8   Declarators                                             [dcl.decl]


1 A declarator declares a single object, function,  or  type,  within  a
  declaration.  The init-declarator-list appearing in a declaration is a
  comma-separated sequence of declarators, each of  which  can  have  an
          init-declarator-list , init-declarator
          declarator initializeropt

2 The two components of a declaration are the specifiers decl-specifier-
  seq; _dcl.spec_) and the declarators init-declarator-list).  The spec-
  ifiers  indicate  the  type,  storage class or other properties of the
  objects, functions or typedefs being declared.  The declarators  spec-
  ify  the  names  of these objects, functions or typedefs, and (option-
  ally) modify the type of the  specifiers  with  operators  such  as  *
  (pointer  to) and () (function returning).  Initial values can also be
  specified in a declarator; initializers are  discussed  in  _dcl.init_
  and _class.init_.

3 Each  init-declarator in a declaration is analyzed separately as if it
  was in a declaration by itself.1)

  1) A declaration with several declarators is usually equivalent to the
  corresponding  sequence of declarations each with a single declarator.
  That is
  T  D1, D2, ... Dn;
  is usually equvalent to
  T  D1; T D2; ... T Dn;
  where T is a decl-specifier-seq and each Di is a init-declarator.  The
  exception  occurs  when  a  name  introduced by one of the declarators
  hides a type name used by the dcl-specifiers, so that  when  the  same
  dcl-specifiers  are used in a subsequent declaration, they do not have
  the same meaning, as in
  struct S { ... };
  S   S, T;                       // declare two instances of struct S
  which is not equivalent to
  struct S { ... };
  S   S;
  S   T;                          // error

4 Declarators have the syntax
          ptr-operator declarator
          direct-declarator ( parameter-declaration-clause ) cv-qualifier-seqopt exception-specificationopt
          direct-declarator [ constant-expressionopt ]
          ( declarator )
          * cv-qualifier-seqopt
          ::opt nested-name-specifier * cv-qualifier-seqopt
          cv-qualifier cv-qualifier-seqopt
          ::opt nested-name-specifieropt type-name
  A class-name has special meaning in a declaration of the class of that
  name and when qualified by that name using the scope resolution opera-
  tor :: (_expr.prim_, _class.ctor_, _class.dtor_).

  8.1  Type names                                             [dcl.name]

1 To specify type conversions explicitly, and as an argument of  sizeof,
  new,  or  typeid,  the name of a type shall be specified.  This can be
  done with a type-id, which  is  syntactically  a  declaration  for  an
  object  or  function of that type that omits the name of the object or
          type-specifier-seq abstract-declaratoropt
          type-specifier type-specifier-seqopt
          ptr-operator abstract-declaratoropt
                  ( parameter-declaration-clause ) cv-qualifier-seqopt exception-specificationopt
          direct-abstract-declaratoropt [ constant-expressionopt ]
          ( abstract-declarator )
  It is possible to identify uniquely  the  location  in  the  abstract-
  declarator  where the identifier would appear if the construction were
  a declarator in a declaration.  The named type is then the same as the
  type of the hypothetical identifier.  [Example:
  int                             // int i
  int *                           // int *pi
  int *[3]                        // int *p[3]
  int (*)[3]                      // int (*p3i)[3]
  int *()                         // int *f()
  int (*)(double)                 // int (*pf)(double)

  name respectively the types int," "pointer to int," "array of 3 point-
  ers to int," "pointer to array of 3 int," "function of (no parameters)
  returning  pointer  to  int,"  and  "pointer  to a function of double)
  returning int.''  ]

2 A type can also be named  (often  more  easily)  by  using  a  typedef

  8.2  Ambiguity resolution                              [dcl.ambig.res]

1 The  ambiguity  arising  from  the similarity between a function-style
  cast and a declaration mentioned in _stmt.ambig_ can also occur in the
  context  of  a  declaration.  In that context, the choice is between a
  function declaration with a redundant  set  of  parentheses  around  a
  parameter name and an object declaration with a function-style cast as
  the  initializer.   Just  as  for   the   ambiguities   mentioned   in
  _stmt.ambig_,  the  resolution is to consider any construct that could
  possibly be a declaration a declaration.  [Note: a declaration can  be
  explicitly  disambiguated by a nonfunction-style cast, by a = to indi-
  cate initialization or by removing the  redundant  parentheses  around
  the parameter name.  ] [Example:
  struct S {
  void foo(double a)
      S w(int(a));                // function declaration
      S x(int());                 // function declaration
      S y((int)a);                // object declaration
      S z = int(a);               // object declaration
   --end example]

2 The  ambiguity  arising  from  the similarity between a function-style
  cast and a type-id can occur in  different  contexts.   The  ambiguity
  appears  as  a  choice  between a function-style cast expression and a
  declaration of a type.  The resolution  is  that  any  construct  that
  could  possibly be a type-id in its syntactic context shall be consid-
  ered a type-id.

3 [Example:
  #include <cstddef>
  char *p;
  void *operator new(size_t, int);
  void foo()  {
          const int x = 63;
          new (int(*p)) int;      // new-placement expression
          new (int(*[x]));        // new type-id

4 For another example,

  template <class T>
  struct S {
          T *p;
  S<int()> x;                     // type-id
  S<int(1)> y;                    // expression (ill-formed)

5 For another example,
  void foo()
          sizeof(int(1));         // expression
          sizeof(int());          // type-id (ill-formed)

6 For another example,
  void foo()
          (int(1));               // expression
          (int())1;               // type-id (ill-formed)
   --end example]

7 Another ambiguity arises in a parameter-declaration-clause of a  func-
  tion  declaration,  or in a type-id that is the operand of a sizeof or
  typeid operator, when a type-name is nested in parentheses.   In  this
  case,  the  choice  is  between the declaration of a parameter of type
  pointer to function and the declaration of a parameter with  redundant
  parentheses  around  the declarator-id.  The resolution is to consider
  the type-name as a simple-type-specifier rather than a  declarator-id.
  class C { };
  void f(int(C)) { }              // void f(int (*fp)(C c)) { }
                                  // not: void f(int C);

  int g(C);

  void foo() {
          f(1);                   // error: cannot convert 1 to function pointer
          f(g);                   // OK
  For another example,
  class C { };
  void h(int *(C[10]));           // void h(int *(*_fp)(C _parm[10]));
                                  // not: void h(int *C[10]);
   --end example]

