动态内存错误

Question

我正在尝试使用动态内存方法而不是向量方法来添加元素。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。 如果我不指定动态内存的大小，程序可以正常工作， 喜欢：dynamic_memory = new int;。我想知道为什么他们会失去参考资料 随着动态内存的大小调整到超过初始容量。 PS：我正在使用 Code::Block 16.01

这是我的程序。

#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：

41107976
42075512
2
3
4
5
6
7
8
9
10

Answer 1

在

void doubleSize(int * dynamic_memory); 

此处定义的 dynamic_memory 会影响成员 dynamic_memory; 的喜剧性和未定义行为。

本地的dynamic_memory重新指向新的缓冲区，但函数退出后成员dynamic_memory继续指向被删除的原始地址。这意味着所有后续的插入都会进入无效内存，Crom 只知道之后会发生什么。

解决方案

什么都不传入，使用成员变量。将函数重新定义为

void doubleSize(); 

其他问题已在 cmets 中解决，需要修复。

Answer 2

感谢大家提供宝贵的 cmets 和建议，尤其是 user4581301 指出了一个喜剧的 hijinks 和未定义的行为。在我将函数重新定义为void doubleSize() 后，它运行良好。这是我的最终工作代码。

#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