struct complex { complex(); complex(double); complex(double,double); }; complex sqrt(complex,complex); complex a(1); // initialize by a call of complex(double) complex b = a; // initialize by a copy of a complex c = complex(1,2); // construct complex(1,2) using complex(double,double), // copy/move it into c complex d = sqrt(b,c); // call sqrt(complex,complex) and copy/move the result into d complex e; // initialize by a call of complex() complex f = 3; // construct complex(3) using complex(double), copy/move it into f complex g = { 1, 2 }; // initialize by a call of complex(double, double)
complex v[6] = { 1, complex(1,2), complex(), 2 };
struct X { int i; float f; complex c; } x = { 99, 88.8, 77.7 };
struct A { A(); };
typedef A global_A;
struct B { };
struct C: public A, public B { C(); };
C::C(): global_A() { } // mem-initializer for base A
struct A { A(); };
struct B: public virtual A { };
struct C: public A, public B { C(); };
C::C(): A() { } // ill-formed: which A?
struct C { C( int ) { } // #1: non-delegating constructor C(): C(42) { } // #2: delegates to #1 C( char c ) : C(42.0) { } // #3: ill-formed due to recursion with #4 C( double d ) : C('a') { } // #4: ill-formed due to recursion with #3 };
struct B1 { B1(int); /* ... */ }; struct B2 { B2(int); /* ... */ }; struct D : B1, B2 { D(int); B1 b; const int c; }; D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ } D d(10);
struct A { A(); }; struct B { B(int); }; struct C { C() { } // initializes members as follows: A a; // OK: calls A::A() const B b; // error: B has no default constructor int i; // OK: i has indeterminate value int j = 5; // OK: j has the value 5 };
struct A { A() = default; // OK A(int v) : v(v) { } // OK const int& v = 42; // OK }; A a1; // error: ill-formed binding of temporary to reference A a2(1); // OK, unfortunately
struct V { V(); V(int); }; struct A : virtual V { A(); A(int); }; struct B : virtual V { B(); B(int); }; struct C : A, B, virtual V { C(); C(int); }; A::A(int i) : V(i) { /* ... */ } B::B(int i) { /* ... */ } C::C(int i) { /* ... */ } V v(1); // use V(int) A a(2); // use V(int) B b(3); // use V() C c(4); // use V()
class X { int a; int b; int i; int j; public: const int& r; X(int i): r(a), b(i), i(i), j(this->i) { } };
class A { public: A(int); }; class B : public A { int j; public: int f(); B() : A(f()), // undefined: calls member function but base A not yet initialized j(f()) { } // well-defined: bases are all initialized }; class C { public: C(int); }; class D : public B, C { int i; public: D() : C(f()), // undefined: calls member function but base C not yet initialized i(f()) { } // well-defined: bases are all initialized };
template<class... Mixins> class X : public Mixins... { public: X(const Mixins&... mixins) : Mixins(mixins)... { } };
struct B1 { B1(int, ...) { } }; struct B2 { B2(double) { } }; int get(); struct D1 : B1 { using B1::B1; // inherits B1(int, ...) int x; int y = get(); }; void test() { D1 d(2, 3, 4); // OK: B1 is initialized by calling B1(2, 3, 4), // then d.x is default-initialized (no initialization is performed), // then d.y is initialized by calling get() D1 e; // error: D1 has a deleted default constructor } struct D2 : B2 { using B2::B2; B1 b; }; D2 f(1.0); // error: B1 has a deleted default constructor struct W { W(int); }; struct X : virtual W { using W::W; X() = delete; }; struct Y : X { using X::X; }; struct Z : Y, virtual W { using Y::Y; }; Z z(0); // OK: initialization of Y does not invoke default constructor of X template<class T> struct Log : T { using T::T; // inherits all constructors from class T ~Log() { std::clog << "Destroying wrapper" << std::endl; } };
struct A { A(int); }; struct B : A { using A::A; }; struct C1 : B { using B::B; }; struct C2 : B { using B::B; }; struct D1 : C1, C2 { using C1::C1; using C2::C2; }; struct V1 : virtual B { using B::B; }; struct V2 : virtual B { using B::B; }; struct D2 : V1, V2 { using V1::V1; using V2::V2; }; D1 d1(0); // ill-formed: ambiguous D2 d2(0); // OK: initializes virtual B base class, which initializes the A base class // then initializes the V1 and V2 base classes as if by a defaulted default constructor struct M { M(); M(int); }; struct N : M { using M::M; }; struct O : M {}; struct P : N, O { using N::N; using O::O; }; P p(0); // OK: use M(0) to initialize N's base class, // use M() to initialize O's base class