  8.3  Meaning of declarators                              [dcl.meaning]

1 A  list  of  declarators  appears after an optional (clause _dcl.dcl_)
  decl-specifier-seq (_dcl.spec_).  Each declarator contains exactly one
  declarator-id;  it  names  the  identifier  that is declared.  The id-
  expression of a declarator-id shall be a simple identifier except  for
  the declaration of some special functions (_class.conv_, _class.dtor_,
  _over.oper_) and for the declaration of  template  specializations  or

  partial  specializations  (_temp.spec_).  A declarator-id shall not be
  qualified  except  for   the   definition   of   a   member   function
  (_class.mfct_)  or static data member (_class.static_) or nested class
  (_class.nest_) outside  of  its  class,  the  definition  or  explicit
  instantiation  of  a function, variable or class member of a namespace
  outside of its namespace, or the definition of a  previously  declared
  explicit  specialization  outside of its namespace, or the declaration
  of a friend function that is a member of another  class  or  namespace
  (_class.friend_).   When  the declarator-id is qualified, the declara-
  tion shall refer to a previously  declared  member  of  the  class  or
  namespace to which the qualifier refers, and the member shall not have
  been introduced by a using-declaration in the scope of  the  class  or
  namespace nominated by the nested-name-specifier of the declarator-id.
  [Note: if the qualifier is the global ::  scope  resolution  operator,
  the  declarator-id  refers  to a name declared in the global namespace
  scope.  ] In the qualified declarator-id for a class or namespace mem-
  ber  definition  that  appears outside of the member's class or names-
  pace, the nested-name-specifier shall not name any of  the  namespaces
  that enclose the member's definition.  [Example:
  namespace A {
          struct B {
                  void f();
          void A::B::f() { }      // ill-formed: the declarator must not be
                                  // qualified with A::
   --end example]

2 An  auto,  static, extern, register, mutable, friend, inline, virtual,
  or typedef specifier applies directly to each declarator-id in a init-
  declarator-list;  the type specified for each declarator-id depends on
  both the decl-specifier-seq and its declarator.

3 Thus, a declaration of a particular identifier has the form
  T D
  where T is a decl-specifier-seq and D is a declarator.  Following is a
  recursive  procedure  for  determining the type specified for the con-
  tained declarator-id by such a declaration.

4 First, the decl-specifier-seq determines a type.  In a declaration
  T D
  the decl-specifier-seq T determines the type  T."   [Example:  in  the
  int unsigned i;
  the  type  specifiers  int  unsigned  determine the type unsigned int"
  (_dcl.type.simple_).  ]

5 In a declaration T D where D is an unadorned identifier  the  type  of
  this identifier is T."

6 In a declaration T D where D has the form
  ( D1 )
  the  type  of  the  contained declarator-id is the same as that of the
  contained declarator-id in the declaration

  T D1
  Parentheses do not alter the type of the embedded  declarator-id,  but
  they can alter the binding of complex declarators.

  8.3.1  Pointers                                              [dcl.ptr]

1 In a declaration T D where D has the form
  * cv-qualifier-seqopt D1
  and  the  type  of the identifier in the declaration T D1 is "derived-
  declarator-type-list T," then the type  of  the  identifier  of  D  is
  "derived-declarator-type-list cv-qualifier-seq pointer to T."  The cv-
  qualifiers apply to the pointer and not to the object pointed to.

2 [Example: the declarations
  const int ci = 10, *pc = &ci, *const cpc = pc, **ppc;
  int i, *p, *const cp = &i;
  declare ci, a constant integer; pc, a pointer to a  constant  integer;
  cpc,  a  constant  pointer  to a constant integer, ppc, a pointer to a
  pointer to a constant integer; i, an integer; p, a pointer to integer;
  and  cp,  a constant pointer to integer.  The value of ci, cpc, and cp
  cannot be changed after  initialization.   The  value  of  pc  can  be
  changed,  and  so  can  the object pointed to by cp.  Examples of some
  correct operations are
  i = ci;
  *cp = ci;
  pc = cpc;
  pc = p;
  ppc = &pc;
  Examples of ill-formed operations are
  ci = 1;                         // error
  ci++;                           // error
  *pc = 2;                        // error
  cp = &ci;                       // error
  cpc++;                          // error
  p = pc;                         // error
  ppc = &p;                       // error
  Each is unacceptable because it would either change the  value  of  an
  object  declared const or allow it to be changed through a cv-unquali-
  fied pointer later, for example:
  *ppc = &ci;                     // OK, but would make p point to ci ...
                                  // ... because of previous error
  *p = 5;                         // clobber ci
   --end example]

3 See also _expr.ass_ and _dcl.init_.

4 [Note: there are no pointers to references; see _dcl.ref_.  Since  the
  address  of  a  bit-field (_class.bit_) cannot be taken, a pointer can
  never point to a bit-field.  ]

  8.3.2  References                                            [dcl.ref]

1 In a declaration T D where D has the form
  & D1
  and the type of the identifier in the declaration T  D1  is  "derived-
  declarator-type-list  T,"  then  the  type  of  the identifier of D is
  "derived-declarator-type-list reference to  T."   Cv-qualified  refer-
  ences  are  ill-formed  except  when  the cv-qualifiers are introduced
  through the use of a typedef (_dcl.typedef_) or  of  a  template  type
  argument  (_temp.arg_),  in  which case the cv-qualifiers are ignored.
  [Example: in
  typedef int& A;
  const A aref = 3;               // ill-formed;
                                  // non-const reference initialized with rvalue
  the type of aref is "reference to int", not "const reference to  int".
  ]  [Note:  a  reference can be thought of as a name of an object.  ] A
  declarator that specifies the type "reference  to  cv  void"  is  ill-

2 [Example:
  void f(double& a) { a += 3.14; }
  // ...
  double d = 0;
  declares  a to be a reference parameter of f so the call f(d) will add
  3.14 to d.
  int v[20];
  // ...
  int& g(int i) { return v[i]; }
  // ...
  g(3) = 7;
  declares the function g() to return  a  reference  to  an  integer  so
  g(3)=7  will  assign  7  to  the  fourth  element of the array v.  For
  another example,
  struct link {
      link* next;

  link* first;
  void h(link*& p)                // p is a reference to pointer
      p->next = first;
      first = p;
      p = 0;
  void k()
          link* q = new link;
  declares p to be a reference to a pointer to link so h(q) will leave q
  with the value zero.  See also _dcl.init.ref_.  ]

