Question about deleting pointers

Say you have this code:

Code:

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float *Pi = new float;
*Pi = 3.141592;
delete Pi;

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Why wouldn't you just use this:

Code:

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float Pi = 3.141592;

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You could. Using a pointer in that situation is just dumb. A much better example would be:

Code:

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float* floats = new float[1000];

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Now you have, basically, an array of floats. Then you can delete it as above. Another example is:

Code:

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myStruct* strct = new myStruct;
SomeFunc(strct);

...
where sizeof(myStruct) > 4

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in this case, you are passing a pointer(DWORD), instead of the entire struct, which increases speed. You can also create pointers to functions, which help a lot when doing some things (callback functions). Its all in knowing when to use a pointer. In your example, there is just no reason. But other times, is speeds execution time up, by not haveing to copy data from location to location.

Z.

One thing you missed:

Code:

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float *i = new float;
delete i;

float *j = new float[100];
delete[] j;

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:)

more reasons: the C++ STL library

Code:

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#include <vektor>
using namespace std;

class CParentClass
{ // members
}

class CFirstChildClass : public CParentClass
{  // Blabla 
}

class CSecondChildClass : public CParentClass
{  // Whatever
}

void SomeFunc()
{
    CParentClass *pFC = new CFirstChildClass;
    // ask for user input and fill class members
    // insert the pointer into a vektor <CParentClass*> object that is always available
}

void SomeOtherFuncThatIsCalledAtAnEntirelyOtherTime()
{
      // you can now access the object
}

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Advantages:
1) Polymorphic access: It doesn't matter which child class the contents of the vektor are.
2) You still have exactly the object you created, not a copy as if you were using vektor<CParentClass>
3) If you used CFirstChildClass obj; and inserted &obj into the vektor, obj would be out of scope in SomeOtherFunc... and most probably deleted.

vector not vektor :D :p

You don't need the STL to use virtual inheritance, which is what goes on here:

Code:

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class Parent {
public:
    virtual void Func() = 0;
};

class ChildA : public Parent {
public:
    void Func() { cout << "Die!" << endl; }
};

class ChildB : public Parent {
public:
    void Func() { cout << "Live!" << endl; }
};

void somecode() {
    Parent *ptr;
    ChildA *thing = new ChildA;
    ChildB *other = new ChildB;

    ptr = thing;
    ptr->Func();

    ptr = other;
    ptr->Func();

    delete thing;
    delete other;
}

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true, but this way I can at the same time show the "no copy" and the polymorphic advantages.

Okay then ;) I just wouldn't mix templates in if they're still on the "*** do pointers do" stage :)

Not quibbling, though :)

Yeah, maybe write an essay about the difference between heap and stack? :D

Aaaargghhh yeah!

Damn that really messed me up when I was learning. Hmm...perhaps another FAQ entry? :)

It's just that I don't have time for it at the moment.

Quote:

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Originally posted by parksie
Okay then ;) I just wouldn't mix templates in if they're still on the "*** do pointers do" stage :)

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Heh, that's pretty much me. I know the basics of what they do, but I'm still a little fuzzy on it.