#if defined( _MSC_VER ) && ( _MSC_VER >= 1020 ) # pragma once #endif
IMO, there is absolutely no reason to /rely/ on non-standard features even if /all/ compilers supported it in this case. Steven Watanabe
Just to make a small point; this is from the C++ standard... [quote] 16.6 Pragma directive [cpp.pragma] 1 A preprocessing directive of the form # pragma pp-tokensopt new-line causes the implementation to behave in an implementation-defined manner. The behavior might cause translation to fail or cause the translator or the resulting program to behave in a non-conforming manner. Any pragma that is not recognized by the implementation is ignored. [unquote] If unrecognized pragmas are ignored, then I don't see why boost developers should jump through a hoop to satisfy the "el-cheapo" compilers. In other words, if a compiler gives a warning about the #pragma-once, then let the programmer turn off the warning locally for the build, which is usually done in a single location within a makefile. On the other hand, every boost.hpp file has to surround the "#pragma once" with the silly looking guards. I tried this experiment just to see what happens. I added the non-existing #pragma to my code and got the following warning: #pragma once_upon_a_time foo.cpp(20) : warning C4068: unknown pragma My opinion is that the boost headers can happily contain the following code: #ifndef __HEADER_FILE_GUARD__ #define __HEADER_FILE_GUARD__ #pragma once ... #endif I have not yet heard about a compiler that doesn't support this #pragma. I would be surprised if a single developer calls up to complain about this. The compilers that warn against this #pragma can turn off the warnings with a single makefile change, like I mentioned before. Regards, -Sid Sacek