Okay I want to write a programme that saves a screen shot every second, but I don't want to use any print screen function:

This is how I'd go about it, with my limited knowledge:

first I'd calculate the resolution of the screen, and then loop through all the pixels saving the pixel colour.

What else do I have to know? Im using C++

That will be too slow. If you are on Windows os then try this function

Or maybe this program.

And I hope you intend to use the same file every time. You will fill up a hard drive pretty quickly if you use a different names.