If line is non-NULL, it will be used as an initial buffer, to avoid
unnecessary mallocing each time this function is called. If buf is
given, and buf needs to be expanded, the var pointed to by buflen
If line is non-NULL, it will be used as an initial buffer, to avoid
unnecessary mallocing each time this function is called. If buf is
given, and buf needs to be expanded, the var pointed to by buflen