#66 problem reading sequential file

[Peter Ottis]

I used to exchanxe globals between various M systems
using my own %GIO utility.This utility guarantees correct
global transfer also in case when they have control
characters in indexes and /or nodes.
It uses a simple method used now mostly in tcp/ip data
tranfer:

<byte1><byte2>string1
<byte3><byte4>string2

where byte1,byte2 are binary data expressing the length of
string1

I use the following code to get the string1 and string2, then
set @string1=string2 does the rest.

READ ;
N BYTE1,BYTE2,VAL1,VAL2,LNG
S EOF=0 U FILE R BYTE1#1,BYTE2#1 S VAL1=$A
(BYTE1),VAL2=$A(BYTE2)
I VAL1=255,VAL2=255 S EOF=1 S RETVAL="" Q ;END
OF GLOBAL OR END OF FILE INDICATED
I VAL1=0,VAL2=0 S RETVAL="" Q ;EMPTY STRING
S LNG=VAL1*256+VAL2 U FILE R RETVAL#LNG
Q

My problem: this code doesn't work with GT.M.

Sometime I'm getting negative values in VAL1 or VAL2 (-
1), and READ VAR#LNG randomly returns

strings of other lenght than LNG.

As open parameters I use the following:
O FILE:(noreadonly:block=2048:record=2044:exception="g
noopen"):0

Maybe using parameters like TERMINATOR="", or
PASTHRU in the OPEN statement would solve the problem,
but they are not implemented.

Please let me know, if you need more detailed input to
understand my problem.
TIA
Peter

[Vinaya Revannaswamy]

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user_id=97924

Could you please provide us a sample input file that
demonstrates the failure. We will use it to run through your
M code and see what might be returning -1. What are the
terminator(s) for lines in the extract file? Was the
exception triggered due to a failure of READ. Was End Of
File reached - GT.M sets $ZEOF when end of file is reached.
You may want to revise your M code to check for $ZEOF after
each READ. Oh! what version of GT.M did you encounter this
problem with, and which flavor of Linux?

Thanks,
Vinaya

[Vinaya Revannaswamy]

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user_id=97924

The default record format is VAR (variable). Please use
FIX:NOWRAP device parameters to see if the problem
disappears. The default recordsize/width is 32767 which
should be fine for a two byte length.

Thanks,
Vinaya

[Peter Ottis]

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I will rephrase my question:

In GT.M I am missing a open parameter for sequential files that
will allow me to read the file in chunks : i.e. READ var#512

Then, regardless if a CR or LF occurs in the record, the variable
will be filled with 512 bytes (exception: last read may end with
less than 512 characters).

This feature is called as open a file in IMAGE mode, or BINARY,
or could be achieved by setting the parameter TERMINATOR=""
to nil.
Thanks
Peter

[Steven Estes]

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user_id=97877

GT.M does not have an "image" mode per se. But you can
get the same effect as follows:

Open "some.file":(Fixed:RecordSize=512:BlockSize=512)
Use "some.file"
Read chunk#512

This technique is used in both GDE and the GTM V5 block
upgrade utility V5CBSU.

Hopefully this helps.