为容器类分配额外的内存

Question

嘿，我正在编写一个模板容器类，在过去的几个小时里一直在尝试为进入容器的额外数据分配新的内存（...撞到砖墙..:| ）

template <typename T>
void Container<T>::insert(T item, int index){
    if ( index < 0){
        cout<<"Invalid location to insert " << index << endl;
        return;
    }


    if (index < sizeC){ 
    //copying original array so that when an item is 
    //placed in the middleeverything else is shifted forward
        T *arryCpy = 0;
        int tmpSize = 0;
        tmpSize = size();
        arryCpy = new T[tmpSize];
        int i = 0, j = 0;
        for ( i = 0; i < tmpSize; i++){
            for ( j = index; j < tmpSize; j++){
                arryCpy[i] = elements[j];
            }
        }
        //overwriting and placing item and location index
        elements[index] = item;
        //copying back everything else after the location at index
        int k = 0, l = 0;
        for ( k =(index+1), l=0; k < sizeC || l < (sizeC-index); k++,l++){
            elements[k] = arryCpy[l];
        }
        delete[] arryCpy;
        arryCpy = 0;
    }

    //seeing if the location is more than the current capacity
    //and hence allocating more memory
    if (index+1 > capacityC){
        int new_capacity = 0;
        int current_size = size();
        new_capacity = ((index+1)-capacityC)+capacityC;
        //variable for new capacity

        T *tmparry2 = 0;
        tmparry2 = new T[new_capacity];
        int n = 0;
        for (n = 0; n < current_size;n++){
            tmparry2[n] = elements[n];
        }
        delete[] elements;
        elements = 0;
        //copying back what we had before
        elements = new T[new_capacity];
        int m = 0;
        for (m = 0; m < current_size; m++){
            elements[m] = tmparry2[m];
        }
            //placing item
        elements[index] = item;
    }

    else{
        elements[index] = item;
    }
    //increasing the current count
    sizeC++;

我的测试条件是 容器cnt4(3); 一旦我点击第四个元素（当我使用 for 例如something.insert("random",3);）时，它就会崩溃并且上面的方法不起作用。我哪里出错了？

Answer 1

有几件事对我来说没有多大意义：

if (index+1 > capacityC){

不应该是这样吗：

if (index >= capacityC){

另外，当你增加数组时，我不明白你为什么要进行两次复制。不应该：

delete[] elements;
elements = 0;

是：

delete[] elements;
elements = tmparray2;

Answer 2

请注意，new T[n] 可能不是您在 T 容器中实际想要的内容，因为这已经创建了 n 个 对象 类型 <代码>T。您真正想要的是保留内存，然后在稍后的某个时间点在该内存中构造T类型的对象。

T* data = static_cast<T*>(operator new[](n * sizeof(T));   // allocate memory
// ...
new(&data[size]) T(arguments);   // construct T object in-place
++size;

为了销毁容器，你必须颠倒这个过程：一一销毁对象，然后释放内存。

while (size) data[--size].~T();   // destruct T object in-place
operator delete[](data);          // release memory