Error 70 on reading file

[Keith Waters]

I keep getting error 70 (Permission denied) when reading from a file.

I have several processes running (all PBDLL6 applications).
One process writes to some files, then closes them and posts an
interprocess message to alert the other processes. They respond
by attempting to read the changed data from the files. Some of
them load the data ok but some fail with error 70.

I thought it was ok in Win32 for more than one process to read
from a file at the same time or am I wrong on that?

I intend to get into synchronization later, but I thought it
would not be necessary with the above outlined scheme.

Keith Waters

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[Edwin Knoppert]

Did you open it shared?

Add: LOCK SHARED

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[email protected]

[Keith Waters]

Edwin

Thanks for prompting me to try LOCK SHARED. It seems to have
done the trick. All works fine now.

I'd looked at the PB documentation for the OPEN statement and
seen LOCK SHARED but didn't realise it was neccessary for what
I'm trying to do. I still don't understand why I have to use
any form of file locking when all I'm doing, after the original
write has completed, is to read from the file. I'm not trying
to read and write which is what the documentation says LOCK SHARED
allows.

Anyway, many thanks
Regards Keith

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[Ian Cairns]

Keith,
The operating system has to be signalled as to how you want file
operations to be handled. PowerBasic defaults to allowing only a
single opening for a file. This prevents another process from
modifying the file you are working on unless you expressly permit it.

When referring to LOCK, the OPEN command is referring to what
OTHER processes will be permitted to do. The deault is LOCK READ WRITE
which locks other operations from any access. If another process attempts
to open an already open file, then you get error 70 - permission denied.

You have to expressly permit access. If you only want other processes to
READ your file, then lock them out of writing with LOCK WRITE. If you want
to permit Reads and Writes, then use LOCK SHARED. I am not sure why you
would use LOCK READ, but it is still there to allow a process to WRITE to
your file without reading it.

Clear as mud?

Regards,

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[email protected]

[Keith Waters]

Ian

Not clear as mud, crystal clear. It's just that I did not
understand the default. You have explained it for me.

Many thanks.

Keith

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