detectMultiScale return illogical result [closed]

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i want use cascade classifier for face detection but illogical result occurred this is my code :

#include "stdafx.h" #include "FaceDetection.h"
using namespace cv;
FaceDetection::FaceDetection(void)
{
    face_cascade = CascadeClassifier();
    face_Cascade_Path = "D:\book\ComputerLessons\haarcascade_frontalface_alt.xml";
    face_cascade.load(face_Cascade_Path);
}
 
Mat FaceDetection::detect(Mat input){
    Mat face = Mat(input);
    faceExist = false;
    if (!face_cascade.empty())
    {
        std::vector<Rect> faces;
        Mat grayInput;
        cvtColor( input, grayInput, COLOR_BGR2GRAY );
        equalizeHist( grayInput, grayInput );
        face_cascade.detectMultiScale( grayInput, faces, 1.1, 2, CASCADE_SCALE_IMAGE, Size(100, 100));
        float maxArea = 0;
        int total = faces.size();
        if (total>0)
        {
            for (size_t i = 0; i < faces.size(); i++)
            {
                Rect r = faces[i];
                if (r.area() > maxArea)
                {
                    faceExist = true;
                    faceBound = r;
                    maxArea = r.area();
                } 
            }
            face = input(faceBound); 
        }
    }
    return face;
}
Rect FaceDetection::getBound(){
    if (faceExist)
    {
        return faceBound;
    }
    else
    {
        return Rect();
    }
}

but when i click faces to expand result this error occured :

and when expand unclear result like this:

and In the following this exception occurred : AccessViolationException

please help me thanks. my opencv version is 3.1;