3 It  is  unspecified  whether  or  not  a  reference  requires  storage

4 There shall be no references to references, no arrays  of  references,
  and  no  pointers to references.  The declaration of a reference shall
  contain an initializer (_dcl.init.ref_) except  when  the  declaration
  contains  an  explicit extern specifier (_dcl.stc_), is a class member
  (_class.mem_) declaration within a class declaration, or is the decla-
  ration  of  a parameter or a return type (_dcl.fct_); see _basic.def_.
  A reference shall be initialized to refer to a valid object  or  func-
  tion.   [Note: in particular, a null reference cannot exist in a well-
  defined program, because the only way to create such a reference would
  be  to  bind  it  to  the  "object"  obtained  by dereferencing a null
  pointer,  which  causes   undefined   behavior.    As   described   in
  _class.bit_, a reference cannot be bound directly to a bit-field.  ]

  8.3.3  Pointers to members                                  [dcl.mptr]

1 In a declaration T D where D has the form
  ::opt nested-name-specifier * cv-qualifier-seqopt D1
  and the nested-name-specifier names a class, and the type of the iden-
  tifier in the declaration T D1  is  "derived-declarator-type-list  T,"
  then  the type of the identifier of D is "derived-declarator-type-list
  cv-qualifier-seq pointer to member of class  nested-name-specifier  of
  type T."

2 [Example:
  class X {
      void f(int);
      int a;
  class Y;

  int X::* pmi = &X::a;
  void (X::* pmf)(int) = &X::f;
  double X::* pmd;
  char Y::* pmc;
  declares  pmi,  pmf,  pmd  and pmc to be a pointer to a member of X of
  type int, a pointer to a member of X of type void(int), a pointer to a
  member of X of type double and a pointer to a member of Y of type char
  respectively.  The declaration of pmd is well-formed even though X has
  no members of type double.  Similarly, the declaration of pmc is well-
  formed even though Y is an incomplete type.  pmi and pmf can  be  used
  like this:
  X obj;
  obj.*pmi = 7;                   // assign 7 to an integer
                                  // member of obj
  (obj.*pmf)(7);                  // call a function member of obj
                                  // with the argument 7
   --end example]

3 A  pointer  to  member  shall  not point to a static member of a class
  (_class.static_), a member with reference type, or cv  void."   [Note:
  see also _expr.unary_ and _expr.mptr.oper_.  The type "pointer to mem-
  ber" is distinct from the type "pointer", that is, a pointer to member
  is declared only by the pointer to member declarator syntax, and never
  by the pointer declarator syntax.  There is  no  "reference-to-member"
  type in C++.  ]

  8.3.4  Arrays                                              [dcl.array]

1 In a declaration T D where D has the form
  D1 [constant-expressionopt]
  and  the  type  of  the identifier in the declaration T D1 is derived-
  declarator-type-list T," then the type of the identifier of  D  is  an
  array  type.   T is called the array element type; this type shall not
  be a reference type, the (possibly cv-qualified) type void, a function
  type   or   an   abstract  class  type.   If  the  constant-expression
  (_expr.const_) is present, it shall be an integral constant expression
  and  its  value  shall  be greater than zero.  The constant expression
  specifies the bound of (number of elements  in)  the  array.   If  the
  value  of  the constant expression is N, the array has N elements num-
  bered 0 to N-1, and the type of  the  identifier  of  D  is  "derived-
  declarator-type-list  array of N T."  An object of array type contains
  a contiguously allocated non-empty set of N sub-objects of type T.  If
  the constant expression is omitted, the type of the identifier of D is
  "derived-declarator-type-list array of unknown bound of T," an  incom-
  plete  object type.  The type "derived-declarator-type-list array of N
  T" is a different type  from  the  type  "derived-declarator-type-list
  array of unknown bound of T," see _basic.types_.  Any type of the form
  "cv-qualifier-seq array of N T" is adjusted to "array of  N  cv-quali-
  fier-seq  T," and similarly for "array of unknown bound of T."  [Exam-
  typedef int A[5], AA[2][3];
  typedef const A CA;             // type is ``array of 5 const int''
  typedef const AA CAA;           // type is ``array of 2 array of 3 const int''
   --end example] [Note: an "array of N cv-qualifier-seq T" has cv-qual-
  ified  type;  such  an  array  has  internal linkage unless explicitly
  declared extern (_dcl.type.cv_) and must be initialized  as  specified
  in _dcl.init_.  ]

2 An  array can be constructed from one of the fundamental types (except
  void), from a pointer, from a pointer to member, from a class, from an
  enumeration type, or from another array.

3 When  several  "array  of"  specifications are adjacent, a multidimen-
  sional array is created; the constant  expressions  that  specify  the
  bounds  of  the arrays can be omitted only for the first member of the
  sequence.  [Note: this elision is useful for  function  parameters  of
  array  types, and when the array is external and the definition, which
  allocates storage, is given elsewhere.  ] The  first  constant-expres-
  sion  can  also  be omitted when the declarator is followed by an ini-
  tializer (_dcl.init_).  In this case the bound is calculated from  the
  number  of  initial  elements (say, N) supplied (_dcl.init.aggr_), and
  the type of the identifier of D is "array of N T."

4 [Example:
  float fa[17], *afp[17];
  declares an array of float numbers and an array of pointers  to  float
  numbers.  For another example,
  static int x3d[3][5][7];
  declares  a  static  three-dimensional  array  of  integers, with rank
  3󬊇.  In complete detail, x3d is an array of three items; each  item
  is  an  array of five arrays; each of the latter arrays is an array of
  seven integers.   Any  of  the  expressions  x3d,  x3d[i],  x3d[i][j],
  x3d[i][j][k] can reasonably appear in an expression.  ]

5 [Note:  conversions  affecting  lvalues of array type are described in
  _conv.array_.   Objects  of  array  types  cannot  be  modified,   see
  _basic.lval_.  ]

6 Except  where  it has been declared for a class (_over.sub_), the sub-
  script operator [] is interpreted in such a way that E1[E2] is identi-
  cal to *((E1)+(E2)).  Because of the conversion rules that apply to +,
  if E1 is an array and E2 an integer, then E1[E2] refers to  the  E2-th
  member  of  E1.   Therefore,  despite  its asymmetric appearance, sub-
  scripting is a commutative operation.

