Re: Scanning for a string in a fle in the IFS, and updating the file.

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

Your calls to lseek() don't make any sense.   What is -7 supposed to do?!

There are 3 parameters to lseek()

a) The file descriptor/handle (the thing returned by open())
b) The offset (position) to seek to.
c) where to base that offset from (the start of the file?  The end of 
the file?  The current position?)

That 3rd parameter has 3 possible values, which according to POSIX 
standards should be represented by the following 3 constants:

D SEEK_SET        C                   CONST(0)
D SEEK_CUR        C                   CONST(1)
D SEEK_END        C                   CONST(2)

SEEK_SET means that the offset is from the start of the file.
SEEK_CUR means that the offset is from the current position
SEEK_END means that the offset is from the end of the file.

So if you want to advance 8 bytes from your current position, you'd do this:

   lseek(FD: 8: SEEK_CUR);

Here's a page that documents this in a little more detail:
http://www.scottklement.com/rpg/ifs_ebook/random.html#SEEKING

For some reason, you're passing the number 8 for the number of bytes to 
move, and the number -7 for the place to start from.  I have no clue 
what that'd do since -7 isn't a valid value for the 3rd parameter.  I 
suspect that it's assuming that you want to move from the current 
position, and therefore moving you 8 bytes.

It's unclear to me what your routine is SUPPOSED to do, so it's hard for 
me to tell you how to fix it.


Booth Martin wrote:
> I am having fun with writing to the IFS but now its time to update a an 
> IFS file and its not going as easil;y as I expected.
>
> I want to see if a specific string is in the first 500 columns of the 
> file, and if the string is found, replace the string with another 
> value.  For now, the two strings are the same length if that makes a 
> difference.
>
> Here's what I have currently.  It works, but not correctly.
>     eval      wSeeking = 'ho ho ho'
>     for       wNdx = 1 to 500                     
>     callp     lSeek(FD: 8: -7)                 
>     callp     Read(FD: %addr(wValue): 8)      
>     if        wValue = wSeeking                   
>     eval      wNewValue = 'hee hee '              
>     callp     lSeek(FD: 8: -7)                 
>     callp     Write(FD: %addr(wNewValue): 8)  
>     endif                                         
>     endfor    
>
> One problem I know I am having is that I am setting the file over by 8, 
> not by 1.