Re: Question about _Rreadn C function

How do you know what the record length is?

I don't know ahead of time what file I'll be opening. I suppose I
could use an API call to determine what the record length is, but is
it already there somewhere?

Perhaps in _RIOFB_T or _RFILE?

Speaking of _RIOFB_T and _RFILE. Is there anyplace in the manual that
gives more info on what is contained in these two structures? The
names of the subfields just don't seem to be enough in some cases.

Charles

On Wed, Sep 24, 2008 at 11:31 AM, Elvis Budimlic
<ebudimlic@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

In locate mode num_bytes will be equal to record length if read was
successful, otherwise it will not (besides the EOF check of course).
Let me know if you need more details on this.

HTH, Elvis



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-----Original Message-----
Subject: [C400-L] Question about _Rreadn C function

All,

I'm calling the _Rread() C function from RPG (thus the cross-posting).

_RIOFB_T *_Rreadn (_RFILE *fp, void *buf, size_t size, int opts)

I'm trying to use the "locate mode" of the function by not passing the
void *buf parameter as I want to move the buffer myself ( via
fp->in_buf) in a later procedure.

However, my question: how can I determine if an error occurred?
According to the manual:

"If attempts are made to read beyond the last record in the file, the
num_bytes field is set to EOF. If it is unsuccessful, the num_bytes
field is set to a value less than size, and errno is changed. If you
are using device files and specify zero as the size, check errno to
determine if the function was successful."

But when in "locate mode" the manual says:
"size Specifies the number of bytes that are to be read and stored in
buf. If locate mode is used, this parameter is ignored."

So I can still detect EOF, but what about other errors?

Thanks!
Charles Wilt


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