c++ - Lua 5.2 - 对象中的 C++ 对象(使用 lua_lightuserdata)

Question

编辑:[答案 2 中的解决方案]

我是 LUA 的新手，在尝试做我想做的事情时遇到了麻烦。我有一个看起来像这样的 C++ 对象:

C++ 对象定义

struct TLimit
{
    bool   enabled;
    double value;

    TLimit() : enabled(false), value(0.0) {}
    ~TLimit() {}
};

class TMeaurement
{
public:
    TMeasurement() : meas(0.0) {}
    ~TMeasurement() {}

    TLimit min;
    TLimit max;
    double meas;
};

我希望能够在 LUA 中访问以下形式的 TMeasurement 类型的对象:

LUA 所需用途

-- objmeas is an instance of TMeasurement
objmeas.min.enabled = true
print(objmeas.min.value);

...等等

另一件事，我不希望 LUA 为 TMeasurement 类型的对象实例分配内存。这将在我的 C++ 代码中完成。我尝试了很多不同的事情，但都没有成功。我现在将发布我的最后一次尝试。

在我的 C++ 代码中，我定义了以下内容:

TLimit - 获取将映射到 __index 的函数

#define LUA_MEAS_LIMIT    "itse.measurement.limit"

extern int llim_get(lua_State* L)
{
    TLimit*     lim = (TLimit*)lua_chekuserdata(L, 1, LUA_MEAS_LIMIT);
    std::string key = std::string(luaL_checkstring(L, 2));

    //-- this is only to check what is going on
    std::cout << "lim.get: " << key << std::endl;

    if(key.find("enabled") == 0)
        lua_pushboolean(L, lim->enabled);
    else if(key.find("value") == 0)
        lua_pushnumber(L, lim->value);
    else
        return 0;   //-- should return some sort of error, but let me get this working first

    return 1;
}

TLimit - 设置将映射到 __newindex 的函数

extern int llim_set(lua_State* L)
{
    TLimit*     lim = (TLimit*)lua_chekuserdata(L, 1, LUA_MEAS_LIMIT);
    std::string key = std::string(luaL_checkstring(L, 2));

    //-- this is only to check what is going on
    std::cout << "limit.set: " << key << " <-" << std::endl;

    if(key.find("enabled") == 0)
        lim->enabled = lua_toboolean(L, 3);
    else if(key.find("value") == 0)
        lim->value = lua_tonumber(L, 3);

    return 0;
}

现在，TMeasurement 类还有一个函数。 (我不会在这个例子中提供成员“meas”的设置函数)。

TMeasurement - 获取 __index 的函数

#define LUA_MEASUREMENT    "itse.measurement"

extern int lmeas_get(lua_State* L)
{
    TMeasurement* test = (TMeasurement*)lua_checkuserdata(L, 1, LUA_MEASUREMENT);
    std::string   key  = std::string(luaL_checkstring(L, 2));

    //-- this is only to check what is going on
    std::cout << "meas." << key << " ->" << std::endl;

    if(key.find("meas") == 0)
        lua_pushinteger(L, test->meas);
    else if(key.find("min") == 0)
    {
        lua_pushlightuserdata(L, &test->min);
        luaL_getmetatable(L, LUA_MEAS_LIMIT);
        lua_setmetatable(L, -2);
    }
    else if(key.find("max") == 0)
    {
        lua_pushlightuserdata(L, &test->max);
        luaL_getmetatable(L, LUA_MEAS_LIMIT);
        lua_setmetatable(L, -2);
    }
    else
        return 0;  //-- should notify of some error... when I make it work

    return 1;
}

现在，代码中为这两个对象创建 mettatable 的部分:

