重新定義，基本類型

Question

我一直在模擬雜貨店的任務，我相信它的相對完成，但我編譯時遇到分段錯誤。如果你能提供一些方向或解決方案，我會非常感激。當一個指針，參考，或指向空迭代器，未分配的存儲器或只讀存儲器被解除引用 謝謝， 泰勒

/********************************************* 
PROGRAMMER: TAYLOR DOUTHITT 
ASSIGNMENT: 5 
FILE: Prog5.cc 
DUE DATE: 10-5-11 
USE: Contains methods defined in Prog5.h 
*********************************************/ 

//#include "/home/onyuksel/courses/340/progs/11f/p5/prog5.h" 
#include "prog5.h" 


int main() 
{ 
    //initialize arrival and departure time 
    int custArrive, custLeave = 0; 
    //set clock to zero 
    int clock = 0; 
    // set count to second customer 
    int count = 2; 
    // variables to track earliest next arrival and earlist next departure 
    int earlyAr = 0; 
    int earlyDept = 0; 
    //variable to track next event 
    int earlyEvent = earlyAr; 

    //create list of customers 
    list <cust> l; 
    //create iterator for list 
    list<cust>::iterator i; 
    //create queue for checkout line 
    queue <cust> q; 
    //create stat object to store final statistics 
    stat s; 

    //create a customer object 
    cust c1; 
    //initilize with 1st cust data 
    c1.atime = 0; 
    c1.wtime = 0; 
    c1.s_checkout = start_checkout(0); 
    c1.id = 1; 

    //add to list 
    l.push_back(c1); 

    //determine earliest next event 
    custArrive = arr_time(clock); 
    earlyEvent = custArrive; 

    //update clock to time of next earliest event 
    clock = custArrive; 



    //Start of Simulation********************* 

    // while simulation is still running 
    while(clock < SIM_TIME) 
    { 
     // if customer is arriving 
     if(clock == custArrive) 
     { 
      // create object for customer 
      cust c; 

      //fill data fields 
      c.id = count; 
      c.atime = custArrive; 
      c.s_checkout = start_checkout(clock); 
      c.wtime = 0; 

      l.push_back(c); // put into list 

      custArrive = arr_time(clock); // calc next arrival 

      i = min_element(l.begin(), l.end(), cmp); // find first to enter checkout 

      count++; //increment customer id number 

      //set earliest next arrival 
      earlyAr = custArrive; 
     } 

     // if customer has finished picking items 
     else if(clock == i -> s_checkout) 
     { 
      //create object to move cust from list to queue 
      cust temp; 
      //copy values from list item to queue item 
      temp.id = i -> id; 
      temp.atime = i -> atime; 
      temp.wtime = i -> wtime; 
      temp.s_checkout = i -> s_checkout; 

      //insert element into queue 
      q.push(temp); 
      //if queue is empty(this is the only element about to be in queue) 
      if(q.size() == 1) 
      { 
       //set wait time to zero 
       q.front().wtime = 0; 
       //use dept_time to obtain departure time 
       custLeave = dept_time(clock); 
      } 
      //set departure as next earliest departure 
      earlyDept = custLeave; 

     } 

     // if customer departed 
     else 
     { 
      //remove customer from queue 
      cust c = q.front(); 
      q.pop(); 

      //use dept_time and update wtime of next cust in queue 
      q.front().wtime = clock - q.front().s_checkout; 

      clock += dept_time(clock); 

      //update stat structure 
      update_fin_stat(s, c, clock); 
     } 
     //determine next earliest event 

     // if list isnt empty 
     if(l.size() > 0) 
     { 
      i = min_element(l.begin(),l.end(), cmp); //find earliest checkout time 
     } 
     else 
     { 
      i -> s_checkout = (1000000); //set value to above sim-time 
     } 
     //if arrival is less than checkout time 
     if(earlyAr < i -> s_checkout) 
     { 
      earlyEvent = earlyAr; //earliest event is arrival 
     } 
    //else the checkout time is less than arrival 
     else 
     { 
      earlyEvent = i -> s_checkout; //earliest event is checkout 
     } 
    //if list not empty and departure less than earliest event 
     if (l.size() > 0 && earlyDept < earlyEvent) 
     { 
      earlyEvent = earlyDept; //earliest event is departure 
     } 

     // Set sim clock to next earliest event time 
     clock = earlyEvent; 
    } 
    print_fin_stat(s); 

    return 0; 
} 

// returns next arrival time 
int arr_time (const int& clock) 
{ 
    int temp = (rand()% (MAX_INT_ARR - MIN_INT_ARR + 1) + MIN_INT_ARR); 
    temp += clock; 
    return temp; 
} 

// returns next departure time 
int dept_time (const int& clock) 
{ 
    int temp = (rand()% (MAX_SERV - MIN_SERV + 1) + MIN_SERV); 
    temp += clock; 
    return temp; 
} 

// returns time to enter checkout line 
int start_checkout (const int& clock) 
{ 
    int temp = (rand()% (MAX_PICK - MIN_PICK + 1) + MIN_PICK); 
    temp += clock; 
    return temp; 
} 

void update_fin_stat(stat& s, const cust& c, const int& clock) 
{ 
    //initialize variables for shop, wait, and service time 
    int shop = 0; 
    int wait = 0; 
    int serv = 0; 


    //calculate shop time, wait time, and service time 

    //calculate shop time 
    shop = c.s_checkout - c.atime; //checkout time - arrival time 

    //calculate wait time 
    wait = c.wtime; 

    //calculate serv time 
    serv = dept_time(clock) - c.wtime; 

    //update values in struct s 
    s.num_dept++; 
    s.tot_shop += shop; 
    s.tot_wait += wait; 
    s.tot_serv += serv; 


    //if number departed is multiple of sample int 
    if(s.num_dept % SAMPLE_INT == 0) 
    { 
     cout << "num = " << s.num_dept << " "; 
     cout << "id = " << c.id << "  "; 
     cout << "shop = " << shop << " "; 
     cout << "wait = " << wait << " "; 
     cout << "serv = " << serv << " "; 
     cout << endl; 
    } 


} 

bool cmp (const cust& c1, const cust& c2) 
{ 
    return c1.s_checkout < c2.s_checkout; 
} 
void print_fin_stat(stat& s) 
{ 
    //print final stats 
    cout << "Number of Customers" << s.num_dept << endl; 
    cout << "Total Sim Time " << SIM_TIME << endl; 

    //compute averages 
    s.avg_shop = s.tot_shop/s.num_dept; 
    s.avg_wait = s.tot_wait/s.num_dept; 
    s.avg_serv = s.tot_serv/s.num_dept; 

    //print averages 
    cout << "Average Shop Time" << s.avg_shop << endl; 
    cout << "Average Wait Time" << s.avg_wait << endl; 
    cout << "Average Serv Time" << s.avg_serv << endl; 
} 

Answer 1

分段錯誤一般發生。最有可能的是，您的list<cust>::iterator i正在被解除引用而未被初始化。

使用-g選項進行編譯並在調試器中運行程序（例如gdb progname）應該會得到代碼行中無效的取消引用。然後，您必須查看較早的執行情況，以找到將迭代器設置爲指向有效內存的位置。