Class members that MUST be initialized by temporary objects in amember initialization list

[Olumide]

Hello C++ gurus,

I've got this basic class thats the backbone of my project and I
frequently use use an instance of it to initialize other objects like
so. However, my latest class, a simple assignment in a constructor did
not work, like so:

class VeryBasicClass{
public:
VeryBasicClass(){};
};

class LatestClass{
public:
LatestClass( VeryBasicClass &vbo );
private:
VeryBasicClass veryBasicObject;
};

LatestClass::LatestClass( VeryBasicClass &vbo )
{
veryBasicObject = vbo; // this does not work
// halts plugin execution
}

The following constructor caused the environment (I'm developing a
plugin) to crash with a BLOCK_TYPE_IS_VALID assert

LatestClass::LatestClass( VeryBasicClass &vbo ):veryBasicObject( vbo )
{
}

The following constructor however worked

LatestClass::LatestClass( VeryBasicClass
&vbo ):veryBasicObject( VeryBasicObject() )
{
}

I would know why the first why the first two constructors failed, and
the only the third works, and I'd hate to be in the dark about these
things. Its better to know whats going on in case something goes
wrong.

All thats unique about VeryBasicClass is that itself contains a member
object that must be initialized by a temporary object in a member
initialization lists of a constructor. I'm not the author of the
members class (its part of the plugin API).

Thanks

- Olumide

[Andre Kostur]

Olumide <50***@web.dewrote in news:30b3ed9c-fdfb-4d2a-b38f-
11**********@t47g2000hsc.googlegroups.com:

Hello C++ gurus,

I've got this basic class thats the backbone of my project and I
frequently use use an instance of it to initialize other objects like
so. However, my latest class, a simple assignment in a constructor did
not work, like so:

class VeryBasicClass{
public:
VeryBasicClass(){};
};

class LatestClass{
public:
LatestClass( VeryBasicClass &vbo );
private:
VeryBasicClass veryBasicObject;
};

LatestClass::LatestClass( VeryBasicClass &vbo )
{
veryBasicObject = vbo; // this does not work
// halts plugin execution
}

The following constructor caused the environment (I'm developing a
plugin) to crash with a BLOCK_TYPE_IS_VALID assert

LatestClass::LatestClass( VeryBasicClass &vbo ):veryBasicObject( vbo )
{
}

The following constructor however worked

LatestClass::LatestClass( VeryBasicClass
&vbo ):veryBasicObject( VeryBasicObject() )
{
}

I would know why the first why the first two constructors failed, and
the only the third works, and I'd hate to be in the dark about these
things. Its better to know whats going on in case something goes
wrong.

All thats unique about VeryBasicClass is that itself contains a member
object that must be initialized by a temporary object in a member
initialization lists of a constructor. I'm not the author of the
members class (its part of the plugin API).

To paraphrase your answer: "The only interesting part of VeryBasicClass
is the part I'm not going to show you".

Provide a _minimal_, _compilable_ example which shows your problem.

[James Kanze]

On Dec 6, 3:53 am, "Alf P. Steinbach" <[e-mail]:

* Olumide:

I've got this basic class thats the backbone of my project and I
frequently use use an instance of it to initialize other objects like
so. However, my latest class, a simple assignment in a constructor did
not work, like so:

class VeryBasicClass{
public:
VeryBasicClass(){};
};

class LatestClass{
public:
LatestClass( VeryBasicClass &vbo );
private:
VeryBasicClass veryBasicObject;
};

LatestClass::LatestClass( VeryBasicClass &vbo )
{
veryBasicObject = vbo; // this does not work
// halts plugin execution
}

The following constructor caused the environment (I'm
developing a plugin) to crash with a BLOCK_TYPE_IS_VALID
assert

Hmmm. It doesn't cause any problems in my environment. Are you
sure you're showing us the complete code, and that
VeryBasicClass is really that simple.

LatestClass::LatestClass( VeryBasicClass &vbo ):veryBasicObject( vbo )
{
}

The following constructor however worked

LatestClass::LatestClass( VeryBasicClass
&vbo ):veryBasicObject( VeryBasicObject() )
{
}

I would know why the first why the first two constructors failed, and
the only the third works, and I'd hate to be in the dark about these
things. Its better to know whats going on in case something goes
wrong.

All thats unique about VeryBasicClass is that itself
contains a member object that must be initialized by a
temporary object in a member initialization lists of a
constructor. I'm not the author of the members class (its
part of the plugin API).

It seems that at the end of writing the above, in the very
last paragraph, a glimmer of insight started to surface. Try
to follow that thought. All that came before is worthless for
diagnosing what the technical problem is.

I'm not that sure. What's the difference between the last two?
About the only thing I can see is that there is something wrong
in the copy constructor of VeryBasicClass, and that the compiler
optimizes the actual call of the copy constructor out in the
last case.

The fact remains that the code he has posted is fine. But since
the code he has posted isn't the code which is causing him
problems, that doesn't help us (or him) much.

--
James Kanze (GABI Software) email:ja*********@gmail.com
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