Class 函数不会永久改变成员变量

Question

我正在尝试在 C++ 中实现 FCFS_{先进先出 (FIFO)，也称为先来先服务 (FCFS)} 算法。

#include<bits/stdc++.h>

using namespace std;

class Process{
public:
  static int count;
  static int cycle_count;
  int id;
  int at;
  int wt;
  int tat;
  int bt;

  Process(){
    id = count++;
  }

  void compute(){
    if (cycle_count < at){
      cycle_count = at;
    }
    cycle_count += bt;
    tat = cycle_count;
    wt = tat - bt;
  }

};

float average_wt(int n, vector<Process> v){
  float avg = 0;
  for (Process i: v){
    avg += i.wt;
  }
  avg /= n;
  return avg;
}

float average_tat(int n, vector<Process> v){
  float avg = 0;
  for (int i = 0; i < n; ++i){
    avg += v[i].tat;
  }
  avg /= n;
  return avg;
}

void print(int n, vector<Process> v){
  cout << "Process\tBurst Time\tArrival Time\tWaiting Time\tTurnaround Time" << endl;
  cout << "-------\t----------\t------------\t------------\t---------------" << endl;
  for(Process i: v){
    i.compute();
    cout << i.id << "\t\t\t" << i.bt << "\t\t\t" << i.at << "\t\t\t\t" << i.wt << "\t\t\t\t" << i.tat << endl;
  }
  cout << "Average Waiting Time: " << average_wt(n, v) << endl;
  cout << "Average Turnaround Time: " << average_tat(n, v) << endl;
  cout << endl;
}


bool sort_on_at(Process a, Process b){
  return a.at < b.at;
}

int Process::count = 0;
int Process::cycle_count = 0;

int main(int argc, char const *argv[]) {


  int n;
  cout << "Enter the number of processes: ";
  cin >> n;
  vector<Process> process(n);
  for(int i = 0; i < n; ++i){
    cout << "Process " << i << ":" << endl;
    cout << "\tArrival Time: ";
    cin >> process[i].at;
    cout << "\tBurst Time: ";
    cin >> process[i].bt;
  }

  sort(process.begin(), process.end(), sort_on_at);
  print(n, process);

  return 0;
}

问题在于此代码正确打印了各个进程的等待和周转时间，但给出的平均等待和周转时间为 0。

预期输出：

Enter the number of processes: 3
Process 0:
    Arrival Time: 0
    Burst Time: 24
Process 1:
    Arrival Time: 0
    Burst Time: 3
Process 2:
    Arrival Time: 0
    Burst Time: 3
Process Burst Time  Arrival Time    Waiting Time    Turnaround Time
------- ----------  ------------    ------------    ---------------
0           24          0               0               24
1           3           0               24              27
2           3           0               27              30
Average Waiting Time: 17
Average Turnaround Time: 27

实际输出：

Enter the number of processes: 3
Process 0:
    Arrival Time: 0
    Burst Time: 24
Process 1:
    Arrival Time: 0
    Burst Time: 3
Process 2:
    Arrival Time: 0
    Burst Time: 3
Process Burst Time  Arrival Time    Waiting Time    Turnaround Time
------- ----------  ------------    ------------    ---------------
0           24          0               0               24
1           3           0               24              27
2           3           0               27              30
Average Waiting Time: 0
Average Turnaround Time: 0

我确实尝试了一些调试，发现 compute() 函数确实更改了值，（因为它为各个进程打印了正确的值）但是由于某种原因 wt 和 tat average_tat() 和 average_wt().

中所有进程的值为 0

如果我能说得更清楚，请告诉我。

Answer 1

wt 是在 compute 方法中计算出来的，但这对 Process:

的 copy 进行操作

for(Process i: v){  // a copy is made
  i.compute();

您需要使用值引用（在本例中为&i）处理向量中存储的原始Process，然后wt将被保存。

for(Process& i: v){
  i.compute();

Class 函数不会永久改变成员变量

Class function does not change member variables permanently

c++

algorithm

scheduling