file reading error

[Prashant Gupta PG]

why is this function reading the last object of file twice

void show()
{
    ifstream f;
    f.open("BANK.PG");
    account a;
    while(1)
    {
        f.read((char*)&a,sizeof(a));
        a.show_details();
        getchar();
        if(f.eof())
        {
            cout<<"\nFile Ended";
            break;
        }
    }
}

[EssGeEich]

Because f.eof() is true if the file ALREADY reached the end of file. You should loop on f.read().

while(f.read( ... ) )
{
    a.show_details();
    getchar();
    // omit f.eof()
}

[Prashant Gupta PG]

Ok thank for the help.But why it is so that f.eof() is true if the file ALREADY reached the end of file.And when does eof() exactly returns false??

[EssGeEich]

It returns false when it didn't reach the end of file.

Let me give you an example:

We have a 4-byte example file.

We will read 2-byte "packets".

1. Read and Store Data. read returns a nonzero value. 2/4 bytes read.
2. eof() returns false. eof flag isn't set.
3. Read and Store Data. read returns a nonzero value. 4/4 bytes read.
4. eof() returns false. eof flag isn't set.
5. Read and Store Data. read returns a zero value. Cannot go over 4/4, eof flag set.
6. eof() returns true as the eof flag is set.

[Prashant Gupta PG]

awesome, I want to give a thumb up to this explanation.