Thread: C++11 equivalent question

I just received Bjarne Stroustrup's The C++ Programming Language fourth edition (C++11)
I am not a seasoned c++ coder and probably will be asking a number of questions in the future.
I will not know if these are C++11 specific in probably most cases.
I am trying to update a translator (basic to c/c++) to C++11 where posible.


The translator produces this code

Code:

   virtual const int   size(void)=0;

The code I wish to represent is:

Code:

   virtual int size() const = 0;

Are these two lines equivalent ?


MingGW g++ 4.8 compiles it fine but the proof is in the running and I'm not to that point yet.


James

No they are not.

Code:

virtual const int   size(void)=0;

This one sets a return type of "const int". Which I don't think the compiler will care about too much. [edit -- wrong -- thanks Salem!] If you returned a pointer to a const int:

Code:

virtual const int *  size(void)=0;

The compiler will complain at you if you try to discard the constness.

Code:

virtual int size() const = 0;

This says that size is a const member function, meaning that it doesn't modify the class. So it can be legally called on a const this pointer, because that const keyword is your guarantee that it won't change the state of the class.

So no... not equivalent. All I could find in the draft standard was a footnote about it being important.

98) As indicated by syntax, cv-qualifiers are a signficant component in function return types.

For the second

In a const member function, the object for which the function is called is accessed through a const access
path; therefore, a const member function shall not modify the object and its non-static data members.

If the member function is declared const, the type of this is const X*,

^^ didn't know that,.

Thank you both. Looks like I need to do some parse mending.

James

Virtual means that the function invocation will be at runtime, so the compiler wouldn't know which function to call at compile time anyway.

O_o

"...when used with code relying on polymorphic behaviors."

There you go; that looks better.

[Edit]

Code:

Derived s;
s.go(); // The compiler knows that this is a `Derived' so is allowed to bypass lookup.

[/Edit]

Soma