Do built-in types have default constructors?

问题:

After reading this article I made a point that int () yields 0 because the temporary int is value initialized and not because int() calls the default constructor for int. (The article is flawed according to my understanding.)

I also said that primitive (built-in) types don\'t have constructors. The original author asked me to check Section $10.4.2 (TC++PL) which says

Built-in types also have default constructors ($6.2.8)

But I still think that the statement \"C++ allows even built-in type (primitive types) to have default constructors.\" is flawed (as per C++03).

I think Bjarne in TC++PL has mixed up \"constructor like notation i.e ()\" with actual constructor call. Value initialization were not introduced at that time when Bjarne was writing the book, right? So is the text in TC++PL incorrect as per C++98 and C++03 ?

What do you guys think?

EDIT

I asked Bjarne personally (via mail) regarding the flawed text in TC++PL and this was his reply

I think you mix up \"actual constructor calls\" with conceptually having a constructor. Built-in types are considered to have constructors (whatever words the standard use to describe their behavior).

回答1:

A constructor is a member function (constructors are fully specified in clause 12 of the C++ Standard, which covers special member functions like constructors and destructors).

A member function can only be defined for a class type (C++03 9.3/1 says \"Functions declared in the definition of a class, excluding those declared with a friend specifier, are called member functions of that class\").

So non-class types (including fundamental types, array types, reference types, pointer types, and enum types) do not have constructors.

I don\'t have a copy of The C++ Programming Language to read the context of the quote that \"Built-in types also have default constructors,\" but I would guess that Stroustrup is either using the term \"constructor\" in a loose, non-technical sense, or the meaning of the term or the way in which it is used in the Standard changed between when the book was published and when the language was standardized. I\'d guess the former is far more likely than the latter.

回答2:

Simple Answer: Technically No.

Long Answer:

No.
But the syntax you use to initialize them makes them look like they are being constructed by a default constructor or a default copy constructor.

int x(5);  // Looks like a constructor. Behaves like one: x is initialized.
int y();   // Fail. Actually a function declaration.
// BUT
int z = int(); // Looks like a constructor. Behaves like a constructor (0 init).

int a(b);  // Again.

So technically there are no constructors for basic-POD types. But for all intents and purposes they act just like they have a copy constructor and default constructor (when initialized with the braces).

If it looks like a duck and quacks like a duck, then its very duck like.

回答3:

As others have pointed out, the Standard contradicts TC++PL in a few instances, often related to terminology. Bjarne Stroustrup himself summarizes the situation well:

(...) However, [TC++PL] is not a reference manual or the standards text. If you need 100% precise and complete information you\'ll have to consult the text of the ISO C++ standard. (...)