Weird thing while trying to avoid pointers in C++

[Zlatomir]

Unless you define the vector as QVector<MyObject&> - then it indeed will take references.

I'm pretty sure you can't do that, since references in C++ have their "oddies" (like the reference is for all it's life bound to an object and it should be set at declaration)

So the remaining solution is QVector<MyObject*>

[high_flyer]

You are correct Zlatomir.
I have never tried it before actually, because it never made any practical sense.
I just assumed it is possible.
Now I tried it, and indeed, the compiler complains.
Thanks for the heads up!

[wysota]

I am not sure even why this code compiles, since you are trying to assign c to t but you didn't define an '=' operator for your Node class.

Node t = n.GetChild(n.GetCount() - 1); //I don't know why this compiles, it should not

Node t = n.GetChild(n.GetCount() - 1); //I don't know why this compiles, it should not

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This is equivalent to:

Node t(n.GetChild(n.GetCount()-1));

Node t(n.GetChild(n.GetCount()-1));

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The copy constructor kicks in here. Besides if you don't declare your own default constructor, copy constructor or assignment operator, the compiler will provide them for you.

Well it does take reference.

void push_back ( const T& x );

void push_back ( const T& x );

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No, it takes a const reference. That's two totally different things.

[ct]

Thanks, I got it. The copy constructor was being called all the time. I got the difference now.

[ct]

One more thing on the topic though. Is it a good practice to avoid using pointers and use the stack space instead of heap ? That way there would be no memory leaks.

[SixDegrees]

No; that will quickly lead to convoluted code in all but the simplest applications. Pointers are fundamental to C/C++; there is no reason to avoid them.

If you're really worried about memory leaks, have a look at the STL auto_ptr class. Or run your code through a tool like valgrind to check for memory leaks, which is something you really ought to be doing anyway.

[high_flyer]

In addition to what has been said, the stack size is usually quite limitted, so any realy world application might soon run out of memory if all you use is the stack.

[Zlatomir]

Just a little addition to what has been said already: don't use auto_ptr it has some usage restriction (like you can't have an container of auto_ptr) and if i remember correctly it is on removal list of the new standard, so you will have to re-write code when you will upgrade to a C++0x compiler.

Instead you can use boost shared_ptr (it should be included in tr1:: namespace it will be in std:: in C++0x) or Qt has QSharedPointer

But anyway you need to understand pointers and memory management, even if Qt simplifies things (see parent-child relationship) you still need to know what is deleted by parent and what you should delete yourself.

[ct]

In addition to what has been said, the stack size is usually quite limitted, so any realy world application might soon run out of memory if all you use is the stack.

Is there a way to find out how much memory is the stack limited to. I'm just writing a prototype and yes memory is a issue. But I would only need around 200-300 mb max. I'm trying to import large text files.

[SixDegrees]

On Linux, you can say 'ulimit -a'; one of the numbers reported is stack size. On my machine, it is currently set at ~8MB, which is fairly typical.

[ct]

Which space does STL containers like vector or hash_map use ?
For example:

int main(int argc,char **argv){
    vector<string> v;
    string s = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"; 
   //sizeof(s) = 8
    for(unsigned long i = 0;i< 18446744073709551615; i++)
           v.push_back(s);
    return 0;
}

int main(int argc,char **argv){
    vector<string> v;
    string s = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"; 
   //sizeof(s) = 8
    for(unsigned long i = 0;i< 18446744073709551615; i++)
           v.push_back(s);
    return 0;
}

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Isn't the vector being created on the stack ? Why doesn't this program crash even when the size goes way past stack limit (~8 MB) .

[high_flyer]

Isn't the vector being created on the stack ?

The vector object yes, the elements no.
Think about it: since the elements are being dynamically added, how could they be added on the stack?
That would mean that the vector has a predefined size.