Question

In standard library, I found that namespace std is declared as a macro.

#define _STD_BEGIN  namespace std {
#define _STD_END        }

1. Is this a best practice when using namespaces?
2. The macro is declared in Microsoft Visual Studio 9.0\VC\include\yvals.h. But I couldn’t find the STL files including this. If it is not included, how it can be used?

Any thoughts..?

Answer 1

Probably not a best practice as it can be difficult to read compared to a vanilla namespace declaration. That said, remember rules don’t always apply universally, and I’m sure there is some scenario where a macro might clean things up considerably.

"But I couldn’t find the STL files including this. If it is not included, how it can be used?".

All files that use this macro include yvals.h somehow. For example <vector> includes <memory>, which includes <iterator>, which includes <xutility>, which includes <climits>, which includes <yvals.h>. The chain may be deep, but it does include it it some point.

And I want to clarify, this only applies to this particular implementation of the standard library; this is in no way standardized.