struct A
{
  int* p;
  std::string s;
};

int main()
{
  A a = A();
  std::cout << a.p << std::endl;
}

struct A
{
  A() : p() {}

  int* p;
  std::string s;
};

R>struct A
R>{
R>  int* p;
R>  std::string s;
R>};

R>int main()
R>{
R>  A a = A();
R>  std::cout << a.p << std::endl;
R>}
R>

struct A
{
    int i;
    A() { } // user-provided default ctor, does not initialize i
};
 
struct B { A a; }; // implicitly-defined default ctor
 
std::cout << B().a.i << '\n'; // value-initializes a B temporary
                              // leaves b.a.i uninitialized in C++03
                              // sets b.a.i to zero in C++11

int *p = nullptr;

R>struct A
R>{
R>    int i;
R>    A() { } // user-provided default ctor, does not initialize i
R>};

To value-initialize an object of type T means:
....
— if T is a non-union class type without a user-declared constructor, then every non-static data member and base-class component of T is value-initialized;

To value-initialize an object of type T means:
....
— otherwise, the object is zero-initialized

To zero-initialize an object of type T means:
— if T is a scalar type (3.9), the object is set to the value of 0 (zero) converted to T;

C++: g++ 4.1.2
flags: -O -std=c++98

J>Какой? Сорри, я не понимаю, чего ты от нас хочешь

#include <iostream>
#include <string>

struct Base
{
  int* p;
  std::string s;
};

struct A : Base
{
  A() : Base() { }
};

int main()
{
  A a;
  std::cout << a.p << std::endl;
}

#include <cassert>

struct A
{
    int *p;
    int *A::*pm;
};

int main()
{
    A a = A();
    assert(a.p == nullptr);
    assert(a.pm == nullptr);
}

R>struct A
R>{
R>    int i;
R>    A() { } // user-provided default ctor, does not initialize i
R>};

R>struct B { A a; }; // implicitly-defined default ctor
R>

std::cout << B().a.i << '\n'; // value-initializes a B temporary
// leaves b.a.i uninitialized in C++03
// sets b.a.i to zero in C++11
// (note that B{}.a.i leaves b.a.i uninitialized in C++11, but for
// a different reason: in post-DR1301 C++11, B{} is aggregate-initialization,
// which then value-initializes A, which has a user-provided ctor)

R>Это ж трындец какой-то, извините за мой француский Выходит, что value-initialization класса B, исправляет "недоработки" конструктора класса A?? Эдакая супер-пупер инициализация. А где в стандарте то место, которое описывает такое поведение, не подскажешь?

7 To value-initialize an object of type T means:
— if T is a (possibly cv-qualified) class type (Clause 9) with a user-provided constructor (12.1), then the
default constructor for T is called (and the initialization is ill-formed if T has no accessible default
constructor);
— if T is a (possibly cv-qualified) non-union class type without a user-provided constructor, then the object
is zero-initialized and, if T’s implicitly-declared default constructor is non-trivial, that constructor is
called.
— if T is an array type, then each element is value-initialized;
— otherwise, the object is zero-initialized.

Since C++11, value-initializing a class without a user-provided constructor, which has a member of a class type with a user-provided constructor zeroes out the member before calling its constructor