c++ - c++ 我的计数器增加了一个额外的计数

Question

我是编程新手并试图自学，但我的计数器显示的比它应该显示的多一个。它应该显示 22，但它显示的是 23。

#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
using namespace std;

//Main and variable data type initializing

void main()
{    float c,l,x,y,z;
    int count;
    string input, output;
    string finput, foutput;
    fstream i,o;    //i = input file;    o = output file;
//Getting the name of the files

    cout << "XZY Multiply Program\n" << endl;
    cout << "Enter the input file name:  c:/";
    cin >> input;
    cout << "Enter the output file name:  c:/";
    cin >> output;

//inserts the beginning of the file and file extension.

    finput = "c:/" + input;
    foutput = "c:/" + output;

//Opens files

    i.open(finput.data(),ios::in);
    o.open(foutput.data(),ios::out);

//Initialize count and sum of variables

    count = 0;
    x=0;
    y=0;
    z=0;

//loop through input file

    while(!i.eof() && !o.eof())
    {   count++;
        if (i.good() && o.good())
        {

                i >> c;
                i >> l;   
                o << fixed << showpoint << setprecision(4);
                o << setw(7) << c;
                o << setprecision(2);
                o << setw(9) << l;
                o << setprecision(3);
                o << setw(10) << (l*c) << endl;

// Adds columns
                x = x+c;
                y = y+l;
               z = z+(l*c);

        } 
         else
        {
        cout << "no good";
        }

    }
     i.close();
     o.close();



    //Display the output of the counter and Sums of columns
            cout << fixed << showpoint << setprecision(2);
            cout << "\n" << count << " lines in file " << endl;
            cout << "X sum = " << setw(8) << right << x << endl;
            cout << "Y sum = " << setw(8) << right << y << endl;
            cout << "Z sum = " << setw(8) << right << z << endl;


}

  7.2830     84.40
  9.1327    124.02
  7.2619    133.16
  6.2527     43.96
  4.2160     24.08
  5.2724     57.80
  5.2025     73.89
 -9.9500     80.53
  0.2790    -12.43
  2.2115      3.37
  3.1222     13.63
 16.2413    223.01
 -4.2026     33.78
 -7.1914     42.89
  4.1417     53.42
  6.1714     61.66
  9.2516     73.68
 15.2419    383.66
  6.2715     93.53
 -3.2016      3.46
 12.2013    213.63
  3.1824     23.85

Answer 1

使用.eof()or.good()作为循环条件几乎总是会产生错误代码，就像在这种情况下一样。

相反，执行输入并在循环条件中检查其结果，如下所示：

while(i >> c >> l)
{   count++;
    o << fixed << showpoint << setprecision(4);
    o << setw(7) << c;
    ...

参考：

• 为什么循环条件内的 iostream::eof 被认为是错误的？
• http://www.parashift.com/c++-faq-lite/input-output.html#faq-15.5

Answer 2

我假设在从输入文件中读取最后一个数字之后，还没有看到文件的结尾。尝试添加

if (!i.good()) break; 

在每个输入语句 ( >>) 之后，以防止在输入失败后执行循环体。