no Member getMat()

edit

I'm trying to call the Method getMat() in a Mat Object. But my compiler throws the Error: "No Member named 'getMat' in 'cv::Mat'"

SOLVED cv::Mat doesn't have getMat() need to use cv::InputArray or cv::OutputArray (Thanks @berak for mentioning that) or initialize the Mat itself. Please look Edit3 for present Error

Edit added Code from the Method

descriptorSize():

//Actually this Method just passes back the Size of the Descriptor size in floats(128)
int descriptorSize() {
    return SIFT_DESCR_WIDTH*SIFT_DESCR_WIDTH*SIFT_DESCR_HIST_BINS;
}

After the initialization of descriptorsit is passed to the Method CalcDescriptors which just sends a pointer of a Value to another Method called CalcSiftDescriptor

calcSiftDescriptor(img, ptf, angle, size*0.f, d, n, descriptors.ptr<float>((int) i));

in this method the pointer is used at this part:

for(i = 0; i < d; i++){
    for(j = 0; j < d; j++){
        int idx = ((i+1)*(d+2) + (j+1))*(n+2);
        hist[idx] += hist[idx+n];
        hist[idx+1] += hist[idx+n+1];
        for(k = 0; k < n; k++){
            dst[(i*d + j)*n + k] = hist[idx+k];     
        }
    }
}

EDIT2

For those, who want to see the full code: GitHub

EDIT3 After using Mat descriptors((int)features.size(), dsize, CV_32F);It works till one point. in the line hist[idx] += v_rco000;I get a EXC_BAD_ACCESS(code=1, address=....) Probably thats because idx seems to be a value which is not logical idx = -2146483626. The calculation of idx looks like this:

int idx = ((r0+1)*d+2)+c0+1)*(n+2)+o0;

As it seems in the Debugger the value that causes the problem is o0. In the following, I post the Area of Code until o0 is calculated. It is totally similar to the workflow in the sift.cpp from OpenCV Contrib.

Point pt(cvRound(ptf.x), cvRound(ptf.y));
float cos_t = cosf(ori*(float)(CV_PI/180));
float sin_t = sinf(ori*(float)(CV_PI/180));
float bins_per_rad = n / 360.f;
float exp_scale = -1.f/(d * d * 0.5f);
float hist_width = SIFT_DESCR_SCL_FCTR * scl;
int radius = cvRound(hist_width * 1.4142135623730951f * (d + 1) * 0.5f);
// Clip the radius to the diagonal of the image to avoid autobuffer too large exception
radius = std::min(radius, (int) sqrt(((double) img.cols)*img.cols + ((double) img.rows)*img.rows));
cos_t /= hist_width;
sin_t /= hist_width;

int i, j, k, len = (radius*2+1)*(radius*2+1), histlen = (d+2)*(d+2)*(n+2);
int rows = img.rows, cols = img.cols;

AutoBuffer<float> buf(len*6 + histlen);
float *X = buf, *Y = X + len, *Mag = Y, *Ori = Mag + len, *W = Ori + len;
float *RBin = W + len, *CBin = RBin + len, *hist = CBin + len;

for( i = 0; i < d+2; i++ )
{
    for( j = 0; j < d+2; j++ )
        for( k = 0; k < n+2; k++ )
            hist[(i*(d+2) + j)*(n+2) + k] = 0.;
}

for( i = -radius, k = 0; i <= radius; i++ )
    for( j = -radius; j <= radius; j++ )
    {
        // Calculate sample's histogram array coords rotated relative to ori.
        // Subtract 0.5 so samples that fall e.g. in the center ...