Using API code how to confirm whether a User is in QC DB (QC Member) or not?

Hi,

Using API I coded to add users to QC projects and changing their roles.

Now, I wanted include one condition whether the user is a member of QC or not. If the user member of QC then i will continue with above API to add users to a particular project and/or change their roles.

So if any one having idea please share syntax for the same.

Thanks In Advance,

Subbarao