C函数返回多个参数给lua

逃离我推掉我的手 2022-04-12 02:44 106阅读 0赞

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。

#include <lua.h>
        #include <lauxlib.h>
    
        #include <stdlib.h> /* For function exit() */
        #include <stdio.h> /* For input/output */
    
        void bail(lua_State *L, char *msg){
            fprintf(stderr, "\nFATAL ERROR:\n %s: %s\n\n",
                msg, lua_tostring(L, -1));
            exit(1);
        }
        int lua_func_from_c(lua_State *L)
        {
            printf("This is C\n");
            int argc = lua_gettop(L);    /* number of arguments */
            const char * str = lua_tostring(L,1);    /* the first argument: string */
            int num = lua_tonumber(L,2); /* the second argument: number */
            
            printf("The first argument: %s\n", str);
            printf("The second argument: %d\n", num);
    
            lua_getglobal(L,"global_var");
            const char * global_str = lua_tostring(L,-1);
            printf("global_var is %s\n", global_str);
    
            int the_second_ret = 2*num;
            lua_pushstring(L, "the first return");
            lua_pushnumber(L, the_second_ret);
            return 2;            /* tell lua how many variables are returned */
        }
        int main(int argc, const char *argv[])
        {
            if(argc != 2)
            {
                return 1;
            }
            lua_State *L = luaL_newstate(); 	/* Create new lua state variable */
    
            /* Load Lua libraries, otherwise, the lua function in *.lua will be nil */
            luaL_openlibs(L);
            
            /* register new lua function in C */
            lua_register(L, "lua_func_from_c", lua_func_from_c);
    
            if( luaL_loadfile(L,argv[1]) ) 	/* Only load the lua script file */
                bail(L, "luaL_loadfile() failed");
    
            if( lua_pcall(L,0,0,0) ) 		/* Run the loaded lua file */
                bail(L, "lua_pcall() failed");
            lua_close(L);                 	/* Close the lua state variable */    
    
            return 0;
        }

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)：

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

执行结果：

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