Question

我正在用模板开发通用列表。此列表由指针阵列 T * 组成, 用于获取元素数的整数和一些方法( 查找, 包含...) 。重要的是要声明我不能使用 std: library 。

我的问题出现在我和一个 List< list<int> & gt; 合作时。

其中一个方法将 T/code> 指针阵列重新重新设定大小大于 T/code> 的运算符。当我有这个 list<List>> 时,我创建了一个比 T/code > 更大的运算符, 并将 T 内容复制到有 memcpy 的运算符的运算符中。内指针( list. T. T )也复制为指针, 而不是重复内存, 所以当我删除 T/code> 指针和重新指派 Tuxpoint 。我已丢失了该指针在 new T 中的数据。



template <typename T>
void CGenericList<T>::resize()
{
    T* auxPointer = new T[this->maxElements*2];
    memcpy (auxPointer,this->pointer,this->maxElements*sizeof(T));
    delete[] this->pointer;     
    this->pointer=auxPointer;
    this->maxElements=2*this->maxElements;
}

template<class T>
class CGenericList
{
public:
    T* pointer;
    int N;
    int maxElements;

    CGenericList();
    CGenericList(int);
    ~CGenericList();
    void resize();  
}


谁能给我做这个的提示吗?

Answer 1

你公布的代码显示有些问题

T* auxPointer = new T[this->maxElements*2];

here you allocate a new array of maxElements*2 - and call the default constructor. Which in your case probably initialises all Listelements.

memcpy (auxPointer,this->pointer,this->maxElements*sizeof(T));

之后您将旧阵列的内容复制到新分配的内存的内存区域。这将将刚刚创建的列表符号和旧阵列 - & gt; 内存泄漏的列表覆盖到刚刚创建的内存区域。

delete[] this->pointer;

Then you delete the array, this calls the destructors of all elements. Which hopefully will delete their content and free their memory.

this->pointer=auxPointer;

最后,您将重新指定新建的数组。列表中的指针指向旧的列表列,并指向不再分配的内存(因为通过删除[]呼叫毁灭器)。

A solution would be to implement an copy constructor for your list and call it for all elements in your array. (DeepCopy) And of course an assignment operator, i almost forgot ;)

CGenericList(const CGenericList<T>& copy);
CGenericList<T>& operator= (const CGenericList<T>& rhs)

可能有些类似情况- 注意这是“ 环境”, 绝对不是例外安全 ;)

template<class T>
class CGenericList
{
public:
    T* pointer;
    int N;
    int maxElements;

    CGenericList();
    CGenericList( const CGenericList<T>& copy );
    CGenericList<T>& operator=(const CGenericList<T>& rhs);
    CGenericList(int);
    ~CGenericList();
    void resize();
};

template <typename T>
void CGenericList<T>::resize()
{
    T* auxPointer = new T[this->maxElements*2];
    for(int i=0; i < this->maxElements; i++)
    {
        auxPointer[i] = this->pointer[i];
    }
    delete[] this->pointer;
    this->pointer = auxPointer;
    this->maxElements = this->maxElements*2;
}

template <typename T>
CGenericList<T>::CGenericList()
    :N(0)
    ,maxElements(0)
{
    this->pointer = new T[1];
}

template <typename T>
CGenericList<T>::CGenericList(const CGenericList<T>& copy)
    :N(copy.N)
    ,maxElements(copy.maxElements)
{
    T* temp = new T[copy.maxElements];
    for(int i=0; i<N; i++ )
    {
        temp[i] = copy.pointer[i];
    }
    this->pointer = temp;
}

template <typename T>
CGenericList<T>& CGenericList<T>::operator=(const CGenericList<T>& rhs)
{
    if( this != &rhs )
    {
        delete[] this->pointer;
        this->pointer = new T[rhs.maxElements];
        for(int i=0; i<rhs.maxElements; i++)
        {
            this->pointer[i] = rhs.pointer[i];
        }
    }
    return *this;
}


template <typename T>
CGenericList<T>::CGenericList(int size)
    :N(0)
    ,maxElements(size)
{
    this->pointer = new T[size];
}

template <typename T>
CGenericList<T>::~CGenericList()
{
    delete[] this->pointer;
}


int main(int /*argc*/, char */*argv*/[])
{
    CGenericList<CGenericList<int> > list;
    list.resize();

    return 0;
}

如果您不喜欢使用 stl, 您可以查看 < a href=" http:// stlport. sourceforge. net/ " rel=" nofollow" >stlport

Answer 2

Your resize is not exception safe. You are first deleting the existing array and then allocating memory for a different size and then assigning auxPointer.
Coming to the problem you are having, check if the below approach helps.

T* auxPointer = new T[this->maxElements*2];       
for ( int i =0; i < this->maxElements; ++i)
   std::swap(auxPointer[i], pointer[i]);

delete[] this->pointer;    
this->pointer = auxPointer;  
this->maxElements=2*this->maxElements;

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