在C++中如何将用户数据从一个LUA块传递到另一个LUA块

除了另一个答案之外,我还想展示一个变量,您可以在其中存储对Lua注册表中的值的引用。这种方法的优点是,您不必将值保留在堆栈上并考虑偏移量是多少。另请参见 27.3.2 – References 在Lua中编程。

这种方法使用三种功能:

1. int luaL_ref (lua_State *L, int t);

   t 并返回该值在该表中的索引。因此,为了在注册表中保存一个值,我们使用

   userDataRef = luaL_ref(L, LUA_REGISTRYINDEX);
   

2. int lua_rawgeti (lua_State *L, int index, lua_Integer n);

   将元素的值推送到堆栈上 n index t[n] 在卢阿)。因此要在索引处检索值 userDataRef 从我们使用的注册表

   lua_rawgeti(L, LUA_REGISTRYINDEX, userDataRef);
   

3. void luaL_unref (lua_State *L, int t, int ref);

   删除索引中存储的引用 ref 在桌子上 t型 裁判 可重复使用。因此要删除引用

   luaL_unref(L, LUA_REGISTRYINDEX, userDataRef);
   

#include <iostream>
#include <lua.hpp>

extern "C" {
int luaopen_my(lua_State *L);
}

int main() {
    lua_State *L = luaL_newstate();
    luaL_openlibs(L);
    luaopen_my(L);
    lua_settop(L, 0);
    /* chunk A */
    luaL_dostring(L, "local vec2 = my.Vec2(3, 4)\n"
                     "function setup()\n"
                       "return vec2\n"
                     "end\n");
    /* chunk B */
    luaL_dostring(L, "function test(p)\n"
                       "print(p.x)\n"
                     "end\n");
    int userDataRef = LUA_NOREF;

    /* call setup function */
    int top = lua_gettop(L);
    lua_getglobal(L, "setup");
    if (lua_pcall(L, 0, LUA_MULTRET, 0)) {
        std::cout << lua_tostring(L, -1) << '\n';
        lua_pop(L, 1);
    }
    /* check the return value */
    if (lua_gettop(L) - top) {
        /* store userdata to a pointer */
        userDataRef = luaL_ref(L, LUA_REGISTRYINDEX);
    }

    /* check if userDataRef is valid */
    if (userDataRef != LUA_NOREF && userDataRef != LUA_REFNIL) {
        /* call test function */
        lua_getglobal(L, "test");
        lua_rawgeti(L, LUA_REGISTRYINDEX, userDataRef);

        /* free the registry slot (if you are done) */
        luaL_unref(L, LUA_REGISTRYINDEX, userDataRef);

        if (lua_pcall(L, 1, 0, 0)) {
            std::cout << lua_tostring(L, -1) << '\n';
            lua_pop(L, 1);
        }
    }
    lua_close(L);
}

也许你想看看 Sol2 Lua-C-API的包装器。它可以用最少的样板做你想做的事。但是,它需要C++ 14。

#include <iostream>

#define SOL_CHECK_ARGUMENTS 1
#include <sol.hpp>

extern "C" int luaopen_my(lua_State *L);

int main() {
    sol::state L;
    L.open_libraries();
    luaopen_my(L);

    /* chunk A */
    L.script("local vec2 = my.Vec2(3, 4)\n"
             "function setup()\n"
               "return vec2\n"
             "end\n");
    /* chunk B */
    L.script("function test(p)\n"
               "print(p.x)\n"
             "end\n");

    auto userDataRef = L["setup"]();
    L["test"](userDataRef);
}

当获取指向userdata数据的原始指针并将其作为lightuserdata推送到参数时,将丢失有关对象类型的所有信息。lightuserdata甚至没有单独的元表。

#include <iostream>
#include <lua.hpp>

extern "C"
{
    int luaopen_my(lua_State *L);
}

int main()
{
    lua_State *L = luaL_newstate();
    luaL_openlibs(L);

    /* chunk A */
    luaL_dostring(L, "local vec2 = {x=3, y=4}\n"
                     "function setup()\n"
                       "return vec2\n"
                     "end\n");
    /* chunk B */
    luaL_dostring(L, "function test(p)\n"
                       "print(p.x)\n"
                     "end\n");

    /* call setup function */
    int top = lua_gettop(L);
    lua_getglobal(L, "setup");

    if (lua_pcall(L, 0, LUA_MULTRET, 0))
    {
        std::cout << lua_tostring(L, -1) << '\n';
        lua_pop(L, 1);

        exit(EXIT_FAILURE); // simpy fail for demo
    }

    /* check the return value */
    if (lua_gettop(L) - top)
    {
        // the top now contains the value returned from setup()

        /* call test function */
        lua_getglobal(L, "test");

        // copy the original value as argument
        lua_pushvalue(L, -2);

        if (lua_pcall(L, 1, 0, 0))
        {
            std::cout << lua_tostring(L, -1) << '\n';
            lua_pop(L, 1);
            exit(EXIT_FAILURE);
        }

         // drop the original value
        lua_pop(L, 1);

    }else
    {
        // nothing is returned, nothing to do
    }
    lua_close(L);
}