分段錯誤錯誤C ++動態數組

Question

因此，我正在編寫一個ArrayList類，該類在內部利用數組和一些函數來維護容量（即收縮和增長函數）。 我收到分段錯誤錯誤，我知道這意味着我正在嘗試訪問我無權訪問的內存，這可能是在我的重載[]運算符中發生的，但是我似乎無法弄清楚是什么引起了問題。 任何幫助，將不勝感激！

ArrayList.cpp

#include "ArrayList.h"
#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int& ArrayList::operator[](unsigned int i){
    try{
        cout << "[] called: i  = " << i << ".........return val = " << foo[i] << endl ; 
        if(i >= numElements)
            throw 1;
        return foo[i];
    }
    catch(int e){
        cout << "An error has occured. Error code " << e;
        switch(e) {
            case 1:{
                            cout << ". You may be trying to access an index that doesn't currently exist in the arraylist!" << endl;
                            break; //1 = IndexOutofBoundException
            }   
        }
    }
}
int ArrayList::size(){
    return numElements;
}
void ArrayList::shrink(){
    int* bar = new int[capacity/2]; //temp array to hold values while I decrease the size
    for(int i = 0; i < capacity/2; i++){
        bar[i] = foo[i];    
    }
    delete foo;
    foo = bar;
    capacity /=2;
}

void ArrayList::grow(){
    int* bar = new int[capacity*2]; //temp array to hold values while I increase the size
    for(int i = 0; i < capacity; i++){
        bar[i] = foo[i];
    }
    for(int i = capacity; i < capacity*2;i++){
        bar[i] = 0;
    }
    delete foo;
    foo = bar;
    capacity *=2;
}

void ArrayList::push_back(int m){
    if(numElements == capacity) //full, double foo
        grow();
    foo[numElements] = m;
    numElements++;
}

void ArrayList::erase(int m){
    bool notFound = true;   
    int i = 0;
    while(notFound){
        if(foo[i] == m){
            notFound = false;    //Ha! Found you!
            for(int j = i; j < capacity; j++){
                foo[j] = foo[j+1]; //moves everything to right of m one spot left
                numElements--;
            }
        }
        else
            i++; //keep looking
    }
    if(numElements*2<capacity)
        shrink();
}

string ArrayList::toString(){
    stringstream sobj;
    string x;
    sobj << "[";
    for(int i = 0; i < numElements; i++){
        if(i == numElements-1) //last iteration, avoids output displaying [1,2,3,4,]
            sobj << foo[i];
        else
            sobj << foo[i] << ",";
    }
    sobj << "]";
    sobj >> x;
    return x;
}

ArrayList::ArrayList(){
    capacity = 1;   
    numElements = 0;
    foo = new int[1];
    foo[0] = 0;
}

ArrayList::~ArrayList(){
    delete foo;
    cout << "Destructor called" << endl;
}

ArrayList.h

#ifndef _ARRAYLIST_H_
#define _ARRAYLIST_H_
#include <string>
class ArrayList
{
 public:
    ArrayList();
    ~ArrayList();

    int& operator[](unsigned int i);

    void push_back(int m); 
    void erase(int m);
    std::string toString();
    int size();

 private: 
  void shrink();
    void grow();

 private:
  int capacity, numElements;
    int* foo;
};

#endif

測試文件

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

int main(int argc,char *argv[])
{
    ArrayList arr;

    for (int i=1;i<=50;i++)
    {
        arr.push_back(i);
    }

    cout << "Should contain numbers 1..50, is ";

    cout << arr.toString() << endl;

    for (int i=arr.size()-1;i>=1;i--)
    {
        arr.erase(arr[i]);
    }   

    cout << "Should contain only 1, is ";
    cout << arr.toString() << endl;

    arr.erase(arr[0]);

    for (int i=2;i<=50;i++)
    {
        if (i<=2)
            arr.push_back(i);
        else
        {
            int j=0;
            while ((j<arr.size()) && (i%arr[j]!=0))
                j++;

            if (j==arr.size())
            {
                arr.push_back(i);
            }
        }
    }

    cout << "Prime numbers between 1 and 50 are: " << arr.toString() << endl;

}

Answer 1

您在ArrayList::erase()函數中出錯。

void ArrayList::erase(int m){
    bool notFound = true;   
    int i = 0;
    while(notFound){
        if(foo[i] == m){
            notFound = false;    //Ha! Found you!
            for(int j = i; j < capacity; j++){
                foo[j] = foo[j+1]; //moves everything to right of m one spot left

                //========================================
                // Problem.
                // This is in the wrong place.
                // It needs to be outside the for loop.
                //========================================
                numElements--;
            }
        }
        else
            i++; //keep looking
    }
    if(numElements*2<capacity)
        shrink();
}

固定功能：

void ArrayList::erase(int m){
    bool notFound = true;   
    int i = 0;
    while(notFound){
        if(foo[i] == m){
            notFound = false;    //Ha! Found you!
            for(int j = i; j < capacity; j++){
                foo[j] = foo[j+1]; //moves everything to right of m one spot left
            }

            //========================================
            // It needs to be outside the for loop.
            //========================================
            numElements--;
        }
        else
            i++; //keep looking
    }
    if(numElements*2<capacity)
        shrink();
}

順便說一句，我能夠通過刪除一行后立即添加一行以打印陣列內容的方式來快速確定問題。

for (int i=arr.size()-1;i>=1;i--)
{
   arr.erase(arr[i]);
   cout << arr.toString() << endl;
}   

該功能的更強大版本為：

void ArrayList::erase(int m){    
   for ( int i = 0; i < numElements; ++i )
   {
      if(foo[i] == m){

         // You need to move only the number of
         // items of the array that have user set
         // numbers.
         for(int j = i; j < numElements-1; j++){
            foo[j] = foo[j+1];
         }

         // This is strictly not necessary but is
         // in the spirit of rest of your code where
         // you initialize to zero all members that have
         // not been explicitly set by the user.
         foo[numElements-1] = 0;

         numElements--;
         break;
      }
   }

   if(numElements*2 < capacity)
      shrink();
}