Question

试图对动态数组sum_array进行排序，但该功能无法正常工作。如果我不将array的大小设置为1，我的循环也会自终止，这样我的声明就可能有问题

**#include<bits/stdc++.h>
#include<algorithm>
#include<vector>

using namespace std;

int main(){

  vector <int> sum_array (1);
  int n;
  cin>>n;
  int sum,marks;
  for (int i = 0; i < 5; i++) {
    cout<<"turn now is ="<<i<<endl;
    sum=0;
    for (int k = 0; k < (n-1); k++) {
    cin>>marks;
    sum=sum+marks;
    cout<<"sum="<<sum<<endl;
    }
  sum_array[i]=sum;
  }
  for (int i = 0; i < 5; i++) {
    cout<<sum_array[i]<<endl;
  }
  sort(sum_array.begin(),sum_array.end());
  cout<<"after"<<endl;
  for (int i = 0; i < 5; i++) {
    cout<<sum_array[i]<<endl;
  }
    return 0;
}**

Answer 1

您正在创建一个整数的向量：

Global variables in header file : 

#define TRUE 1
#define FALSE 0

int finished = FALSE

pthread_cond_t qServiced = PTHREAD_COND_INITIALIZER;
pthread_cond_t qEmpty = PTHREAD_COND_INITIALIZER;
pthread_cond_t qElement = PTHREAD_COND_INITIALIZER;

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

int main()
{
    Create 1 writer thread
    Create 2 reader threads

    Writer join <- Success 
    Reader join <- Program hangs here


void* writer()
{
    int totalQueued = 0; 
    int tasks = 20; 

    while(!finished)
    {
        pthread_mutex_lock(&mutex); 

        while(isFull(q))
        {
            pthread_cond_wait(&qEmpty, &mutex); 
        }

        if(totalQueued < tasks)
        {
            for(j = 0; j < 2; j++) //Add 2 numbers at a time 
            {
                if(!(isFull(q)))
                {
                    //Assume random numbers added to queue 
                    totalQueued++;
                }
            }
            pthread_cond_signal(&qElement);
            pthread_cond_wait(&qServiced, &mutex);
        }
        else
        {
            finished = TRUE; 
        }
        pthread_mutex_unlock(&mutex); 
    } 

    //Thread exits
}

void* reader()
{
    while(!finished)
    {
        pthread_mutex_lock(&mutex);

        while(isEmpty(q)) //If the queue is empty 
        {
            pthread_cond_signal(&qEmpty);
            pthread_cond_wait(&qElement, &mutex);
        }

        int n = dequeue(q); 
        printf("%d\n", n); 

        pthread_cond_signal(&qServiced); //Signal that task has been serviced
        pthread_mutex_unlock(&mutex);
    }
}

然后，您将访问元素超出向量的范围（这是未定义的行为）。

std::vector<int> sum_array(1);

for (int i = 0; i < 5; i++) { // ... sum_array[i] = sum; }仅对一个元素的向量进行排序，因此它什么也没做。

由于您不知道向量的大小，因此应将其初始化为空向量：

std::sort

并将元素推入std::vector<int> sum_array;：

sum_array

面对cpp中的sort函数的问题

1 个答案: