将C++方法作为函数指针传递

Question

    bool sendRequest(DataFieldList& requestParams,
                     DataFieldList& responseParams,
                     std::string context, void(*sendFailure)() = NULL);

    sendRequest(paramList, responseList, "Could not set background lighting control brightness limit", HBCMaxBrightnessLimitSendFailure);

    void HBCMaxBrightnessLimitSendFailure();

当我构建这个应用程序时，我得到错误：

    lightingsystemcomponent.cpp(969): error C3867: 'Lighting::SystemComponent_impl::HBCMaxBrightnessLimitSendFailure': function call missing argument list; use '&Lighting::SystemComponent_impl::HBCMaxBrightnessLimitSendFailure' to create a pointer to member

我也试过：

    sendRequest(paramList, responseList, "Could not set background lighting control brightness limit", HBCMaxBrightnessLimitSendFailure());

这将错误更改为：

    lightingsystemcomponent.cpp(969): error C2664: 'bool Lighting::SystemComponent_impl::sendRequest(DataFieldList &, DataFieldList &,std::string,void (__cdecl *)(void))' : cannot convert argument 4 from 'void' to 'void (__cdecl *)(void)'

    bool sendRequest(DataFieldList& requestParams,
                     DataFieldList& responseParams,
                     std::string context,
                     std::function<void()> sendFailure = NULL);

    void LightingEngine::sendRequest(DataFieldList& requestParams,
                                     DataFieldList& responseParams,
                                     std::string context,
                                     std::function<void()> sendFailure) {
    if ( sendFailure != NULL ) {
        sendFailure();
    }

    error C2064:  term does not evaluate to a function taking 0 arguments

下面是调用这个例程的类和我传递的回调函数的示例：

    void component::onFailure() {
        ...Do something...
    }

    void component::update() {
        ... Some set-up to build paramlist ...
        LightingEngine* engine = getLightingEngine();
        assert(engine != nullptr);
        engine->sendRequest(&paramList, &responseList, "Some context text", [this]()->void { onFailure(); });            
    }

Answer 1

可以将SendFailure声明为成员函数指针。

bool sendRequest(DataFieldList& requestParams,
                 DataFieldList& responseParams,
                 std::string context, 
                 void(Lighting::SystemComponent_impl::*sendFailure)() = nullptr);

这将允许您写一个非常长的行：

sendRequest(paramList, responseList, "Could not set background lighting control brightness limit", &Lighting::SystemComponent_impl::HBCMaxBrightnessLimitSendFailure);

另一种选择是使用std::function。

bool sendRequest(DataFieldList& requestParams,
                 DataFieldList& responseParams,
                 std::string context, 
                 const std::function<void()> &sendFailure = nullptr);

并调用sendrequest，如下所示：

sendRequest(paramList, responseList, "Could not set background lighting control brightness limit", [this]{ HBCMaxBrightnessLimitSendFailure() });

template <typename Func>
bool sendRequest(DataFieldList& requestParams,
                 DataFieldList& responseParams,
                 std::string context, 
                 Func sendFailure);

bool sendRequest(DataFieldList& requestParams,
                 DataFieldList& responseParams,
                 std::string context);

sendRequest(paramList, responseList, "Could not set background lighting control brightness limit", [this]{ HBCMaxBrightnessLimitSendFailure() });