C++ 文件处理:ios::ate 无法正常工作

Question

在下面提到的代码中，当我应用 ios::out 时它可以正常工作，但在 ios::ate 的情况下却不是这样，它显示文件中的某个位置 -1 并且无法写入文件。

其次peek()函数用在什么地方

代码:

int main ()

{
    char p[80];
    fstream file("text1.txt",ios::in|ios::ate);
    cout<<"Starting position of the file is "<<file.tellg()<<endl;
    getch();
    if(file.is_open())
        cout<<"file is open\n";
    else
        cout<<"file is not open\n";
    getch();
    file.seekp(0);
    while(file>>p)
    {
        cout<<p<<endl;
    }
    file.clear();
    if(file<<"Now if we add text to the file")//Not working
        cout<<"\n Data entry possible\n";
    else
        cout<<"\n Data entry not possible\n";
    file.flush();
    cout<<"\nThe current position of the file pointer is "<<file.tellg()<<endl;//Showing position -1
    file.clear();
    file.seekp(0);
    if(file.eof())
        cout<<"\n the eof\n";
    while(file>>p)
    {
        cout<<p<<endl;
    }
    file.close();
    return 0;
}

输出:

Starting position of the file is 30
file is open
Now
if
we
add
text
to
the
file

Data entry not possible

The current position of the file pointer is -1
Now
if
we
add
text
to
the
file

Answer 1

ate 并不意味着 out 所以如果你想写入文件你仍然需要使用 out

fstream file("text1.txt",ios::in|ios::out|ios::ate);