对象 && 类

class A
{
public:
    int a;
    int b;
    int c;
};
int main()
{
    A f ( );　　//不行
    A c {1,2};
    A d {1,2,3};
}    

class A
{
public:
    int a;
    int b;
    int c;
    A(int d,int e,int f) {}
};
int main()
{
    A c{1,2};　　　　//no instance of constructor "A::A" matches the argument list;
    A c{1,2,3};
    A c(1,2);　　　 //no instance of constructor "A::A" matches the argument list;
    A c(1,2,3);
}