error: request for member '..' in '..&

Question

I have a class with two constructors, one that takes no arguments and one that takes one argument.

Creating objects using the constructor that takes one argument works as expected. However, if I create objects using the constructor that takes no arguments, I get an error.

For instance, if I compile this code (using g++ 4.0.1)...

class Foo
{
  public:
    Foo() {};
    Foo(int a) {};
    void bar() {};
};

int main()
{
  // this works...
  Foo foo1(1);
  foo1.bar();

  // this does not...
  Foo foo2();
  foo2.bar();

  return 0;
}

... I get the following error:

nonclass.cpp: In function ‘int main(int, const char**)’:
nonclass.cpp:17: error: request for member ‘bar’ in ‘foo2’, which is of non-class type ‘Foo ()()’

Why is this, and how do I make it work?

Answer 1

I ran into a case where I got that error message and had

Foo foo(Bar());

and was basically trying to pass in a temporary Bar object to the Foo constructor. Turns out the compiler was translating this to

Foo foo(Bar(*)());

that is, a function declaration whose name is foo that returns a Foo that takes in an argument -- a function pointer returning a Bar with 0 arguments. When passing in temporaries like this, better to use Bar{} instead of Bar() to eliminate ambiguity.

Answer 2

If you want to declare a new substance with no parameter (knowing that the object have default parameters) don't write

 type substance1();

but

 type substance;