Read/Write at the same time

What I am doing is opening my file using fstream at the start of the main and closing it at the end. In between I am writi开发者_StackOverflow中文版ng "Hello World" and after that reading what I wrote but the result is always weired charecters and not the "Hello World". I did do a cast to char but that didnt help. Any way I can do this?

You need to interpose an fseek call when you switch from reading to writing, or viceversa. (Of course, you also need to fopen for "r+" or the like, so that both reading and writing are allowed, but I imagine you are already aware of that -- the need for seeking in order to switch between reading and writing is a lesser known fact).

As this page puts it,

For the modes where both read and writing (or appending) are allowed (those which include a "+" sign), the stream should be flushed (fflush) or repositioned (fseek, fsetpos, rewind) between either a reading operation followed by a writing operation or a writing operation followed by a reading operation.

I'd be amused if this works, because I always had to open a file twice to do that: once for reading and once for writing. Even then, I had to write the whole file out and close it (which flushed the OS buffers) before I could be sure I could read the whole file and not get an early EOF.

Nowadays, since I use Unix-style operating systems, I would just use the pipe() function. Not sure if that works in Windows (because so much doesn't, like select() on files).

Make sure you are seeking to the beginning of the file before reading, like so:

fileFStream.seekg(0, ios_base::beg);

If that doesn't work, post your code.