> It looks to me like sqrtf is available with MSVC++ (C++), but not MSVC (C).
> MSVC++ math.h declares sqrtf only when __cplusplus is set.
> I think VXL_MATH_HAS_SQRTF should not be set under MSVC. Do you agree?
Sure, that's the idea of the configure script (which we don't use with MSVC):
Check whether a feature is functioning or not by trying it out, then set
the corresponding macro.
Actually, then, the configure script should run the C compiler, not the C++
compiler, but since this seems to be an unnecessary distinction on non-MSVC,
it could be kept as is.