hello lua

http://manual.luaer.cn/

http://www.lua.org/pil/contents.html

 #include <cstdio>
 #include <string>
 extern "C"{
 #include "lua.h"
 #include "lauxlib.h"
 #include "lualib.h"
 };
 
 static int foo(lua_State* L)
 {
     int n = lua_gettop(L);
     lua_Number sum = ;
     int i = ;
     for (i=; i <= n; ++i)
     {
         if (!lua_isnumber(L, i))
         {
             lua_pushstring(L, "incorrect argument");
             lua_error(L);
         }
         sum += lua_tonumber(L, i);
     }
     lua_pushnumber(L, sum/n);
     lua_pushnumber(L, sum);
     return ;
 }
 
 int main(void)
 {
     char buff[] = {};
     int error = ;
 
     lua_State *L = luaL_newstate();
     luaL_openlibs(L);
 
     lua_createtable(L, , );
     lua_setfield(L, LUA_GLOBALSINDEX, "t_test");
     lua_getfield(L, LUA_GLOBALSINDEX, "t_test");
     lua_pushstring(L, "test");
     lua_setfield(L, -, "test");
 
     lua_pushcfunction(L, foo);
     lua_setfield(L, -, "foo");
 
     lua_settop(L, );
 
     while (fgets(buff, sizeof(buff), stdin) != NULL)
     {
         size_t sz = strlen(buff);
         error = luaL_loadbuffer(L, buff, sz, "line")
                 || lua_pcall(L, , , );
         if (error)
         {
             fprintf(stderr, "%s", lua_tostring(L, -));
             lua_pop(L, );
         }
     }
 
     /*int err = luaL_loadfile(L, "hangj.lua") || lua_pcall(L, 0, LUA_MULTRET, 0);
     if (err)
     {
         fprintf(stderr, "%s", lua_tostring(L, -1));
         lua_pop(L, 1);
     }*/
 
     lua_getfield(L, LUA_GLOBALSINDEX, "hangj");
     const char* str = lua_tostring(L, -);
     if (str)
         printf("hangj: %s\n", str);
     lua_remove(L, -);
 
     lua_close(L);
     getchar();
     return ;
 }

int lua_gettop (lua_State *L);

返回栈顶元素的 index，因为 index 是从 1 开始的，所以返回值等于栈中元素的个数。0 表示空栈。