c++中静态变量不但要在头文件中declare，还要在实现的cpp中declare。当然也可以赋个初始值。
class foo
{
int _i;
public:
foo(int i) : _i(i) {}
};
class bar
{
public:
static int j;
static foo f;
};
int bar::j = 0;
foo bar::f(1);c++ 静态变量报错 undefined reference to static members,布布扣,bubuko.com
c++ 静态变量报错 undefined reference to static members
原文：http://www.cnblogs.com/bigben0123/p/3593335.html