To my knowledge, functions do not get added to the stack until run-time after they are called in the main function.

So how can a pointer to a function have a function's memory address if it doesn't exist in memory?

For example:

using namespace std;
#include <iostream>

void func() {
}  

int main() {
  void (*ptr)() = func; 
  cout << reinterpret_cast<void*>(ptr) << endl; //prints 0x8048644 even though func never gets added to the stack
}

Also, this next question is a little less important to me, so if you only know the answer to my first question, then that is fine. But anyway, why does the value of the pointer ( the memory address of the function ) differ when I declare a function prototype and implement the function after main?

In the first example, it printed out 0x8048644 no matter how many times I ran the program. In the next example, it printed out 0x8048680 no matter how many times I ran the program.

For example:

using namespace std;
#include <iostream>

void func();

int main() {
  void ( *ptr )() = func;
  cout << reinterpret_cast<void*>(ptr) << endl;
}

void func(){
}