7 A consistent rule is followed for multidimensional arrays.  If E is an
  n-dimensional  array of rank ij...k, then E appearing in an expres-
  sion is converted to a pointer to an (n-1)-dimensional array with rank
  j...k.   If  the  *  operator,  either explicitly or implicitly as a
  result of subscripting, is applied to this pointer, the result is  the
  pointed-to  (n-1)-dimensional  array, which itself is immediately con-
  verted into a pointer.

8 [Example: consider
  int x[3][5];
  Here x is a 35 array of integers.  When x appears in  an  expression,
  it  is  converted  to  a pointer to (the first of three) five-membered
  arrays of integers.  In the expression x[i], which  is  equivalent  to
  *(x+i),  x  is  first converted to a pointer as described; then x+i is
  converted to the type of x, which involves multiplying i by the length
  of  the  object  to  which  the  pointer  points,  namely five integer
  objects.  The results are added and indirection applied  to  yield  an
  array  (of  five integers), which in turn is converted to a pointer to
  the first of the integers.  If there is  another  subscript  the  same
  argument applies again; this time the result is an integer.  ]

9 [Note: it follows from all this that arrays in C++ are stored row-wise
  (last subscript varies fastest) and that the first  subscript  in  the
  declaration helps determine the amount of storage consumed by an array
  but plays no other part in subscript calculations.  ]

  8.3.5  Functions                                             [dcl.fct]

1 In a declaration T D where D has the form
  D1 ( parameter-declaration-clause ) cv-qualifier-seqopt exception-specificationopt
  and the type of the contained declarator-id in the declaration T D1 is
  derived-declarator-type-list T," the type of the declarator-id in D is

  "derived-declarator-type-list  function   of   (parameter-declaration-
  clause)  cv-qualifier-seqopt  returning  T";  a type of this form is a
  function type2).
          parameter-declaration-listopt ...opt
          parameter-declaration-list , ...
          parameter-declaration-list , parameter-declaration
          decl-specifier-seq declarator
          decl-specifier-seq declarator = assignment-expression
          decl-specifier-seq abstract-declaratoropt
          decl-specifier-seq abstract-declaratoropt = assignment-expression

2 The  parameter-declaration-clause determines the arguments that can be
  specified, and their processing, when the function is called.   [Note:
  the  parameter-declaration-clause  is  used  to  convert the arguments
  specified on the function call; see _expr.call_.  ] If the  parameter-
  declaration-clause  is  empty,  the  function takes no arguments.  The
  parameter list (void) is  equivalent  to  the  empty  parameter  list.
  Except  for  this  special  case,  void  shall not be a parameter type
  (though types derived from void, such as void*, can).  If the  parame-
  ter-declaration-clause  terminates  with  an  ellipsis,  the number of
  arguments shall be equal to or greater than the number  of  parameters
  specified.   Where  syntactically correct, ", ..."  is synonymous with
  "...".  [Example: the declaration
  int printf(const char*, ...);
  declares a function that can be called with varying numbers and  types
  of arguments.
  printf("hello world");
  printf("a=%d b=%d", a, b);
  However, the first argument must be of a type that can be converted to
  a const char*.  ] [Note: the  standard  header  <cstdarg>  contains  a
  mechanism  for  accessing  arguments  passed  using  the ellipsis (see
  _expr.call_ and _lib.support.runtime_).  ]

3 A single name can be used for several different functions in a  single
  scope; this is function overloading (clause _over_).  All declarations
  for a function with a given parameter list shall agree exactly both in
  the  type  of the value returned and in the number and type of parame-
  ters; the presence or absence of the ellipsis is  considered  part  of
  the  function  type.   The  type of a function is determined using the
  following rules.  The type of each parameter is  determined  from  its
  own  decl-specifier-seq and declarator.  After determining the type of
  each parameter, any parameter  of  type  "array  of  T"  or  "function
  returning  T" is adjusted to be "pointer to T" or "pointer to function
  returning T," respectively.  After producing  the  list  of  parameter
  types,  several  transformations take place upon these types to deter-
  mine the function type.  Any cv-qualifier modifying a  parameter  type
  2) As indicated by the syntax, cv-qualifiers are a significant  compo-
  nent in function return types.

  is   deleted.    [Example:   the   type   void(*)(const  int)  becomes
  void(*)(int)  --end example] Such cv-qualifiers affect only the  defi-
  nition  of  the parameter within the body of the function; they do not
  affect the function type.  If  a  storage-class-specifier  modifies  a
  parameter  type,  the  specifier is deleted.  [Example: register char*
  becomes char*  --end  example]  Such  storage-class-specifiers  affect
  only  the definition of the parameter within the body of the function;
  they do not affect the function type.  The resulting  list  of  trans-
  formed parameter types is the function's parameter type list.

4 A  cv-qualifier-seq shall only be part of the function type for a non-
  static member function, the function type to which a pointer to member
  refers,  or the top-level function type of a function typedef declara-
  tion.  The effect of a cv-qualifier-seq in a  function  declarator  is
  not  the  same as adding cv-qualification on top of the function type,
  i.e., it does not create a cv-qualified function type.  In fact, if at
  any  time  in the determination of a type a cv-qualified function type
  is formed, the program is ill-formed.  [Example:
  typedef void F();
  struct S {
          const F f;              // ill-formed:
                                  // not equivalent to: void f() const;
   --end example] The return type, the parameter type list and  the  cv-
  qualifier-seq,  but  not  the default arguments (_dcl.fct.default_) or
  the exception specification (_except.spec_), are part of the  function
  type.   [Note:  function  types are checked during the assignments and
  initializations of pointer-to-functions,  reference-to-functions,  and
  pointer-to-member-functions.  ]

5 [Example: the declaration
  int fseek(FILE*, long, int);
  declares a function taking three arguments of the specified types, and
  returning int (_dcl.type_).  ]

6 If the type of a parameter includes a type of  the  form  "pointer  to
  array  of  unknown bound of T" or "reference to array of unknown bound
  of  T," the program is ill-formed.3) Functions shall not have a return
  type of type array or function, although they may have a  return  type
  of type pointer or reference to such things.  There shall be no arrays
  of functions, although there can be arrays of pointers  to  functions.
  Types  shall not be defined in return or parameter types.  The type of
  a parameter or the return type for a function declaration that is  not
  a definition may be an incomplete class type.

