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

[Stephen Sinclair]

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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>
>
>
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