default params to clsas member functions

[puzzlecracker]

not sure of the stardard: which one is right, if both which one is
preferable?

class FOO{
void foo(const string &, const string &username="true");
.....

}

void FOO::foo(const string & cycle, const string &username="true")
{


........


};



OR

class FOO{
void foo(const string &, const string &);
.....

};

void FOO::foo(const string & cycle, const string &username="true")
{


........


}



thx

 

[Victor Bazarov]

not sure of the stardard: which one is right, if both which one is
preferable?

class FOO{
void foo(const string &, const string &username="true");
....

}

void FOO::foo(const string & cycle, const string &username="true")

Redefinition of a default argument value is prohibited.

{


.......


};



OR

class FOO{
void foo(const string &, const string &);
....

};

void FOO::foo(const string & cycle, const string &username="true")
{


.......


}

Preferable to have the default argument value in the declaration, i.e.
in your case, in the class definition. The reason is that the default
argument value is used by the users of the class. The implementation
of that particular member function usually can't care less if the value
passed to it was because it was omitted in the code or because it was
specified to the exact same value as the default. And the user of the
class normally can't see the implementation. So, how is the default
value going to be available to him?

V

 

[Ron Natalie]

not sure of the stardard: which one is right, if both which one is
preferable?

You have to put the defaulted argument at the point of declaration that
the caller sees. This almost certainly means that it's defined
in the class definition.

You can't specify it again in another declaration or definition.

Niehter of your examples are right. This is the right way

class FOO {
void foo(const string&, const string& username="true"); // HERE
};

// not here
void FOO::foo(const string& cycle, const string& username) {

 

[puzzlecracker]

You have to put the defaulted argument at the point of declaration that

the caller sees. This almost certainly means that it's defined
in the class definition.
You can't specify it again in another declaration or definition.

you CANNOT or SHOULDNOT?

 

[Michael Olea]

you CANNOT or SHOULDNOT?

I believe it is illegal according to the standard - some compilers allow it,
some don't.

 

[Ron Natalie]

you CANNOT or SHOULDNOT?

Can not. It's not allowed.

 

[Peter Koch Larsen]

not sure of the stardard: which one is right, if both which one is
preferable?

class FOO{
void foo(const string &, const string &username="true");
....

}

[snip]

Others have explained the correct way, but best is not to use default
parameters if you can. Thus prefer

class FOO{
void foo(const string &, const string &username="true");
void foo(const string & s) { foo(s"true"); }
.....

}

 

[Victor Bazarov]

not sure of the stardard: which one is right, if both which one is
preferable?

class FOO{
void foo(const string &, const string &username="true");
....

}

[snip]

Others have explained the correct way, but best is not to use default
parameters if you can. Thus prefer

class FOO{
void foo(const string &, const string &username="true");
void foo(const string & s) { foo(s"true"); }

What's up with your posts today? The two lines above are just wrong.
They should be

void foo(const string &, const string & username); // no default
void foo(const string & s) { foo(s, "true"); } // calling the buddy

....

}

V

 

[Rolf Magnus]

you CANNOT or SHOULDNOT?

Well, you can, but the compiler won't accept your program then ;-)

 

[Rolf Magnus]

Others have explained the correct way, but best is not to use default
parameters if you can. Thus prefer

class FOO{
void foo(const string &, const string &username="true");
void foo(const string & s) { foo(s"true"); }
....

}

Why? It's more to type, more to maintain, more to read in the interface
documentation, and to me, it seems to offer no benefit.