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

[Gary Scavone]

Hi Nick and Stephen,

I didn't have a problem compiling and running either example using gcc 4.2.1 on OS-X.  Again, did you check to make sure you were using the latest release of STK?

--gary

On 2013-06-19, at 12:43 PM, Stephen Sinclair <sinclair at music.mcgill.ca> wrote:

> By the way, I tried compiling STK without the errorString_ member
> variable and then your initial examples worked fine.  I guess the
> lesson is that an ostringstream is not a "value" and can't be copied,
> so shouldn't be used to contain data, but only to construct it.
> 
> On Wed, Jun 19, 2013 at 6:03 PM, Nick Dika <nhdika at gmail.com> wrote:
>> 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
>>> 
>>> _______________________________________________
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>>> Stk at ccrma.stanford.edu
>>> http://ccrma-mail.stanford.edu/mailman/listinfo/stk
>> 
>> 
>> 
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