为什么从文档 OpenCV 剂量中找到的源代码人脸检测没有显示任何东西

嗨，我的代码在这里(根据docs opencv)

#include "opencv2/objdetect.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/imgproc.hpp"
#include <iostream>
#include <stdio.h>
using namespace std;
using namespace cv;
/* Function Headers */
void detectAndDisplay( Mat frame );
/* Global variables */
String face_cascade_name = "haarcascade_frontalface_alt.xml";
String eyes_cascade_name = "haarcascade_eye_tree_eyeglasses.xml";
CascadeClassifier face_cascade;
CascadeClassifier eyes_cascade;
String window_name = "Capture - Face detection";
/* @function main */
int main( void )
    {
    VideoCapture capture;
    Mat frame;
    //-- 1. Load the cascades
    if( !face_cascade.load( face_cascade_name ) ){ printf("--(!)Error loading face cascaden"); return -1; };
    if( !eyes_cascade.load( eyes_cascade_name ) ){ printf("--(!)Error loading eyes cascaden"); return -1; };
    //-- 2. Read the video stream
    capture.open( -1 );
    if ( ! capture.isOpened() ) { printf("--(!)Error opening video capturen"); return -1; }
    while (  capture.read(frame) )
        {
        if( frame.empty() )
            {
            printf(" --(!) No captured frame -- Break!");
            break;
            }
        //-- 3. Apply the classifier to the frame
        detectAndDisplay( frame );
        int c = waitKey(10);
        if( (char)c == 27 ) { break; } // escape
        }
    return 0;
    }
/* @function detectAndDisplay */
void detectAndDisplay( Mat frame )
    {
    std::vector<Rect> faces;
    Mat frame_gray;
    cvtColor( frame, frame_gray, COLOR_BGR2GRAY );
    equalizeHist( frame_gray, frame_gray );
    //-- Detect faces
    face_cascade.detectMultiScale( frame_gray, faces, 1.1, 2, 0|CASCADE_SCALE_IMAGE, Size(30, 30) );
    for( size_t i = 0; i < faces.size(); i++ )
        {
        Point center( faces[i].x + faces[i].width/2, faces[i].y + faces[i].height/2 );
        ellipse( frame, center, Size( faces[i].width/2, faces[i].height/2), 0, 0, 360, Scalar( 255, 0, 255 ), 4, 8, 0 );
        Mat faceROI = frame_gray( faces[i] );
        std::vector<Rect> eyes;
        //-- In each face, detect eyes
        eyes_cascade.detectMultiScale( faceROI, eyes, 1.1, 2, 0 |CASCADE_SCALE_IMAGE, Size(30, 30) );
        for( size_t j = 0; j < eyes.size(); j++ )
            {
            Point eye_center( faces[i].x + eyes[j].x + eyes[j].width/2, faces[i].y + eyes[j].y + eyes[j].height/2 );
            int radius = cvRound( (eyes[j].width + eyes[j].height)*0.25 );
            circle( frame, eye_center, radius, Scalar( 255, 0, 0 ), 4, 8, 0 );
            }
        }
    //-- Show what you got
    }

我使用预构建的opencv和我的程序没有任何错误，但它不工作!如果提示找不到PDB文件，这是为了调试，不影响程序的执行。对于没有这个警告，我去工具>选项>调试器>检查微软符号服务器警告现在没有，但它不工作?!

问题在哪里??!!!!!!!11