From help-request at octave dot org Mon Jul 25 04:54:31 2005
Subject: Re: Octave/C++
From: Mike Morley <mjm80 at cam dot ac dot uk>
To: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
Cc: help at octave dot org
Date: 25 Jul 2005 10:50:45 +0100

I tried the code you provided this morning linking to the header files, and 
it appears to work.

The problem I now have is how do I run commands to the robot?

I've looked at make_int.cc but I don't really understand the syntax I need 
to use to make things work.

Ideally, what I need is some way of issuing a command in octave like:

robotcommand (robot, motor1go, speed) that would run the C++ command 
robot.command (MOTOR_1_GO, speed)

So what I guess I need is some switch statement to convert the string into 
the appropriate robot command statement, and then pick up the other 
variable to pass to the robot. However, I'm not sure how to implement this.

Mike


On Jul 22 2005, John W. Eaton wrote:

> On 22-Jul-2005, Mike Morley wrote:
> 
> | It occured to me that I needed to allocate some memory to my robot, 
> | otherwise it would cease to be when the C++ subroutine exited. I now 
> | have the code:
> | 
> | #include<iostream>
> | #include<octave/oct.h>
> | #include<octave/dynamic-ld.h>
> 
> You probably don't need to include dynamic-ld.h.
> 
> | #include<string>
> | 
> | using namespace std;
> 
> I would recommend avoiding this and instead prefixing all the names
> you actually use from the std namespace with "std::".
> 
> | extern "C" {
> |   #include "robot_instr.h"
> |   #include "robot_link.h"
> | }
> 
> This works, but it would be better if the robot_instr.h and
> robot_link.h files could be mad C++ friendly.
> 
> | class Bot: public octave_base_value
> | {
> |  public:
> |   //constructor
> |   Bot(void): octave_base_value()
> |   {
> |     robot_link robot;
> |   }
> 
> This doesn't look right.  It simply creates a local variable in the
> constructor, which will disappear when the constructor exits.  Perhaps
> you want to have a robot_link object as a class data member, and
> then a constructor like
> 
>   Bot (void) : robot (), octave_base_value () { }
> 
> (assuming the robot_link object is called robot)?
> 
> 
> |   //destructor
> |   ~Bot(void)
> |   {
> |       delete this;
> |   }
> 
> It is almost certainly an error to "delete this".  Your constructor
> doesn't use new, so your destructor should not use delete.
> 
> |   DEFUN_DLD(BotMake,,nargouts,
> | 	    "BotMake creates a new robot to link in to")
> | {
> |     Bot *b = new Bot();
> |   return octave_value(b);
> | }
> 
> |   DEFUN_DLD(BotKill,args,,
> | 	    "BotKill destroys the Bot")
> | {
> |   if (args.length() == 1) {
> |     delete ((Bot*)&args(0));
> |   }
> | }
> 
> I dont' think you really want this function.  When the octave_value
> object that holds your Bot object is deleted, it will call the
> destructor for its Rep object, which will delete the memory.
> 
> Here is a complete working example (but using a simple typedef for the
> robot_link object, so that I could avoid having to find the files for
> that):
> 
> #include<iostream>
> #include<octave/oct.h>
> 
> typedef int robot_link;
> 
> class Bot : public octave_base_value
> {
> public:
> 
>   Bot (void) : robot (), octave_base_value () { }
> 
>   bool is_defined (void) const { return true; }
> 
> private:
> 
>   robot_link robot;
> 
>   DECLARE_OCTAVE_ALLOCATOR
> 
>   DECLARE_OV_TYPEID_FUNCTIONS_AND_DATA
> };
> 
> DEFINE_OCTAVE_ALLOCATOR (Bot);
> 
> DEFINE_OV_TYPEID_FUNCTIONS_AND_DATA (Bot, "Bot", "Bot");
> 
> DEFUN_DLD (BotMake, , ,
> 	   "BotMake creates a new robot to link in to")
> {
>   static bool type_loaded = false;
> 
>   if (! type_loaded)
>     {
>       Bot::register_type ();
>       mlock ("BotMake");
> 
>       // Install Bot ops here...
>     }
> 
>   octave_value retval;
> 
>   return octave_value (new Bot ());
> }
> 
> Compiling this with
> 
>   mkoctfile BotMake.cc
> 
> and running
> 
>   while true, x = BotMake; end
> 
> in Octave does not result in a memory leak.
> 
> You will need a few more functions in your Bot class to make it
> useful.  See the example make_int.cc that is included in the Octave
> sources.
> 
> jwe
> 
> 
> 
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> 

-- 
            Mike Morley -  Trinity College           
               Part IB Natural Sciences

 E1 Burrell's Field | mjm80 at cam dot ac dot uk|  | 07862 282608

    First & Third Trinity Boat Club May Ball 2005
mike at trinityball dot co dot uk| | || publicity@trinityball.co.uk

    Cambridge Union Society -- External Committee






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Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
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