title: Reading and writing to files simultaneously?
body: <p>Moved the question here. Suppose, I want to store 1,000,000,000 integers and cannot use my memory. I would use a file(which can easily handle so much data ).
  How can I let it read and write and the same time.
  Using <code>fstream file("file.txt', ios::out | ios::in );</code> doesn't create a file, in the first place. But supposing the file exists, I am unable to use to do reading and writing simultaneously.
  WHat I mean is this :
  Let the contents of the file be <code>111111</code>
  Then if I run : -</p>
  
  <pre><code>#include &lt;fstream&gt;
  #include &lt;iostream&gt;
  using namespace std;
  int main()
  {
    fstream file("file.txt",ios:in|ios::out);
    char x;
    while( file&gt;&gt;x)
    {
      file&lt;&lt;'0';
    }
   return 0;
  }
  </code></pre>
  
  <p>Shouldn't the file's contents now be <code>101010</code> ? Read one character and then overwrite the next one with 0 ? Or incase the entire contents were read at once into some buffer, should there not be atleast one 0 in the file ? <code>1111110</code> ?
  But the contents remain unaltered. Please explain.
  Thank you.</p>