  3) This excludes parameters of  type  "ptr-arr-seq  T2"  where  T2  is
  "pointer  to  array of unknown bound of T" and where ptr-arr-seq means
  any sequence of "pointer to" and "array of" derived declarator  types.
  This exclusion applies to the parameters of the function, and if a pa-
  rameter is a pointer to function or pointer to member function then to
  its parameters also, etc.

7 A typedef of function type may be used to declare a function but shall
  not be used to define a function (_dcl.fct.def_).  [Example:
  typedef void F();
  F  fv;                          // OK: equivalent to void fv();
  F  fv { }                       // ill-formed
  void fv() { }                   // OK: definition of fv
   --end example] A typedef of a function type whose declarator includes
  a cv-qualifier-seq shall be used only to declare the function type for
  a nonstatic member function, to declare the function type to  which  a
  pointer to member refers, or to declare the top-level function type of
  another function typedef declaration.  [Example:
  typedef int FIC(int) const;
  FIC f;                          // ill-formed: does not declare a member function
  struct S {
          FIC f;                  // OK
  FIC S::*pm = &S::f;             // OK
   --end example]

8 An identifier can optionally be provided as a parameter name; if  pre-
  sent  in  a  function definition (_dcl.fct.def_), it names a parameter
  (sometimes called "formal argument").  [Note: in particular, parameter
  names  are  also optional in function definitions and names used for a
  parameter in different declarations and the definition of  a  function
  need  not  be  the same.  If a parameter name is present in a function
  declaration that is not a definition, it cannot be used outside of the
  parameter-declaration-clause  since it goes out of scope at the end of
  the function declarator (_basic.scope_).  ]

9 [Example: the declaration
  int i,
      (*pif)(const char*, const char*);
  declares an integer i, a pointer pi to an integer, a function f taking
  no  arguments and returning an integer, a function fpi taking an inte-
  ger argument and returning a pointer to an integer, a pointer pif to a
  function  which  takes two pointers to constant characters and returns
  an integer, a function fpif taking an integer argument and returning a
  pointer  to  a  function that takes an integer argument and returns an
  integer.  It is especially useful to compare fpi and pif.  The binding
  of *fpi(int) is *(fpi(int)), so the declaration suggests, and the same
  construction in an expression requires, the calling of a function fpi,
  and  then  using  indirection through the (pointer) result to yield an
  integer.  In the declarator  (*pif)(const  char*,  const  char*),  the
  extra parentheses are necessary to indicate that indirection through a
  pointer to a function yields a function,  which  is  then  called.   ]
  [Note:  typedefs  are  sometimes  convenient when the return type of a
  function is complex.  For example, the function fpif above could  have
  been declared
  typedef int  IFUNC(int);
  IFUNC*  fpif(int);

   --end note]

  8.3.6  Default arguments                             [dcl.fct.default]

1 If  an expression is specified in a parameter declaration this expres-
  sion is used as a default argument.  Default arguments will be used in
  calls where trailing arguments are missing.

2 [Example: the declaration
  void point(int = 3, int = 4);
  declares  a  function  that can be called with zero, one, or two argu-
  ments of type int.  It can be called in any of these ways:
  point(1,2);  point(1);  point();
  The last two  calls  are  equivalent  to  point(1,4)  and  point(3,4),
  respectively.  ]

3 A  default  argument expression shall be specified only in the parame-
  ter-declaration-clause of a function declaration  or  in  a  template-
  parameter  (_temp.param_).  If it is specified in a parameter-declara-
  tion-clause, it shall not  occur  within  a  declarator  or  abstract-
  declarator of a parameter-declaration.4)

4 For  non-template  functions,  default arguments can be added in later
  declarations of a function in the same scope.  Declarations in differ-
  ent  scopes  have completely distinct sets of default arguments.  That
  is, declarations in inner scopes do not acquire default arguments from
  declarations  in  outer  scopes,  and vice versa.  In a given function
  declaration, all parameters subsequent to a parameter with  a  default
  argument  shall  have  default  arguments supplied in this or previous
  declarations.  A default argument shall not be redefined  by  a  later
  declaration (not even to the same value).  [Example:
  void f(int, int);
  void f(int, int = 7);
  void h()
      f(3);                       // OK, calls f(3, 7)
      void f(int = 1, int);       // error: does not use default
                                  // from surrounding scope

  4)  This  means  that default arguments cannot appear, for example, in
  declarations of pointers to functions,  references  to  functions,  or
  typedef declarations.

  void m()
      void f(int, int);           // has no defaults
      f(4);                       // error: wrong number of arguments
      void f(int, int = 5);       // OK
      f(4);                       // OK, calls f(4, 5);
      void f(int, int = 5);       // error: cannot redefine, even to
                                  // same value
  void n()
      f(6);                       // OK, calls f(6, 7)
    --end  example]  For  a  given  inline function defined in different
  translation units, the accumulated sets of default  arguments  at  the
  end of the translation units shall be the same; see _basic.def.odr_.

5 A  default argument expression is implicitly converted (clause _conv_)
  to the parameter type.  The default argument expression has  the  same
  semantic constraints as the initializer expression in a declaration of
  a variable of the parameter type, using the copy-initialization seman-
  tics  (_dcl.init_).   The  names  in the expression are bound, and the
  semantic constraints are checked, at the point where the default argu-
  ment  expression  appears.   Name lookup and checking of semantic con-
  straints for default arguments in function  templates  and  in  member
  functions   of   class   templates   are  performed  as  described  in
  _temp.inst_.  [Example: in the following code, g will be  called  with
  the value f(1):
  int a = 1;
  int f(int);
  int g(int x = f(a));            // default argument: f(::a)

  void h() {
      a = 2;
          int a = 3;
          g();                    // g(f(::a))
    --end  example]  [Note:  in  member  function declarations, names in
  default  argument  expressions  are  looked   up   as   described   in
  _basic.lookup.unqual_.   Access  checking  applies to names in default
  argument expressions as described in clause _class.access_.  ]

