c++ - 检测到堆损坏 C++ 自定义 vector

Question

嘿，我正在重温我参加的类(class)中的一些旧项目，并且在重做这个项目时，当在驱动程序中调用我的 clear() 函数时，我不断收到此错误，

检测到堆损坏:在正常 block 之后(#142)CRT 检测到应用程序在 HEAP 缓冲区结束后写入内存

这是我自定义的 Vector 类

#include "MyVector.h"

//insert header files
#include <iostream>
#include <string>

//setup access to necessary libraries
using namespace std;

MyVector::MyVector()
{
    // initialize member data
    size = 0;
    capacity = 2;

    //initialize new array
    classArray = new int[capacity];
}

MyVector::MyVector(int maxCapacity)
{
    // initialize member data
    size = 0;
    capacity = maxCapacity;

    // initialize new array
    classArray = new int[capacity];
}

MyVector::~MyVector()
{
    if (classArray != NULL)
    {
        delete [] classArray;
        classArray = NULL;
    }
}

int MyVector::getSize()
{
    return size;
}

int MyVector::getCapacity()
{
    return capacity;
}

void MyVector::clear()
{
    // delete the array
    delete[] classArray;

    // reinitialize the array
    capacity = 2;
    size = 0;

    classArray = new int[capacity];
}

void MyVector::push_back(int n)
{
    if (size > capacity)
    {
        // setup the special case of an array with 0 elements
        if (size == 0)
        {
            clear();
        }
        else
        {
            // declare a temporary pointer and allocate a new array
            capacity = capacity * 2;
            int* tempArray = new int[capacity];

            // copy the values from the old array to the temporary array
            for (int i = 0; i < size; i++)
            {
                tempArray[i] = classArray[i];
            }

            // call the destructor
            delete[] classArray;

            // assign the classArray pointer to the new array
            classArray = tempArray;
        }
    }

    // pushback a new value to the array
    classArray[size] = n;

    // increment size
    size++;
}

int MyVector::at(int n)
{
    // check if n is within the bounds of the array
    if (n >= size)
    {
        throw n;
    }

    // if not return the value of the index requested
    else
    {
        return classArray[n];
    }
}

这是我的驱动程序代码，

//insert header files
#include <iostream>
#include <string>
#include "MyVector.h"

//setup access to necessary libraries
using namespace std;

//declare constants
#pragma region Constants
const int TEST_VALUE1 = 21;
const int TEST_VALUE2 = 31;
const int TEST_VALUE3 = 41;

const int MAX = 12;
#pragma endregion

int main()
{
    // Create a default vector 
    MyVector sam;

    // push some data into sam
    cout << "\nPushing three values into sam";
    sam.push_back(TEST_VALUE1);
    sam.push_back(TEST_VALUE2);
    sam.push_back(TEST_VALUE3);

    cout << "\nThe values in sam are: ";

    // test for out of bounds condition here
    // and test exception 
    for (int i = 0; i < sam.getSize() + 1; i++)
    {
        try
        {
            cout << sam.at(i) << " ";
        }
        catch (int badIndex)
        {
            cout << "\nOut of bounds at index " << badIndex << endl;
        }
    }
    cout << "\n--------------\n";

    // clear sam and display its size and capacity
    sam.clear(); //********ERROR BEING THROWN HERE*********
    cout << "\nsam has been cleared.";
    cout << "\nSam's size is now " << sam.getSize();
    cout << "\nSam's capacity is now " << sam.getCapacity() << endl;
    cout << "---------------\n";

    // Push 12 values into the vector - it should grow
    cout << "\nPush 12 values into sam.";
    for (int i = 0; i < MAX; i++)
        sam.push_back(i);

    cout << "\nSam's size is now " << sam.getSize();
    cout << "\nSam's capcacity is now " << sam.getCapacity() << endl;
    cout << "---------------\n";

    cout << "\nTest to see if contents are correct...";
    // display the values in the vector
    for (int i = 0; i < sam.getSize(); i++)
    {

        cout << sam.at(i) << " ";
    }
    cout << "\n--------------\n";

    cout << "\n\nTest Complete...";

    cout << endl;
    system("PAUSE");
    return 0;
}

我来回查看了我的旧项目好几次，但我不明白为什么在尝试删除某些内容时会出现此错误。我的意思是，当我尝试分配无法分配但无法删除的内容时，听起来通常会发生这种情况？

感谢任何帮助!

Answer 1

您的push_back 代码可以简化为:

if (size > capacity)
{
    // resize
}
classArray[size] = n;
size++;

但请注意，您从 size == 0 和 capacity == 2 开始，然后对 push_back 进行了三次调用。在第三个上，size == 2 和 capacity == 2。 size > capacity 仍然是 false，因此您将写入未初始化内存的 classArray[2](无需调整大小)。这是未定义的行为。

您想检查 size >= capacity 以调整大小。

请注意，您的类还有另一个严重的问题:您未能编写复制构造函数，因此如果您复制它，两个拷贝都会尝试释放相同的内存。请参见三法则(在 C++11 中更新为五法则)。