Member function redeclaration not allowed when constructing temporary object

[Marco Wedekind]

Hello all,

I have a strange compiler behaviour with this code:

---- Begin of code snippet ----

class Base
{
public:
static unsigned int ClassId();

};

class Derived
{
public:
static unsigned int ClassId() { return 2; };

};

class Test
{
public:
Test(unsigned int p1) {};

};

int main(int argc, char * argv[])
{
// This works
Test a(Derived::Clas sId());

// This crashes
Test(Derived::C lassId());

return 0;

}

---- End of code snippet ----

The line

Test(Derived::C lassId());

failes to compile with gcc 3.3.5 and Visual Studio 8. With gcc I get
the following error message:

test.cpp: In function `int main(int, char**)':
test.cpp:24: error: prototype for `Test Derived::ClassI d()' does not
match any
in class `Derived'
test.cpp:11: error: candidate is: static unsigned int
Derived::ClassI d()
test.cpp:24: error: `Test Derived::ClassI d()' and `static unsigned int
Derived::ClassI d()' cannot be overloaded
test.cpp:24: error: prototype for `Test Derived::ClassI d()' does not
match any
in class `Derived'
test.cpp:11: error: candidate is: static unsigned int
Derived::ClassI d()
test.cpp:24: error: `Test Derived::ClassI d()' and `static unsigned int
Derived::ClassI d()' cannot be overloaded
test.cpp:24: error: declaration of `Test Derived::ClassI d()' outside of
class
is not definition

So why does it fail with a temporary object in such a way? Should the
compiler not handle this case equivalent to the "non-temporary case"?
Do you have any hints on this behaviour?

Thanks and best regards

Marco

[Michiel.Salters]

Tom Widmer wrote:

Marco Wedekind wrote:

One thing I still do not understand is: Why does it drop the
parentheses?

C declaration syntax compatibility. C allowed extraneous parentheses,
hence C++ does too. e.g.
int (i);
is legal in C and C++ as a declaration of an integer, i.

Tom

Please keep the original text - I'd have to lookit up myself.

Anyway, what you had is Test(Derived::C lassId()); in which the
outer parantheses can be dropped. However, the grammar for declarations
allows just a single pair. Expressions allow any number, so the
expression
Test((Derived:: ClassId())); can be interpreted in only one way - as the
creation of a temporary Test from the expression (Derived::Class Id()).

HTH,
Michiel Salters

[Marco Wedekind]

> Anyway, what you had is Test(Derived::C lassId()); in which the

outer parantheses can be dropped. However, the grammar for declarations
allows just a single pair. Expressions allow any number, so the
expression
Test((Derived:: ClassId())); can be interpreted in only one way - as the
creation of a temporary Test from the expression (Derived::Class Id()).

Hello Michiel,

thanks for your reply. It works, although it just looks a little odd to
me. I will have to remember this...

Thanks for all your replies

Marco