c++ - 未分配正在释放的指针，动态数组 C++

Question

我有 a similar issue with C , 但我现在的问题实际上是 more similar to this.

不幸的是，我只是在学习C++，我看不到如何将解决方案应用于我之前的问题(如果它确实适用)，而后一个帖子是他的代码的特定问题，即更多比我自己的复杂。

相关代码如下:

double n1, n2; //temporary data for user entry
int pcount = 0; //size of my array
struct point{double x; double y;};
point *p = new point[1]; //my array
point *tmp;  //temporary array while resizing

while (points >> n1 >> n2){ //for each element the user enters, 
    pcount++; //increase the array size
    tmp = new point[pcount]; //allocate new memory for the array
    tmp = p; //copy the elements from the old to the temporary
    delete [] p; //delete the old array
    p = new point[pcount]; //allocate memory for the new array
    p = tmp; //copy the elements from the temporary to the new array
    delete [] tmp; //delete the temporary
    p[pcount-1].x = n1; //now push back the new element
    p[pcount-1].y = n2;
}

如您所见，p 和 tmp 指向具有初始大小的数组，并在几行内被释放。至关重要的是，我看不到如何“未分配正在释放的指针”- p 在声明中分配，在循环内分配 tmp，然后是 p被释放并重新分配，然后 tmp 被释放，所以循环继续...

我也尝试通过两个循环实现，但是打印的“点”是 (0, 0)，无论它们实际是什么 - 我无法找出原因？

while (points >> n1 >> n2){
    pcount++;
}
p = new point[pcount];
int i = 0;
while (points >> n1 >> n2){
    p[i].x = n1;
    p[i].y = n2;
    i++;
}

Answer 1

这里几乎每一行都有一个错误:

point *p = new point[1]; // Allocation #1
tmp = new point[pcount]; // Allocation #2
tmp = p;                 // Allocation #2 lost (memory leak)
delete [] p;             // Now 'tmp' is "pointing to junk"
p = new point[pcount];   // Allocation #3
p = tmp;                 // Allocation #3 lost (memory leak), and 'p' is "pointing to junk"
delete [] tmp;           // Segmentation fault, since 'tmp' is "pointing to junk"
p[pcount-1].x = n1;      // Segmentation fault, since 'p' is "pointing to junk"
p[pcount-1].y = n2;      // Segmentation fault, since 'p' is "pointing to junk"