How to design and implement lowpass filter and bundle in Dll to use in VC++

I have used the following code in lpf.m file.

 function z=lpf(x,n,fc,s)
 hl  = fdesign.lowpass('N,Fc', n, fc, s);
 Hdl = design(hl, 'butter');
 z=filter(Hdl,x);

Builded C Shared library.

Included and added all the files required to run malab code in VC++ workspace and then called the function declared in header file as

 mlfLpf(int nargout, mxArray** z, mxArray* x
                   , mxArray* n, mxArray* fc, mxArray* s);

On calling mlfLpf it is returning always zero.While if running lpf.m in matlab passing same parameters as passed in VC++ then it is returning filtered values.What could be the issue.