[Stk] unhandled exception when using BlitSaw with std::vector

[Nick Dika]

Thanks Stephen for your detailed explanation. I realize what I was doing
with the array example was sloppy, the goal was really to get it working
with Vector and push_back() so that I can scale the container as needed. I
will try your suggestion later and see if I'm able to get it working.

n


On Wed, Jun 19, 2013 at 9:45 AM, Stephen Sinclair
<sinclair at music.mcgill.ca>wrote:

> Hi Nick,
>
> On Wed, Jun 19, 2013 at 3:09 PM, Nick Dika <nhdika at gmail.com> wrote:
> > Thanks Stephen. Here's a simplified version of what I'm doing.
> >
> > This works:
> >
> > stk::BlitSaw oscArray[10];
> >
> > for( int i=0; i < 10; i++ )
> > {
> > stk::BlitSaw saw;
> > saw.setHarmonics(0);
> > saw.setFrequency(220);
> > oscArray[i] = saw;
> > }
>
> Actually in g++-4.7 at least, this code does not compile.  The BlitSaw
> class is unassignable.
>
> (I'm not 100% sure why, but it seems to be because objects of class
> Stk contain a std::ostringstream member which is unassignable.)
>
>
> > This breaks:
> >
> > std::vector<stk::BlitSaw> oscs;
> >
> > for( int i=0; i < 10; i++ )
> > {
> > stk::BlitSaw saw;
> > saw.setHarmonics(0);
> > saw.setFrequency(220);
> > oscs.push_back(saw);
> > }
>
> This is effectively equivalent to the above code so I'm not 100% why
> it's breaking things but probably the object is not being properly
> copied within the vector.  In particular, since you have a vector of
> instances of BlitSaw, when the internal array in the std::vector is
> re-allocated, perhaps the new, copied memory is not properly
> initialized 100%, since the object type is not assignable.  Just a
> guess, but it's weird behaviour for sure, but due to undefined
> behaviour because this isn't how you should do what you're trying to
> do.
>
> >
> > the second example causes an unhandled exception/access violation reading
> > from a location. As mentioned this appears to happen after
> > StkFrames::resize() is called (I don't fully understand why this would be
> > called).
>
> All Generators, which BlitSaw is one, have an StkFrame called
> lastFrames_, and it's resize() method is called during initialization.
>  Not sure why it's leading to an exception but like your array doesn't
> contain valid BlitSaw instances.
>
> Anyways, to elaborate, the way you're initializing things isn't
> fundamentally wrong, so it could indicate some bugs somewhere, but
> it's certainly not the ideal way to work with Stk objects.  You are
> creating an array of objects, such that their constructors are called,
> and then a loop you are constructing a new object on the stack,
> setting its parameters, and then copying that object over top of the
> objects already in the array and letting it destruct.  Not the most
> efficient approach.
>
> (Note, your push_back() call also doesn't compile in g++-4.7.)
>
> Instead I'd suggest either directly initializing the objects that are
> already in the array, or initializing them and then storing their
> pointers in the array.  i.e., either:
>
> #include <iostream>
> #include <Stk.h>
> #include <BlitSaw.h>
>
> int main()
> {
>     stk::BlitSaw oscs[10];
>
>     for( int i=0; i < 10; i++ )
>     {
>         stk::BlitSaw *saw = &oscs[i];
>         saw->setHarmonics(0);
>         saw->setFrequency(220);
>     }
>
>     return 0;
> }
>
>
> .. or ..
>
>
> #include <iostream>
> #include <memory>
> #include <Stk.h>
> #include <BlitSaw.h>
>
> int main()
> {
>     std::vector<std::unique_ptr<stk::BlitSaw>> oscs;
>
>     for( int i=0; i < 10; i++ )
>     {
>         std::unique_ptr<stk::BlitSaw> saw(new stk::BlitSaw);
>         saw->setHarmonics(0);
>         saw->setFrequency(220);
>         oscs.push_back(std::move(saw));
>     }
>
>     return 0;
> }
>
>
> Steve
>
> _______________________________________________
> Stk mailing list
> Stk at ccrma.stanford.edu
> http://ccrma-mail.stanford.edu/mailman/listinfo/stk
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://ccrma-mail.stanford.edu/pipermail/stk/attachments/20130619/22fb074d/attachment-0001.html