C++一个错，不会改？

Question

#include <iostream.h>

#include <string.h>

class CStudent

{

friend void SetAge(int age);

public:

CStudent(char *n, int a);

~CStudent();

 void SetAge(int age);

private:

char *name;

int age;

static int nTotalObj;

};

int CStudent::nTotalObj = 0;

CStudent::CStudent(char *n, int a)

:age(a)

{

int nLen = strlen(n);

name = new char[nLen+1];

strcpy(name,n);

name[nLen] = '\0';

nTotalObj++;

}

CStudent::~CStudent()

{

delete[] name;

nTotalObj--;

}

void CStudent::SetAge(int age)

{

this->age = age;

}

void main()

{

CStudent stu1("张三",25);

CStudent str2("李四",26);

cout<<"CStudent::nTotalObj="<<CStudent::nTotalObj<<endl;

}

错误信息：

D:\soft\编程软件\Cpp1.cpp(38) : error C2248: 'nTotalObj' : cannot access private member declared in class 'CStudent'