The following tests failed on a Solaris build:

>>>>> processing /export/home/eaton/local/build/octave-4.4.1-rc1/liboctave/util/oct-inttypes.cc-tst
***** assert (uint8 (char (128)), uint8 (128))
!!!!! test failed
ASSERT errors for:  assert (uint8 (char (128)),uint8 (128))

  Location  |  Observed  |  Expected  |  Reason
     ()           0           128        Abs err 128 exceeds tol 0 by 1e+02
***** assert (uint8 (char (255)), uint8 (255))
!!!!! test failed
ASSERT errors for:  assert (uint8 (char (255)),uint8 (255))

  Location  |  Observed  |  Expected  |  Reason
     ()           0           255        Abs err 255 exceeds tol 0 by 3e+02
***** assert (int8 (char (128)), int8 (128))
!!!!! test failed
ASSERT errors for:  assert (int8 (char (128)),int8 (128))

  Location  |  Observed  |  Expected  |  Reason
     ()          -128         127        Abs err 255 exceeds tol 0 by 3e+02
***** assert (int8 (char (255)), int8 (255))
!!!!! test failed
ASSERT errors for:  assert (int8 (char (255)),int8 (255))

  Location  |  Observed  |  Expected  |  Reason
     ()           -1          127        Abs err 128 exceeds tol 0 by 1e+02
***** assert (uint16 (char (128)), uint16 (128))
!!!!! test failed
ASSERT errors for:  assert (uint16 (char (128)),uint16 (128))

  Location  |  Observed  |  Expected  |  Reason
     ()           0           128        Abs err 128 exceeds tol 0 by 1e+02
***** assert (uint16 (char (255)), uint16 (255))
!!!!! test failed
ASSERT errors for:  assert (uint16 (char (255)),uint16 (255))

  Location  |  Observed  |  Expected  |  Reason
     ()           0           255        Abs err 255 exceeds tol 0 by 3e+02
***** assert (int16 (char (128)), int16 (128))
!!!!! test failed
ASSERT errors for:  assert (int16 (char (128)),int16 (128))

  Location  |  Observed  |  Expected  |  Reason
     ()          -128         128        Abs err 256 exceeds tol 0 by 3e+02
***** assert (int16 (char (255)), int16 (255))
!!!!! test failed
ASSERT errors for:  assert (int16 (char (255)),int16 (255))

  Location  |  Observed  |  Expected  |  Reason
     ()           -1          255        Abs err 256 exceeds tol 0 by 3e+02
***** assert (uint32 (char (128)), uint32 (128))
!!!!! test failed
ASSERT errors for:  assert (uint32 (char (128)),uint32 (128))

  Location  |  Observed  |  Expected  |  Reason
     ()           0           128        Abs err 128 exceeds tol 0 by 1e+02
***** assert (uint32 (char (255)), uint32 (255))
!!!!! test failed
ASSERT errors for:  assert (uint32 (char (255)),uint32 (255))

  Location  |  Observed  |  Expected  |  Reason
     ()           0           255        Abs err 255 exceeds tol 0 by 3e+02
***** assert (int32 (char (128)), int32 (128))
!!!!! test failed
ASSERT errors for:  assert (int32 (char (128)),int32 (128))

  Location  |  Observed  |  Expected  |  Reason
     ()          -128         128        Abs err 256 exceeds tol 0 by 3e+02
***** assert (int32 (char (255)), int32 (255))
!!!!! test failed
ASSERT errors for:  assert (int32 (char (255)),int32 (255))

  Location  |  Observed  |  Expected  |  Reason
     ()           -1          255        Abs err 256 exceeds tol 0 by 3e+02
***** assert (uint64 (char (128)), uint64 (128))
!!!!! test failed
ASSERT errors for:  assert (uint64 (char (128)),uint64 (128))

  Location  |  Observed  |  Expected  |  Reason
     ()           0           128        Abs err 128 exceeds tol 0 by 1e+02
***** assert (uint64 (char (255)), uint64 (255))
!!!!! test failed
ASSERT errors for:  assert (uint64 (char (255)),uint64 (255))

  Location  |  Observed  |  Expected  |  Reason
     ()           0           255        Abs err 255 exceeds tol 0 by 3e+02
***** assert (int64 (char (128)), int64 (128))
!!!!! test failed
ASSERT errors for:  assert (int64 (char (128)),int64 (128))

  Location  |  Observed  |  Expected  |  Reason
     ()          -128         128        Abs err 256 exceeds tol 0 by 3e+02
***** assert (int64 (char (255)), int64 (255))
!!!!! test failed
ASSERT errors for:  assert (int64 (char (255)),int64 (255))

  Location  |  Observed  |  Expected  |  Reason
     ()           -1          255        Abs err 256 exceeds tol 0 by 3e+02

This is happening because the overload for constructing intNDArray<T> objects from char is not defined because OCTAVE_HAVE_OVERLOAD_CHAR_INT8_TYPES is not defined.  This configuration variable is set correctly, as these overloads are not possible on this system.  So we need another solution for storing or converting character types.

The constructor is in oct-inttypes.h:

#if defined (OCTAVE_HAVE_OVERLOAD_CHAR_INT8_TYPES)
  // Always treat characters as unsigned.
  octave_int (char c)
    : ival (octave_int_base<T>::truncate_int (static_cast<unsigned char> (c)))
  { }
#endif

It would be good if we could do this at the level of intNDArray<T>, but if not, we will have to do it by overloading the as_{u,}int{8,16,32,64} functions in octave_value and fixing any other locations where this constructor is called individually.

I set the OS field to Solaris/SunOS because that's where the bug was discovered, but this probably applies to any system where OCTAVE_HAVE_OVERLOAD_CHAR_INT8_TYPES is not defined.  If you force that value on another system, you should see the same problem.

There is also one more place in oct-stream.cc where this configuration variable is used, but in that case, it should not change behavior.