Short question

[Charles Keepax]

Just a little quick question what is the effect of putting a const after
a member function definition.

Charles

[Victor Bazarov]

"Charles Keepax" <s9******@sms.ed.ac.uk> wrote...

Just a little quick question what is the effect of putting a const after
a member function definition.

It makes the function 'const'. Inside it 'this' designates
a constant object. Functions can be overloaded based on that.
For a non-const object non-const function is preferred, for
a const object only a const function will be called.

struct A {
A() {}
void foo() const;
void foo();
};

int main() {
A a;
a.foo(); // non-const is called
const A ca;
ca.foo(); // const is called
}

Doesn't the book on C++ that you're using for study explain
all that?

Victor

[John Harrison]

"Charles Keepax" <s9******@sms.ed.ac.uk> wrote in message
news:bf**********@scotsman.ed.ac.uk...

Just a little quick question what is the effect of putting a const after
a member function definition.

Charles

Its a guarantee that the member function will not alter the object it is
called on. It means that the member function can be called on a const object
or via a const reference or const pointer.

John

[Josephine Schafer]

"Charles Keepax" <s9******@sms.ed.ac.uk> wrote in message
news:bf**********@scotsman.ed.ac.uk...

Just a little quick question what is the effect of putting a const after
a member function definition.

Little quick answer :-)
The function does not modify the state of the object/class..
There are two camps on what that implies -
bitwise constness or abstract state constness.
Bitwise constness implies that no member variable gets modified.
For abstract constness consider a class
class A{
public :
void copy () ; // changes what p points to, not p..hence not const

private:
char *p;
};

Even if there is bitwise constness ( p unchanged) but if the contents of
what p points to get changed then
it is not abstract state constness.

--
With best wishes
J.Schafer