What is the meaning of template<> with empty angle brackets in C++?

Question

template<>
class A{
//some class data
};

I have seen this kind of code many times. what is the use of template<> in the ab

Answer 1

template<> introduces a total specialization of a template. Your example by itself isn't actually valid; you need a more detailed scenario before it becomes useful:

template 
class A
{
    // body for the general case
};

template <>
class A
{
    // body that only applies for T = bool
};

int main()
{
    // ...
    A  ai; // uses the first class definition
    A ab; // uses the second class definition
    // ...
}

It looks strange because it's a special case of a more powerful feature, which is called "partial specialization."