MinGW g++ 编译带静态变量的类时的问题,求高手解释一下！

打算建一个类，每生成一个对象就自动获取一个唯一的ID。

main.cpp

#include "stdio.h"

#include "CNode.h"

int main(int argc, char** argv)
{
    CNode cNode1;
    CNode cNode2;
    CNode cNode3;

    printf("cNode1.ID = %d\n ", cNode1.ulID);
    printf("cNode2.ID = %d\n ", cNode2.ulID);
    printf("cNode3.ID = %d\n ", cNode3.ulID);

}
 

 

CNode.h

 

#ifndef CNODE__
#define CNODE__

class CNode {
public:
    CNode();
    virtual ~CNode();
    static unsigned int ulIDCreator;
    unsigned int     ulID;

};

unsigned int CNode::ulIDCreator = 0;

#endif
 

 

CNode.cpp

#include "CNode.h"

CNode::CNode(){
    ulID = ++ulIDCreator;
}

CNode::~CNode(){

}

 

 

*** Internal Builder is used for build               ****
g++ -O0 -g3 -Wall -c -fmessage-length=0 -osrc\CNode.o ..\src\CNode.cpp
g++ -oArctic.exe src\Main.o src\CNode.o
src\CNode.o: In function `ZN5CNodeC1Ev':
E:/EclipseWorkspace/Arctic/Debug/../src/CNode.cpp:9: multiple definition of `CNode::CNode()'
src\Main.o:E:/EclipseWorkspace/Arctic/Debug/../src/Main.cpp:13: first defined here
src\CNode.o: In function `ZN5CNodeD1Ev':
E:/EclipseWorkspace/Arctic/Debug/../src/CNode.cpp:13: multiple definition of `CNode::~CNode()'
src\Main.o:E:/EclipseWorkspace/Arctic/Debug/../src/Main.cpp:13: first defined here
src\CNode.o: In function `ZN5CNodeD0Ev':
E:/EclipseWorkspace/Arctic/Debug/../src/CNode.cpp:13: multiple definition of `CNode::~CNode()'
src\Main.o:E:/EclipseWorkspace/Arctic/Debug/../src/Main.cpp:13: first defined here
src\CNode.o: In function `ZN5CNodeC2Ev':
E:/EclipseWorkspace/Arctic/Debug/../src/CNode.cpp:9: multiple definition of `CNode::ulIDCreator'
src\Main.o:E:/EclipseWorkspace/Arctic/Debug/../src/Main.cpp:13: first defined here
collect2: ld returned 1 exit status
Build error occurred, build is stopped
Time consumed: 687  ms. 

很奇怪的问题！怀疑是在不同文件中编译再连接在一块有问题。

于是去掉了CNode.cpp,只剩CNode.h。结果问题消失，

#ifndef CNODE__
#define CNODE__

class CNode {
public:
    CNode(){ulID = ++ulIDCreator;};
    virtual ~CNode(){};
    static unsigned int ulIDCreator;
    unsigned int     ulID;

};

unsigned int CNode::ulIDCreator = 0;

#endif
 

console:

cNode1.ID = 1
 cNode2.ID = 2
 cNode3.ID = 3