我试图从C ++中的Lua脚本(userdata
)获取chunk A
(通过我的示例中的函数返回变量)然后,然后,将此userdata
从C ++传递回Lua脚本(chunk B
)(通过我的函数参数)例如)所以userdata
可以用于chunk B
,就像它在chunk A
中一样。
MyBindings.h
class Vec2
{
public:
Vec2():x(0), y(0){};
Vec2(float x, float y):x(x), y(y){};
float x, y;
};
MyBindings.i
%module my
%{
#include "MyBindings.h"
%}
%include "MyBindings.h"
main.cpp
#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");
void *userDataPtr = nullptr;
/* 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 */
if (lua_isuserdata(L, -1))
userDataPtr = lua_touserdata(L, -1);
}
/* check if userDataPtr is valid */
if (userDataPtr != nullptr)
{
/* call test function */
lua_getglobal(L, "test");
lua_pushlightuserdata(L, userDataPtr); /* pass userdata as an argument */
if (lua_pcall(L, 1, 0, 0))
{
std::cout << lua_tostring(L, -1) << '\n';
lua_pop(L, 1);
}
}
lua_close(L);
}
结果我得到:
[string“local vec2 = my.Vec2(3,4)...”]:6:尝试索引userdata值(本地'p')
我期望的结果:
3
是否有可能从userdata
获得chunk A
然后将其传递给chunk B
所以它可以像在chunk A
中那样使用?
除了另一个答案,我想展示一个变体,你在Lua注册表中存储对值的引用。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。另见“Lua编程”中的27.3.2 – References。
这种方法使用三个功能:
int luaL_ref (lua_State *L, int t);
从堆栈弹出最高值,将其存储在索引t
的表中,并返回该表中值的索引。因此,要在我们使用的注册表中保存值
userDataRef = luaL_ref(L, LUA_REGISTRYINDEX);
int lua_rawgeti (lua_State *L, int index, lua_Integer n);
在n
(Lua的index
)中将表格的元素t[n]
的值推入堆栈。因此,从我们使用的注册表中检索索引userDataRef
的值
lua_rawgeti(L, LUA_REGISTRYINDEX, userDataRef);
void luaL_unref (lua_State *L, int t, int ref);
删除存储在ref
表中的索引t
处的引用,以便可以对引用进行垃圾回收并且可以重用索引ref
。因此,从我们使用的注册表中删除参考userDataRef
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Lua-C-API的Sol2包装器。它可以用最少的样板做到你想要的。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);
}
当您获得指向userdata数据的原始指针并将其作为lightuserdata推送到参数时,您将丢失有关对象类型的所有信息。 lightuserdata甚至没有单独的元表。
正确的方法是按原样传递Lua值。将原始返回值保留在Lua堆栈上,或将其复制到其他Lua容器(您的Lua表中用于临时表或Lua注册表),然后将该值复制到Lua堆栈以将其作为参数传递。这样您就不必了解绑定实现。您甚至不必关心这是用户数据还是任何其他Lua类型。
根据您的代码,这可能如下所示:
#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);
}