Fstream and simultaneous I/O

[clros]

It is possible create a stream (fstream) to read data and then write other information without close the stream?

I use fstream("miFile",ios::bynary) (or fstream("myFile", ios::in | ios::out | ios::binary) )

After reading the information from the file, I try to write with write() method but it always fails...

[Ultima]

dun think that is possible without threading. try reading it, store it, edit the data, then open stream and write again?

[simeonz]

As far as I know fstream is actually intended for read + write combos. The following code works and I believe is standard compliant. It should output "b\nc\nd\n". The only thing I am not sure is whether you have to seek before reading or writing for the first time. I mean, I believe that you are supposed to seekp before you write and seekg before you read, when you switch from reading to writing, but I am not sure if you have to do either at the very beginning. Someone can confirm?

#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    char c;

    //Write some consecutive alphabetic characters to a file
    {
        ofstream file("test.txt", ios::out | ios::binary);

        for (c = 'a'; c <= 'c'; ++c)
        {
            file.write(&c, 1);
        }
    }

    //Read every character from a file, increment it and write it back
    {
        fstream file("test.txt", ios::in | ios::out | ios::binary);

        long pos = 0;

        while (file.read(&c, 1))
        {
            ++c;
            file.seekp(pos);
            file.write(&c, 1);
            ++pos;
            file.seekg(pos);
        }
    }

    //Read every character from a file and output it on a separate line
    {
        ifstream file("test.txt", ios::in | ios::binary);

        while (file.read(&c, 1))
        {
            cout << c << endl;
        }
    }
}