segmentation fault error in Opencv c++ - c++

Question

I am trying to code a program on opencv to decide whether a human has approached ahead the camera. After I run the execution file, I get the captured video for few seconds and encounter the segmentation fault error.
The code is like this
Here are headers:
#include "opencv2/objdetect.hpp"
#include "opencv2/videoio.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/imgproc.hpp"
#include <iostream>
#include <stdio.h>
using namespace std;
using namespace cv;
//define static variable
static int cApp = 0;//number of approached frame
static double last = 0;
//define functions
void detectAndDisplay( Mat frame );
bool computeArea( double width, double height, double lastArea);
double runningAverage(int M);
//define opencv function and classifier
String upperbody_cascade_name = "home/pi/opencv- 3.0.0/data/haarcascades/haarcascade_upperbody.xml";
CascadeClassifier upper_cascade;
String window_name = "Capture - upper body detection";
Here is the main function:
int main( void )
{
//define variable
VideoCapture capture;
Mat frame;
//-- 1. Load the cascades
upper_cascade.load("/home/pi/opencv-3.0.0/data/haarcascades/haarcascade_upperbody.xml");
//-- 2. Read the video stream
capture.open( -1 );
if ( ! capture.isOpened() ) { printf("--(!)Error opening video capture\n"); return -1; }
while ( capture.read(frame) )
{
if( frame.empty() )
{
printf(" --(!) No captured frame -- Break!");
break;
}
//-- 3. Apply the classifier to the frame
detectAndDisplay( frame );
char c = (char)waitKey(10);
if( c == 27 ) { break; } // escape
}
capture.release();
return 0;
}
Here is the detectAndDisplay function:
void detectAndDisplay( Mat frame )
{
std::vector<Rect> upperbodys;
Mat frame_gray;
cvtColor( frame, frame_gray, COLOR_BGR2GRAY );
equalizeHist( frame_gray, frame_gray );
//-- Detect upperbodys
upper_cascade.detectMultiScale( frame_gray, upperbodys, 1.05, 3, 0|CASCADE_SCALE_IMAGE, Size(30, 30) );
Point center( upperbodys[0].x + upperbodys[0].width/2, upperbodys[0].y + upperbodys[0].height/2 );
ellipse( frame, center, Size( upperbodys[0].width/2, upperbodys[0].height/2 ), 0, 0, 360, Scalar( 255, 0, 255 ), 4, 8, 0 );
bool ifApproached = computeArea(upperbodys[0].width/2, upperbodys[0].height/2, last);
if (ifApproached == true) {
cApp++;
}
if (cApp == 3) {
cout << "have approached" << endl;
cApp = cApp - 3;
}
//-- Show what you got
imshow( window_name, frame );
}
Here is the computeArea function:
bool computeArea( double width, double height, double lastArea) {
double newArea = width * height;
bool ifApproached = false;
//double presentArea = newArea;
double presentArea = runningAverage(newArea);
double DifferenceBewteenAreas = presentArea - lastArea;
if (DifferenceBewteenAreas > 1) {//threshold
ifApproached = true;
}
last = presentArea;
return ifApproached;
}
Here is runningAverage function:
double runningAverage(int M) {
//M is measurement
//#define LM_SIZE 5
static int LM[5];
static int index =0;
static long sum = 0;
static int count =0;
//keep sum updated to improve speed
sum = sum - LM[index];
LM[index] = M;
sum = sum + LM[index];
index++;
index = index % 5;
if (count < 5) {
count++;
}
return (double)(sum / (double)count);
}
I have searched many opencv segmentation fault questions, some said this segmentation fault was caused by wrong array used, but my case has little use of array. Others said misused of function characters could also cause this kind of errors, I agree with this, some of my characters could be wrong here.

Answer 1

Actually I found that I should not use upperbodys[0] in the code, because sometimes there are no object being detected at all,so there could be some memory read error happens, I used upperbodys[i] instead and it works well then.
void detectAndDisplay( Mat frame )
{
std::vector<Rect> upperbodys;
Mat frame_gray;
cvtColor( frame, frame_gray, COLOR_BGR2GRAY );
equalizeHist( frame_gray, frame_gray );
//-- Detect upperbodys
upper_cascade.detectMultiScale( frame_gray, upperbodys, 1.05, 3, 0|CASCADE_SCALE_IMAGE, Size(30, 30) );
int size = upperbodys.size();
double newArea = -1;
for (int i = 0 ; i < size; i++) {
Point center( upperbodys[i].x + upperbodys[i].width/2, upperbodys[i].y + upperbodys[i].height/2 );
ellipse( frame, center, Size( upperbodys[i].width/2, upperbodys[i].height/2 ), 0, 0, 360, Scalar( 255, 0, 255 ), 4, 8, 0 );
//bool ifApproached = computeArea(upperbodys[i].width/2, upperbodys[i].height/2, last);
//////////////////////////////////////////
newArea = upperbodys[i].width/2 * upperbodys[i].height/2;
if (newArea != -1) {
cout << "UpperBodys has value, index = " << i << endl;
break;
}
}
bool ifApproached = false;
//double presentArea = runningAverage(newArea);
double presentArea = newArea;
double DifferenceBewteenAreas = presentArea - last;
if (DifferenceBewteenAreas > 1) {//threshold
ifApproached = true;
}
last = presentArea;
//////////////////////////////////////////
if (ifApproached == true) {
cApp++;
}
if (cApp == 3) {
cout << "have approached" << endl;
cApp = cApp - 3;
}
//-- Show what you got
imshow( window_name, frame );
}