[Insight-developers] Who defines GNU_LIBSTDCXX_V3?

[Paul Hughett]

I am trying to compile Insight with gcc 2.95.2 and gnu libstdc++
2.90.8 but the compilation fails when it tries to find the header file
vector.h.  When I look at the relevant code (e.g. in vcl_vector.h), it
tries to include <vector> if the macro GNU_LIBSTDCXX_V3 is defined but
<vector.h> if it isn't.  (I have simplified the logic somewhat.)  Now
this macro should presumably be defined if gnu libstdc++ v3 is
installed and gnu libstdc++ 2.90.8 advertises itself as v3.
Nevertheless, GNU_LIBSTDCXX_V3 is never--as far as I can tell--defined
anywhere in the libstdc++ headers or in the configure scripts for
Insight.

So--have I correctly understood what GNU_LIBSTDCXX_V3 should mean?  Then
why is it never defined?  Where should it be defined?

Paul Hughett