C++ 未声明的标识符错误

Question

我收到一个未声明的标识符错误，我不知道为什么。我什至重写了完整的东西，以确保我没有打错字。谁能告诉我为什么会出现这个错误？

我的文件是

Connection.hpp

#pragma once

#include "../LogicSimulator.hpp"
#include "CircuitObject.hpp"

class Connection
{
public:
    Connection(CircuitObject& c1, CircuitObject& c2, LogicSimulator& 
        simulator);
private:
    int state;
    CircuitObject& c1;
    CircuitObject& c2;
    LogicSimulator& simulator;
};

不要介意CircuitObjects，他们不会给出任何错误，错误是：未声明的'LogicSimulator'

Connection.cpp

#pragma once

#include "Connection.hpp"
#include "../LogicSimulator.hpp"
#include "CircuitObject.hpp"

Connection::Connection(CircuitObject& c1, CircuitObject& c2, LogicSimulator& 
    simulator) : c1(c1), c2(c2), simulator(simulator)
{
    state = c1.State;
}

错误：未声明的“LogicSimulator”

LogicSimulator.hpp

#pragma once

#include "Simulator\CircuitObject.hpp"
#include "Simulator\Connection.hpp"
#include <SFML\Graphics.hpp>
#include <vector>

class LogicSimulator
{
public:
    std::vector<CircuitObject*> circuitObjects;
    std::vector<CircuitObject*> selectedCircuitObjects;
    std::vector<Connection*> connections;
    sf::RenderWindow Window;

    void Init();
private:
    void start();
    void draw();
};

不要介意LogicSimulator.cpp，它不会给出任何错误。

---

错误：未声明的“连接”（是的，在连接逻辑模拟器中未声明）

Answer 1

正如我在 cmets 中所写的，这很可能是由您的循环包含引起的。 Connection.hpp 包含 LogicSimulator.hpp，而 LogicSimulator.hpp 本身包含 Connection.hpp。

在您的情况下，您甚至不需要包含。对于指针和引用，前向声明很好：

Connection.hpp：

#pragma once

class CircuitObject;
class LogicSimulator;

class Connection
{
public:
    Connection(CircuitObject& c1, CircuitObject& c2, LogicSimulator& 
        simulator);
private:
    int state;
    CircuitObject& c1;
    CircuitObject& c2;
    LogicSimulator& simulator;
};

LogicSimulator.hpp：

#pragma once

#include <SFML\Graphics.hpp>
#include <vector>

class CircuitObject;
class Connection;

class LogicSimulator
{
public:
    std::vector<CircuitObject*> circuitObjects;
    std::vector<CircuitObject*> selectedCircuitObjects;
    std::vector<Connection*> connections;
    sf::RenderWindow Window;

    void Init();
private:
    void start();
    void draw();
};