including a header file twice in c++

Question

What happens if I include iostream or any other header file twice in my file? I know the compiler does not throw error.

Will the code gets added twice

Answer 1

Header files are simple beasts. When you #include

all that happens is that the contents of header basically get copy-pasted into the file. To stop headers from being included multiple times, include guards are used, which is why in most header files you'll see something akin to

#ifndef SOME_HEADER_FILE_GUARD 
#define SOME_HEADER_FILE_GUARD

//Contents of Header

#endif