c++ - 无法从其他类获取单例类的实例

Question

我面临的问题在某种程度上与“循环包含”或“未完成的类(class)”有关

我有 2 个类:

ControllerManager，这个类声明为Singleton，这个类有一个对象AuxController。

AuxController，这个类有个函数需要获取ControllerManager的实例

问题是:编译源码时，编译失败，报错“类型不完整”或“类型无效”

有什么办法可以解决这个问题吗？ 或者有没有其他方法可以重新设计代码结构？

源代码 Controller 管理器.h

#ifndef CONTROLLERMANAGER_H
#define CONTROLLERMANAGER_H
#include "auxcontroller.h"

class ControllerManager
{
/* This class is defined as Singleton class */
private:
    /* 1. define a private static instance */
    static ControllerManager *inst;

public:
    /* 2. define a public static accessor */
    static ControllerManager *getInstance(){
        /* 3. do lazy initialization */
        if(!inst){
            inst = new ControllerManager();
        }
        return inst;
    }

protected:
    /* 4. Define all accessors to be protected */
    ControllerManager();
    ~ControllerManager();

/* property */
private:
    int m_code;

public:
    int getCode()
    {
        return m_code;
    }

    void setCode(int _code)
    {
        m_code = _code;
    }

/* below code causes fail of compilation */
public:

    AuxController m_auxcontroller;

};

#endif // CONTROLLERMANAGER_H

Controller 管理器.cpp

#include "controllermanager.h"

/* 5. initialize static variable */
ControllerManager *ControllerManager::inst = 0;
ControllerManager::ControllerManager()
{
    m_code = 15;
}

ControllerManager::~ControllerManager()
{
    delete inst;
}

辅助 Controller .h

#ifndef AUXCONTROLLER_H
#define AUXCONTROLLER_H

/* if do NOT include controllermanager.h with below line,
 * and declare ControllerManager class as a forward declaration:
 *
 * class ControllerManager;
 *
 * compiler will stop due to "incomplete type"
 */
#include "controllermanager.h"



class AuxController
{
public:
    AuxController();
    void setControllerCode(int code);
};

#endif // AUXCONTROLLER_H

辅助 Controller .cpp

#include "auxcontroller.h"

AuxController::AuxController()
{

}

void AuxController::setControllerCode(int code)
{
    /* if do NOT include controllermanager.h ,
     * and declare ControllerManager class as a forward declaration in the header file:
     *
     * class ControllerManager;
     *
     * compiler will stop due to "incomplete type" at this line
     *
     */
    ControllerManager::getInstance()->setCode(code);
}

主要.cpp

#include "controllermanager.h"

int main(int argc, char *argv[])
{
    ControllerManager *ctlMng = ControllerManager::getInstance();
    ctlMng->setCode(10);
    return 0;
}

Answer 1

不要在 auxcontroller.h 中包含“controllermanager.h”，但要在 auxcontroller.cpp 中包含它。

一般情况下，如果可以避免的话，您不应该将头文件包含在其他头文件中。请改用前向声明。但是一定要包含 cpp 文件中所有必需的头文件。