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Use of static keyword instead of global object

P: n/a
Hi,

I wish to share an object through a bunch of functions without
declaring it globally. I have achieved this through the following
function:

VideoReceiver* getReceiver()
{
static VideoReceiver *vr = new VideoReceiver();
return vr;
}

So, the first time it is called a new VideoReceiver object is created.
Subsequent calls return this object (without creating new ones).

E.g, All one needs to do to access the VideoReceiver is:

function blah()
{
VideoReceiver vr = getReceiver();
vr->update()

//do blah
}

Are there any problems or issues I should be aware of using this type
of code? Is it a no-no? I make multiple calls to getReceiver() each
frame.

It was originally a hack to get going but now that I've advanced a
reasonable way I'm considering just leaving it, since it is currently
working as expected.

Thanks for any advice or suggestions,
Sam.

Feb 13 '07 #1
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5 Replies


P: n/a
"Sa********@gmail.com" <Sa********@gmail.comwrote in
news:11*********************@a75g2000cwd.googlegro ups.com:
Hi,

I wish to share an object through a bunch of functions without
declaring it globally. I have achieved this through the following
function:

VideoReceiver* getReceiver()
{
static VideoReceiver *vr = new VideoReceiver();
return vr;
}
Why dynamically allocate it? Why not simply make it a static local
variable?
So, the first time it is called a new VideoReceiver object is created.
Subsequent calls return this object (without creating new ones).

E.g, All one needs to do to access the VideoReceiver is:

function blah()
{
VideoReceiver vr = getReceiver();
I assume you meant "VideoReceiver * vr"....
vr->update()

//do blah
}

Are there any problems or issues I should be aware of using this type
of code? Is it a no-no? I make multiple calls to getReceiver() each
frame.
I don't think that the object will ever be destroyed. With a local
static it will (sometime after main....)
It was originally a hack to get going but now that I've advanced a
reasonable way I'm considering just leaving it, since it is currently
working as expected.

Thanks for any advice or suggestions,
Perhaps make it a static local variable and return a reference to it.
Feb 13 '07 #2

P: n/a
On Feb 12, 7:54 pm, "Sam.Gun...@gmail.com" <Sam.Gun...@gmail.com>
wrote:
Hi,

I wish to share an object through a bunch of functions without
declaring it globally. I have achieved this through the following
function:

VideoReceiver* getReceiver()
{
static VideoReceiver *vr = new VideoReceiver();
return vr;

}

So, the first time it is called a new VideoReceiver object is created.
Subsequent calls return this object (without creating new ones).

E.g, All one needs to do to access the VideoReceiver is:

function blah()
{
VideoReceiver vr = getReceiver();
vr->update()

//do blah

}

Are there any problems or issues I should be aware of using this type
of code? Is it a no-no? I make multiple calls to getReceiver() each
frame.

It was originally a hack to get going but now that I've advanced a
reasonable way I'm considering just leaving it, since it is currently
working as expected.

Thanks for any advice or suggestions,
Sam.
The function is fine except I would return
a reference to the object - this way there
is no chance of anyone deleting the object
by accident.

Also, as another poster said, there's no
need for dynamic allocation - just use a
static local.

But for multi-threaded programs, the construction
of the object is not safe. See, for instance,
Modern C++ Design for a good discussion on this.

Some times, this is ok. For instance, I use a
static local log object inside a function. But
I make sure it is used (and hence constructed)
in the main thread before any other threads are
invoked.

Feb 13 '07 #3

P: n/a
On 12 Feb 2007 16:54:54 -0800, "Sa********@gmail.com" <Sa********@gmail.com>
wrote:
>Hi,

I wish to share an object through a bunch of functions without
declaring it globally. I have achieved this through the following
function:

VideoReceiver* getReceiver()
{
static VideoReceiver *vr = new VideoReceiver();
return vr;
}

So, the first time it is called a new VideoReceiver object is created.
Subsequent calls return this object (without creating new ones).

E.g, All one needs to do to access the VideoReceiver is:

function blah()
{
VideoReceiver vr = getReceiver();
vr->update()

//do blah
}

Are there any problems or issues I should be aware of using this type
of code? Is it a no-no? I make multiple calls to getReceiver() each
frame.

It was originally a hack to get going but now that I've advanced a
reasonable way I'm considering just leaving it, since it is currently
working as expected.

Thanks for any advice or suggestions,
Sam.
There is no problem with this kind of code, except that the VideoReceiver
object is never destroyed.

Your solution is actually a common implementation of the Singleton pattern in
C++. A more typical code would be:
MyClass& getClassInstance()
{
MyClass myClass;
return myClass;
}
The pattern you are using also solves a common problems with globals:
initialization order.

