c++ - 如何在成员初始化列表中传递类成员的指针？

Question

我有一个名为 HighWaterDetector 的类:

class HighWaterDetector
{
public:
    HighWaterDetector(Device* device);
    Device * devicePtr;
    Output * output1Ptr;
    CloudMsgParser * cloudMsgParserPtr;
    Output output1;
    NCD2Relay ncd2Relay;
    CloudMsgParser cloudMsgParser;
};

构造函数:

HighWaterDetector::HighWaterDetector(Device* device): ncd2Relay(), output1(1, &ncd2Relay){
}

我正在尝试在 HighWaterDetector 的成员初始化列表中初始化 Output 的实例，但 Output 需要您将指针传递给 NCD2Relay 的实例，该实例也是 HighWaterDetector 类的成员。我的程序在输出构造函数内崩溃。这是这样做的错误方法吗？我做错了什么？

输出类:

class Output
{
public:
    Output(ushort relayNum, NCD2Relay* ncd2RelayPtr);
    ushort relayNum;
    OutputStatus outputStatus;
    int setOutputOn(void);
    int setOutputOff(void);
    void process(void);
    NCD2Relay* ncd2RelayPtr;
};


//Output Constructor
Output::Output(ushort relayNum, NCD2Relay* ncd2RelayPtr) {
    this->relayNum = relayNum;
    this->ncd2RelayPtr = ncd2RelayPtr; //DOESNT CRASH IF I COMMENT THIS OUT
    this->outputStatus.outFail = 0;
    Serial.print("Initializing output ");
    Serial.println(this->relayNum);
    this->setOutputOff();
}

Answer 1

您是否注意到编译器警告？还是他们开到最大？您的成员的声明顺序可能是原因:

class HighWaterDetector
{
public:
    HighWaterDetector(Device* device);
    Device * devicePtr;
    Output * output1Ptr;
    CloudMsgParser * cloudMsgParserPtr;
    Output output1;                     // <- This is constructed before
    NCD2Relay ncd2Relay;                // <- This...
    CloudMsgParser cloudMsgParser;
};

但是你的构造函数是这样的:

HighWaterDetector::HighWaterDetector(Device* device): ncd2Relay(), output1(1, &ncd2Relay){ ... }

在上面的上下文中，在 output1 的构造函数中使用 ncd2Relay 的地址只是使用指向未初始化对象的指针，当您最终取消引用它时，它是未定义的行为在它的 build 之前。因此，您需要在类定义中强制执行排序...

仅引用 C++ 标准:(强调我的)[class.base.init/13]

In a non-delegating constructor, initialization proceeds in the following order:

• First, and only for the constructor of the most derived class ([intro.object]), virtual base classes are initialized in the order they appear on a depth-first left-to-right traversal of the directed acyclic graph of base classes, where “left-to-right” is the order of appearance of the base classes in the derived class base-specifier-list.

• Then, direct base classes are initialized in declaration order as they appear in the base-specifier-list (regardless of the order of the mem-initializers).

• Then, non-static data members are initialized in the order they were declared in the class definition (again regardless of the order of the mem-initializers).

• Finally, the compound-statement of the constructor body is executed.