错误：C++ 中未解析的外部符号错误

问：

编译问题是由全局变量 [ ] 引起的，这里是最小的例子All_Sockets

main.cpp

#include <winsock2.h>
#include <windows.h>
#include <vector>
#include "global.h"


int main() {

    std::vector<SOCKET> All_Sockets(10, INVALID_SOCKET);    // definition of global var

    getchar();
    return 1;
}

全球.h

#pragma once
#include <vector>
#include <Windows.h>

extern std::vector<SOCKET> All_Sockets;      // declaration of global variable

文件1.cpp

#include "global.h"
#include <windows.h>

void ftn1(){
    int i = 2;
    SOCKET Client_socket = All_Sockets[i];      // usage of global var
}

我正在Visual Studio中构建此项目，并出现以下链接错误

1>file1.obj : error LNK2001: unresolved external symbol "class std::vector<unsigned int,class std::allocator<unsigned int> > All_Sockets"