[Octave-bug-tracker] [bug #54527] Crash when concatenating empty elements with sparse matrices.

[Rik]

Follow-up Comment #4, bug #54527 (project octave):

The problem seems to be in Sparse.cc with the cat function.

There is this bit of code which is designed to handle concatenating empty
matrices


const Sparse<T>& spi = sparse_list[i];
// Skipping empty matrices.  See the comment in Array.cc.
if (spi.isempty ())
  continue;


Using gdb, I get


(gdb) display-sparse-array spi
sparse object: (const Sparse<double> &) @0x1fe7f10: {
  _vptr.Sparse = 0x7f33ae18d5b0 <vtable for SparseMatrix+16>, rep = 0x2277af0,

  dimensions = {rep = 0x1fcff50}}
dimensions.rep[0] = ndims: 2
dims: {1, 0}

dimensions.rep[1] = 0
rep = {d = 0x0, r = 0x0, c = 0x1ff4770, nzmx = 0, nrows = 1, ncols = 0, count
= {
    count = 1}}
rep.d = Invalid number 0 of repetitions.
(gdb) p spi.isempty ()
$3 = false
(gdb) p spi.numel ()
$4 = 0


The killer is that isempty () is returning false for this very empty matrix.

Looking at isempty in Sparse.h I find


  bool isempty (void) const { return (rows () < 1 && cols () < 1); }


That looks very suspect.  I think '&&' should be '||' in this case.  Or maybe
we should just do things the way we do in Array.h


Array.h:  bool isempty (void) const { return numel () == 0; }




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