被释放的指针未分配，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（如果确实适用的话），而后一个帖子是他的代码的一个特定问题，那就是更多比我自己复杂。

以下是相关代码：

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 指向具有初始大小并在几行内释放的数组。至关重要的是，我看不到“未分配被释放的指针”-p 在声明时分配，tmp 在循环内，然后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来实现，但是打印的“点”是(0, 0)，不管它们实际上是什么 - 我不知道为什么？

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

您似乎误解了指针的工作原理。 tmp 在循环的第二行中被分配了一个新的 point[]，但是在第三行中，tmp 被另一个值覆盖，破坏了对刚刚分配的内存的任何引用......这会导致内存泄漏。我知道，这不是你的问题，但我认为你应该考虑一下整个事情......

Answer 2

这里几乎每一行都有错误：

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"