[Octave-bug-tracker] [bug #48185] mexCallMATLAB doesn't exit mex file on error on first call

[Joseph Young]

URL:
  <http://savannah.gnu.org/bugs/?48185>

                 Summary: mexCallMATLAB doesn't exit mex file on error on
first call
                 Project: GNU Octave
            Submitted by: josyoun
            Submitted on: Thu 09 Jun 2016 01:57:32 AM GMT
                Category: Interpreter
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: josyoun
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.0
        Operating System: GNU/Linux

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Details:

It doesn't look like mexCallMATLAB exits the routine when an error occurs on
the first call.  Subsequent calls exit normally.  In general, mexCallMATLAB
should immediately exit the mex file on error, which makes the return value a
little superfluous.  Consider the code:

$ cat test01.cpp 
#include "mex.h"
#include <array>
#include <iostream>

void mexFunction(
    int nOutput,mxArray* pOutput[],
    int nInput,mxArray const * pInput[]
) try {

    // Calling convention should be
    // f_x = test01(f,x)
    auto f = const_cast <mxArray*> (pInput[0]);
    auto x = const_cast <mxArray*> (pInput[1]);

    // Call the function
    auto input = std::array <mxArray *,2> {f,x};
    auto output = std::array <mxArray *,1> ();
    auto err=mexCallMATLAB(1,output.data(),2,input.data(),"feval");
    if(err)
        throw std::runtime_error("There's a MATLAB/Octave error");

    // Assign the return value
    pOutput[0]=output[0];

    // Return nothing
    return;

} catch(std::runtime_error const & e) {
    std::cerr << "Exception!!!!!" << std::endl;
    return;
}

which is compiled with:

g++ -std=c++14 -g -fPIC -I /usr/include/octave-4.0.0/octave/ test01.cpp
-shared -o test01.mex

And the driver code:

$ cat driver01.m
f = @(x)x+1
x = {1}
y = test01(f,x)

This should error since we can't add a cell array to a number.  When we run
the routine:

$ octave
octave: no graphical display found
octave: disabling GUI features
GNU Octave, version 4.0.0
Copyright (C) 2015 John W. Eaton and others.
This is free software; see the source code for copying conditions.
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octave:1> driver01
f =

@(x) x + 1

x = 
{
  [1,1] =  1
}
error: binary operator '+' not implemented for 'cell' by 'scalar' operations
error: called from
    driver01> at line -1 column -1
    driver01 at line 3 column 3
Exception!!!!!
y = [](0x0)

We see that the exception is thrown and that y is assigned a null value.  If
we run the routine a second time:

octave:2> driver01
f =

@(x) x + 1

x = 
{
  [1,1] =  1
}
error: binary operator '+' not implemented for 'cell' by 'scalar' operations
error: called from
    driver01> at line -1 column -1
    driver01 at line 3 column 3

The exception is not thrown and y is not assigned a value.  I believe the
behavior in the second case to be correct and the behavior in the first case
to be a bug.




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