[Insight-developers] pragma once

[Stephen R. Aylward]

We have a situation where multiple libraries are being distributed in 
both ITK and VTK.  Long story short - we can build work-arounds that are 
backward compatible using cmake directives, except I haven't found a 
workaround for the #ifdef wrapping of headers (given that the headers in 
two different places use the same #define variable, and may be directly 
included by the user).   So, I'm considering the "#pragma once" directive.

Thanks!
Stephen


Kent Williams wrote:
> The standard behavior of C/C++ compilers is to ignore #pragmas they 
> don't implement.
> 
> I would think that given that we use #ifdef file guards everywhere, it 
> would be safe to use #pragma once.  If it isn't honored, everything will 
> still work, with the possible overhead of including something already 
> included.
> 
> Is there a situation where using #pragma once is anything more than a 
> hint to the compiler to short-circuit parsing an include file?
> 
> Stephen R. Aylward wrote:
> 
>> Hi,
>>
>> Has anyone already investigated whether or not all of the supported 
>> ITK compilers honor the "#pragma once" directive?
>>
>> Thanks,
>> Stephen
>>
> 
> 

-- 
=============================================================
Stephen R. Aylward, Ph.D.
Chief Medical Scientist
Kitware, Inc.
http://www.kitware.com