Question

我想从键盘获取用户输入（整数值）并将其写入文件中。然后，选择18-80的值并写入另一个文件。我的程序运行直到键盘输入并将它们写入文件。但我不知道如何在条件下选择一些值并将它们写在另一个文件中。

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


int main()
{

   ofstream age;
   age.open("age.txt",ios::out);  
   cout<<"Input the ages from keyboard: "<<endl;

   for(int i=0;i<3;i++)
   {
       int n;
       cin>>n;        //value inputted from keyboard
       age<<n<<endl;
   }

   ifstream agein;
   agein.open("age.txt");   //Reading that existing file

   ofstream ageout;
   ageout.open("information.txt");   //writing in another file
   {
       int m;
       if(m>18 && m<=80)      //picking value from 18-80
       ageout<<m<<endl;
   }

       age.close();
       agein.close();
       ageout.close();
       return 0;
}

Answer 1

即使您从读/写切换，也不要忘记在重新打开文件之前关闭文件你走了：

using namespace std;

int main()
{
    ofstream age;
    age.open("age.txt", ios::out);
    cout << "Input the ages from keyboard: " << endl;

    for (int i = 0;i<3;i++)
    {
        int n;
        cin >> n;        //value inputted from keyboard
        age << n << endl;
    }

    age.close();// Do NOT forget that before reopening it

    ifstream agein;
    agein.open("age.txt");   //Reading that existing file

    ofstream ageout;
    ageout.open("information.txt");//writing in another file
    if(ageout)//Checks if the file exists
    {
        string str;
        int m;
        while (agein >> m) //Get an int from a file
            if (m>18 && m <= 80)      //picking value from 18-80
                ageout << m << endl;
    }
    agein.close();
    ageout.close();
    return 0;
}

从文件中读取选定的值并将其写入c ++中的新文件中

1 个答案: