Opening a file for both reading and writing

Opening a file for both reading and writing

[Shin-Cheng Mu]

Is it allowed to open a file for both reading and writing?

I opened the same file for reading and writing in 2 seperate
channels. Some anomalies happened, e.g. reading from a position
after overwriting some old data doesn't get the newly written
value.

So if I want read/write file access, is there a simple way
to do so besides using UNIX module? I prefer the core library
because Marshalling works better with standard channel library.

Thanks.

sincerely,
Shin-Cheng Mu

Re: Opening a file for both reading and writing

[Xavier Leroy]

> Is it allowed to open a file for both reading and writing?

Yes, but you must be careful about calling flush at the right times.

> I opened the same file for reading and writing in 2 seperate
> channels. Some anomalies happened, e.g. reading from a position
> after overwriting some old data doesn't get the newly written
> value.

Probably you didn't call flush on the output channel to save buffered
writes to the disk file.  Just remember to flush each time you switch
from "write" mode to "read" mode, and you should be relatively safe.

Regards,

- Xavier Leroy