用 C++ 编写状态机

Question

我正在尝试编写基于口香糖机的状态机。我有一个基本状态的接口class，而我有使用这个接口的特定状态。我有四种状态，no_quarter、has_quarter、sold 和 sold_out 状态。我还有一个口香糖机 class 可以处理这些状态，并且根据我的机器所处的状态，它会 class 并执行所需的操作。这是我的代码有问题，我也会 post 我的函数。

Gumball_Machine.h

class Gumball_Machine
{
private:
    int gumball_count;
    State *current_state;
    No_Quarter_State *nqs;
    Has_Quarter_State *hqs;
    Sold_State *ss;
    Sold_Out_State *sos;

public:

    Gumball_Machine(int inventory)
    {
        gumball_count = inventory;
        nqs = new No_Quarter_State(this);
        hqs = new Has_Quarter_State(this);
        ss = new Sold_State(this);
        sos = new Sold_Out_State(this);
        if (gumball_count == 0)
            set_state(sos);
        else
            set_state(nqs);
    }

    void insert_quarter()
    {
        current_state->insert_quarter();
    }

    void eject_quarter()
    {
        current_state->eject_quarter();
    }

    void turn_crank()
    {
        current_state->turn_crank();
    }

    void dispense()
    {
        current_state->dispense();
    }

    void set_state(State *new_state)
    {
        current_state = new_state;
    }

    State *get_no_quarter_state()
    {
        return nqs;
    }

    State *get_has_quarter_state()
    {
        return hqs;
    }

    State *get_sold_state()
    {
        return ss;
    }

    State *get_sold_out_state()
    {
        return sos;
    }

No_Quarter_State.h

#ifndef NO_QUARTER_STATE_H_INCLUDED
#define NO_QUARTER_STATE_H_INCLUDED
#include "State.h"

class No_Quarter_State: public State
{
public:
    No_Quarter_State(Gumball_Machine *gbm);
    void insert_quarter();
    void eject_quarter();
    void turn_crank();
    void dispense();
};

#endif // NO_QUARTER_STATE_H_INCLUDED

No_Quarter_State.cpp

#include "No_Quarter_State.h"
#include "Gumball_Machine.h"

No_Quarter_State::No_Quarter_State(Gumball_Machine *machine)
{
    machine = machine;
}

void No_Quarter_State::insert_quarter()
{
    cout << "You inserted a quarter.\n";
    machine->set_state(machine->get_has_quarter_state());
}

void No_Quarter_State::eject_quarter()
{
    cout << "You must insert a quarter before you can eject one.\n";
}

void No_Quarter_State::turn_crank()
{
    cout << "You must insert a quarter before you can crank the handle.\n";
}

void No_Quarter_State::dispense()
{
    cout << "You need to pay first before you can get a gumball.\n";
}

我遇到问题的行在 No_Quarter_State.cpp

machine->set_state(machine->get_has_quarter_state());

这给我一个运行时间错误。我见过这样的例子，但我不完全确定这在 C++ 中是否合法。我正在尝试切换口香糖机对象的状态。

我收到的错误是一般性无响应错误："test.ext has stopped working"。我正在使用 CodeBlocks 对此进行编码。

Answer 1

在构造函数中，假设成员变量machine被参数隐藏

No_Quarter_State::No_Quarter_State(Gumball_Machine *machine)
{
    machine = machine;
}

您可以改用 initializer list syntax 来解决此问题：^{感谢 Sneftel 和 NathanOliver}

No_Quarter_State::No_Quarter_State(Gumball_Machine *machine)
    : machine(machine)
{
}

但是，在常规方法函数中，如果您将方法参数命名为与成员变量相同的名称，则必须使用 this->。用于避免该问题的典型样式是在成员名称前添加 m_ 或附加 _。

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