[clug] stdio library, feof(3) can't detect EOF in a script [was Re: using 'dd' in a pipeline.]

steve jenkin sjenkin at canb.auug.org.au
Mon Nov 24 19:22:12 MST 2014

On 25 Nov 2014, at 11:10 am, John Mills <johnmi at effect.net.au> wrote:

> Well, my solution is not correct. Nor complete so far...:-)


Thanks for continuing to help and work through this.

How many mistakes can I make in the one thread?
Apparently it’s unlimited :)
My bad for not actually running your script & checking for myself :(

I checked and stdio (fread()) ignored / deleted nulls, at least on one system. Not sure how to count the nulls (\0) in those files.

This behaviour goes back to the earliest days of ‘C’ where everything was an int and logical “false” was zero, “true” was non-zero, nulls marked the end of strings [still do] and simple input/output was not “8-bit safe”...

This, roughly, was all you needed to copy from stdin to stdout. No, I haven’t compiled any version of this :)

 while (ch=getc(stdin))
    (void) putc(ch, stdout) ;

It incorrectly terminates when a null is encountered (at least, it used to).
While stdio library is very useful for line-based text, if you needed to process binary files, read(2) & write(2) syscalls were needed - which meant handling buffering and syncs yourself.

All my best

Steve Jenkin, IT Systems and Design 
0412 786 915 (+61 412 786 915)
PO Box 48, Kippax ACT 2615, AUSTRALIA

mailto:sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin

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