c++将派生类的成员指针强制转换为基类指针

Question

我目前正在使用HttpServer，并遇到以下问题：

我想注册我的控制器，当我收到请求时，我想检查其中一个控制器是否有所请求URL的处理程序，然后调用该处理程序。

到目前为止还不错，但我不知道如何用c++解决它，用PHP会很容易。

在Easteregg控制器函数getControllerCallbacks中，我想返回可用的回调，但它不会编译，因为我不能将派生类的成员函数指针强制转换为基类(controller)的成员函数指示器(EastereggController)。我曾想过让ControllerCallback成为一个"模板类"，但后来我必须知道ControllerHandler中控制器的类，我不知道，因为我有一个std:：vector

我对C++还很陌生，也许我忽略了一些东西。

这是我现在的代码：

控制器.h

#ifndef CONTROLLER_H
#define CONTROLLER_H
#include "Config.h"
#include "Request.h"
#include "ControllerCallback.h"
namespace HttpServer {
class ControllerCallback;
class Controller {
public:
Controller();
virtual std::vector<ControllerCallback> getControllerCallbacks() = 0;
private:
Config *config;
const Request *request;
};
}
#endif // CONTROLLER_H

EastereggController.h

#ifndef EASTEREGGCONTROLLER_H
#define EASTEREGGCONTROLLER_H
#include "../HttpServer/Controller.h"
namespace Controller {
class EastereggController: public HttpServer::Controller  {
public:
EastereggController() {};
std::vector<HttpServer::ControllerCallback> getControllerCallbacks();
HttpServer::Reply easteregg();
};
}
#endif // EASTEREGGCONTROLLER_H

EastereggController.cpp

#include "EastereggController.h"
namespace Controller {
std::vector<HttpServer::ControllerCallback> EastereggController::getControllerCallbacks() {
std::vector<HttpServer::ControllerCallback> controllerCallbacks;
HttpServer::ControllerCallback callback;
callback.pathTemplate = "/easteregg";
callback.handlerFunctionPtr = &EastereggController::easteregg;
return controllerCallbacks;
}
HttpServer::Reply EastereggController::easteregg() {
HttpServer::Reply rep;
rep.content.append("you have found an eastereggn");
rep.status = HttpServer::Reply::ok;
rep.headers.resize(2);
rep.headers[0].name = "Content-Length";
rep.headers[0].value = std::to_string(rep.content.size());
rep.headers[1].name = "Content-Type";
rep.headers[1].value = "text/plain";
return rep;
}
}

ControllerCallback.h

#ifndef CONTROLLERCALLBACK_H
#define CONTROLLERCALLBACK_H

#include "Reply.h"
#include <string>
namespace HttpServer {
class Controller;
class ControllerCallback {
public:
ControllerCallback()
: pathTemplate("") {};
//,handlerFunctionPtr(nullptr){}
std::string pathTemplate;
Reply(Controller::*handlerFunctionPtr)();
};
}
#endif

ControllerHandler.h

#ifndef CONTROLLERHANDLER_H
#define CONTROLLERHANDLER_H
#include <vector>
#include <string>
#include "Controller.h"
#include "Config.h"
#include "Request.h"
#include "Reply.h"
namespace HttpServer {
class ControllerHandler {
public:
ControllerHandler(Config &conf);
void registerController(Controller &controller);
bool invokeController(std::string requestPath, Request &req, Reply &rep);
private:
Config &config;
std::vector<Controller *> controllers;
};
}
#endif // CONTROLLERHANDLER_H

ControllerHandler.cpp

#include "ControllerHandler.h"
#include "Controller.h"
#include "PathHandler.h"
namespace HttpServer {
ControllerHandler::ControllerHandler(Config &conf)
: config(conf) {
}
void ControllerHandler::registerController(Controller &controller) {
controllers.push_back(&controller);
}
bool ControllerHandler::invokeController(std::string requestPath, Request &req, Reply &rep) {
PathHandler pathHandler(requestPath, ':');
for(Controller *controller : controllers) {
std::vector<ControllerCallback> callbacks = controller->getControllerCallbacks();
for(ControllerCallback controllerCallback : callbacks) {
if(pathHandler.compare(controllerCallback.pathTemplate)) {
rep = ((*controller).*(controllerCallback.handlerFunctionPtr))();
return true;
}
}
}
return false;
}
}

Answer 1

我终于找到了答案(我不得不承认这是一个语法错误)

在尝试不同的解决方案时(在这里发布之前)，我有以下片段：

EastereggController.cpp

callback.handlerFunctionPtr = reinterpret_cast<HttpServer::Reply HttpServer::Controller::*>(&EastereggController::easteregg);

这在语法上是错误的，但我没有注意到，因为我有以下编译错误：

error: invalid cast from type 'HttpServer::Reply (Controller::EastereggController::*)()' to type 'HttpServer::Reply HttpServer::Controller::*()'
callback.handlerFunctionPtr = reinterpret_cast<HttpServer::Reply HttpServer::Controller::*()>(&EastereggController::easteregg);

现在正确的版本：

callback.handlerFunctionPtr = reinterpret_cast<HttpServer::Reply(HttpServer::Controller::*)()>(&EastereggController::easteregg);

只是加了括号，现在就可以了。