6 The default arguments in a member  function  definition  that  appears
  outside  of the class definition are added to the set of default argu-
  ments provided by the member function declaration in the class defini-
  tion.  [Example:
  class C {
          void f(int i = 3);
          void g(int i, int j = 99);

  void C::f(int i = 3)            // error: default argument already
  { }                             // specified in class scope
  void C::g(int i = 88, int j)    // in this translation unit,
  { }                             // C::g can be called with no argument
   --end example]

7 Local  variables  shall  not  be used in default argument expressions.
  void f()
      int i;
      extern void g(int x = i);   // error
      // ...
   --end example]

8 The keyword this shall not be used in a default argument of  a  member
  function.  [Example:
  class A {
      void f(A* p = this) { }     // error
   --end example]

9 Default arguments are evaluated each time the function is called.  The
  order of evaluation of  function  arguments  is  unspecified.   Conse-
  quently,  parameters  of a function shall not be used in default argu-
  ment expressions, even if they are not  evaluated.   Parameters  of  a
  function  declared  before  a default argument expression are in scope
  and can hide namespace and class member names.  [Example:
  int a;
  int f(int a, int b = a);                // error: parameter a
                                          // used as default argument
  typedef int I;
  int g(float I, int b = I(2));           // error: parameter I found
  int h(int a, int b = sizeof(a));        // error, parameter a used
                                          // in default argument
   --end example] Similarly, a nonstatic member shall not be used  in  a
  default  argument  expression,  even if it is not evaluated, unless it
  appears as the id-expression  of  a  class  member  access  expression
  (_expr.ref_)  or  unless  it  is  used  to  form  a  pointer to member
  (_expr.unary.op_).  [Example: the declaration of X::mem1() in the fol-
  lowing  example  is  ill-formed  because no object is supplied for the
  nonstatic member X::a used as an initializer.
  int b;
  class X {
      int a;
      int mem1(int i = a);        // error: nonstatic member a
                                  // used as default argument
      int mem2(int i = b);        // OK;  use X::b
      static int b;
  The declaration of X::mem2() is meaningful, however, since  no  object
  is  needed  to  access  the static member X::b.  Classes, objects, and
  members are described in clause _class_.  ] A default argument is  not

  part of the type of a function.  [Example:
  int f(int = 0);

  void h()
      int j = f(1);
      int k = f();                // OK, means f(0)

  int (*p1)(int) = &f;
  int (*p2)() = &f;               // error: type mismatch
    --end example] When a declaration of a function is introduced by way
  of  a  using-declaration  (_namespace.udecl_),  any  default  argument
  information associated with the declaration is made known as well.  If
  the function is redeclared thereafter in the namespace with additional
  default  arguments,  the  additional  arguments  are also known at any
  point following the redeclaration where the  using-declaration  is  in

10A  virtual  function call (_class.virtual_) uses the default arguments
  in the declaration of the virtual function determined  by  the  static
  type  of  the pointer or reference denoting the object.  An overriding
  function in a derived class does not acquire  default  arguments  from
  the function it overrides.  [Example:
  struct A {
      virtual void f(int a = 7);
  struct B : public A {
      void f(int a);
  void m()
      B* pb = new B;
      A* pa = pb;
      pa->f();                    // OK, calls pa->B::f(7)
      pb->f();                    // error: wrong number of arguments for B::f()
   --end example]

  8.4  Function definitions                                [dcl.fct.def]

1 Function definitions have the form
          decl-specifier-seqopt declarator ctor-initializeropt function-body
          decl-specifier-seqopt declarator function-try-block

  The declarator in a function-definition shall have the form
  D1 ( parameter-declaration-clause ) cv-qualifier-seqopt exception-specificationopt
  as described in _dcl.fct_.  A function shall be defined only in names-
  pace or class scope.

2 [Example: a simple example of a complete function definition is
  int max(int a, int b, int c)
      int m = (a > b) ? a : b;
      return (m > c) ? m : c;
  Here int is the decl-specifier-seq; max(int a, int b, int  c)  is  the
  declarator; { /* ... */ } is the function-body.  ]

3 A ctor-initializer is used only in a constructor; see _class.ctor_ and

4 A cv-qualifier-seq can be part of a non-static member function  decla-
  ration,  non-static  member  function definition, or pointer to member
  function only; see _class.this_.  It is part of the function type.

5 [Note: unused parameters need not be named.  For example,
  void print(int a, int)
      printf("a = %d\n",a);
   --end note]

  8.5  Initializers                                           [dcl.init]

1 A declarator can specify an initial value  for  the  identifier  being
  declared.  The identifier designates an object or reference being ini-
  tialized.  The process of initialization described in the remainder of
  _dcl.init_  applies also to initializations specified by other syntac-
  tic contexts, such as the initialization of function  parameters  with
  argument  expressions  (_expr.call_)  or  the initialization of return
  values (_stmt.return_).
          = initializer-clause
          ( expression-list )
          { initializer-list ,opt }
          { }
          initializer-list , initializer-clause

2 Automatic, register, static, and external variables of namespace scope
  can  be  initialized  by  arbitrary expressions involving literals and
  previously declared variables and functions.  [Example:
  int f(int);
  int a = 2;
  int b = f(a);
  int c(b);
   --end example]

3 [Note:  default  argument  expressions  are   more   restricted;   see

4 The  order  of  initialization  of  static  objects  is  described  in
  _basic.start_ and _stmt.dcl_.  ]

5 To zero-initialize storage for an object of type T means:

  --if T is a scalar type (_basic.types_), the storage  is  set  to  the
    value of 0 (zero) converted to T;

  --if  T is a non-union class type, the storage for each nonstatic data
    member and each base-class subobject is zero-initialized;

  --if  T  is  a  union type, the storage for its first data member5) is

  --if T is an array type, the storage for each element is zero-initial-

  --if T is a reference type, no initialization is performed.

  To default-initialize an object of type T means:

  --if T is a non-POD class type (clause _class_), the default construc-
    tor for T is called (and the initialization is ill-formed if  T  has
    no accessible default constructor);

  --if T is an array type, each element is default-initialized;

  --otherwise, the storage for the object is zero-initialized.

  A program that calls for default-initialization of an entity of refer-
  ence type is ill-formed.  If T is a cv-qualified type, the cv-unquali-
  fied version of T is used for these definitions of zero-initialization
  and default-initialization.

