一个快排的测试程序，但是没办法实现，求解答

Question

代码：

 #include <iostream>
#include <vector>
#include <cstdbool>
using namespace std;

bool SwitchInt (int& a, int &b){
    if (a == b) return true;
    a += b;
    b = a - b;
    a -= b;
    return true;
}

bool QuickSort (vector<int> &ivec, vector<int>::iterator small, vector<int>::iterator big){
    if (small == big) return true;
    vector<int>::iterator start = small;
    vector<int>::iterator end = big;
    vector<int>::iterator flag = small;
    while (small != big){
        if (*small > *flag){
            SwitchInt(*small, *flag);
            flag = small;
            small++;
            continue;
        }
        if (*big < *flag){
            SwitchInt(*big, *flag);
            flag = big;
            big--;
            continue;
        }
    }
    QuickSort(ivec, start, small);
    QuickSort(ivec, big, end);
    return true;
}

int main (void){
    vector<int> ivec;
    int num = 0;
    while (cin >> num){
        ivec.push_back(num);}
    QuickSort(ivec, ivec.begin(), ivec.end());
    for (int num: ivec)
        cout << num;
    return 0;
}

运行时有指针超界的错误，但是我检查不出来

Answer 1

//
//  bool SwitchInt (int& a, int &b){
//      if (a == b) return true;
//      a += b;
//      b = a - b;
//      a -= b;
//      return true;
//  }
//  标准SWAP方法, 比上面的更快
void SwitchInt (int& a, int &b){
    int t =a;
    a=b;
    b=t;
}

//  vector<int> &ivec 参数无用，去掉
//  bool 返回值无用，去掉
//  big 使用标准库end语法
/*bool*/ void QuickSort (/*vector<int> &ivec,*/ vector<int>::iterator small, vector<int>::iterator big)
{
    if (small == big) return /*true*/;
    vector<int>::iterator start = small;
    vector<int>::iterator end = big;
    vector<int>::iterator flag = small;
    //随机选取flag, 将小于等于此值的放在左边，大于此值的放于右边
    for (small++; small != big; small++){
        if (*small <= *flag){
            SwitchInt(*small, *flag);
            flag++;
            SwitchInt(*small, *flag);

            //           flag = small;
            //           small++;
            //           continue;
        }
        //       if (*big < *flag){
        //           SwitchInt(*big, *flag);
        //           flag = big;
        //           big--; 
        //           continue;
        //       }

    };


    cout  << &*start << ' ' << &*flag << ' ' <<  '\n';
    //QuickSort(/*ivec,*/ start, small);
    QuickSort(/*ivec,*/ start, flag);
    // QuickSort(/*ivec,*/ big, end);
    QuickSort(/*ivec,*/ ++flag, end);


    return /*true*/;
}






int _tmain(int argc, _TCHAR* argv[])
{
    srand(time(0));

    vector<int> ivec;
    int num = 0;
    //     while (cin >> num){
    //         ivec.push_back(num);}
    for (int n=0; n<10; n++)
    {
        cout << (num = rand()) << " ";
        ivec.push_back(num);
    }
    cout << "\n";

    QuickSort(/*ivec,*/ ivec.begin(), ivec.end());
    for_each(ivec.begin(), ivec.end(),
        [](int num){ cout << num << " ";});


    getchar();
    return 0;
}