[Octave-bug-tracker] [bug #50050] MEX mxAssert macro expands wrongly.

[Kai Torben Ohlhus]

URL:
  <http://savannah.gnu.org/bugs/?50050>

                 Summary: MEX mxAssert macro expands wrongly.
                 Project: GNU Octave
            Submitted by: siko1056
            Submitted on: Fri 13 Jan 2017 05:54:33 PM CET
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: Need Info
             Assigned to: siko1056
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.2.0
        Operating System: Any

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Details:

The SeDuMi bug tracker filed a bug https://github.com/sqlp/sedumi/issues/24
that seems to be more an issue of Octave. I assume the source of the error to
lie inside the if statement of lines 311 and 328 in
http://hg.savannah.gnu.org/hgweb/octave/file/tip/libinterp/corefcn/mexproto.h

namely


if (! expr)


I created the following MCVE mex file to check my assumption. Basically, it
does the same as the erroneous file from the SeDuMi-Tracker, namely checking
that there is at least one input and at most one output:


#include "mex.h"

/* mex -g mxAssertError.c; clear -f; clear all; a = mxAssertError(1,2) */

void mexFunction( int nlhs, mxArray *plhs[],
  int nrhs, const mxArray *prhs[])
{
  mexPrintf ("nrhs = %d\n", nrhs);
  mexPrintf ("nlhs = %d\n", nlhs);
  mexPrintf ("!nrhs = %d\n", !nrhs);
  mexPrintf ("!nlhs = %d\n", !nlhs);
  mexPrintf (" !nrhs  >= 1  = %d\n",  !nrhs  >= 1);
  mexPrintf ("(!nrhs) >= 1  = %d\n", (!nrhs) >= 1);
  mexPrintf ("!(nrhs  >= 1) = %d\n", !(nrhs  >= 1));
  mexPrintf (" !nlhs  <= 1  = %d\n", ! nlhs  <= 1);
  mexPrintf ("(!nlhs) <= 1  = %d\n", (!nlhs) <= 1);
  mexPrintf ("!(nlhs  <= 1) = %d\n", !(nlhs  <= 1));

  mxAssert ( nrhs >= 1 , "works.");
  mxAssert ((nrhs >= 1), "works.");
  mxAssert ((nlhs <= 1), "works.");
  mxAssert ( nlhs <= 1 , "does not work in Octave.");
  
  plhs[0] = mxCreateDoubleMatrix(1,1,mxREAL);
}


Matlab R2016b does:


>> mex -g mxAssertError.c; clear -f; clear all; a = mxAssertError(1,2)
Building with 'gcc'.
Warning: You are using gcc version '6.2.1'. The version of gcc is not
supported. The version currently
supported with MEX is '4.9.x'. For a list of currently supported compilers
see:
http://www.mathworks.com/support/compilers/current_release. 
MEX completed successfully.
nrhs = 2
nlhs = 1
!nrhs = 0
!nlhs = 0
 !nrhs  >= 1  = 0
(!nrhs) >= 1  = 0
!(nrhs  >= 1) = 0
 !nlhs  <= 1  = 1
(!nlhs) <= 1  = 1
!(nlhs  <= 1) = 0

a =

     0

>> 


and Octave 4.2.0:


>> mex -g mxAssertError.c; clear -f; clear all; a = mxAssertError(1,2)

nrhs = 2
nlhs = 1
!nrhs = 0
!nlhs = 0
 !nrhs  >= 1  = 0
(!nrhs) >= 1  = 0
!(nrhs  >= 1) = 0
 !nlhs  <= 1  = 1
(!nlhs) <= 1  = 1
!(nlhs  <= 1) = 0
error: mxAssertError: Assertion failed: nlhs <= 1, at line 22 of file
"mxAssertError.c".
does not work in Octave.


Do you agree, that the Macros expand in a wrong fashion?

My suggested fix is 


if (! (expr))


in the two lines, what works for me. I would also like to apply this patch to
stable for 4.2.1.

Another issue is, that why is mxAssert expanded anyways? I thought it was only
available with "mex -g", but SeDuMi compiles without "-g". Maybe another bug?




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