visual studio -已经定义了c++类

我一点也不明白。我有一个名为"network.h"的头文件，其中有函数类的声明。在"network.cpp"文件中，我有这些函数。当我想在main.cpp中包含"network.h"并编译我的项目(Microsoft Visual Studio 2007)时，我得到了这个消息:

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，但在这里我不知道哪里出了问题。

network.h

#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 -------------------------------------

所以，我从network.h中删除了networkClass network;，并在main.cpp中声明它。现在，当我想运行函数，例如network.bind();，我得到错误:main.obj : error LNK2019: unresolved external symbol "public: void __thiscall networkClass::bind(void)" (?bind@networkClass@@QAEXXZ) referenced in function _main