Question about pointer to the map

[tradevol]

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,float>* bData;

void myFunction(){ //get data from *bData
map<string,floattemp = *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]

tr******@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,float>* bData;

void myFunction(){ //get data from *bData
map<string,floattemp = *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,float>& bData;

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

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

--
Ian Collins.

[tradevol]

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,stringbData 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 <[e-mail]:

[e-mail] 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,float>* bData;

void myFunction(){ //get data from *bData
* * map<string,floattemp = *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,float>& bData;

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

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

};

--
Ian Collins.

[Ian Collins]

tr******@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 <[e-mail]:

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

So B changes to something like

class B
{
map<string,float>& 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,stringbData 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.