初始化类的静态(非常量)变量。

Question

我有TestMethods.h

#pragma once

// strings and c-strings
#include <iostream>
#include <cstring>
#include <string>

class TestMethods
{
private:
    static int nextNodeID;
    // I tried the following line instead ...it says the in-class initializer must be constant ... but this is not a constant...it needs to increment.
    //static int nextNodeID = 0;
    int nodeID;

    std::string fnPFRfile; // Name of location data file for this node.


public:
    TestMethods();
    ~TestMethods();

    int currentNodeID();
};

// Initialize the nextNodeID
int TestMethods::nextNodeID = 0;
// I tried this down here ... it says the variable is multiply defined.  

我有TestMethods.cpp

#include "stdafx.h"
#include "TestMethods.h"

TestMethods::TestMethods()
{
    nodeID = nextNodeID;
    ++nextNodeID;
}
TestMethods::~TestMethods()
{
}
int TestMethods::currentNodeID()
{
    return nextNodeID;
}

我在这里看过这个例子：Unique id of class instance

看上去和我的差不多。我试过两种最好的解决方案。对我来说都不管用。很明显我漏掉了什么。有人能指出是什么吗？

Answer 1

您需要将TestMethods::nextNodeID的定义移到cpp文件中。如果将其包含在头文件中，则包含头文件的每个文件都将在其中定义它，从而导致多个防御。

如果您有C++17支持，可以使用inline关键字在类中声明静态变量，如下

class ExampleClass {

private:
    inline static int counter = 0;
public:
    ExampleClass() {
        ++counter;
    }
};