Re: Simple const-related question

"Daniel T." <>
Mon, 18 Feb 2008 16:47:22 -0800 (PST)
On Feb 18, 5:45 pm, wrote:

On Feb 18, 6:30 pm, wrote:

Is "const Object* pA = new Object(1)" the same as "const Object A(1)"
in terms of creating const objects that should not be modified through
cast-to-non-const pointers. See the following example:

const int* createInt()
    return new int(1);


void myFunc( const int* const_param )
    cout << "const_param == " << *const_param << endl;

    int *non_const_param = const_cast<int*>( const_param );
    *non_const_param = 999;

    cout << "const_param == " << *const_param << endl;


int main(int argc, char* argv[])
          int a = 1;
    const int b = 1;
          int* c = new int(1);
    const int* d = new int(1);
    const int* e = createInt();

    myFunc( &a ); // ok
    myFunc( &b ); // bad
    myFunc( c ); // ok
    myFunc( d ); // bad (?)
    myFunc( e ); // bad (?)

    return 0;


I guess my real question is what does "new int(1)" or "new MyObject()"
create - is it always non-const object, or does it depend on the
context as in the following:

MyObject *p1 = new MyObject(); // p1 is non-const
const MyObject *p2 = new MyObject(); // p2 is ???

What about:

MyObject* myFunction()
    return new MyObject();


MyObject* p1 = myFunction(); // p1 is non-const
const MyObject *p2 = myFunction(); // p2 is ???

Get out of the Java habit of putting () after the class name when
calling new. I'm pretty sure that "new Object();" and "new Object;" do
different things.

In answer to your question, the object returned by new is inherently
non-const, but once placed in a const pointer, non-const functions can
no longer be called on that object through that pointer. That doesn't
mean the object is const though, note for example:

Object* o = new Object;
const Object* o2 = o;

o->non_const_func(); // perfectly OK even though the object is being
held in a pointer to const elsewhere.

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