cmath vs math.h (And similar c-prefixed vs .h extension headers)

Question

I\'ve seen some information about differences between things like iostream vs iostream.h. From what I gathered from those the difference between th

Answer 1

The headers whose names start with c are derived from the headers of the C standard library. The corresponding headers with the c prefix removed and a .h suffix added are identical (or very nearly identical) to the C standard library headers.

defines the relevant symbols under the std namespace; defines them globally.

(I just learned it's not quite that simple; see Alf's answer.)