Question

我正在尝试使用动态内存方法而不是vector 方法来添加元素。最初，动态内存的最大大小设置为5.但是，一旦我尝试增加超过当前动态内存的容量，第0或第1个索引的元素就会丢失它们的引用。如果我没有指定动态内存的大小，程序工作正常，喜欢：dynamic_memory = new int;我想知道为什么他们失去了他们的参考随着动态内存的调整大小超过初始容量。 PS：我正在使用 Code :: Block 16.01

这是我的计划。

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

class DynamicVector
{
    public:
        DynamicVector();
        virtual ~DynamicVector();
        void insertElement(int input);
        int showCapacity();
        int showSize();
        void doubleSize(int * dynamic_memory);
        friend ostream& operator << (ostream& outs, const DynamicVector obj);

    private:
        int * dynamic_memory;
        int max_count; // this is similar to the capacity of the vector
        int current_count; // this is similar to size of a vector
};

DynamicVector::DynamicVector()
{
    max_count = 5;
    dynamic_memory = new int[max_count];
    current_count = 0;
}

DynamicVector::~DynamicVector()
{
    delete [] dynamic_memory;
}

int DynamicVector::showCapacity(){
    return max_count;
}

void DynamicVector::insertElement(int input)
{
    if (current_count >= max_count)
        doubleSize(dynamic_memory);

    dynamic_memory[current_count] = input;
    current_count++;
}

void DynamicVector::doubleSize(int * dynamic_memory){
    int * tmp = new int[max_count];
    for (int i = 0; i < max_count; i++)
        tmp[i] = dynamic_memory[i];

    delete [] dynamic_memory;

    max_count = max_count * 2;

    dynamic_memory = new int[max_count];

    for (int i = 0; i < max_count; i++)
        dynamic_memory[i] = tmp[i];

    delete [] tmp;
}

int DynamicVector::showSize(){
    return current_count;
}

ostream& operator <<(ostream& outs, const DynamicVector obj)
{
    for (int i = 0; i < obj.current_count; i++)
        outs << obj.dynamic_memory[i] << endl;
    return outs;
}

int main()
{
    DynamicVector v;
    int numberOfIntendedElement = 11;
    cout << "Previously, the capacity of vector was: " << v.showCapacity() << endl;
    for (int i = 0; i < numberOfIntendedElement; i++)
        v.insertElement(i);

    cout << "The capacity of the new vector is: " << v.showCapacity() << endl;
    cout << "The size of the new vector is: " << v.showSize() << endl;
    cout << "The values in the dynamic vector are: \n" << v << endl;
    return 0;
}

结果：

Answer 1

在

void doubleSize(int * dynamic_memory);

此处定义的dynamic_memory会影响成员dynamic_memory;的喜剧喜剧和未定义的行为。

本地dynamic_memory被重新指向新缓冲区，但成员dynamic_memory在函数退出后继续指向已删除的原始地址。这意味着所有后续插入都会进入无效内存，而Crom只知道之后会发生什么。

解决方案

传递任何内容并使用成员变量。将该功能重新定义为

void doubleSize();

其他问题在评论中得到解决，需要修复。

Answer 2

谢谢大家，您的宝贵意见和建议，特别是用户指示喜剧性hijinks和未定义行为的用户4581301。在我将函数重新定义为void doubleSize()后，它运行正常。这是我最后的工作代码。

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

class DynamicVector
{
    public:
        DynamicVector();
        virtual ~DynamicVector();
        void insertElement(int input);
        int showCapacity();
        int showSize();
        void doubleSize();
        friend ostream& operator << (ostream& outs, const DynamicVector obj);

    private:
        int * dynamic_memory;
        int max_count; // this is similar to the capacity of the vector
        int current_count; // this is similar to size of a vector
};

DynamicVector::DynamicVector()
{
    max_count = 5;
    dynamic_memory = new int[max_count];
    current_count = 0;
}

DynamicVector::~DynamicVector()
{
    delete [] dynamic_memory;
}

int DynamicVector::showCapacity(){
    return max_count;
}

void DynamicVector::insertElement(int input)
{
    if (current_count >= max_count)
        doubleSize();

    dynamic_memory[current_count] = input;
    current_count++;
}

void DynamicVector::doubleSize(){
    int * tmp = new int[max_count];
    for (int i = 0; i < max_count; i++)
        tmp[i] = dynamic_memory[i];

    delete [] dynamic_memory;

    max_count = max_count * 2;

    dynamic_memory = new int[max_count];

    for (int i = 0; i < max_count/2; i++)
        dynamic_memory[i] = tmp[i];

    delete [] tmp;
}

int DynamicVector::showSize(){
    return current_count;
}

ostream& operator <<(ostream& outs, const DynamicVector obj)
{
    for (int i = 0; i < obj.current_count; i++)
        outs << obj.dynamic_memory[i] << endl;
    return outs;
}

int main()
{
    DynamicVector v;
    int numberOfIntendedElement = 11;
    cout << "Previously, the capacity of vector was: " << v.showCapacity() << endl;
    for (int i = 0; i < numberOfIntendedElement; i++)
        v.insertElement(i);

    cout << "The capacity of the new vector is: " << v.showCapacity() << endl;
    cout << "The size of the new vector is: " << v.showSize() << endl;
    cout << "The values in the dynamic vector are: \n" << v << endl;

    return 0;
}

输出

Previously, the capacity of vector was: 5
The capacity of the new vector is: 20
The size of the new vector is: 11
The values in the dynamic vector are:
0
1
2
3
4
5
6
7
8
9
10

动态内存出错

2 个答案: