class C : public B
{
public:
void C::Test();
};
What is the point of specifying C in the declaration of the member function?
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1we used to do it because it made cut/paste and searching between the definition/declaration easier. But with modern IDEs there is no need and it's now illegal.Martin Beckett– Martin Beckett2011-05-09 21:26:49 +00:00Commented May 9, 2011 at 21:26
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@Martin Becket: Strictly speaking, it was already illegal even in C++98. Even if there was a time when it was legal, it must have been some pre-standard period.AnT stands with Russia– AnT stands with Russia2011-05-09 23:51:13 +00:00Commented May 9, 2011 at 23:51
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4 Answers
You shouldn't do this. Many modern compilers will treat this as a syntax error, for example, g++ 4.2.1 will!
Comments
This is only neccessary when defining the method outside of the class:
class C : public B
{
public:
void Test();
};
void C::Test() { ... }
3 Comments
Fred Foo
But not when declaring it inside the class definition, as your example seems to imply.
Christian Rau
What do you mean (pehaps you refer to an erroneous post, which I edited shortly after posting, actually copy-and-pasted from the question and forgot to remove the error).
Fred Foo
Yes, I referred to the earlier version. Looks fine now.
Not only there's no point, it is downright illegal (see 8.3/1 in the language standard). In general in C++ language qualified names are allowed only when you are referring to a previously declared entity, but not when you are introducing a new entity (there are some exceptions from this rule, but none of them apply here).
The code you posted would require a diagnostic message from any conforming compiler, since your member function declaration is invalid.
answered May 9, 2011 at 21:23
AnT stands with Russia
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2 Comments
GManNickG
I know it's illegal, but I'm failing to find why. Is there a note somewhere, or is it in the grammar?
AnT stands with Russia
@GMan: It is in 8.3/1. Basically, qualified names can only be used to refer to previously declared entities, but not to introduce new entities. See also this defect: open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#482. The old (defective) wording was more explicit, but with regard to this example nothing really changed in the new wording.
There is no point, no need to do this. Since the declaration of Test is inside the scope of the declaration of C, the compiler knows that the function Test is a member of C.
