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I've recently upgraded my compiler from gcc-4.2 to gcc-4.3 and found that
boost compilation is failing with an error saying undefined symbol CHAR_BIT.

I've gone thru mailing list and found out this is fixed in cvs version
(which is upcoming boost-1.35)
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Boost 1.35 is close (release candidate 1 has just been released)

However it does NOT support gcc-4.3 though the latest subversion trunk may
well include more v4.3 fixes than the release. In fact there are a few known
issues.

gcc v4.3 was released too late in the boost release cycle for changes to be
incorporated.

Paul