为什么会出现超出范围的错误？

Question

I can't seem to find where my issue is. Its a three file program with aDie class in one file, aHistogram class in another file, and the main.cpp file. It is supposed to print a histogram constructed with X's to show how many times the die landed on each of the six faces. I cant move forward because of the vector error... There may be other issues with the program that i haven't worked out yet, but I just want to know about the vector error. Thank you.

main.cpp:

#include <iostream>
#include <stdlib.h> //srand and rand
#include <time.h> //Time
#include <vector>
#include <algorithm>
#include "aHistogram.h"
#include "aDie.h"

using namespace std;

int main()
{
    srand (time(NULL));
    int numRolls;
    const int maxLengthOfLine = 50;

    cout << "How many rolls? " << endl;
    cin >> numRolls;

    aDie fairDie;
    aHistogram fairHistogram;

    //For Loop rolls the die and updates the histogram vector ~~binHistogram.
    for(int i = 0; i < numRolls; i++)
    {
        int face = fairDie.roll();
        fairHistogram.update(face);
    }

    cout << "*******************" << endl;
    cout << "*****Histogram*****" << endl;
    cout << "*******************" << endl;

    fairHistogram.display(maxLengthOfLine);


}

aDie.h:

#ifndef ADIE_H_INCLUDED
#define ADIE_H_INCLUDED

#include <stdlib.h>
#include <time.h>
#include <vector>
#include <algorithm>

using namespace std;

/********************************************/
/*******Definition of aDie class*************/
/********************************************/
class aDie
{
    public:
        int roll(); //return an integer between 1 and 6 to represent what face appears when the die is rolled.
        aDie(); //Default constructor
        ~aDie(); //Destructor

    private:

        int numFaces = 6;
};

int aDie::roll()
{
    return ((rand() % numFaces) + 1); //returns a random number between 1 and 6
}

aDie::aDie()
{
    cout << "Dice Roll...." << endl;
    return;
}

aDie::~aDie()
{
    return;
}

#endif // ADIE_H_INCLUDED

aHistogram.h:

#ifndef AHISTOGRAM_H_INCLUDED
#define AHISTOGRAM_H_INCLUDED

#include <algorithm>
#include <stdlib.h>
#include <vector>

using namespace std;

/********************************************/
/*******Definition of aHistogram class*******/
/********************************************/

class aHistogram
{
    public:
        void update(int face);
        void display(int maxLengthOfLine);
        int Count(int face);
        void clear();

        aHistogram(); //Constructor
        ~aHistogram(); //Destructor

    private:
        vector<int> binHistogram;
        const int numFaces = 6;
        int totalRolls;
        int largeBin = 0;
        double xScale;
};

//Adds a count to each face every time the die lands on said face.
void aHistogram::update(int face)
{
    binHistogram.at(face) += 1;
    return;
}

//Displays the histogram with X's
//maxLengthOfLine represents the maximum number of x’s to be printed for the largest bin count.
void aHistogram::display(int maxLengthOfLine)
{
    xScale = maxLengthOfLine / largeBin;
    for(int i = 1; i <= 6; i++)
    {
        cout << i << " : " << Count(i) << " : ";
        int numXs = xScale * binHistogram.at(i);
        for(int j = 0; j < numXs; j++)
        {
            cout << "X";
        }
    }
}

//To be called AFTER aHistogram::update
//Returns a count of how many times for each face of the die
int aHistogram::Count(int face)
{
    //For Loop determines the largest bin count
    for (int i = 1; i < numFaces; i++)
    {
        while (binHistogram[i] >= largeBin)
        {
            largeBin = binHistogram.at(i);
        }
    }

    //
    return binHistogram.at(face);
}

void aHistogram::clear()
{
    binHistogram.clear();
    return;
}

//Defines the DEFAULT CONSTRUCTOR. Sets all elements of the histogram to zero.
aHistogram::aHistogram()
{
    return;
}

//Defines the DESTRUCTOR. Clears vector after use.
aHistogram::~aHistogram()
{
    binHistogram.clear(); //Clears vector
    return;
}



#endif // AHISTOGRAM_H_INCLUDED

Answer 1

I didnt find the place where you initialize the histogram this might be the problem. But even if you fix that, you will hit two other bugs:

for (int i = 1; i < numFaces; i++)
{
    while (binHistogram[i] >= largeBin)
    {
        largeBin = binHistogram.at(i);
    }
}

you are accessing elements 1....6 when probably it should be 0...5 . Same problem in the line where you have

largeBin = binHistogram.at(i);

which is most likely the line that causes the error (the one above wont be so nice to tell you what is the problem but just crash your program).

Answer 2

You never change the size of the vector in the aHistogram class, which means its size will always zero. Any index will be out of bounds.

For things like histograms I would actually recommend you to use std::unorderd_map instead of std::vector , with the "face" being the key and the count being the data. Then you could do eg

binHistogramMap[face] += 1;

without worrying about the element for face not existing (it will be created and initialized to zero if the entry doesn't exist).