I'm trying to write an object to file "List.dat" using multiple I/O class object of fstream. It works when i open the file to write and read from it. But it doesn't seem to work when i open the file to read first to check the written objects before writing a new object to it.

What do you pass as the second argument (the openmode argument) to the fstream constructor? (By the way, the fstream constructor is described on page 666 of the C++ Standard, so it must be a bit of a devil ;-)

ios::in in open() for reading and for second time ios::out in open() for writing in file.

When you open it the second time (i.e. for writing), you need to make sure you close it first. You can't open it if it is already open. Also, you should check the status of the file after opening (and before every read or write operation.) But you left me wondering why you've taken this approach. Normally, if you want to read and write the same file, you would open it for both read and write (passing ios::in | ios::out) or else you might as well create two objects, and ifstream and an ofstream.

Thanks, I suppose It was missing the close() at the end, but then i thought to use two different objects to open it anytime for read or write.