链接器错误未解析的外部符号与我的cnt变量 [英] Linker error unresolved external symbol with my cnt variable

问题描述

我有一个与静态变量有关的链接问题.这是我第一次尝试使用静态变量.我正在创建一个向量，并希望cnt变量在所有Student对象上都是静态的.

I'm having a linking issue with a static variable. This is the first time I've tried to use a static variable. I am creating a vector and want the cnt variable to be static accross all Student objects.

我一直在努力寻找答案.我读过其他有此问题的人，他们没有声明静态变量，而是需要专门为静态变量创建一个新对象.

I've searched around trying to figure this out. I've read others having this problem where they weren't declaring the static var and they needed to create a new object specifically for the static variable.

我认为在构造函数中声明并设置了sCnt变量.在类中实现静态成员变量的正确方法是什么?

I thought in constructor the sCnt variable is declared and set. What is the proper way to implement a static member variable in a class?

Student.h

Student.h

#pragma once
#include <iostream>

using namespace std;

class Student
{
public:
    Student();
    Student(string ID);
    virtual ~Student(void);
    void cntReset();
    int getCnt() const;
    int getID() const;
    bool operator< (const Student& s) const;
    bool operator== (const Student& s) const;

protected:
    int id;
    static int sCnt;

private:
};

Student.cpp

Student.cpp

#include "Student.h"

Student::Student()
{
    id = 0;
    sCnt = 0;
}

Student::Student(string ID)
{
    id = atoi(ID.c_str());
    sCnt = 0;
}

推荐答案

您只需要定义一次即可.将以下内容添加到cpp文件中:

You need to define it, exactly once. Add the following to the cpp file:

int Student::sCnt = 0; // Note the ' = 0' is optional as statics are
                       // are zero-initialised.

假定应该计算Student实例的数量，请不要在Student构造函数中将其设置为0，在Student析构函数中对其进行递增和递减.

Assuming it is supposed to count the number of Student instances don't set it to 0 in the Student constructors, increment it and decrement in the Student destructor.

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