Add header file inclusion guards

[GoogleCodeExporter]

'#pragma once' is not well supported beyond MSVC and recent versions of GCC. By 
providing header 
guards as well as #pragma once, one can obtain both the performance benefit of 
#pragma once, and 
wider  portability.

See: http://en.wikipedia.org/wiki/Pragma_once#Advantages_and_disadvantages

Original issue reported on code.google.com by swiftcoder on 29 Jul 2009 at 6:15

[GoogleCodeExporter]

My standard practice, especially with external library headers, is to use a 
generated
UUID value (with underscores substituted for dashes) as part of the header guard
#define name.  If all external header names are unique, one UUID can be used in
combination with the header file name for the whole project.

An example would be:
{{{
#pragma once

#ifndef YAML_H_32DC4090_EB12_4bb6_8366_5A5F9A71B700
#define YAML_H_32DC4090_EB12_4bb6_8366_5A5F9A71B700

// Header contents go here

#endif // YAML_H_32DC4090_EB12_4bb6_8366_5A5F9A71B700
}}}

This way, no reasonable project will have header guard conflicts with the 
yaml-cpp
library.

Original comment by rtweeks21 on 29 Jul 2009 at 6:27

[GoogleCodeExporter]

Good idea. I've only ever used MSVC and gcc, so I've never quite known how 
portable
it is. And thanks, rtweeks, for the UUID suggestion.

Original comment by jbe...@gmail.com on 29 Jul 2009 at 10:32

• Changed state: Fixed