Header File Duplicate reference

Q:.h the role of IFNDEF/DEFINE/ENDIF in the header file?

A: Prevent the header file from being repeatedly referenced.

Description

Some header files that are duplicated only add to the workload of the compilation and do not cause too much problem, just less compile efficiency.

Some can cause errors, such as defining global variables in a header file (although this is not recommended, it is true that the C specification allows it).

If the header file is included in the loop, some compilers will handle it intelligently, just like once, some will error, some direct deadlock , causing the compiler to crash (this is only a very low-level compiler will appear in almost invisible).

Anyway, with ifnde xxx #define XXX or other way to avoid the header file duplication, only the benefits of no harm, is a good habit .

Header File Duplicate reference