C++ - 发布元表

(没关系 nsLUA::safeFunction<...> 位，它只是一个模板函数，将在“安全模式”下执行 < > 中的函数...它会弹出一个 MessaegBox 时遇到错误)

static const luaL_Reg lmeas_limit_f[] = { { NULL, NULL} };
static const luaL_Reg lmeas_limit[] =
{
        { "__index",    nsLUA::safeFunction<llim_get> },
        { "__newindex", nsLUA::safeFunction<lllim_set> },
        { NULL,      NULL }
};
//-----------------------------------------------------------------------------

static const luaL_Reg lmeas_f[] =  { { NULL, NULL} };
static const luaL_Reg lmeas[] =
{
        { "__index", nsLUA::safeFunction<lmeas_get> },
        { NULL,   NULL }
};
//-----------------------------------------------------------------------------

int luaopen_meas(lua_State* L)
{
    //-- Create Measurement Limit Table
    luaL_newmetatable(L, LUA_MEAS_LIMIT);
    luaL_setfuncs(L, lmeas_limit, 0);
    luaL_newlib(L, lmeas_limit_f);

    //-- Create Measurement Table
    luaL_newmetatable(L, LUA_MEASUREMENT);
    luaL_setfuncs(L, lmeas, 0);
    luaL_newlib(L, lmeas_f);

    return 1;
}

最后，我在 C++ 中的主要函数初始化 LUA，创建对象 TMeasurement 的实例，将其作为全局传递给 LUA 并执行 lua 脚本。大多数此功能包含在另一个名为 LEngine 的类中:

C++ - 主要函数

int main(int argc, char* argv[])
{
    if(argc < 2)
        return show_help();

    nsLUA::LEngine eng;

    eng.runScript(std::string(argv[1]));

    return 0;
}
//-----------------------------------------------------------------------------

int LEngine::runScript(std::string scrName)
{
    //-- This initialices LUA engine, openlibs, etc if not already done. It also
    //   registers whatever library I tell it so by calling appropriate "luaL_requiref"
    luaInit();

    if(m_lua)    //-- m_lua is the lua_State*, member of LEngine, and initialized in luaInit()
    {
        LMeasurement measurement;

        measurement.value = 4.5;   //-- for testing purposes

        lua_pushlightuserdata(m_lua, &tst);
        luaL_getmetatable(m_lua, LUA_MEASUREMENT);
        lua_setmetatable(m_lua, -2);
        lua_setglobal(m_lua, "step");

        if(luaL_loadfile(m_lua, scrName.c_str()) || lua_pcall(m_lua, 0, 0, 0))
            processLuaError();   //-- Pops-up a messagebox with the error
    }

    return 0;
}

现在，问题终于来了。当我执行任何 lua 脚本时，我可以毫无问题地访问步骤，但我只能第一次访问“min”或“max”内的 memebr ...任何后续访问都会出错。

LUA - 示例一

print(step.meas);        -- Ok
print(step.min.enabled); -- Ok
print(step.min.enabled); -- Error: attempt to index field 'min' (a nil value)

此脚本生成的输出是:

                              first script line: print(step.meas);
meas.meas ->                     this comes from lmeas_get function
4.5                              this is the actual print from lua sentence
                              second script line: print(step.min.enabled)
meas.min ->                      accessing step.min, call to function lmeas_get
limit.get: enabled ->            accessing min.enabled, call to function llim_get
false                            actual print from script sentence
                              third script line: print(step.min.enabled)
limit.get: min ->                accessing min from limit object, call to llim_get ???????

所以。在我第一次访问字段“min”(或“max”)之后，任何后续访问它的尝试都将返回“尝试访问索引...”错误。我是先访问 __index (local e = step.min.enabled) 函数还是访问 __newindex 函数 (step.min.enabled = true) 并不重要。

似乎我在第一次访问对象步骤的最小元表时弄乱了 LUA 堆栈。它以某种方式将“指向步骤的指针”从 LUA_MEASUREMENT 元表“替换”为 LUA_MEAS_LIMIT...我只是不知道为什么。

