delete operation

[mickey22]

I have created a pointer to a data in a class A and passing this pointer to a function in another class B.when I try to delete this pointer in class A I get run time exception.
But if I dont delete the object of class B I dont get any error it runs fine.But I have to delete the object of class B.I have illustrated theexample..Cou ld anyone help with it?

[CODE=cpp]//func2.h

class b
{
private:
float * data2;
b(float *);
~b();
test2();
};

//func2.cpp
void b::b(float *_data2)
{
data2=_data2;
}

void b::~b()
{
if(data2!=NULL) { delete[] data2; data2=NULL; }
}

//func1.h

class a
{
private:
float *data1;
a();
~a();
test();
};

//func1.cpp
void a::a()
{
data1=NULL;
}

void a::~a()
{
if(data1!=NULL) { delete[] data1; data1=NULL; }
}

void a::test()
{
b *obj=NULL;
obj=new b(data1);
delete b;
b=NULL;
}[/CODE]


Thanks

[weaknessforcats]

It looks like your constructor and destructor are private. They should be public.

Next the constructor takes a float* argument and you jusy copy the argument to the class data member. Then you delete the class data member in the destructor.

If the float* argument points to a float on the stack, you will crash at run time trying to delete a variable you didn't allocate.

You need to rewrite your constructor to allocate a new float on the heap and put that address in your class data member. Now you can safely delete in the destructor.

[code=cpp]
void b::b(float *_data2)
{
data2 = new float(*_data2);
}
[/code]

[mickey22]

Thank you ..using new operator solved my problem.

One question: is it not required to initialise data2 in class B to NULL before using new operator?

If yes can I intialise in this way :
data2=NULL;
data2=new float(*_data2);

[mickey0]

I see many strange things (for me):
1. the underscore _, normally is used in the data member of a class and not as member parameters (the opposite you're doing);
2. in the destructor check if _data != NULL, is unuseful;
3. I never heard that destructor/constructor have to return a type (void). Maybe some compiler accepts it but not mine
4. It's a good practice write class name with "uppercase" ( "class B" and not "class b")

One question: is it not required to initialise data2 in class B to NULL before using new operator?

correct; it isn't required;
but I initialize it like this:

class B () {
  float* _data;
public:
      B(float* data) : _data( new double(*data)) { }
};

If yes can I intialise in this way :
data2=NULL;
data2=new float(*_data2);

yes, you can; it's the same that 'weaknessforcat s' wrote.

[mickey22]

Hi all,

When I initialise in this way,

b::b(float *_data2)
{
data2 = new float(*_data2);
}

copying of the data from class A is not done properly.data2 contains some weird values.

So I tried to do as:

b::b(float *_data2,int _x,int _y)
{
x=_x;
y=_y;
data2=new float[x*y];
data2=_data2;
}

I get a runtime exception when I try to run this but the copying of data is done properly.
I am trying to copy data say float *data1 of one class A to a member variable float *data2 in another class B.
Could anyone help me with this please?
Thanks.

[weaknessforcats]

b::b(float *_data2)
{
data2 = new float(*_data2);
}

You don't show your main(). However, this is correct assuming _data2 points to a valid float.

BTW: The underscore does not mean a member variable. Member variables are identifed by using the this pointer:

[code=cpp]
b::b(float *data2)
{
this->data2 = new float(*data2);
}
[/code]

b::b(float *_data2,int _x,int _y)
{
x=_x;
y=_y;
data2=new float[x*y];
data2=_data2;
}

data2 is a pointer. When you assign _data2 (also a pointer) to data2 all that happens is a) the address in _data2 is copied to data2 and b) the address returned by new has been overwritten resulting in a leak.

Further, why allocate an array of float to hold the value of a single float?

This is a completely erronous approach.

How about posting code where the error occurs?

[mickey22]

yes I have observed there is memory leak when I copy the adresses of the pointers and delete them in class A and class B.Thats where I get an error when I try to peform delete in class A.
delete[] data2;

How can I copy the values pointed by data2 to data1 point to the same values having data1 and data2 as different adresses so that I can delete them in both the classes?Can you suggest me the way?

[weaknessforcats]

How can I copy the values pointed by data2 to data1 point to the same values having data1 and data2 as different adresses so that I can delete them in both the classes?Can you suggest me the way?

If I read this correctly, you are wanting data2 and data1 to point to the same value? And then, when you delete in the destructors there are no problems.

If this is what you want, then you can't use pointers in your classes. Instead, you use a reference counted handle object. There is one here complete with code that you can use: http://bytes.com/forum/thread651599.html.

[mickey22]

Actually I have solved using the copy function memcpy and just copied the data pointed by data1 to pointer data2.Now I dont have any problem in the delete operations .

thanks a lot .

[Airslash]

Can't you just copy the values of your pointers by dereferencing them ?

Like this :

[code=c]
Class A {
public:
A();
float* var_A_;

}

Class B {
public:
B();
copy(A obj);

private:
floar* var_B_;
}

B::copy(A* obj) {
Float* var1 = A->var_A_;
Float* var2 = *var1;
}
[/code]

Just a quick thouht about the situation, you assign the value of the pointer in A (not the Adress) to the new variable.

Another trick would be to use the copyconstructor of your float type.
Float* var2 = new Float(var1);

anyways just my thought