为什么在 C++ .h 文件中设置宏定义和命名空间？

Question

I am reading this open source project :

I have two questions:

1. I found the

#ifndef _RANGE_REQUEST_GENERATOR_H_
#define _RANGE_REQUEST_GENERATOR_H_
#endif

and I only find the _RANGE_REQUEST_GENERATOR_H_ in this .h file, other place not use it.

so, what's the usage of the macro definition?

2. there use the namespace wrap the functions.

namespace slowhttptest {
    //functions
}

what's the purpose? why do not use std , is it better?

Answer 1

Question #1

See Purpose of Header guards

Question #2

Consider the case where you are using libraries. And two libraries would both like to have a function named Push() . We could name them: LibraryFoo_Push() , and LibraryBar_Push() , or we could use namespaces. Namespaces have some additional benefits with lookups as well.

And see C++ When is it OK to extend the `std` namespace? for when you are allowed to add stuff to the std namespace.