Non member function can be declared multiple times while member function can only be declared once?

Question

Non mumber function can be delcared multiple times while member function can only be declared once? Is this right ? My example seems saying yes.

But Why ?

class Base{
public:
    int foo(int i);
    //int foo(int i=10); //error C2535: 'void Base::foo(int)' : member function already defined or declared
};

//but it seems ok to declare it multiple times
int foo(int i);
int foo(int i=10);

int foo(int i)
{
    return i;
}

int main (void)
{
    int i = foo();//i is 10 
}

@Captain Giraffe: A linker matches up actual calls with definitions; it doesn't depend on declarations. The _compiler_ has earlier used those declarations to resolve the calls. — MSalters, Sep 23 '11 at 07:55
@all, thanks for all the good answers/comments/links, this matter is now clear ! — RoundPi, Sep 23 '11 at 13:49

score 6 · Accepted Answer · edited May 23 '17 at 12:19

6

From the Standard (2003), §8.3.6/4 says,

For non-template functions, default arguments can be added in later declarations of a function in the same scope.

Example from the Standard itself:

void f(int, int);
void f(int, int = 7);

The second declaration adds default value!

Also see §8.3.6/6.

And an interesting (and somewhat related) topic:

Default argument in the middle of parameter list?

And §9.3/2,

Except for member function definitions that appear outside of a class definition, and except for explicit specializations of member functions of class templates and member function templates (14.7) appearing outside of the class definition, a member function shall not be redeclared.

Hope that helps.

edited May 23 '17 at 12:19

Community

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1

answered Sep 22 '11 at 17:14

Nawaz

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Then isn't that perfect, @James? The quoted part of the standard says it applies to non-template functions. – Rob Kennedy Sep 22 '11 at 17:37
@UncleBens: Thanks. That quote is very precise. I added it to my answer. And yeah, after re-reading the question, I felt that the answer seems incomplete and I was looking for another quote from the spec. You did it before me. – Nawaz Sep 22 '11 at 17:55
This seems odd to me, is it the linker that adds default arguments in these cases? – Captain Giraffe Sep 22 '11 at 18:24
1

@CaptainGiraffe: No. It's compiler itself. See this also : http://stackoverflow.com/questions/5637679/default-argument-in-the-middle-of-parameter-list – Nawaz Sep 22 '11 at 18:27
@Nawaz There seems to be a theme going, me questioning/adding a side-effect from one of your statements + Johannes - litb having stated the question + your answer before :) I find this quite amusing =) Anyway you have my utmost respect for your knowledge and patience. Thanks. – Captain Giraffe Sep 22 '11 at 19:17
@CaptainGiraffe: Honestly, I didn't understand your comment :| – Nawaz Sep 22 '11 at 19:21
The one about the linker or the last one about -litb being ubiquitous to my comments/your answers? Not important. Just thanks. – Captain Giraffe Sep 22 '11 at 19:29
@CaptainGiraffe: Of course, the last one.. below my comment in which I gave you a link to Johannes's question and my answer. – Nawaz Sep 22 '11 at 19:31
@Nawas I'm trying hard here to just say thanks for your efforts ok! – Captain Giraffe Sep 22 '11 at 19:52

score 1 · Answer 2 · answered Sep 22 '11 at 17:36

You get the same result with this simplified version:

int foo() ;
int foo() ; // OK -- extern functions may be declared more than once
class C {
  int foo() ;
  int foo() ; // Error -- member function may not be declared more than once
} ;

Perhaps the reason is historical -- lots of C code used redeclaration of extern functions, so they had to be allowed.

score 0 · Answer 3 · answered Sep 22 '11 at 17:17

0

It certainity works - but I think it is bad practice.

answered Sep 22 '11 at 17:17

Ed Heal

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Non member function can be declared multiple times while member function can only be declared once?

3 Answers3