6 The memory occupied by any object of static storage duration shall  be
  zero-initialized  at  program  startup before any other initialization
  takes place.  [Note: in some cases, additional initialization is  done
  later.  ]

7 An  object whose initializer is an empty set of parentheses, i.e., (),
  shall be default-initialized.

8 [Note: since () is not permitted by the syntax for initializer,
  X a();
  is not the declaration of an object of class X, but the declaration of
  a function taking no argument and returning an X.  The form () is per-
  mitted  in  certain   other   initialization   contexts   (_expr.new_,
  _expr.type.conv_, _class.base.init_).  ]

  5) This member must not be static, by virtue of  the  requirements  in

9 If  no  initializer  is  specified for an object, and the object is of
  (possibly cv-qualified) non-POD class type  (or  array  thereof),  the
  object  shall be default-initialized; if the object is of const-quali-
  fied type, the  underlying  class  type  shall  have  a  user-declared
  default constructor.  Otherwise, if no initializer is specified for an
  object, the object and its subobjects, if any, have  an  indeterminate
  initial  value6); if the object or any of its subobjects are of const-
  qualified type, the program is ill-formed.

10An initializer for a static member is in the  scope  of  the  member's
  class.  [Example:
  int a;

  struct X {
      static int a;
      static int b;

  int X::a = 1;
  int X::b = a;                   // X::b = X::a
   --end example]

11The  form  of  initialization  (using  parentheses  or =) is generally
  insignificant, but does matter when the entity being initialized has a
  class  type;  see below.  A parenthesized initializer can be a list of
  expressions only when the entity being initialized has a class type.

12The initialization that occurs in argument passing,  function  return,
  throwing   an   exception   (_except.throw_),  handling  an  exception
  (_except.handle_),    and     brace-enclosed     initializer     lists
  (_dcl.init.aggr_)  is  called copy-initialization and is equivalent to
  the form
  T x = a;
  The  initialization  that  occurs  in  new  expressions  (_expr.new_),
  static_cast expressions (_expr.static.cast_), functional notation type
  conversions  (_expr.type.conv_),  and  base  and  member  initializers
  (_class.base.init_)  is called direct-initialization and is equivalent
  to the form
  T x(a);

13If T is a scalar type, then a declaration of the form
  T x = { a };
  is equivalent to
  T x = a;

14The semantics of initializers are as follows.  The destination type is
  the  type  of the object or reference being initialized and the source
  type is the type of the initializer expression.  The  source  type  is
  not  defined  when  the  initializer is brace-enclosed or when it is a
  6) This does not apply to aggregate objects with automatic storage du-
  ration initialized with an incomplete brace-enclosed initializer-list;
  see _dcl.init.aggr_.

  parenthesized list of expressions.

  --If the destination type is a reference type, see _dcl.init.ref_.

  --If the destination type is an array of characters  or  an  array  of
    wchar_t,   and   the   initializer   is   a   string   literal,  see

  --Otherwise, if the destination type is an array, see _dcl.init.aggr_.

  --If the destination type is a (possibly cv-qualified) class type:

    --If  the  class is an aggregate (_dcl.init.aggr_), and the initial-
      izer is a brace-enclosed list, see _dcl.init.aggr_.

    --If the initialization is direct-initialization, or if it is  copy-
      initialization where the cv-unqualified version of the source type
      is the same class as, or a derived class of, the class of the des-
      tination,  constructors  are considered.  The applicable construc-
      tors are enumerated (_over.match.ctor_), and the best one is  cho-
      sen  through  overload resolution (_over.match_).  The constructor
      so selected is called to initialize the object, with the  initial-
      izer expression(s) as its argument(s).  If no constructor applies,
      or the overload resolution is  ambiguous,  the  initialization  is

    --Otherwise  (i.e.,  for  the  remaining copy-initialization cases),
      user-defined conversion sequences that can convert from the source
      type  to  the  destination  type or (when a conversion function is
      used) to a derived class thereof are enumerated  as  described  in
      _over.match.copy_,  and  the  best  one is chosen through overload
      resolution (_over.match_).  If the conversion cannot be done or is
      ambiguous,   the   initialization  is  ill-formed.   The  function
      selected is called with the initializer expression  as  its  argu-
      ment;  if  the  function  is a constructor, the call initializes a
      temporary of the destination type.  The result of the call  (which
      is the temporary for the constructor case) is then used to direct-
      initialize, according to the rules above, the object that  is  the
      destination  of  the  copy-initialization.   In  certain cases, an
      implementation is permitted to eliminate the copying  inherent  in
      this direct-initialization by constructing the intermediate result
      directly into the object being initialized; see _class.temporary_,

  --Otherwise,  if  the  source  type is a (possibly cv-qualified) class
    type, conversion functions are considered.  The  applicable  conver-
    sion  functions are enumerated (_over.match.conv_), and the best one
    is chosen through overload  resolution  (_over.match_).   The  user-
    defined  conversion so selected is called to convert the initializer
    expression into the object being  initialized.   If  the  conversion
    cannot be done or is ambiguous, the initialization is ill-formed.

  --Otherwise,  the initial value of the object being initialized is the
    (possibly converted) value of the initializer expression.   Standard

    conversions  (clause  _conv_) will be used, if necessary, to convert
    the initializer expression to the cv-unqualified version of the des-
    tination  type;  no user-defined conversions are considered.  If the
    conversion cannot be done, the initialization is ill-formed.  [Note:
    an  expression of type "cv1 T" can initialize an object of type "cv2
    T" independently of the cv-qualifiers cv1 and cv2.
      int a;
      const int b = a;
      int c = b;
     --end note]

  8.5.1  Aggregates                                      [dcl.init.aggr]

1 An aggregate is an array or a class (clause  _class_)  with  no  user-
  declared  constructors  (_class.ctor_),  no  private or protected non-
  static data members (clause _class.access_), no base  classes  (clause
  _class.derived_), and no virtual functions (_class.virtual_).

