Re: multiple plot lines with plot '-'

[Ethan A M. <sf...@us...>]

On Friday, May 18, 2012 02:25:15 am pl...@pi... wrote:
> If you are suggesting that associating a file descriptor with a file; 
> opening; reading; closing; reopening (with implies a seek(0) ) ; and 
> rereading   is the same as opening ; reading upto 'e' marker *in the 
> data* then continuing to read the same opened device,  I have to say 
> your reasoning is getting a bit contrived.
> 
> I find it hard to see that as being the same behaviour.

Nevertheless, from the point of view of the program itself, or of the
programmers working on it, these cases are handled exactly the same way.
You can find the code near the top of the routine df_open() in datafile.c

In pseudocode:

   if (*filename == '-')
		data_fp = stdin;
   else if (*filename == '<')
		data_fp = fpopen( some piped command stored in filename );
   else 
		data_fp = fopen( filename );

Other routines then read line by line from data_fp as needed.
In two of the three cases, pipe and stdin, backing up to the beginning
in order to re-read is not possible. The code never uses fseek().

	Ethan