swift234

Use `sizeof` for buffer lengths in snprintf

Rather than duplicating the constant value, use the `sizeof` operator to have
the value propogate from the static buffer allocation.  Any standards conforming
implementation of `snprintf` will null-terminate the output unless the buffer is
NULL (a zero-sized buffer is passed to the call).  On Windows, where this is not
the case, the function is named `_snprintf` which ensures that we do not
accidentally end up with the incorrect behaviour.