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Re: fstream - problem with reading/writing to file

On 2009-02-19 20:33Z, Tim McDaniel wrote:
> On Thu, 19 Feb 2009, Pavel Kudrna <> wrote:
>> I have found problem with read and write to file using fstream. The
>> following example opens existing file for read+write, separately
>> writes "Hello" and " world!" and in between it tries to read one
>> character from the file. The problem is that without call to seekg()
>> or tellg() the read fails and without seekp() or tellp() the second
>> write of " world!" to the file fails too.  The same program works on
>> linux with gcc 3.2.2.
> I'm pretty sure that at least the C standard for stdio said that,
> between a read and a write (and the reverse), it was necessary to do a
> seek on the file.  But I don't have a citation for that, and I don't

I think you mean C99, which says

"output shall not be directly followed by input without an intervening
call to the fflush function or to a file positioning function"

and vice versa.

> know much about C++ I/O to know what rules exist there.  I only
> mention this in case it might prompt someone else who knows where to
> look.

The C++ standard refers to the C standard for low-level stuff like this.

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