C++；实例化 class 的多个实例会导致内存错误

Question

这是我的 source.cpp:

#include "BST.h"

using namespace std;

int main(){
    BST<int> test1;
    BST<int> test2;
    test1.insert(10);
    test1.insert(15);
    test1.insert(12);
    test1.insert(14);
    test1.insert(19);
    test1.test();
    cout << test1.contain(1) << endl;
    cout << test1.isEmpty() << endl;
    //cout << test2.isEmpty() << endl;
    cin.get();
    return 0;
}

这是我的头文件：

//Haris
#include <iostream>
#include "Vector.h"

template <typename Comparable>
class BST
{
public:
    int size = 0;
    int currentRootindex = 0;
    BST(){
        for (int i = 0; i < 1000; i++){
            data[i] = NULL;
        }
    }
    ~BST(){

    }

    void insert(Comparable obj){


        if (data[0] == NULL){
            data[0] = obj;
            size++;


        }
        else{

            for (int index = 0; index < size; index++){
                if (data[currentRootindex] < obj && data[(2 * currentRootindex) + 2] == NULL){
                    data[(2 * currentRootindex) + 2] = obj;
                    size++;


                    break;
                }
                else if (data[currentRootindex] >= obj && data[(2 * currentRootindex) + 1] == NULL){
                    data[(2 * currentRootindex) + 1] = obj;


                    size++;
                    break;
                }
                else if (data[currentRootindex] < obj){
                    currentRootindex = ((2 * currentRootindex) + 2);


                }
                else{
                    currentRootindex = ((2 * currentRootindex) + 1);


                }

            }
        }
        currentRootindex = 0;
    }
    bool isEmpty(){
        if (data[0] == NULL){
            return true;
        }
        else
            return false;
    }
    bool contain(Comparable obj){
        for (int index = 0; index < size; index++){
             if (data[currentRootindex] < obj){
                currentRootindex = ((2 * currentRootindex) + 2);


            }
             else if (data[currentRootindex] > obj){
                 currentRootindex = ((2 * currentRootindex) + 1);


             }
             else
                 return true;

        }
        return false;
    }
    void test(){

        cout << data[5] << endl;


    }


private:
    Vector<Comparable> data;

};

如果我从 source.cpp 中注释掉 BST<int>test2，代码将按预期运行。但是当我在 BST<int>test1 之后实例化 BST<int>test2 时，我得到 Application Error: The memory could not be read。我没有声明任何静态变量，因此 none 个变量在不同对象之间共享。

此外，我使用的 Vector 头文件是

#ifndef VECTOR_H
#define VECTOR_H

#include <algorithm>
#include <iostream>

template <typename Object>
class Vector
{
public:
    explicit Vector( int initSize = 0 )
    : theSize{ initSize }, theCapacity{ initSize + SPARE_CAPACITY }
    { objects = new Object[ theCapacity ]; }

    Vector( const Vector & rhs )
    : theSize{ rhs.theSize }, theCapacity{ rhs.theCapacity }, objects{ nullptr }
    {
        objects = new Object[ theCapacity ];
        for( int k = 0; k < theSize; ++k )
            objects[ k ] = rhs.objects[ k ];
    }

    Vector & operator= ( const Vector & rhs )
    {
        Vector copy = rhs;
        std::swap( *this, copy );
        return *this;
    }

    ~Vector( )
    { delete [ ] objects; }

    Vector( Vector && rhs )
    : theSize{ rhs.theSize }, theCapacity{ rhs.theCapacity }, objects{ rhs.objects }
    {
        rhs.objects = nullptr;
        rhs.theSize = 0;
        rhs.theCapacity = 0;
    }

    Vector & operator= ( Vector && rhs )
    {
        std::swap( theSize, rhs.theSize );
        std::swap( theCapacity, rhs.theCapacity );
        std::swap( objects, rhs.objects );

        return *this;
    }

    bool empty( ) const
    { return size( ) == 0; }
    int size( ) const
    { return theSize; }
    int capacity( ) const
    { return theCapacity; }

    Object & operator[]( int index )
    {
        return objects[ index ];
    }

    const Object & operator[]( int index ) const
    {
        return objects[ index ];
    }

    void resize( int newSize )
    {
        if( newSize > theCapacity )
            reserve( newSize * 2 );
        theSize = newSize;
    }

    void reserve( int newCapacity )
    {
        if( newCapacity < theSize )
            return;

        Object *newArray = new Object[ newCapacity ];
        for( int k = 0; k < theSize; ++k )
            newArray[ k ] = std::move( objects[ k ] );

        theCapacity = newCapacity;
        std::swap( objects, newArray );
        delete [ ] newArray;
    }

    // Stacky stuff
    void push_back( const Object & x )
    {
        if( theSize == theCapacity )
            reserve( 2 * theCapacity + 1 );
        objects[ theSize++ ] = x;
    }
    // Stacky stuff
    void push_back( Object && x )
    {
        if( theSize == theCapacity )
            reserve( 2 * theCapacity + 1 );
        objects[ theSize++ ] = std::move( x );
    }

    void pop_back( )
    {
        --theSize;
    }

    const Object & back ( ) const
    {
        return objects[ theSize - 1 ];
    }

    // Iterator stuff: not bounds checked
    typedef Object * iterator;
    typedef const Object * const_iterator;

    iterator begin( )
    { return &objects[ 0 ]; }
    const_iterator begin( ) const
    { return &objects[ 0 ]; }
    iterator end( )
    { return &objects[ size( ) ]; }
    const_iterator end( ) const
    { return &objects[ size( ) ]; }

    static const int SPARE_CAPACITY = 2;

private:
    int theSize;
    int theCapacity;
    Object * objects;
};

#endif

Answer 1

您正在访问数据向量的越界索引。默认向量构造函数初始化大小为 0（尽管它分配了 2 个额外元素），但随后您立即尝试访问索引 999:

BST(){
    for (int i = 0; i < 1000; i++){
        data[i] = NULL;
    }
}

第二个对象与问题无关。即使只有一个对象，代码仍在访问它不应该访问的内存。

将数据向量更改为大小为 1000 的初始化修复了此特定代码的越界错误，但我怀疑 BST class 将来会导致更多此类错误，因为我看不到任何错误检查数据向量的大小。

C++；实例化 class 的多个实例会导致内存错误

C++; instantiating multiple instances of a class results in memory error

c++

memory

runtime-error