Question

is it possible to use a method of an abstract class?
how can i use a method of a class without having an instance?

Answer 1

If you declare a method as static, you can call it directly without needing a class instance. Otherwise you will need to have an instance of a derived class.

Since an abstract class cannot be instantiated directly, you cannot call a method of an abstract class directly unless it is a static method. But you can call a static method of an abstract class directly, here is a quick example:

#include <iostream>
#include <ostream>
#include <fstream>
using namespace std;

class stest{
  public:
   static void test();
   virtual void a() = 0;
  };

void stest::test(){ cout << "test\n"; }

int main(){
  stest::test();
  return 0;
}

Alternatively, if you have an instance of a class that is derived from an abstract class, you can treat it as an instance of the abstract class, and can call any methods on it.