Question about pointer to the map

[tradevol@yahoo.com]

Hi,

Here is what I want to do.

I have class A contains class B.

class A{

public:
B b;
map<string, floatmyData;
}

class B{
B(map* data){
bData = data;
}

map<string,floa t>* bData;

void myFunction(){ //get data from *bData
map<string,floa ttemp = *bData;

}

}

my purpose is to have data udpated continuously on class A on map
myData, since its pointer is passed to B. B can call myFunction and be
sure it is using the most current data from myData after find call.

new to C++, made a mess in the codes. It seems I cannot even assign
temp after deference bData.

Any suggestions?

Thanks

Chris

[Ian Collins]

Re: Question about pointer to the map

tradevol@yahoo. com wrote:

Hi,
>
Here is what I want to do.
>
I have class A contains class B.
>
class A{
>
public:
B b;
map<string, floatmyData;
}
>
class B{
B(map* data){
bData = data;
}
>
map<string,floa t>* bData;
>
void myFunction(){ //get data from *bData
map<string,floa ttemp = *bData;
>

Dodgy design issues aside, you really don't want to do this! You are
attempting to copy the map when all you probably want to do is access
the data.

Use a reference instead of a pointer and use the reference throughout.

So B changes to something like

class B
{
map<string,floa t>& bData;

B(map& data)
: bData( data ) {}

void myFunction()
{
// access map.
//
float test = bData["test"];
}
};

--
Ian Collins.

[tradevol@yahoo.com]

Re: Question about pointer to the map

Thanks a lot, Ian. This is the kind of answer I am looking for.

One more C++ 101 question:

I am not quite comfortable with reference usage. So when I assign
map<string,stri ngbData with a reference to data, even if I treat
bData inside class B as a object instead of pointer (as calling
bData.find() instead of bData->find()), behind the scene, is only the
pointer passed (instead of making a local copy)?

Thanks

Chris

On Aug 1, 3:33 pm, Ian Collins <ian-n...@hotmail.co mwrote:

trade...@yahoo. com wrote:

Hi,

>

Here is what I want to do.

>

I have class A contains class B.

>

class A{

>

public:
 B b;
 map<string, floatmyData;
}

>

class B{
B(map* data){
 bData = data;
}

>

map<string,floa t>* bData;

>

void myFunction(){ //get data from *bData
    map<string,floa ttemp = *bData;

>
Dodgy design issues aside, you really don't want to do this!  You are
attempting to copy the map when all you probably want to do is access
the data.
>
Use a reference instead of a pointer and use the reference throughout.
>
So B changes to something like
>
class B
{
  map<string,floa t>& bData;
>
  B(map& data)
   : bData( data ) {}
>
  void myFunction()
  {
    // access map.
    //
    float test = bData["test"];
  }
>
};
>
--
Ian Collins.

[Ian Collins]

Re: Question about pointer to the map

tradevol@yahoo. com wrote:

Thanks a lot, Ian. This is the kind of answer I am looking for.
>

[please don't top-post]

On Aug 1, 3:33 pm, Ian Collins <ian-n...@hotmail.co mwrote:

>Use a reference instead of a pointer and use the reference
>throughout.
>>
>So B changes to something like
>>
>class B
>{
> map<string,floa t>& bData;
>>
> B(map& data)
> : bData( data ) {}
>>
> void myFunction()
> {
> // access map.
> //
> float test = bData["test"];
> }
>>
>};

One more C++ 101 question:
>
I am not quite comfortable with reference usage. So when I assign
map<string,stri ngbData with a reference to data, even if I treat
bData inside class B as a object instead of pointer (as calling
bData.find() instead of bData->find()), behind the scene, is only the
pointer passed (instead of making a local copy)?
>

Yes, there isn't any copying going on.

--
Ian Collins.