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According to http://tinyurl.com/6zeyhu, cflags affects both the C and C++ compilers, while cxxflags affects only the C++ compiler; I use cxxflags as a matter of habit, but in the case of -arch, I suppose cflags would be more appropriate (although I'm not aware of any C code inside of Boost anyway).

Interesting, this caught me by surprise since I thought that cflags was only for C, cxxflags for C++ and compileflags for both. It is documented that way at http://tinyurl.com/63rjal at least. A small testing revealed that http://tinyurl.com/6zeyhu appears to be correct under my environment. cflags affected both C and C++ and compileflags was rejected as an unknown feature. The environment was as follows: Boost.Build V2 (Milestone 12) Boost.Jam 03.1.16 gcc 4.2.2 What would be the correct description of these features? I appreciate all your input. Thanks, Gevorg