Why does changing the order of including psapi.h gives compilation erros?(Indentifier BOOL is undefined)
问题 I am using Visual Studio Community 2017 to code c++. When I run the following code everything works fine. #include "pch.h" #include<Windows.h> #include<Psapi.h> #include <iostream> #include <conio.h> int main() { std::cout << "Really!! How do you do it?"; _getch(); } But if I change the order of #include s by including psapi.h before Windows.h , compiler goes badass and throws 198 errors at me, which surprisingly(maybe only to me) includes Identifier "BOOL" is undefined . Why is this