Re: newline in strread format

[Daniel J Sebald]

On 06/23/2014 10:57 PM, John W. Eaton wrote:
> I think the following should work, but it's throwing an error:
>
> octave:1> [a, b, c] = strread ("1 2 3\n4 5 6\n7 8 9\n", "%f %f %f\n")
> strread: FORMAT does not match data
> error: called from 'strread' in file
> /home/jwe/src/octave-stable/scripts/io/strread.m near line 745, column 13
> error: called from:
> error: /home/jwe/src/octave-stable/scripts/io/strread.m at line 755,
> column 9
>
> I took a look at strread.m but I'm not sure what the right approach is
> for a fix. It appears to me that newlines are removed from the string
> and that it is split on the field delimiter. But the newline
> character remains in the list of format specifiers.
>
> I noticed the problem in the stable sources, but it seems to also be
> present in the current sources on the default branch.
>
> Any clues would be much appreciated.

I suppose that "\n" could in theory be a valid literal.  That's where 
the interpretation part of this routine is failing, i.e., "\n" as not 
being accepted as a literal.  Consider that the following works:

octave:3> [a, b, c] = strread ("1 2 3L\n4 5 6L\n7 8 9L\n", "%f %f %fL")
a =

   1
   4
   7

b =

   2
   5
   8

c =

   3
   6
   9

The newline character is always the character that can be treated as a 
"new line" in the data string.  That is, if we replace literal "L" with 
"\n":

[a, b, c] = strread ("1 2 3\n\n4 5 6\n\n7 8 9\n\n", "%f %f %f\n")

one would think that we should get the same result.  (Notice the two 
newline characters in the data string.)  But that fails as well.

octave:4> [a, b, c] = strread ("1 2 3\n\n4 5 6\n\n7 8 9\n\n", "%f %f %f\n")
strread: FORMAT does not match data
error: called from 'strread' in file 
/usr/local/src/octave/octave-for_loop_test/build-dev/../octave-dev/scripts/io/strread.m 
near line 745, column 13
error: called from:
error: 
/usr/local/src/octave/octave-for_loop_test/build-dev/../octave-dev/scripts/io/strread.m 
at line 755, column 9

One could maybe make sense of the single literal newline characters in 
the following way:

octave:4> [a, b, c, d, e, f, g, h, i] = strread ("1 2 3\n4 5 6\n7 8 
9\n", "%f %f %f\n%f %f %f\n%f %f %f\n")
warning: strread: unable to parse text or file with given format string
warning: called from
    strread at line 659 column 7
error: element number 1 undefined in return list

but as seen above, that fails too.

Dan