动态双向变换中的C++元素

Question

我有一个向文本文件中添加元素的问题。文件包含如下数字：1 2 3 4.但是，当我尝试从文件中提取数字时，deque被填充了更多的数字。

#include <iostream> 
#include <stdlib.h> 
#include <fstream> 
#include <stdio.h> 

using namespace std; 

int temp; 
int br = 1; 

struct delem 
{ 

    int key; 
    delem *next; 

} *l = NULL, *r = NULL; 

void push_l(int n) 
{ 

    delem *p;  
    p = l;   
    l = new delem;  
    l->key = n; 
    l->next = p;    
    if (r == NULL) 
    { 

     r = l; 
    } 

} 

void push_r(int n)    
{ 

    delem *p;   
    p = r;    
    r = new delem;  
    r->key = n;    
    r->next = NULL; 
    if (l == NULL)    
    { 

     l = r; 

    } 
    else     
     p->next = r; 

} 

int pop_l(int &n)    
{ 
    delem *p;     
    if (l)      
    { 
     n = l->key;   
     p = l;     
     l = l->next;  
     if (l== NULL)    
      r = NULL;   
     delete p;    
     return 1; 
    } 
    else 
     return 0; 
} 

int pop_r(int &n) 
{ 
    delem *p;     
    if (r)      
    { 

     n = r->key;     
     if (l == r)   
     { 
      delete r;   
      l = r = NULL; 
     } 
     else 
     { 
      p = l;      
      while (p->next != r) 
       p = p->next;     
       //p++; 
       n = r->key;       
       p->next = NULL;   
       delete r;     
       r = p;      
       return 1; 
     } 

     } 
     else 
     return 0; 

} 

void get(int n) 
{ 

    int i, t; 
    for (i = 1; i < br; i++) 
    { 

     pop_l(t); 
     if (i == n) 
     { 

      temp = t; 

     } 

     push_r(t); 

    } 

} 

void print_deque() 
{ 

    for (int i = 1; i<br; i++) 
    { 

     get(i); 
     cout << temp << " "; 

    } 

} 

void find_number() 
{ 

    int n; 
    int total = 0; 
    int count = 0; 
    double average = 0; 
    ifstream deque_file; 
    deque_file.open("deque.txt", ios::in); 

    if (deque_file) 
    { 

     while (!deque_file.eof()) 
     { 

      deque_file >> n; 
      push_l(n); 

     } 

     while(pop_l(n)) 
     { 

      total+=n; 
      count++; 

     } 

     average = total/count; 

     cout<<"\n\nSum: " << total << " Count: " << count << " Average: " << average << endl << endl; 

    } 
    else 
     cout << "Error while opening input file!" << endl; 

    deque_file.close(); 

} 

int main() 
{ 

    int ch; 
    ifstream fd; 
    fd.open("deque.txt", ios::in); 
    while (fd) 
    { 

     fd >> ch; 
     push_r(ch); 
     br++; 

    } 

    print_deque(); 
    find_number(); 

    system("pause"); 
    return 0; 

} 

如何避免添加最后一个数字两次？

Answer 1

不要做while (fd)（或while (!fd.eof())）。

取而代之的是while (fd >> ch)。

原因是eofbit标志没有设置，直到你第一次尝试从文件末尾读取，导致你的循环迭代一次到多次。