訪問沖突寫入位置0x00000000。 指針問題

Question

我在分配某些代碼時遇到麻煩。 該程序基於面向大學生的在線競賽問題存檔。

這是頭文件：

#include <iostream>
#include <cmath>
using namespace std;

class Vito
{
public:
    Vito(int relative_count); //constructor
    ~Vito(); //destructor
    int min(); //finds minimum "distance" between vito's relatives

private:
    int *streets; //pointer to array of street numbers
    int sum(int index); //generates sum of distances for each of vito's relatives
    void getStreetNums(); //retrieves street numbers from user
    int relatives; //used globaly to set number of repititions
};

Vito::Vito(int relative_count = 0)
{
    int *streets = new int[relative_count]; //allocates memory for array streets
    relatives = relative_count;
    getStreetNums();
}

Vito::~Vito()
{ delete [] streets; } //releases memory used by class

void Vito::getStreetNums()
{
    cout << "Enter all street numbers, seperated by a space: ";
    int street_num;
    for (int i = 0; i < relatives; i++)
    { 
        cin >> street_num; 
        streets[i] = street_num;
    }
}

int Vito::min()
{
    int MIN = 65546, test_distance; //initialized to maximum possible value for an integer in C++

    for (int i = 0; i < relatives; i++)
    {
        test_distance = sum(i);

        if( MIN > test_distance )
        { MIN = test_distance; }
    }
    return MIN;
}

int Vito::sum(int index)
{
    int SUM = 0, street_num;
    street_num = *(streets+index); //set value for determining distances between one house and the others

    for (int i = 0; i < relatives; i++)
    { SUM += abs( street_num - streets[i] ); }

    return SUM;
}

這是主要的：

#include <iostream>
#include "proj_02.h"
using namespace std;

int main()
{
    int relatives, tests;
    cout << "This program will supply a minimum distance between homes based on a given number of relatives and street numbers their homes are on. All entered values must be integers." << endl << endl;
    cout << "Enter how many tests will be run: "; 
    cin  >> tests;
    for (int i = 0; i < tests; i++)
    {
        cout << "Enter how many relatives will be used in test " << i+1 << ": ";
        cin  >> relatives;
        Vito family(relatives);

        cout << "For this case, the minimum distance between each relatives house compared to each other is: " << family.min() << endl << endl;

    }
}

執行后，我收到一條錯誤消息，內容為“ 0xC0000005：訪問沖突寫入位置0x00000000”。 這里：

void Vito::getStreetNums()
{
    cout << "Enter all street numbers, seperated by a space: ";
    int street_num;
    for (int i = 0; i < relatives; i++)
    { 
        cin >> street_num; 
        streets[i] = street_num;
    }
}

調試顯示為街道設置了空的內存地址，但是我在構造函數中為它分配了內存。 誰能解釋這是怎么回事？

Answer 1

Vito::Vito(int relative_count = 0)
{
    int *streets = new int[relative_count]; //allocates memory for array streets

在構造函數中，您定義了一個局部變量streets ，並為其分配內存。 局部可變的streets遮蓋了班級成員的streets 。 更改為：

Vito::Vito(int relative_count = 0)
{
    streets = new int[relative_count]; //allocates memory for array streets