Question

Consider the following sample program in which a loop is running;

int main()
{

  for (int i = 0; i<= 300; ++i) {

  }

}

Pretty basic, now let’s suppose I want to print out the value of i every second:

cout << "i= " << i << "\n";

A simple loop like the following might suffice, where “elaspedTime” is a ficticious integer containing the number of seconds the program has been running magically updated by the OS:

int lastTime = 0;
while (true) {
  if (elapsedTime > lastTime) { // Another second has passed
    cout << "i= " << "\n";
    lastTime = elapsedTime;
  }
}

The ultimate goal here is to give an output like the following (assuming the loop ran exactly 100 times per second because it was on an old, slow CPU):

$ ./myprog
i= 100
i= 200
i= 300

These are simple functions and routines, despite this, I see no way to perform such an operation in a “classical” c++ program which typically has just a main() function. Despite the simplicity is this the point at which I need to learn multi-threading? Or, is it possible to call functions from main() and not wait for their return but without that called function “hogging” the thread?

Answer 1

What’s wrong with doing this? No multitasking required.

int lastTime = 0;
while (true) {
  if (std::time() > lastTime) { // Another second has passed
    cout << "i= " << i << "\n";
    // potentially expensive code goes here, which updates "i"
    lastTime = std::time();
  }
}