Unable to call a member function, and declaring an object using the constructor

Question

There is an issue with my code. I created a simple class that has a constructor with default arguments. I understand that if I don't pass in any arguments to the constructor, the default values will take over, otherwise they will be overwritten by the parameters. Here is the code of my class:

// This class models a person
class Person {
 public:
  // Constructor
  Person(string name = "noname", int age = 0, char gender = 'U')
      : name_(name),
        age_(age),
        gender_(gender) {
  }

  // Accessor for name_
  const string& name() const {
    return name_;
  }
  // Accessor for age_
  int age() const {
    return age_;
  }

  // Accessor for gender_
  char gender() const {
    return gender_;
  }

  // Mutator for name_
  void set_name(const string& name) {
    name_ = name;
  }

  // Mutator for age_
  void set_age(int age) {
    age_ = age;
  }

  // Mutator for gender_
  void set_gender(char gender) {
    gender_ = gender;
  }

  // Returns a string representation of our person
  string ToString() {
    ostringstream ss;
    // Add our base ToString to the stream
    ss << name_ << "\nAge: " << age_ << "\nGender: " << gender_ << endl;
    return ss.str();
  }

 private:
  string name_;
  int age_;
  char gender_;
};

// Program starts here
int main() {
  // Create an instance of our base class
  Person me("Abraham Lincoln", 56, 'M');
  cout << me.ToString() << endl;

  // Calls the default constructor.
  Person someone;
  cout << someone.ToString() << endl;

  // This is a pun.
  Person sometwo();
  cout << sometwo.ToString() << endl;

  // This ends our program
  return 0;
}

The first example initializes the object with the passed in arguments. The second example creates an object, and since no arguments are passed in, the default values take over. And calling the toString() function indeed confirms this. Now when I create the second example, I get a compilation error:

base_main.cpp: In function ‘int main()’:
base_main.cpp:24:19: error: request for member ‘ToString’ in ‘sometwo’, which is of non-class type ‘Person()’
   cout << sometwo.ToString() << endl;
                   ^

What's this? It's interesting that if I comment out the line // cout << sometwo.ToString() << endl; the error is removed. So the issue is not in the constructor. How do I read this error exactly? What is a non-class type 'Person()'?

I understand that down the forms below are synonyms, they call the constructor with the default arguments. The first one just calls the constructor implicitly, but the second one calls the constructor explicitly without passing in any arguments. Am I right or not?

Person person1;
Person person2();

`Person sometwo();` declares a function, not a variable. Don't use the parens: `Person sometwo;` — 1201ProgramAlarm, Aug 16 '18 at 04:49
Nested _Definitions_ are not allowed inside a function, but _declarations_ are. — 1201ProgramAlarm, Aug 16 '18 at 04:54
@1201ProgramAlarm So how does this work, is that function declared inside another function able to be called by that function only? Is this a good way to restrict the function to be called by one or two functions only, but not just from any function, by putting the declaration in the local scope instead of the global scope? — Galaxy, Aug 16 '18 at 04:59
@Galaxy The function can be called in any scope where it is declared, and there can be any number of declarations of it. (There's no practical benefit to this that I know of – it's an old C thing that's stuck around for decades.) — molbdnilo, Aug 16 '18 at 05:18

Unable to call a member function, and declaring an object using the constructor

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