Re: Regarding auto_ptr and strict ownership

From:

Thomas Maeder <maeder@glue.ch>

Newsgroups:

comp.lang.c++.moderated

Date:

Fri, 15 Feb 2008 14:52:04 CST

Message-ID:

<m2bq6i2m7c.fsf@glue.ch> <a697be97-29bd-487d-ac60-61fc61dffb8c@s13g2000prd.googlegroups.com>

smawsk <sk.smawsk@gmail.com> writes:

But when I test this on VC6 compiler, i get different results than
expected.

For one thing, this is a very old, pre-Standard compiler.

class X
{
private:
    int x;
public:
    X(int xx)
    {
        x = xx;
    }

    void printX()
    {
        cout<<x<<endl;
    }
};

int main()
{

    std::auto_ptr<X> ai(new X(10));
    ai->printX(); // Prints 10
    std::auto_ptr<X> ai2;

    ai2 = ai;

    ai2->printX(); // Prints 10
    ai->printX(); // This should fail.....But surprisingly this too
prints 10

Your program has undefined behavior.

return 0;
}

Can some one let me know why ai->printX() works successfully?

You are just a bit unlucky. With a bit more luck, your program would
crash.

If the ownership has been transferred, then the line should give an
error at runtime.

Am I missing some thing here?

The undefinedness of undefined behavior.

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