C++ fstream无法覆盖我的文本文件的内容

我曾试图编写一个程序，使用fstream从文本文件中读取和写入整数，但在执行该程序并从中退出后，该文件根本不会更改，并且内容保持不变

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下面是我的文件应该做什么的简短描述：

此应用程序读取文件，修改其内容，然后将修改写回同一文件。 该文件包括3行整数。第一行表示第三行的整数数。第二行指示第三行上的哪个整数被选中为活动整数。 文件中的第三行列出了最大值为10的所有整数。 屏幕上不断显示的菜单。在菜单的右下方，程序显示文件第三行中的所有整数 该程序还显示当前选定的活动整数。 用户可以通过按菜单中的一个扩展键来选择菜单项 按“插入”将在所选整数之前插入一个整数，并使新插入的整数处于活动状态。整数由用户键入。如果列表已满，则无法插入。 按“删除”删除活动整数。 按“排序”将列表按升序排序。排序后的活动整数与排序前的活动整数相同。 按“选择”选择列表中的下一个整数。如果选择了最后一个整数，此选项将选择列表中的第一项。 按“向右移动”将所选整数向右移动一个位置。如果选择了最后一个整数，则无法向右移动。 按“向左移动”将所选整数向左移动一个位置。如果选择第一个整数，则无法向左移动。 按“退出”结束应用程序。 程序将文件内容保存到数组中，修改数组，然后将数组内容写回文件。 [我的节目：]

//Description: Grade averages
#include<iostream>
#include<cstdlib>
#include<fstream>//allows file streams
#include<conio.h>
#include<dos.h>
#include <iomanip>
#include <string>
#include <windows.h>
using namespace std;
void menu();//declaration of the menu funtion
int main()
{
    int num = 0;
    int next = 0;
    fstream f_stream;//declares the stream that allows the program to read/write from the file
    f_stream.open("base.txt");//opens the file
    if (f_stream.fail())//checks if the file is present
    {
        cout << "base.txt is missing. program cannot run :(" << endl;//displays an error if the file can't be found
        exit(1);
    }
    cout << "input stream successfully opened" << endl;//confirms that the file is available
    int ch =0;
    int values[12];//declares the array that will store the file's integers
    do
    {
        menu();//displays a menu for inputs
        while (!f_stream.eof())//runs until the end of the file is reached
        {
            f_stream >> next;//grabs values from the file
            values[num] = next;//assigns a file input to an expression in the array
            num++;//this keeps tally of the number of items in the file
        }
        cout << endl;
        cout << "Here is the list of numbers on the third line: " << endl << endl;
        for (int t = 2; t < num; t++)//this displays the values on the third line
        {
            cout << values[t] << endl;
        }
        cout << endl;
        int num_of_integers = num - 2;//this is the number of files in the 3rd line. the first and second line numbers are subtracted
        int active  = values[1];//the integer from the second line displays the number that is active
        int activenumber = values[active];//grabs the active number
        cout << "Number of integers: " << values[0] << endl;
        cout << "Current active integer: " << activenumber << endl;

        ch=getch();//grabs keyboard input
        if (ch == 0||ch == 224)//
            ch=getch();//only allows special keys to be used
        int newactivenumber;
        int lastorder = num - 1;//this is the last element in the array
        if (ch == 82)//if the "insert" key is pressed
        {
            if (num == 12)//if the maximum number of integers is present in the file
            {
                cout << "Cannot insert an integer before " << activenumber << endl << "Please delete an integer before inserting" << endl;
            }
            else if (values[active] == values[3])//if the active integer is the very first number on the second line
            {
                cout << "Please enter an integer to insert at the end of the number line" << endl;
                cin >> values[num-1];
            }
            else//inserts a number before the active integer
            {
                cout << "Please enter an integer to insert before " << activenumber << endl;
                int previous = active - 1;
                cin >> values[previous];
            }
        }
        else if (ch == 83)//if the "delete" key is pressed
        {
            cout << values[active] << " was deleted." << endl;
            int temp, temp1;
            for (int p = active; p<(lastorder);p++)//shifts all values in the array to the left
            {
                temp1 = p + 1;
                values[p] = values[temp1];
            }
            int new_integers = num_of_integers - 1;
            values[0] = new_integers;//since a value was deleted, the new amount of integers is recorded
            num--;
        }
        else if (ch == 80)//if the "arrow down" key is pressed
        {
            if (values[1] == lastorder)//if the last number on the list is the active number, then the first number on the list will become the new active number
            {
                newactivenumber = 2;
                values[1] = newactivenumber;
            }
            else//the next number of the list will become the new  active number
            {
                newactivenumber = values[1] + 1;
                values[1] = newactivenumber;
            }
            cout << values[newactivenumber] << " is now selected" << endl;

