用无参构造结构体对象后无法调用结构体函数？解决办法

用无参构造结构体对象后无法调用结构体函数？
声明以下结构体：

C/C++ code

struct Foo{        Foo(int){}    Foo(){}    void fun(){}};

C/C++ code

    Foo a(10);    a.fun();    Foo b();    b.fun();//error: request for member ‘fun’ in ‘b’, which is of non-class type ‘Foo ()()’

C/C++ code

    Foo a(10);    a.fun();    Foo b;    b.fun();

C/C++ code

Foo b();