-dr
Feb 13 '07 #4

P: n/a
On Feb 12, 9:16 pm, Dave Rahardja
<drahardja_atsign_pobox_dot_...@pobox.comwrote:
On 12 Feb 2007 16:54:54 -0800, "Sam.Gun...@gmail.com" <Sam.Gun...@gmail.com>
wrote:
Hi,
I wish to share an object through a bunch of functions without
declaring it globally. I have achieved this through the following
function:
VideoReceiver* getReceiver()
{
static VideoReceiver *vr = new VideoReceiver();
return vr;
}
So, the first time it is called a new VideoReceiver object is created.
Subsequent calls return this object (without creating new ones).
E.g, All one needs to do to access the VideoReceiver is:
function blah()
{
VideoReceiver vr = getReceiver();
vr->update()
//do blah
}
Are there any problems or issues I should be aware of using this type
of code? Is it a no-no? I make multiple calls to getReceiver() each
frame.
It was originally a hack to get going but now that I've advanced a
reasonable way I'm considering just leaving it, since it is currently
working as expected.
Thanks for any advice or suggestions,
Sam.

There is no problem with this kind of code, except that the VideoReceiver
object is never destroyed.

Your solution is actually a common implementation of the Singleton pattern in
C++. A more typical code would be:

MyClass& getClassInstance()
{
MyClass myClass;
return myClass;

}

The pattern you are using also solves a common problems with globals:
initialization order.

-dr

Like dr says, this is the singleton pattern and is quite useful. I
find it useful to use a singleton as a non-copyable as well like so:

class Singleton
{
public:
virtual ~Singleton() {}

protected:

Singleton() {}

Singleton( const Singleton& singleton ) {}

Singleton&
operator=( const Singleton& singleton ) {}
} ;

class MyClass : public Singleton
{
public:
static MyClass&
Instance()
{
if( !_instance )
{
boost::shared_ptr< MyClass temp( new MyClass() ) ;
_instance = temp ;
}

return _instnace ;
}

void
foo() ;

private:

static boost::shared_ptr< MyClass _instance ;
} ;
And then you can just do:

MyClass::Instance().foo() ;

or

MyClass& inst = MyClass::Instance() ;
inst.foo() ;

To use it in code.

HTH,
Paul Davis

Feb 13 '07 #5

P: n/a
On Feb 13, 3:58 am, "paul.joseph.da...@gmail.com"
<paul.joseph.da...@gmail.comwrote:
On Feb 12, 9:16 pm, Dave Rahardja

<drahardja_atsign_pobox_dot_...@pobox.comwrote:
On 12 Feb 2007 16:54:54 -0800, "Sam.Gun...@gmail.com" <Sam.Gun...@gmail.com>
wrote:
>Hi,
>I wish to share an object through a bunch of functions without
>declaring it globally. I have achieved this through the following
>function:
>VideoReceiver* getReceiver()
>{
static VideoReceiver *vr = new VideoReceiver();
return vr;
>}
>So, the first time it is called a new VideoReceiver object is created.
>Subsequent calls return this object (without creating new ones).
>E.g, All one needs to do to access the VideoReceiver is:
>function blah()
>{
VideoReceiver vr = getReceiver();
vr->update()
//do blah
>}
>Are there any problems or issues I should be aware of using this type
>of code? Is it a no-no? I make multiple calls to getReceiver() each
>frame.
>It was originally a hack to get going but now that I've advanced a
>reasonable way I'm considering just leaving it, since it is currently
>working as expected.
>Thanks for any advice or suggestions,
>Sam.
There is no problem with this kind of code, except that the VideoReceiver
object is never destroyed.
Your solution is actually a common implementation of the Singleton pattern in
C++. A more typical code would be:
MyClass& getClassInstance()
{
MyClass myClass;
return myClass;
}
The pattern you are using also solves a common problems with globals:
initialization order.
-dr

Like dr says, this is the singleton pattern and is quite useful. I
find it useful to use a singleton as a non-copyable as well like so:

class Singleton
{
public:
virtual ~Singleton() {}

protected:

Singleton() {}

Singleton( const Singleton& singleton ) {}

Singleton&
operator=( const Singleton& singleton ) {}

} ;

class MyClass : public Singleton
{
public:
static MyClass&
Instance()
{
if( !_instance )
{
boost::shared_ptr< MyClass temp( new MyClass() ) ;
_instance = temp ;
}

return _instnace ;
}

void
foo() ;

private:

static boost::shared_ptr< MyClass _instance ;

} ;

And then you can just do:

MyClass::Instance().foo() ;

or

MyClass& inst = MyClass::Instance() ;
inst.foo() ;

To use it in code.

HTH,
Paul Davis

Totally looked this over after I posted and realized I messed up a
couple points.

in Instance():

should be:

return *( _instance.get() ) ;

And don't forget to put:

boost::shared_ptr< MyClass MyClass::_instance, in a source file
somewhere.

Sorry if thats just confusing.

Paul Davis

Feb 13 '07 #6

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