请帮忙...我怎么搞砸了这么多？

谢谢你，抱歉发了这么长的帖子……我只是不知道如何让它更短。

Answer 1

首先，感谢@siffiejoe 和@greatwolf 的帖子。是他们向我解释了我做错了什么。

现在，我的解决方案。我很确定这个解决方案并不是最好的，但它满足了我目前的需求。如果有人有任何建议，查看/发现潜在的错误，或者只是想发表评论，请这样做。

解决方案 - 想法

由于在 LUA 中，所有 lightuserdata 共享相同的元表，我决定让所有我想将 lightuserdata 指针传递给 LUA 的结构和类共享相同的继承 self 称为 LMetaPointer。此类将发布元表并将 __index 和 __newindex 映射到给定的静态方法 LMetaPointer::__index 和 LMetaPointer::__newindex。该类还包含一个 static std::map(列表)指针，指向曾经创建的所有 LMetaPointer 实例。该类的构造函数确保将新创建的实例添加到该映射中。

每当在 lua 中，元方法 __index 或 __newindex 被调用时，相应的 LMetaPointer::__index 或 LMetaPointer::__newindex 被执行。该方法在map中查找对应的负责方法调用的指针，并调用自己的get或set方法，这些方法在中定义为纯虚函数LMetaPointer 类。

我知道这可能有点令人困惑，所以我现在将发布类 LMetaPointer 的定义

解决方案——框架:LMetaPointer类

//-----------------------------------------------------------------------------
#define LUA_METAPOINTER     "itse.metapointer"    //-- Name given to the metatable for all lightuserdata (instances of LMetaPointer in C++)
//-----------------------------------------------------------------------------

class LMetaPointer
{
private:
    static lua_State*                           m_lua;           //-- All LMetaPointers will share a common lua State
    static const luaL_Reg                       m_lmembers[];    //-- Member functions (for later expansion)
    static const luaL_Reg                       m_lfunctions[];  //-- Metamethods
    static std::map<LMetaPointer*, std::string> m_pointers;      //-- List of all LMetaPointer instances

    std::string m_name;                  //-- Name of LUA global variable pointing to me.

    static int __index(lua_State* L);    //-- Shall be mapped to __index metamethod of the metatable for all lightuserdata pointers
    static int __newindex(lua_State* L); //-- Shall be mapped to __newindex metamethod of the metatable for all lightuserdata pointers

    void initialize(lua_State* L);       //-- Creates the metatable (only once) and publishes it

protected:
public:
    LMetaPointer(lua_State* L);
    virtual ~LMetaPointer();

    inline lua_State*  lua()    { return m_lua;             }
    inline std::string global() { return m_name;            }
    inline size_t      size()   { return m_pointers.size(); }

    void setGlobal(std::string n);      //-- Shall make this pointer globally accessible to LUA

    virtual int get(lua_State* L) = 0;  //-- To be implemented by inherited classes
    virtual int set(lua_State* L) = 0;  //-- To be implemented by inherited classes

    LMetaPointer* operator [](std::string n);
};

下面是类的实现

//-----------------------------------------------------------------------------
#define lua_checkmpointer(L)    (LMetaPointer*)luaL_checkudata(L, 1, LUA_METAPOINTER)
//-----------------------------------------------------------------------------
lua_State* LMetaPointer::m_lua = NULL;
std::map<LMetaPointer*, std::string> LMetaPointer::m_pointers;
const luaL_Reg LMetaPointer::m_lmembers[]   = { { NULL, NULL } };
const luaL_Reg LMetaPointer::m_lfunctions[] =
{
        { "__index",    LMetaPointer::__index    },
        { "__newindex", LMetaPointer::__newindex },
        { NULL, NULL }
};
//-----------------------------------------------------------------------------

LMetaPointer::LMetaPointer(lua_State* L) : m_name("")
{
    //-- Make sure we have created the metatable
    initialize(L);

    //-- Add this pointer as of kind LUA_METAPOINTER metatable. This bit of code
    //   might not be necessary here. (To be removed)
    lua_pushlightuserdata(m_lua, this);
    luaL_getmetatable(m_lua, LUA_METAPOINTER);
    lua_setmetatable(m_lua, -2);

    //-- Add myself to the map of all metapointers
    m_pointers[this] = m_name;
}
//-----------------------------------------------------------------------------

