Wiley Ammons wrote on 29/06/2007 14:32:26:
I have prototyped open and close and I am using Scott's readline
almost
verbatim as an external procedure to my program. I have an interface
process that determines the type of message I have received by
reading the
header inside each file. There is a group of 3 programs that read the
list
of files, and then opens each file to see if it should process them.
The problem I am facing is that when I open, readline and close an
IFS
file in the first program, subsequent programs called by the same
parent
process open the same file and get line 2 of the file instead of line
1
like that first program. They therefore never process the
transaction. Any
help would be appreciated, thanks for your time.
The readline in the form you have it is limited to handling one file at a
time, and it is not designed to partially read a file, and then re-read it
from the beginning. It helps to understand that readline is in a sense
'virtualizing' access to the file. One of the main benefits of readline()
is that it reads data in chunks from the file, in order to maximize I/O
performance.
If it helps, here is my copy of readline:
//ReadLine - Get a line at a time from an IFS file
P $_readline B export
D $_readline PI 10I 0
D fd 10I 0 value
D text * value
D maxlen 10I 0 value
D rdbuf S 1024A static
D rdpos S 10I 0 static
D rdlen S 10I 0 static
Note the use of the 'static' keyword. That means that these variables
retain their values across calls to this procedure within a given
activation group. Also note that the buffer is is 1kB in size.
D p_retstr S *
D RetStr S 32766A based(p_retstr)
D len S 10I 0
c eval len = 0
c eval p_retstr = text
c eval %subst(RetStr:1:MaxLen) = *blanks
c dow 1=1
C* Load the buffer
c if rdpos>=rdlen
I'm guessing that your first line (the file header) is less than 1 kB
long. Suppose your file is 2 kB long and the first line is 256 bytes
long. Then, after reading the first line in program 1, you call this
routine from program 2. When you hit this line, rdpos = 256, and rdlen =
1024. Therefore, we don't read from the file again, and just continue
processing what is left in the buffer.
Hope this helps,
Adam
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