int cvCreateTrackbar(char* trackbar_name, char* window_name, int* value, int count, CvTrackbarCallback on_change) {
    void *fptr;
    int retval;

    fptr = dlsym(_Chhighgui_handle, "cvCreateTrackbar_chdl");
    if(fptr == NULL) {
        fprintf(_stderr, "Error: %s(): dlsym(): %s\n", __func__,  dlerror());
        return -1;
    }
    dlrunfun(fptr, &retval, cvCreateTrackbar, trackbar_name, window_name, value, count, on_change);
    return retval;
}