LMetaPointer::~LMetaPointer()
{
    //-- Remove myself from the map of metapointers
    std::map<LMetaPointer*, std::string>::iterator found = m_pointers.find(this);

    if(found != m_pointers.end())
        m_pointers.erase(found);
}
//-----------------------------------------------------------------------------

int LMetaPointer::__index(lua_State* L)
{
    //-- Obtain the object that called us and call its get method.
    //   Since get and set are pure virtual, all inherited classes of LMetaPointer
    //   must implement it, and, upon the call from here, the correct 'get' method
    //   will be called.
    LMetaPointer* p = lua_checkmpointer(L);
    return p->get(L);
}
//-----------------------------------------------------------------------------

int LMetaPointer::__newindex(lua_State* L)
{
    //-- Obtain the object that called us and call its set method
    //   Since get and set are pure virtual, all inherited classes of LMetaPointer
    //   must implement it, and, upon the call from here, the correct 'get' method
    //   will be called.
    LMetaPointer* p = lua_checkmpointer(L);
    return p->set(L);
}
//-----------------------------------------------------------------------------

void LMetaPointer::initialize(lua_State* L)
{
    //-- Only create the metatable the first time and instance of LMetaPointer is created
    if(!m_lua)
    {
        m_lua = L;

        luaL_newmetatable(m_lua, LUA_METAPOINTER);
        luaL_setfuncs(L, m_lfunctions, 0);
        luaL_newlib(L, m_lmembers);
    }
}
//-----------------------------------------------------------------------------

void LMetaPointer::setGlobal(std::string n)
{
    //-- Make myself (this) a global variable in LUA with name given by 'n'
    std::map<LMetaPointer*, std::string>::iterator found = m_pointers.find(this);

    if(found != m_pointers.end())
    {
        m_name = n;
        found->second = m_name;

        lua_pushlightuserdata(m_lua, this);
        luaL_getmetatable(m_lua, LUA_METAPOINTER);
        lua_setmetatable(m_lua, -2);
        lua_setglobal(m_lua, m_name.c_str());
    }
}
//-----------------------------------------------------------------------------

LMetaPointer* LMetaPointer::operator [](std::string n)
{
    //-- Simply for completeness, allow all metapointer access all other by their
    //   name. (Notice though that since names are only assigned to instances made
    //   global, this operator will only work properly when searching for a pointer
    //   made global. ALl othe rpointers have an empty name.
    std::map<LMetaPointer*, std::string>::iterator iter = m_pointers.begin();

    while(iter != m_pointers.end())
    {
        if(iter->second == n)
            return iter->first;
        ++iter;
    }

    return NULL;
}

现在，这个类将允许我定义任何其他结构或类，并向 LUA 传递一个指向它的指针 (lightuserdata)，而无需混合方法或名称。对于我最初问题中的示例，这意味着定义以下内容:

注意:我对示例进行了一些扩展，现在称为 LMeasLimit 的是以前的 TLimit，LMeasurement 是新的类和 LTest 是前面的 TMeaasurement

解决方案 - 实现

//-------------------------------------------------------------------------

struct LMeasLimit : public LMetaPointer
{
    bool   enabled;     //-- Is the limit enabled?
    double value;       //-- Limit value;

    LMeasLimit(lua_State* L) : LMetaPointer(L), enabled(false), value(0.0) {}
    ~LMeasLimit() {}

    int get(lua_State* L);   //-- Implements LMetaPointer::get
    int set(lua_State* L);   //-- Implements LMetaPointer::set
};
//-------------------------------------------------------------------------

struct LMeasurement : public LMetaPointer
{
    double      value;      //-- Measurement
    LStepResult result;     //-- Result of test
    std::string message;    //-- Message to display

    LMeasurement(lua_State* L) : LMetaPointer(L), value(0.0), result(srNothing), message("") {}
    ~LMeasurement() {}

    int get(lua_State* L);   //-- Implements LMetaPointer::get
    int set(lua_State* L);   //-- Implements LMetaPointer::set
};
//-------------------------------------------------------------------------

struct LTest : public LMetaPointer
{
    int          id;    //-- ID of test
    std::string  name;  //-- Name of test
    LMeasLimit   max;   //-- Max limit for measure
    LMeasLimit   min;   //-- Min limit for measure
    LMeasurement meas;  //-- Measurement

