Re: Correct constness

You need to clarify the semantics of the external view of the class and
the methods, and the rest should follow.

Firstly, does the class semantically contain (as opposed to refer to)
the Settings object, as for example the data content of a "string" or
"vector" type? From the naming and your description, this does not
appear to be the intent. Accordingly, the SetSettings would also be
const if it does not change the ConfigManager object itself (i.e. if
the compiler does not complain), as you are not semantically modifying
its content, only what it refers to.

Secondly, you have not made it clear what SetSettings will do, as this
will affect its constness. It seems unlikely that it is to copy a
Settings into the Settings object pointed to by s_, since the
appropriate way of doing this from your description of GetSettings is
that you would do that as
    *setmng.GetSettings() = SomeSettings;
or
    setmng.GetSettings()->SetValue();
and a SetSettings should be removed. If SetSettings is supposed to set
the member pointer s_, then it clearly cannot be const.

Incidentally, I use the convention where possible for a
parameter/return type that a pointer implies a transfer of ownership,
and a reference implies no transfer. Accordingly, I would have changed
your GetSettings to
         Settings& GetSettings() const { return *s_; }

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