What's rong with this code

[B.E]

I wanted to test the contractor using the following code
class Test
{ public:
Test(int y) {}
};

int main()
{ int x;
Test(x);
}
Why does it not work?

[AR]

Probably because you aren't calling a constructor, merely a non-existant function called Test()

Code: Select all

class Test
{
public:
     Test(int y)
     {
         cout << y;
     }
};

int main()
{
    Test *t = new Test(36);
    delete t;
    return 0;
}

[B.E]

but why doesen't the other code work. it's called the with the requied params for the constructor

[Colonel Kernel]

This is probably an example of C++'s "most vexing parse" (named so by Scott Meyers in Effective STL).

http://archives.devshed.com/a/ng/468-18 ... -operators

BTW #1, new and delete aren't necessary to make this work (if you're looking for the shortest version):

Code: Select all

int main()
{
    Test t(36);
    return 0;
}

BTW #2, it would help if you define "not working" better next time. You did mean you got a compile error, right?

[Candy]

I wanted to test the contractor using the following code
class Test
{ public:
Test(int y) {}
};

int main()
{ int x;
Test(x);
}
Why does it not work?

It doesn't work since you don't give the object a name.

Code: Select all

class Test
{    public:
         Test(int y) {}
};

int main()
{   int x;
    Test n(x);
}

will work.

[B.E]

But why does
Test ((int) x); work?
x is raady an int.

[Colonel Kernel]

Because it's the "most vexing parse". The compiler is getting confused about whether you're declaring an object instance or declaring a local function. The cast disambiguates it.