bugGNU Octave - Bugs: bug #65390, scanf sets error message when...

 
 

bug #65390: scanf sets error message when input ends with newline

Submitter:  A.R. Burgers <arb>
Submitted:  Fri 01 Mar 2024 03:10:47 PM UTC
   
 
Category:  Octave Function Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Regression
Status:  Confirmed Assigned to:  None
Originator Name:  Open/Closed:  * Open
Release:  * stable Operating System:  * GNU/Linux
Fixed Release:  None Planned Release:  None
* Mandatory Fields

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Sat 02 Mar 2024 10:06:13 PM UTC, comment #13: 

I checked in jwe's changeset on stable here:

https://hg.savannah.gnu.org/hgweb/octave/rev/9c08824262af

On the development branch, I restored the BIST test that check that the error message is empty:

https://hg.savannah.gnu.org/hgweb/octave/rev/2ff2d201a344

This will now produce a failing test on dev.

Rik <rik5>
Group administrator
Sat 02 Mar 2024 09:45:17 PM UTC, comment #12: 

@Dmitri: I'm fine with checking in jwe's patch for now.  I will include some BIST tests and do that soon.

Rik <rik5>
Group administrator
Sat 02 Mar 2024 07:55:40 PM UTC, comment #11: 

I vote to apply jwe patch and deal with misleading error message post 9.1 release. At the moment a workaround is to specify "\n" explicitly in the format string.


octave:12> s = "1 2\n3 4\n"
s = 1 2
3 4

octave:13> [a,b,c,d] = sscanf (s, '%f %f\n', [2 inf])
a =

   1   3
   2   4

b = 4
c =
d = 9
octave:14>


Dmitri.
--

Dmitri A. Sergatskov <dasergatskov>
Sat 02 Mar 2024 07:43:51 PM UTC, comment #10: 

I just spent an hour on this and am still no closer to a solution.  There are several levels of function calls and the code is manipulating the stream state bits to communicate information in an out-of-band manner up and down the stack.  It would probably be wiser to actually have R/W parameters to the various functions so that we could easily distinguish between a true error on the stream and an EOF which should really just break out of various looping structures.

Rik <rik5>
Group administrator
Sat 02 Mar 2024 06:50:31 PM UTC, comment #9: 

I hate this function, so many corner cases.

@jwe: The patch correctly restores reading two values instead of three.  However, the third output (error message) is wrong.  See below.


octave:1> s = "1 2\n"
s = 1 2

octave:2> [a,b,c,d] = sscanf (s, '%f %f')
a =

   1
   2

b = 2
c = sscanf: format failed to match
d = 5


The output 'c' should be empty because there is no error.


Separately, bug #63467 is definitely related and is also solved by jwe's patch.

Rik <rik5>
Group administrator
Sat 02 Mar 2024 01:10:30 AM UTC, comment #8: 
Hendrik K <koerhen>
Fri 01 Mar 2024 10:37:11 PM UTC, comment #7: 

Works for me.

Dmitri.
--

Dmitri A. Sergatskov <dasergatskov>
Fri 01 Mar 2024 10:18:41 PM UTC, comment #6: 

Maybe the attached change?  It attempts to make the stream state handling for floating point conversions (performed in the octave_scan_conv<double> specialization) the same as what is used in the octave_scan_1 function that is used to process integer conversions.



(file #55762)

John W. Eaton <jwe>
Group administrator
Fri 01 Mar 2024 07:31:38 PM UTC, comment #5: 

Confirmed.  Changing release to stable as the bug is present there as well.

Rik <rik5>
Group administrator
Fri 01 Mar 2024 07:25:57 PM UTC, comment #4: 

Bisected to:

changeset:   31542:2f08a53e0a23
parent:      31540:ce5b4a00b022
user:        Rik <rik@octave.org>
date:        Fri Nov 25 08:30:30 2022 -0800
summary:     Fix scanf handling of exceptional values (NA, NaN, Inf) at EOF (bug #63383)


31540 is good, 31542 is bad.

Dmitri.
--

Dmitri A. Sergatskov <dasergatskov>
Fri 01 Mar 2024 06:09:49 PM UTC, comment #3: 

The same with "sscanf":

octave:1> s1 = sprintf("1 2")
s1 = 1 2
octave:2> a1 = sscanf(s1, '%f  %f')
a1 =

   1
   2

octave:3> s2 = sprintf("1 2\n")
s2 = 1 2

octave:4> a2 = sscanf(s2, '%f  %f')
a2 =

   1
   2
   2


So "\n" seems to break the "Xscanf"

Dmitri.
--

Dmitri A. Sergatskov <dasergatskov>
Fri 01 Mar 2024 03:51:08 PM UTC, comment #2: 

This is also regression. I cannot reproduce this on octave 8.4 nor  7.3.

Dmitri.
--

Dmitri A. Sergatskov <dasergatskov>
Fri 01 Mar 2024 03:31:12 PM UTC, comment #1: 

Confirmed with 9.0.91. A simplified case:

$ cat tst2.dat
1        2

octave:1> fd = fopen("tst2.dat", "r")
fd = 19
octave:2> ar = fscanf(fd, '%f  %f')
ar =

   1
   2
   2


Dmitri.
--

Dmitri A. Sergatskov <dasergatskov>
Fri 01 Mar 2024 03:10:47 PM UTC, original submission:  

This example shows a case where fscanf fails I think to correctly read an input:


np = 101;
x = linspace(0, 1, np)';
a = [x, x.^2];
dlmwrite('tst.dat', a, '\t');
fd = fopen('tst.dat', 'r');
ar = fscanf(fd, '%g %g', [2, Inf])';
fclose(fd);
ar(np - 5: end, :)
try
  [a(np - 5 : end, :), ar(np - 5 : end, :)]
catch me
  error('ran into %s', me.message);
end


octave output, featuring an extra row at the end:


ans =
   0.9500   0.9025
   0.9600   0.9216
   0.9700   0.9409
   0.9800   0.9604
   0.9900   0.9801
   1.0000   1.0000
   1.0000        0

error: ran into horizontal dimensions mismatch (6x2 vs 7x2)
error: called from
    tst at line 12 column 3


matlab output:


ans =
    0.9500    0.9025
    0.9600    0.9216
    0.9700    0.9409
    0.9800    0.9604
    0.9900    0.9801
    1.0000    1.0000

ans =
    0.9500    0.9025    0.9500    0.9025
    0.9600    0.9216    0.9600    0.9216
    0.9700    0.9409    0.9700    0.9409
    0.9800    0.9604    0.9800    0.9604
    0.9900    0.9801    0.9900    0.9801
    1.0000    1.0000    1.0000    1.0000


A.R. Burgers <arb>

 

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Attached Files
file #55762:  scanf-patch.txt added by jwe (1KiB - text/plain)

 

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Items that depend on this one: None found

 

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    Follow 6 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2024-03-02 rik5 Summaryfscanf produces 1 line too much scanf sets error message when input ends with newline
    2024-03-02 rik5 Dependencies- Depends on bugs #63467
    2024-03-01 jwe Attached File- Added scanf-patch.txt, #55762
    2024-03-01 rik5 Item GroupIncorrect Result Regression
        StatusNone Confirmed
        Releasedev stable

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