Which choice is an include guard for the header file my_library.h?
my_library.h
#ifdef MY_LIBRARY_H #define MY_LIBRARY_H // my_library.h content #endif /* MY_LIBRARY_H */
#define MY_LIBRARY_H #include MY_LIBRARY_H // my_library.h content #undef MY_LIBRARY_H
#ifndef MY_LIBRARY_H #define MY_LIBRARY_H // my_library.h content #endif /* MY_LIBRARY_H */
#ifdef MY_LIBRARY_H #undef MY_LIBRARY_H // my_library.h content #endif /* MY_LIBRARY_H */