Why can the compiler recognized "infinity" in interval.h?

[Chiaki-meow]

Hi, currently I am learning raytracing by raytracing in one weekend, and I have a question in 6.8 An Interval Class:
in my opinion, the constant "infinity" definition is in file rtweenend.h, and if I wanna use this global variable, I need to contain rtweekend.h in interval.h, but clearly it will introduce "including loop" or some other name...
But as I see the source code, there is no file needed to be included in interval.h. And I really don't understand why!

Thanks for your readingTT, hoping someone could answer my questions.

[hollasch]

From the section Common Constants and Utility Functions, after the initial rtweekend.h listing:

Program files will include rtweekend.h first, so all other header files (where the bulk of our
code will reside) can implicitly assume that rtweekend.h has already been included. Header files
still need to explicitly include any other necessary header files.

[Chiaki-meow]

Thanks! It seems that my static code analysis tool cannot recognize it. It seems to be clearer with an “extern” for me!
Thanks for your answer again:D

[hollasch]

Yeah, we use a very unconventional style with our code just to make things simpler for non-C++ programmers to understand. For my own implementation, I'd definitely use a different (more standard) C++ layout.