存在内存访问异常，但我不确定我的代码有什么问题

Question

I'm testing some case of quick sort in visual studio but I got and error and I'm not sure what's wrong with my code.

Here's my code.

#include <iostream>
#include <cstdlib>
#include <ctime>


using namespace std;
void Swap(int *arr, int a, int b) {
    int temp = arr[a];
    arr[a] = arr[b];
    arr[b] = temp;
}

void BubbleSort(int *arr, int len) {
    for (int i = 0; i < len - 1; i++) {
        for (int j = 0; j < len - 1 - i; j++) {
            if (arr[j] > arr[j + 1]) {
                Swap(arr, j, j + 1);
            }
        }
    }
}

void QuickSort(int *arr, int left, int right) {
    if (left >= right) {
        return;
    }
    int pivot = arr[left];
    int low = left;
    int high = right + 1;

    while (low <= high) {
        while (arr[++low] <= pivot && low <= right);
        while (arr[--high] >= pivot && high > left);
            if (low > high) {
                Swap(arr, left, high);
            }
            else {
                Swap(arr, low, high);
            }
    }
    QuickSort(arr, left, high - 1);
    QuickSort(arr, high + 1, right);
}




int main() {
    srand((unsigned)time(NULL));
    int *arr = new int[10000];

    for (int i = 0; i < 10000; i++) {
        arr[i] = rand() % 10000;
    }

    BubbleSort(arr, 10000);
    QuickSort(arr, 0, 9999);

    delete[] arr;
    return 0;
}

It doesn't matter if I allocate little size of memory but this code's case got an error with my QuickSort() function.

Answer 1

When the pivot is the largest element, the first inner while loop will run until ++low is > right , causing an array out of bounds access. You have to check low < right before accessing arr[++low] . Same thing applies for the 2nd loop.

Also, use std::swap instead of rolling your own, use std::size_t for array indices, and the C++ <random> library instead of the C rand() function. And don't do using namespace std .