Re: IFS I/O in COBOL -- COBOL400-L


On 18/05/2006, at 10:27 PM, Adrienne McConnon wrote:

Below is the code that was used to display the displays above. I didchange the first parm to be 'by reference' instead of by value. Asyou can see by the results below, it is still writing garbage.

Ah, I thought you were using write but I see you are using fwrite.Different set of parameters required. See below.

Currently, I will be R/W to byte-stream files. I have anotherquestion - is there any benefit to maniputating these files inlibraries?

If by "these files" you mean stream files then they can't exist inlibraries. You can use fwrite (and its sister APIs) on *FILE objectsbut that's a dumb idea. COBOL has better support for *FILE objects inits native I/O operation codes.

Does the files origin have any impact over which API's I use?

Of course. Use stream file APIs for stream files and native op-codesfor *FILE objects.

One possible exception is the C _Rxxxxxx APIs which will handle *FILEobjects but again COBOL has much better native support.

Thanks again for your help!

Adrienne



0107.30                DISPLAY 'IFS-FWRITE'.
0107.32                DISPLAY 'LENGTH=', LENGTH OF BUFFER.
0107.33                DISPLAY 'Buffer before write:' BUFFER.
0107.36
0107.37                CALL PROCEDURE '_C_IFS_fwrite'
0107.38                    USING BY REFERENCE BUFFER,
0107.39                           BY VALUE LENGTH OF BUFFER,
0107.40                           BY VALUE FILE-PTR.
0107.41       *        CALL PROCEDURE '_C_IFS_fwrite'
0107.42       *            USING BY VALUE ADDRESS OF BUFFER,

fwrite requires FOUR parameters. You are only passing three. You needto pass the buffer, the size, the count, and the file pointer. I'msurprised that your code works at all--it probably depends on whateveris previously in your code. You should be coding something like:


        CALL PROCEDURE '_C_IFS_fwrite'
                 USING BY REFERENCE BUFFER,
                 BY VALUE LENGTH OF BUFFER,
                                  COUNT,
                                  FILE-PTR.

COUNT should be set to the value 1. NOTE: SIZE and COUNT work together.In your case, because you are writing bytes, you can set SIZE to 200and COUNT to 1 or SIZE to 1 and COUNT to 200.

In your code the COUNT is taken from the first four bytes of the valueof FILE-PTR so you are writing 200 bytes times whatever that valuehappens to be. In essence you are writing the 200 bytes from yourbuffer plus whatever crap happens to be in storage after the buffer forhowever many bytes is indicated by the first 4 bytes of FILE-PTR.

Personally I think you'd be better off avoiding fwrite and just use thelower-level Unix file descriptor based APIs. That is use open, read,write, and close. Give fopen, fread, fwrite, fclose, _C_IFS_fopen,_C_IFS_fread, _C_IFS_fwrite, and _C_IFS_fclose a miss. The Unix filedescriptor APIs are simply easier to use.


Regards,
Simon Coulter.
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