    LTest(lua_State* L) : LMetaPointer(L), id(0), name(""), min(L), max(L), meas(L) {}
    ~LTest() {}

    int get(lua_State* L);   //-- Implements LMetaPointer::get
    int set(lua_State* L);   //-- Implements LMetaPointer::set
};

//-----------------------------------------------------------------------------

以及不同类的不同方法的定义

int LMeasLimit::get(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("enabled") == 0)
        lua_pushboolean(L, enabled);
    else if(key.find("value") == 0)
        lua_pushnumber(L, value);
    else
        return 0;

    return 1;
}
//-----------------------------------------------------------------------------

int LMeasLimit::set(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("enabled") == 0)
        enabled = lua_toboolean(L, 3);
    else if(key.find("value") == 0)
        value = lua_tonumber(L, 3);

    return 0;
}
//-----------------------------------------------------------------------------




int LMeasurement::get(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("value") == 0)
        lua_pushnumber(L, value);
    else if(key.find("result") == 0)
        lua_pushunsigned(L, result);
    else if(key.find("message") == 0)
        lua_pushstring(L, message.c_str());
    else
        return 0;

    return 1;
}
//-----------------------------------------------------------------------------

int LMeasurement::set(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("value") == 0)
        value = lua_tonumber(L, 3);
    else if(key.find("result") == 0)
        result = LStepResult(lua_tounsigned(L, 3));
    else if(key.find("message") == 0)
        message = std::string(lua_tostring(L, 3));

    return 0;
}
//-----------------------------------------------------------------------------



int LTest::get(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("id") == 0)
        lua_pushinteger(L, id);
    else if(key.find("name") == 0)
        lua_pushstring(L, name.c_str());
    else if(key.find("min") == 0)
    {
        lua_pushlightuserdata(L, &min);
        luaL_getmetatable(L, LUA_METAPOINTER);
        lua_setmetatable(L, -2);
    }
    else if(key.find("max") == 0)
    {
        lua_pushlightuserdata(L, &max);
        luaL_getmetatable(L, LUA_METAPOINTER);
        lua_setmetatable(L, -2);
    }
    else if(key.find("meas") == 0)
    {
        lua_pushlightuserdata(L, &meas);
        luaL_getmetatable(L, LUA_METAPOINTER);
        lua_setmetatable(L, -2);
    }
    else
        return 0;

    return 1;
}
//-----------------------------------------------------------------------------

int LTest::set(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("id") == 0)
        id = lua_tointeger(L, 3);
    else if(key.find("name") == 0)
        name = std::string(lua_tostring(L, 3));

    return 0;
}

解决方案 - 将所有内容放在一起最后的修改是在我们原始问题的 LEngine::runScript 中。

int LEngine::runScript(std::string scrName)
{
    luaInit();

    if(m_lua)
    {
        LTest tst(m_lua);

        tst.name = std::string("mierda_esta");
        tst.setGlobal("step");

        if(luaL_loadfile(m_lua, scrName.c_str()) || lua_pcall(m_lua, 0, 0, 0))
            processLuaError();
    }

    return 0;
}

最后，我将展示我用于测试的 LUA 脚本之一及其输出。

测试 - LUA 脚本

print("step.id          = " .. step.id)
print("step.name        = " .. step.name)
print(step.min.enabled)
print("step.min.value   = " .. step.min.value)


step.id = 1
step.name = "nombre del test";
step.min.enabled = true;
step.min.value   = 5.6;

print("step.id          = " .. step.id)
print("step.name        = " .. step.name)
print(step.min.enabled)
print("step.min.value   = " .. step.min.value)

测试 - 输出

step.id          = 0
step.name        = mierda_esta
false
step.min.value   = 0
step.id          = 1
step.name        = nombre del test
true
step.min.value   = 5.6

所以，现在一切似乎都如我所愿。我仍然需要修改此 LMetaPointer 以便能够以与我们在 C++ 中类似的方式调用任何继承类的成员函数。但这将是另一个故事。

再次感谢@siffiejoe 和@greatwolf 的时间和回复。