C++ What is the earliest undefined behavior can manifest itself?

Question

I\'m aware that undefined behavior can potentially cause anything, which makes any program containing UB potentially meaningless. I was wondering if there is any way to iden

Answer 1

As your code somewhat demonstrates, undefined behavior is almost always a condition of runtime state at the time the behavior is attempted. A slight modification of your code can make this painfully obvious:

void causeUndefinedBehavior()
{
   //any code that causes undefined behavior
   //every time it is run
   char* a = nullptr;
   *a;
}


int main()
{
 srand(time(NULL));
 //code before call
 //...
 if (rand() % 973 == 0)
    causeUndefinedBehavior();
 //code after call
 //...
}

You could execute this a thousand times or more and never trip the UB execute-condition. that doesn't change the fact the function itself is clearly UB, but detecting it at compile time in context of the invoker is not trivial.