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#include <iostream>
using namespace std;
 
 
template <typename T> class Stack {
  typedef typename T::ThisDoesntExist StaticAssert; // T::NotExisting doesn't exist at all!
};
 
 
void f1(Stack<char>); // No instantiation, compiles
 
class Exercise {
  //Stack<double> &rsd; // No instantiation, compiles (references don't need instantiation, are similar to pointers in this)
 
  Stack<int>    si; // Instantiation! Doesn't compile!!
};
 
 
int main(){
 
  Stack<char> *sc; // No Instantiation, this compiles successfully since a pointer doesn't need instantiation
 
  //f1(*sc); // Instantiation of char! Doesn't compile!!
 
  //int iObj = sizeof(Stack< std::string >); // Instantiation of std::string, doesn't compile!!
 
}

prog.cpp: In instantiation of ‘class Stack<int>’:
prog.cpp:15:17:   required from here
prog.cpp:6:39: error: ‘int’ is not a class, struct, or union type
   typedef typename T::ThisDoesntExist StaticAssert; // T::NotExisting doesn't exist at all!
                                       ^
prog.cpp: In function ‘int main()’:
prog.cpp:21:16: warning: unused variable ‘sc’ [-Wunused-variable]
   Stack<char> *sc; // No Instantiation, this compiles successfully since a pointer doesn't need instantiation
                ^

Standard output is empty