So, you used the VLFeat SIFT successfuly in Matlab but you need to use the library with C++ and you can't find the functions reference nor a tutorial? Well I have been there, done that and sharing the code for integrating VLFeat's SIFT with OpenCV.
Actually I harvest the below code from the 'Toolbox' folder of VLFeat, from the source of the dot mex files. With minor modification the ' VLSIFT' function takes an OpenCV IplImage (grayscale) and returns pointers to the frames and descriptors found as well as the number of the frames. I removed the selection for exporting the descriptors in double; they always be exported as the vl_uint8 datatype.
