While reading C++, I have been looking into iostream header file to understand a bit more about header file organization. I am not able to understand much of the code in there.
For example the header starts with #ifndef _GLIBCXX_IOSTREAM. Does this check whether _GLIBCXX_IOSTREAM has been defined or not? If so then who is supposed to use this variable _GLIBCXX_IOSTREAM? I know it is not a good question but I am kind of curious.