为什么我的推回功能不起作用，只会出现段错误

Question

I'm Such a C++ noob and im trying to understand the code im covering better so I built this class to learn the fundamentals of overloading operators as well as push back and pop back functions ie make my own variable array. This is not a class assignment I am just trying to teach myself the code.

This was actually a computer science programming test question that I did and im trying to learn from it just in case they throw something similar at me again. I started out in java and now doing C++.

    #include"IntArray.h"
    #include<iostream>
using namespace std;

IntArray::IntArray()
{
    size=0;
    capacity=1;
    data = new int[capacity];
    cout<<"constructor fired off"<<endl;
}

IntArray::~IntArray()
{
    delete [] data;
    cout<<"Destructor fired off"<<endl;
}
IntArray::IntArray (const IntArray & m)
{
    size=m.size;
    capacity=m.capacity;
    data= new int[capacity];
    cout<<"copy constructor fired off"<<endl;

}
IntArray IntArray::operator= (const IntArray & other)
{
    cout<<"operator= fired off"<<endl;
    if(this != &other)//comparing the addresses
    {
        delete [] data;
        size= other.size;
        capacity = other.capacity;
        data = new int[capacity];
        for (int index=0; index<size; index++)
        {
            data[index]=other.data[index];
        }
    }
    return *this;
}

int& IntArray::operator[] (int n)
{
    if(n<0||n>=size)
    {


    cout<<"Array not big enough"<<endl;
    return n;
    }

    IntArray a;
    return a[n];
}
IntArray& IntArray::push_back(int n)
{
    data[size]=n;
    size++;
    if(size==capacity)
        capacity=capacity*2;
    return *this;
}
IntArray& IntArray::pop_back()
{
    if(size>0)
        size--;
}
double IntArray::average()
{
    double sum=0;
    int count=0;
    for(int index=0; index<size; index++)
    {
        sum+=data[index];
        count++;
    }
    return sum/count;
}
int IntArray::getSize()
{
    return size;
}
int IntArray::getCapacity()
{
    return capacity;
}

My h file

#ifndef INTARRAY_H_INCLUDED
#define INTARRAY_H_INCLUDED

class IntArray
{
    private:
    int size;
    int capacity;
    int *data;

    public:
    IntArray();
    ~IntArray();
    IntArray (const IntArray &);
    IntArray operator= (const IntArray &);

    int& operator[] (int);
    IntArray& push_back(int);
    IntArray& pop_back();
    double average();
    int getSize();
    int getCapacity();
};

#endif // INTARRAY_H_INCLUDED

Answer 1

This isn't going to help much but there is too much that is sub optimal for me to go into.

If this a programming exercise then you need come up with a better design really. I would avoid raw pointers with new and delete, look into smart pointers.

If you actually intend to use this, I wouldn't the standard provides a type that will meet your needs.

#include <vector>
:::
std::vector<int> i5(5); //five ints
i5.push_back(6); //now six
i5.pop_back(); //five again
i5.clear(); //non

Answer 2

1. Your assignment operator should return an IntArray&
2. Your copy constructor sets the size and capacity to the same thing as the rhs and creates the array, but doesn't copy the elements over
3. Your operator[] is returning a reference to a local variable. If you want to build bounds-checking into your operator[] , you should throw an exception, not return a number.
4. Your operator[] is creating a new IntArray and calling its operator[] , creating an infinite loop. You should return data[i]
5. You are not returning anything from pop_back which says it returns an IntArray&
6. In push_back , you have to check whether your array is at capacity, and if it is, resize capacity and data . As it is now, you're never resizing your array and you're not checking first whether it needs resizing before adding the element. This is probably why you're getting segfault

Answer 3

You never allocate additional storage in your push_back() function. You simply double the capacity and that's all. This will not magically extend the storage for your int s. You need to allocate a new block with new capacity, copy the contents to this new block and then delete the old block.