Question

我在MSVS 2010下编译某些代码时遇到问题，我收到了C2678错误。我在这里找到了对该错误的描述：

http://msdn.microsoft.com/en-us/library/ys0bw32s(v=vs.100).aspx

但我不明白“钉住本地会员”是什么意思。

有人可以解释一下吗？

以下是生成该错误的代码的一部分：

#pragma once

#include <functional>
#include <vector>
#include <memory.h>

template<typename callbackCodes_e, callbackCodes_e endOfCodes, typename param_t>
class CCallbackContainer
{
    typedef std::function<void(param_t)> callback_t;

public:
    struct callbackInfo_t
    {
        callbackCodes_e code;
        callback_t callback;
        param_t param;
        size_t countdownToAutoDelete;
    };

    CCallbackContainer() {};
    ~CCallbackContainer() {};

    typedef std::function<void(param_t)> callback_t;
    typedef callbackInfo_t HANDLE;

    std::vector<callbackInfo_t> m_Callbacks[endOfCodes];
    void callbackCall(callbackInfo_t const & callbackInfo);

public:
    inline bool validCode(callbackCodes_e code) { return code < endOfCodes; }

    HANDLE callbackSet(callbackCodes_e code, callback_t callback, DWORD param, size_t countdownToAutoDelete = 1);
    void callbackClear(HANDLE callbackToRemove);
    void callbackCall(callbackCodes_e code)
    {
        auto callbackList = m_Callbacks[code];
        for(auto i: callbackList)
        {
            i->callback(i->param);
        }
        for_each(auto i = callbackList.rbegin(); i != callbackList.rend(); ++i)
        {
            if (--(i->countdownToAutoDelete) < 1)
            {
                callbackList.erase(i);
            }
        }
    }
};

// template implimentation has to be in header file
template<typename callbackCodes_e, callbackCodes_e endOfCodes, typename param_t>
typename CCallbackContainer<callbackCodes_e, endOfCodes, param_t>::HANDLE // return
    CCallbackContainer<callbackCodes_e, endOfCodes, param_t>::callbackSet // function name
        (callbackCodes_e code, callback_t callback, DWORD param, size_t countdownToAutoDelete) // parameters
{
    ASSERT(validCode(code));
    callbackInfo_t callbackInfo = { code, callback, param, countdownToAutoDelete };
    ASSERT(std::find(m_Callbacks[code].begin(), m_Callbacks[code].end(), callback) == m_Callbacks[code].end());
    m_Callbacks[code].push_back(callbackInfo);
    return callbackInfo;
}

template<typename callbackCodes_e, callbackCodes_e endOfCodes, typename param_t>
void // return type
    CCallbackContainer<callbackCodes_e, endOfCodes, param_t>::callbackClear // function name
        (typename CCallbackContainer<callbackCodes_e, endOfCodes, param_t>::HANDLE callbackToRemove) // parameters
{
    callbackCodes_e code = callbackToRemove.code;
    ASSERT(validCode(code));
    auto iCallbackInfo = std::find(m_Callbacks[code].begin(), m_Callbacks[code].end(), callbackToRemove);
    ASSERT(iCallbackInfo == m_Callbacks[code].end());
    m_Callbacks[code].erase(iCallbackInfo);
}

template<typename callbackCodes_e, callbackCodes_e endOfCodes, typename param_t>
void // return type
    CCallbackContainer<callbackCodes_e, endOfCodes, param_t>::callbackCall // function name
        (callbackInfo_t const & callbackInfo) // parameters
{
    callbackInfo.callback(callbackInfo.param);
    if (--callbackInfo.countdownToAutoDelete < 1)
    {
        callbackClear(callbackInfo);
    }
}

template<typename callbackCodes_e, callbackCodes_e endOfCodes, typename param_t>
void // return type
    CCallbackContainer<callbackCodes_e, endOfCodes, param_t>::callbackCall // function name
        (callbackCodes_e code) // parameters
{
    auto callbackList = m_Callbacks[code];
    for(auto i: callbackList)
    {
        i->callback(i->param);
    }
    for_each(auto i = callbackList.rbegin(); i != callbackList.rend(); ++i)
    {
        if (--(i->countdownToAutoDelete) < 1)
        {
            callbackList.erase(i);
        }
    }
}

然而，错误实际上是由算法中的某些东西产生的：

14>c:\program files (x86)\microsoft visual studio 10.0\vc\include\algorithm(41): error C2678: binary '==' : no operator found which takes a left-hand operand of type 'CCallbackContainer::callbackInfo_t' (or there is no acceptable conversion)
14>          with
14>          [
14>              callbackCodes_t=CBalloonHelp::callbackCodes_t,
14>              endOfCodes=eCallbackEnd,
14>              param_t=DWORD
14>          ]
14>          could be 'built-in C++ operator==(std::_Bool_type, std::_Bool_type)'
14>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\functional(277): or       'bool std::tr1::operator ==(std::tr1::_Unutterable,const std::tr1::function &)' [found using argument-dependent lookup]
14>          with
14>          [
14>              param_t=DWORD,
14>              _Fty=void (DWORD)
14>          ]
14>          c:\projects\cv-7646\og50\include\gxcoll.h(67): or       'BOOL operator ==(const GXNDX &,const GXNDX &)' [found using argument-dependent lookup]
14>          c:\program files (x86)\microsoft sdks\windows\v7.0a\include\guiddef.h(192): or       'int operator ==(const GUID &,const GUID &)' [found using argument-dependent lookup]

// ... other operator==() tests that didn't match the signature.

在我看来，callbackInfo_t的默认运算符==（）存在问题，但我不确定原因。

Answer 1

固定是C ++ .NET中使用的术语。当ref'ed类（用ref class声明的那些）需要访问某些本地成员变量时，它必须 pin 它，因为托管引用可以在内存中移动，但是原生指针必须留在固定的地方。一旦你 pin 成员变量，你就会获得一个本机指针，一切正常。当对象取消固定时，它将再次移动。有关详细信息，请搜索pin_ptr<>模板。

但是您的代码根本没有ref class，因此固定评论只会误导您！

您的问题很简单，就是您没有向operator==()结构提供callback_t！

只要这样做，或者更适合你情况的任何事情：

 struct callbackInfo_t
    {
        callbackCodes_e code;
        callback_t callback;
        param_t param;
        size_t countdownToAutoDelete;

        bool operator==(const callbackInfo_t &o) const
        {
           return code == o.code && callback == o.callback &&
                  param == o.param && countdownToAutoDelete == o.countdownToAutoDelete;
        }
    };

但请注意，显然，您比较的任何成员变量也必须具有可比性，否则代码将再次失败并显示类似的消息。

“钉住本地会员”是什么意思？

1 个答案: