dynamic size change in parameters of mex function

I am trying to convert a user defined class function into mex function. I am passing class object as parameter. I am converting it into a structure as mex function does not support user defined class objects. Every time I call this mex function the parameters of the object (in my case structure parameters are changing the size). Hence, when I try to call mex function it gives an error that certain parameter does not have correct size. Is there any solution to this?

[Geoff Hayes]

Amit - how are you converting your class object into a structure? Please include the code that does this translation. As well, please describe which parameters of the struct is change. Give before and after examples.