Need clarity on structure alignment

[David Thompson]

I remember seeing something that left me with the impression that C (C++?)
guarantees that a struct will be aligned on a pointer-size boundary (using
the std mem mgr). (?) Something about 4-byte struct alignment (on a 32-bit
machine no doubt) sticks in my mind.

Space returned by malloc (and realloc and calloc) must be correctly
(sufficiently) aligned for _any_ C datatype on a given implementation.
This is not limited to pointers, but if you happen to be using structs
whose only large components are pointers, on a machine with nontrivial
alignment requirements, you might notice it with respect to pointers.