c++ - 已经定义的C++类

我不明白一个人的想法。我有一个名为“ network.h”的头文件，并且带有函数的类声明。在“ network.cpp”文件中，我具有这些功能。当要在main.cpp中包含“ network.h”并编译我的项目（Microsoft Visual Studio 2007）时，出现以下消息：

network.obj : error LNK2005: "class networkClass network" (?network@@3VnetworkClass@@A) already defined in main.obj

我知道我们不能例如创建两个相同的变量，但是在此我不知道出了什么问题。

资源：

网络

#ifndef H_NETWORK
#define H_NETWORK

    #include <string>
    #include <SFML/Network.hpp>




    struct getClientsStruct
    {
        std::string nick;
        sf::IpAddress clientIp;

    };

    getClientsStruct receiveClientIfno();

    class networkClass
    {
    public:
        void sendMyInfo();
        void bind();
        getClientsStruct receiveClientIfno();


    };

    networkClass network;


    #endif

network.cpp

#include <SFML/Network.hpp>
#include "network.h"
#include <iostream>
#include <string>


sf::UdpSocket searchSocket;

//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!





    void sendMyInfo()
    {
        sf::UdpSocket searchSocket;


        std::string myLocalAddress = sf::IpAddress::getLocalAddress().toString();

        char dataSend[100] = "DANE.......";
        sf::IpAddress recipient = "255.255.255.255";
        unsigned short portSending = 54000;
        if (searchSocket.send(dataSend, 100, recipient, portSending) != sf::Socket::Done)
        {
            // error...
            std::cout << "Sending ERROR" << std::endl;
        }
        else
            std::cout << "Sending SUCCESSED" << std::endl;
    }

    void bind()
    {
        // bind the socket to a port
        if (searchSocket.bind(54000) != sf::Socket::Done)
        {
            std::cout << "ERROR binding" << std::endl;
        }
        else
            std::cout << "BIND success" << std::endl;

    }

    getClientsStruct receiveClientIfno()
    {
        getClientsStruct ClientInfo;
        searchSocket.setBlocking(0);
        char dataReceived[100];
        std::size_t received;
        sf::IpAddress sender;
        unsigned short portReceive;






        if (searchSocket.receive(dataReceived, 100, received, sender, portReceive) != sf::Socket::Done)
            {   // error...
                std::cout << "Receive ERROR" << std::endl;
            }



        std::cout << "Received " << received << " bytes from " << sender << " on port " << portReceive << std::endl;


        return ClientInfo;

    }

- - - - - - - - - - - - - - - - - 编辑 - - - - - - - - ----------------------

因此，我从network.h中删除了networkClass network;，并在main.cpp中对其进行了声明。现在，当我想运行例如network.bind();的功能时，出现错误：main.obj : error LNK2019: unresolved external symbol "public: void __thiscall networkClass::bind(void)" (?bind@networkClass@@QAEXXZ) referenced in function _main

最佳答案

标头应包含在多个编译单元（cpp文件）中。不幸的是，您在network.h中定义了一个全局对象network。因此，它将被声明多次（一次是在编译network.cpp时，另一次是在编译main.cpp时）。

全局变量（如果不能通过其他方式避免它们）应该仅以extern的形式出现在标题中：

    extern networkClass network;  // you say this variable exist somewhere else

然后，您必须将定义放入一个cpp文件中。顺便说一句，如果您的类不是绝对需要它，则不应在类标题中定义它。而是在main.cpp中定义它。而且，如果您完全可以避免使用全局变量，请摆脱它。

network.cpp中的另一个问题是您的语法定义了独立于全局类的全局函数。每当在类之外定义类函数时，都必须在其名称前加上类名称。例如：

void networkClass::bind()  // say which class the function is a member
...

关于c++ - 已经定义的C++类，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/30278789/