        }
        else if (ch == 77)//if "arrow right" is pressed, the active number is shifter to the right
        {
            if (values[active] == values[num-1])//disallows shifting if the active number is the last number on the list
            {
                cout << "I'm sorry, Dave. I'm afraid I can't do that." << endl;

            }
            else
            {
                int temp;
                temp = values[active];
                int rightno = active + 1;
                values[active] = values[rightno];
                values[rightno] = temp;
                cout << "The active number has been moved 1 position right in the list" << endl;

            }
        }
        else if (ch == 60)//IF the F2 key is pressed, the array numbers are sorted from smallest to greatest
        {
            int i;
            int temporary = values[active];
            for(i=2;i<num;i++)
            {
                for(int j=2;j<num-i-1;j++)
                {
                    if(values[j]>values[j+1])
                    {
                        int temp = values[j];
                        values[j] = values[j+1];
                        values[j+1] = temp;
                    }
                }
            }
            //displaying result
            cout<<"Sorted list"<<endl;
            for(i=2;i<num;i++)
            {
                cout<<values[i] << endl;
            }
            for(i=2;i<num;i++)//this loop ensures that the active number remain the same, even after the sorting
            {
                if (values[i] == activenumber)
                {
                    values[1] = i;
                }
            }

        }
        else if (ch == 75)//if "arrow left" is pressed, it shifts active number to the left
        {
            if (values[active] == values[2])//
            {
                cout << "I'm sorry, Dave. I,'m afraid I can't do that." << endl;

            }
            else
            {
                int temp;
                temp = values[active];
                int leftno = active - 1;
                values[active] = values[leftno];
                values[leftno] = temp;
                cout << "The active number has been moved 1 position left in the list" << endl;

            }
        }
        else if (ch == 59)//terminates program if F1 is pressed
        {
            f_stream.close();
            cout << "streams successfully closed" << endl;
            break;
        }
        else//if an invalid key is pressed
        {
            cout << "Try again" << endl;

        }
        for (int out = 0; out < num; out++)//exports array values to the file
        {
            if (out == 0 || out == 1)
            {
                f_stream << values[out] << '\n';
            }
            else if (values[out]==0)
            {
                f_stream << "";
            }
            else if (out != num-1)
            {
                f_stream << values[out] << " ";
            }
            else
            {
                f_stream << values[out];
            }
        }
        system("PAUSE");
        system("CLS");
    }
    while (ch != 59);
    f_stream.close();
    cout << "streams successfully closed" << endl;
    return 0;
}
void menu()//self-explanatory
{
    cout<<"Menu:" << endl;
    cout << setiosflags(ios::left) <<  setw(14)<< "1.Insert" << "Press the \"Insert\" key" << endl;
    cout << setiosflags(ios::left) <<  setw(14)<< "2.Delete" << "Press the \"Delete\" key" << endl;
    cout << setiosflags(ios::left) <<  setw(14)<< "3.Sort" << "Press the \"F2\" key:" << endl;
    cout << setiosflags(ios::left) <<  setw(14)<< "4.Select" << "Press the \"Down Arrow\" key" << endl;
    cout << setiosflags(ios::left) <<  setw(14)<< "5.Move Right" << "Press the \"Right Arrow\" key" << endl;
    cout << setiosflags(ios::left) <<  setw(14)<< "6.Move Left" << "Press the \"Left Arrow\" key" << endl;
    cout << setiosflags(ios::left) <<  setw(14)<< "7.Exit"<< "Press the \"F1\" key" << endl;
}

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使用fstream数据类型时，指定文件访问的类型至关重要。在您的代码中有许多方法可以实现这一点，但对我来说最简单的方法似乎是：

fstream f_stream;
f_stream.open("base.txt", ios::in | ios:out) 

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下面是我的文件应该做什么的简短描述：。。。真的吗？你可以打开一个fstream进行输入或输出，而不是同时打开两者。

fstream f_stream;
f_stream.open("base.txt", ios::in | ios:out)