(arg) do
print(i,arg[i])
end

io.write("[lua] Script returning data back to Cn")

local temp = {}
temp[1]=9
temp[2]=8
temp[3]=7
temp[4]=6
temp[5]=5
temp["test1 key"]="test1 value"
temp[6]="test 6"
temp["test 99"]=99

for i,n in pairs(temp)
do
print (i,n)
end

return temp,9,1

*/?
int _tmain(int argc,_TCHAR* argv[])??
{??
??? int status;??
?
??? // lua_open: 创建一个新的lua环境??
???? lua_State* state = lua_open();??
?
??? // 在state环境上打开标准库，??
??? // 标准库包括：??
??? // luaopen_base??
??? // luaopen_package??
??? // luaopen_table??
??? // luaopen_io??
??? // luaopen_os??
??? // luaopen_string??
??? // luaopen_math??
??? // luaopen_debug??
???? luaL_openlibs(state);? /* open libraries */?
?
???? status = luaL_loadfile( state,"c:args.lua" );??
?
???? std::cout << "[C++] Passing 'arg' array to script" << std::endl;??
?
??? // 创建一个新的表??
???? lua_newtable( state );??
?
??? //??
??? // set first element "1" to value 45??
??? //??
??? // 调用lua的函数，都是通过压栈出栈来完成的??
??? // 为表执行一个t[k]=v的操作,则需要先将k压栈，再将v压栈，再调用操作函数??
??? // 这个操作函数会使用栈上的元素，并“可能”将弹出元素和压入元素??
??? // lua_rawset直接赋值（不触发metamethods方法）。??
??????
??? // lua_rawset/lua_settable使用:??
??? // 它从栈中获取参数。以table在栈中的索引作为参数，??
??? // 并将栈中的key和value出栈。??
??? // lua_pushnumber函数调用之前，??
??? // table是在栈顶位置(索引为-1)。index和value入栈之后，??
??? // table索引变为-3。??
???? lua_pushnumber( state,1 );??
???? lua_pushnumber( state,45 );??
???? lua_rawset( state,-3 );??
?
??? // set second element "2" to value 99??
???? lua_pushnumber( state,2 );??
???? lua_pushnumber( state,99 );??
???? lua_rawset( state,-3 );??
?
??? // set the number of elements (index to the last array element)??
??? // lua_pushliteral压入一个字符串，不需要指定长度??
??? // 如果lua_pushlstring,则需要指定长度??
???? lua_pushliteral( state,"n" );??
???? lua_pushnumber( state,2 );??
???? lua_rawset( state,-3 );??
?
??? // set the name of the array that the script will access??
??? // Pops a value from the stack and sets it as the new value of global name.??
??? // 从栈顶弹出一个值，并将其设置全局变量"arg"的新值。??
???? lua_setglobal( state,"arg" );??
?
?
???? std::cout << "[C++] Running script" << std::endl;??
?
??? int result = 0;??
??? if (status == 0)??
???? {??
???????? result = lua_pcall( state,LUA_MULTRET,0 );??
???? }??
??? else?
???? {??
???????? std::cout << "bad" << std::endl;??
???? }??
?
??? if (result != 0)??
???? {??
???????? std::cerr << "[C++] script failed" << std::endl;??
???? }??
?
???? std::cout << "[C++] These values were returned from the script" << std::endl;??
?
??? // lua_gettop返回栈顶的索引??
??? // 如果索引为0，则表示栈为空??
??? while (lua_gettop( state ))??
???? {??
??????? switch (lua_type( state,lua_gettop( state ) ))??
???????? {??
??????? case LUA_TNUMBER:??
???????????? {??
???????????????? std::cout << "script returned " << lua_tonumber( state,lua_gettop( state ) ) << std::endl;??
??????????????? break;??
???????????? }??
??????? case LUA_TTABLE:????
???????????? {??
???????????????? std::cout << "script returned a table" << std::endl;??
??????????????????
??????????????? // 简单的遍历表的功能??
??????????????? // ***好像lua不保存表的元素的添加顺序***??
?
??????????????? // 压入第一个键??
???????????????? lua_pushnil(state);? /* 第一个 key */?
??????????????? int t = -2;??
??????????????? while (lua_next(state,t) != 0)??
???????????????? {??
??????????????????? /* 'key' (索引-2) 和 'value' (索引-1) */?
??????????????????? const char* key = "unknown";??
??????????????????? const char* value;??
??????????????????? if(lua_type(state,-2) == LUA_TSTRING)??
???????????????????? {??
???????????????????????? key = lua_tostring(state,-2);??
???????????????????????? value = lua_tostring(state,-1);??
???????????????????? }??
??????????????????? else if(lua_type(state,-2) == LUA_TNUMBER)??
???????????????????? {??
??????????????????????? // 因为lua_tostring会更改栈上的元素，??
??????????????????????? // 所以不能直接在key上进行lua_tostring??
??????????????????????? // 因此，复制一个key，压入栈顶，进行lua_tostring??
???????????????????????? lua_pushvalue(state,-2);??
???????????????????????? key = lua_tostring(state,-1);??
???????????????????????? lua_pop(state,1);??
???????????????????????? value = lua_tostring(state,-1);??
???????????????????? }??
??????????????????? else?
???????????????????? {??
???????????????????????? value = lua_tostring(state,-1);??
???????????????????? }??
?
???????????????????? std::cout??? <<"key="<< key??
???????????????????????????????? << ",value=" << value << std::endl;??
?
??????????????????? /* 移除 'value' ；保留 'key' 做下一次迭代 */?
???????????????????? lua_pop(state,1);??
???????????????? }??
?
??????????????? break;??
???????????? }??
??????? case LUA_TSTRING:??
???????????? {??
???????????????? std::cout << "script returned " << lua_tostring( state,lua_gettop( state ) ) << std::endl;??
??????????????? break;??
???????????? }??
??????? case LUA_TBOOLEAN:??
???????????? {??
???????????????? std::cout << "script returned " << lua_toboolean( state,lua_gettop( state ) ) << std::endl;??
??????????????? break;??
???????????? }??
??????? default:??
???????????? std::cout << "script returned unknown param" << std::endl;??
??????????? break;??
???????? }??
???????? lua_pop( state,1 );??
???? }??
???? lua_close( state );??
??? return 0;??
}?

本例用了一个控制台工程，输出如下：

[C++] Passing 'arg' array to script [C++] Running script [lua] These args were passed into the script from C 1?????? 45 2?????? 99 [lua] Script returning data back to C 1?????? 9 2?????? 8 3?????? 7 4?????? 6 5?????? 5 6?????? test 6 test 99 99 test1 key?????? test1 value [C++] These values were returned from the script script returned 1 script returned 9 script returned a table key=1,value=9 key=2,value=8 key=3,value=7 key=4,value=6 key=5,value=5 key=6,value=test 6 key=test 99,value=99 key=test1 key,value=test1 value