和我一起写lua － C和lua的参数传递与返回值

lua通过一个运行时栈来维护参数传递及返回，使用lua_to*等函数获取lua传递到C函数的参数，使用lua_push*从C函数返回值到lua脚本。此外也可以使用lua_getglobal从C函数获取lua脚本定义的全局变量。具体参看例子(test_lua.c)：

点击(此处)折叠或打开

1. #include <lua.h>
   
2. #include <lauxlib.h>
   
3. 
   
4. #include <stdlib.h> /* For function exit() */
   
5. #include <stdio.h> /* For input/output */
   
6. 
   
7. void bail(lua_State *L, char *msg){
   
8.     fprintf(stderr, "\nFATAL ERROR:\n %s: %s\n\n",
   
9.         msg, lua_tostring(L, -1));
   
10.     exit(1);
    
11. }
    
12. int lua_func_from_c(lua_State *L)
    
13. {
    
14.     printf("This is C\n");
    
15.     int argc = lua_gettop(L);    /* number of arguments */
    
16.     const char * str = lua_tostring(L,1);    /* the first argument: string */
    
17.     int num = lua_tonumber(L,2); /* the second argument: number */
    
18.     
    
19.     printf("The first argument: %s\n", str);
    
20.     printf("The second argument: %d\n", num);
    
21. 
    
22.     lua_getglobal(L,"global_var");
    
23.     const char * global_str = lua_tostring(L,-1);
    
24.     printf("global_var is %s\n", global_str);
    
25. 
    
26.     int the_second_ret = 2*num;
    
27.     lua_pushstring(L, "the first return");
    
28.     lua_pushnumber(L, the_second_ret);
    
29.     return 2;            /* tell lua how many variables are returned */
    
30. }
    
31. int main(int argc, const char *argv[])
    
32. {
    
33.     if(argc != 2)
    
34.     {
    
35.         return 1;
    
36.     }
    
37.     lua_State *L = luaL_newstate(); /* Create new lua state variable */
    
38. 
    
39.     /* Load Lua libraries, otherwise, the lua function in *.lua will be nil */
40.     luaL_openlibs(L);
    
41.     
    
42.     /* register new lua function in C */
    
43.     lua_register(L, "lua_func_from_c", lua_func_from_c);
    
44. 
    
45.     if( luaL_loadfile(L,argv[1]) ) /* Only load the lua script file */
    
46.         bail(L, "luaL_loadfile() failed");
    
47. 
    
48.     if( lua_pcall(L,0,0,0) ) /* Run the loaded lua file */
    
49.         bail(L, "lua_pcall() failed");
    
50.     lua_close(L);                 /* Close the lua state variable */    
    
51. 
    
52.     return 0;
    
53. }

lua脚本（my.lua）如下所示(在lua脚本中，如果变量不用local明确声明为局部变量，则默认为全局变量)：

点击(此处)折叠或打开

1. print("Hello world")
   
2. global_var = "this is a global string"
   
3. first, second = lua_func_from_c("the first one", 2)
   
4. print("the first returned", first)
   
5. print("the second returned", second)

执行结果：

$ ./a.out my.lua 

Hello world

This is C

The first argument: the first one

The second argument: 2

global_var is this is a global string

the first returnedthe first return

the second returned4