check type of curve

Hello & good morning!
Although my question might seem almost tooooo simple to answer (I am an absolute beginner...), I'd like to ask the following and hope for some answers:
As in my program I generate two kinds of curves (BSplines & Beziers), I have different possibilities of calling functions on them. Some of them take only BSplines, some only Beziers. The problems occur, when accidentially calling the wrong function on the wrong parameters - the program's execution ends in a lovely "abnormal termination".
So what I'd like to know now is, if there is a possibility to implement something like:
function(parameter)
{
if (parameter.hasWrongTypeA)
AfxMessageBox("...");
or: Convert A to B;
if (parameter.hasRightTypeB)
{
functionbody...
}
}

Thanks a lot in advance!
Agnes