Re: Use Octave's interpreter in my C++ program...

[John Swensen]

On May 22, 2008, at 5:26 PM, address@hidden wrote:

> Hello,
> I would like to use Octave in a C++ multithreaded application.  Is  
> there
> something like this (see code below) in Octave so I can get an  
> instance of
> Octave and use it throughout the life of my OctaveUser object?  I'll  
> even
> take something close to this. :)
>
> class OctaveUser
> {
>   private:
>     OctaveInstance *p_oi;
>   public:
>    OctaveUser()
>    {
>        oi = OctaveFactory::createInstance();
>    }
>    void cppMethod()
>    {
>        Matrix m(2,2);
>        m(0,0)=1; m(0,1)=2;
>        m(1,0)=3; m(1,1)=4;
>        oi.feval("invert", m);
>
>        // call 'testFromCpp.m' file.
>        octave_value_list result = feval ("testFromCpp", octave_value  
> (m),
> 1 );
>        ...//do something with the value in C++
>    }
>
>    ~OctaveUser()
>    {
>        delete _oi;
>    }
> };
>
> Thanks!
> Molamini

Included is a bit of pseudo-code that I wrote to an Octave user  
offline from the mailing list that I think would be the "meat" of such  
a class.  This listing, however, is unique to the Octave sources since  
the change to the sumbol_table in a singleton class as described in  
the explanation.  Hope this helps.  If I had more time, I would  
implement it, but would be willing to give help if you want to muck  
around with this.  However, take note of David Bateman's warning about  
thread-safety.  I suppose if you ensure you only call into octave one  
command at a time, then Bob is your uncle.

<begin previous email>
I think the better way of doing this would be to create a symbol_record
and insert it into the symbol_table singleton class.  Then you could use
the octave_call() function one the variable that you just pushed into
the octave environment.  Then, pull the resulting variable out of the
symbol_table and pull the data from the contained octave_value().  Below
is a bit of pseudo-code that seems like it should work.  I hope this
helps.  If this does end up working, would you be willing to write and
email to the mailing list with how you did it.  I think this would be
useful for others to know about, since I haven't seen someone do this
before.  Also, not that the pseudocode I give below is based on the most
recent octave from the source code repository.  Between 3.0.x and what
is in the repository, I think there was a major change in the symbol
table.  Before, it was just a global variable.  Now it is a singleton
class.  The changes between 3.0.1 and the current repository tip are
significant, but the basic idea should be the same.

unsigned int imageArry[1024*768];
unsigned int resultImageArry[1024*768];

captureImage (imageArry);

Matrix octImageArry(768,1024); // Note, octave indexes as row x col
// COPY YOUR IMAGE DATA INTO THIS MATRIX
for (int row = 0; row < size; ++row)
{
 for (int column = 0; column < size; ++column)
 {
   // I'm not sure how your image is indexed in memory, so you should  
populate the matrix properly
   octImageArry (row, column) = imageArry[col][row];
 }
}

// Wrap your octave_value Matrix up in a symbol_record object
symbol_table::symbol_record symrec_imageArry ("imageArry",  
octImageArry);

// Insert your symbol_record into the symbol_table
symbol_table::insert_symbol_record (symrec_imageArry);

// Call your routine to process the image
octave_call("resultImageArry=processImageData(imageArry);");

// Pull the newly created symbol record called "resultImageArry" out  
of the symbol_table
symbol_record symrec_resultImageArry =  
symbol_table::find_symbol("resultImageArry");

// Pull the octave_value out of the result symbol_record
octave_value octResultImageArry = symrec_resultImageArry.varval();

// COPY THE DATA OUT OF THIS OCTAVE_VALUE AND BACK INTO YOUR C/C++ ARRAY
<end previous email>