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分类: Python/Ruby

2013-01-12 00:25:38

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):

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  1. #include <lua.h>
  2. #include <lauxlib.h>

  3. #include <stdlib.h> /* For function exit() */
  4. #include <stdio.h> /* For input/output */

  5. void bail(lua_State *L, char *msg){
  6.     fprintf(stderr, "\nFATAL ERROR:\n %s: %s\n\n",
  7.         msg, lua_tostring(L, -1));
  8.     exit(1);
  9. }
  10. int lua_func_from_c(lua_State *L)
  11. {
  12.     printf("This is C\n");
  13.     int argc = lua_gettop(L);    /* number of arguments */
  14.     const char * str = lua_tostring(L,1);    /* the first argument: string */
  15.     int num = lua_tonumber(L,2); /* the second argument: number */
  16.     
  17.     printf("The first argument: %s\n", str);
  18.     printf("The second argument: %d\n", num);

  19.     lua_getglobal(L,"global_var");
  20.     const char * global_str = lua_tostring(L,-1);
  21.     printf("global_var is %s\n", global_str);

  22.     int the_second_ret = 2*num;
  23.     lua_pushstring(L, "the first return");
  24.     lua_pushnumber(L, the_second_ret);
  25.     return 2;            /* tell lua how many variables are returned */
  26. }
  27. int main(int argc, const char *argv[])
  28. {
  29.     if(argc != 2)
  30.     {
  31.         return 1;
  32.     }
  33.     lua_State *L = luaL_newstate(); /* Create new lua state variable */

  34.     /* Load Lua libraries, otherwise, the lua function in *.lua will be nil */
  35.     luaL_openlibs(L);
  36.     
  37.     /* register new lua function in C */
  38.     lua_register(L, "lua_func_from_c", lua_func_from_c);

  39.     if( luaL_loadfile(L,argv[1]) ) /* Only load the lua script file */
  40.         bail(L, "luaL_loadfile() failed");

  41.     if( lua_pcall(L,0,0,0) ) /* Run the loaded lua file */
  42.         bail(L, "lua_pcall() failed");
  43.     lua_close(L);                 /* Close the lua state variable */    

  44.     return 0;
  45. }
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):

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  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 returned the first return
the second returned 4

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