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 = 0;
    int i = 0;
    for (i=1; 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 2;
}

int main(void)
{
    char buff[256] = {0};
    int error = 0;

    lua_State *L = luaL_newstate();
    luaL_openlibs(L);

    lua_createtable(L, 0, 0);
    lua_setfield(L, LUA_GLOBALSINDEX, "t_test");
    lua_getfield(L, LUA_GLOBALSINDEX, "t_test");
    lua_pushstring(L, "test");
    lua_setfield(L, -2, "test");

    lua_pushcfunction(L, foo);
    lua_setfield(L, -2, "foo");
    
    lua_settop(L, 0);

    while (fgets(buff, sizeof(buff), stdin) != NULL)
    {
        size_t sz = strlen(buff);
        error = luaL_loadbuffer(L, buff, sz, "line")
                || lua_pcall(L, 0, 0, 0);
        if (error)
        {
            fprintf(stderr, "%s", lua_tostring(L, -1));
            lua_pop(L, 1);
        }
    }

    /*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, -1);
    if (str)
        printf("hangj: %s
", str);
    lua_remove(L, -1);

    lua_close(L);
    getchar();
    return 0;
}

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。