我如何使用这些类？(How do I work with these classes? [duplicate])

我如何使用这些类？(How do I work with these classes? [duplicate])

这个问题在这里已经有了答案：

在C ++ 2答案中 声明公共静态变量时出现链接错误

我是C ++新手，我尝试启动一个项目，每次创建一个ATM类的新实例时，它都会将accountID设置为1并显示当前帐户ID。 这是我的代码：

// Bank ATM.cpp : Defines the entry point for the console application. #include "stdafx.h" #include "ATM.h" int main() { ATM abunch[15]; for (int i = 0; i < 15; i++){ abunch[i] = ATM(); } return 0; } //ATM.h #include "stdafx.h" #ifndef atm #define atm class ATM { static int accountID; public: ATM(); }; int ATM::accountID = 0; #endif //ATM.cpp #include "stdafx.h" #include "ATM.h" #include <iostream> ATM::ATM() { ++accountID; std::cout << accountID; }

我收到以下错误消息：

我究竟做错了什么？

This question already has an answer here:

Link error when declaring public static variables in C++ 2 answers

I am new to C++ and I am trying to start a project where every time I create a new instance of the ATM class it incements accountID by 1 and displays the current account ID. This is my code:

// Bank ATM.cpp : Defines the entry point for the console application. #include "stdafx.h" #include "ATM.h" int main() { ATM abunch[15]; for (int i = 0; i < 15; i++){ abunch[i] = ATM(); } return 0; } //ATM.h #include "stdafx.h" #ifndef atm #define atm class ATM { static int accountID; public: ATM(); }; int ATM::accountID = 0; #endif //ATM.cpp #include "stdafx.h" #include "ATM.h" #include <iostream> ATM::ATM() { ++accountID; std::cout << accountID; }

I get The following error message:

What am I doing wrong?

最满意答案

由于ATM::accountID是在.h文件中声明的，在类之外，每当该文件包含在另一个文件中时，它都会进行全局声明。 你包括两次; 在main.cpp和ATM.cpp 。 这是一个禁忌。

声明需要转移到ATM.cpp

//ATM.h #include "stdafx.h" #ifndef atm #define atm class ATM { static int accountID; public: ATM(); }; int ATM::accountID = 0; // <--- remove this line #endif //ATM.cpp #include "stdafx.h" #include "ATM.h" #include <iostream> int ATM::accountID = 0; // <----put it here ATM::ATM() { ++accountID; std::cout << accountID; }

Because ATM::accountID is declared in a .h file, outside of a class, it is globally declared every time that file is included in another file. You include it twice; in main.cpp and in ATM.cpp. That's a no-no.

The declaration needs to move to ATM.cpp

//ATM.h #include "stdafx.h" #ifndef atm #define atm class ATM { static int accountID; public: ATM(); }; int ATM::accountID = 0; // <--- remove this line #endif //ATM.cpp #include "stdafx.h" #include "ATM.h" #include <iostream> int ATM::accountID = 0; // <----put it here ATM::ATM() { ++accountID; std::cout << accountID; }