2 When  an  aggregate  is initialized the initializer can be an initial-
  izer-clause consisting of a brace-enclosed,  comma-separated  list  of
  initializers  for  the members of the aggregate, written in increasing
  subscript or member order.  If the aggregate  contains  subaggregates,
  this  rule  applies  recursively  to  the members of the subaggregate.
  struct A {
          int x;
          struct B {
                  int i;
                  int j;
          } b;
  } a = { 1, { 2, 3 } };
  initializes a.x with 1, a.b.i with 2, a.b.j with 3.  ]

3 An aggregate that is a class can also be  initialized  with  a  single
  expression not enclosed in braces, as described in _dcl.init_.

4 An  array  of  unknown size initialized with a brace-enclosed initial-
  izer-list containing n initializers, where n  shall  be  greater  than
  zero, is defined as having n elements (_dcl.array_).  [Example:
  int x[] = { 1, 3, 5 };
  declares  and  initializes x as a one-dimensional array that has three
  elements since no size was specified and there are three initializers.
  ]  An  empty  initializer list {} shall not be used as the initializer
  for an array of unknown bound.7)

5 Static  data  members are not considered members of the class for pur-
  poses of aggregate initialization.  [Example:

  7) The syntax provides for empty  initializer-lists,  but  nonetheless
  C++ does not have zero length arrays.

  struct A {
          int i;
          static int s;
          int j;
  } a = { 1, 2 };
  Here, the second initializer 2 initializes a.j and not the static data
  member A::s.  ]

6 An  initializer-list  is  ill-formed  if  the  number  of initializers
  exceeds the number of members or elements to initialize.  [Example:
  char cv[4] = { 'a', 's', 'd', 'f', 0 };         // error
  is ill-formed.  ]

7 If there are fewer initializers in the list than there are members  in
  the  aggregate,  then  each member not explicitly initialized shall be
  default-initialized (_dcl.init_).  [Example:
  struct S { int a; char* b; int c; };
  S ss = { 1, "asdf" };
  initializes ss.a with 1, ss.b with "asdf", and ss.c with the value  of
  an expression of the form int(), that is, 0.  ]

8 An  initializer  for  an aggregate member that is an empty class shall
  have the form of an empty initializer-list {}.  [Example:
  struct S { };
  struct A {
          S s;
          int i;
  } a = { { } , 3 };
   --end example] An empty initializer-list can be  used  to  initialize
  any aggregate.  If the aggregate is not an empty class, then each mem-
  ber of the aggregate shall be initialized with a value of the form T()
  (_expr.type.conv_),  where  T represents the type of the uninitialized

9 If an incomplete or empty initializer-list leaves a member  of  refer-
  ence type uninitialized, the program is ill-formed.

10When initializing a multi-dimensional array, the initializers initial-
  ize the elements with the last (rightmost) index of the array  varying
  the fastest (_dcl.array_).  [Example:
  int x[2][2] = { 3, 1, 4, 2 };
  initializes  x[0][0]  to 3, x[0][1] to 1, x[1][0] to 4, and x[1][1] to
  2.  On the other hand,
  float y[4][3] = {
      { 1 }, { 2 }, { 3 }, { 4 }
  initializes the first column  of  y  (regarded  as  a  two-dimensional
  array) and leaves the rest zero.  ]

11Braces  can  be elided in an initializer-list as follows.  If the ini-
  tializer-list begins with a left brace, then the succeeding comma-sep-
  arated list of initializers initializes the members of a subaggregate;
  it is erroneous for there to be more initializers than  members.   If,
  however, the initializer-list for a subaggregate does not begin with a

  left brace, then only enough initializers from the list are  taken  to
  initialize the members of the subaggregate; any remaining initializers
  are left to initialize the next member of the aggregate of  which  the
  current subaggregate is a member.  [Example:
  float y[4][3] = {
      { 1, 3, 5 },
      { 2, 4, 6 },
      { 3, 5, 7 },
  is  a  completely-braced  initialization:  1,  3, and 5 initialize the
  first row of the array y[0], namely  y[0][0],  y[0][1],  and  y[0][2].
  Likewise the next two lines initialize y[1] and y[2].  The initializer
  ends early and therefore y[3]'s elements are initialized as if explic-
  itly  initialized with an expression of the form float(), that is, are
  initialized with 0.0.  In the following example, braces  in  the  ini-
  tializer-list  are  elided;  however the initializer-list has the same
  effect as the completely-braced initializer-list of the above example,
  float y[4][3] = {
      1, 3, 5, 2, 4, 6, 3, 5, 7
  The  initializer  for y begins with a left brace, but the one for y[0]
  does not, therefore three elements from the list are  used.   Likewise
  the next three are taken successively for y[1] and y[2].   --end exam-

12All implicit type conversions (clause _conv_) are considered when ini-
  tializing  the  aggregate  member with an initializer from an initial-
  izer-list.  If the initializer can initialize a member, the member  is
  initialized.  Otherwise, if the member is itself a non-empty subaggre-
  gate, brace elision is assumed and the initializer is  considered  for
  the initialization of the first member of the subaggregate.  [Example:
  struct A {
      int i;
      operator int();
  struct B {
      A a1, a2;
      int z;
  A a;
  B b = { 4, a, a };
  Braces are elided around the initializer for b.a1.i.  b.a1.i  is  ini-
  tialized  with  4, b.a2 is initialized with a, b.z is initialized with
  whatever a.operator int() returns.  ]

13[Note: An aggregate array or an aggregate class may contain members of
  a  class  type  with a user-declared constructor (_class.ctor_).  Ini-
  tialization   of   these   aggregate   objects   is    described    in
  _class.expl.init_.  ]

14When  an  aggregate with static storage duration is initialized with a
  brace-enclosed initializer-list, if all the member initializer expres-
  sions  are  constant expressions, and the aggregate is a POD type, the
  initialization shall be done during the static phase of initialization

  (_basic.start.init_);  otherwise,  it  is unspecified whether the ini-
  tialization of members with constant expressions  takes  place  during
  the static phase or during the dynamic phase of initialization.

15When  a  union  is  initialized with a brace-enclosed initializer, the
  braces shall only contain an initializer for the first member  of  the
  union.  [Example:
  union u { int a; char* b; };

  u a = { 1 };
  u b = a;
  u c = 1;                        // error
  u d = { 0, "asdf" };            // error
  u e = { "asdf" };               // error
    --end example] [Note: as described above, the braces around the ini-
  tializer for a union member can be omitted if the union is a member of
  another aggregate.  ]

  8.5.2  Character arrays                              [dcl.init.string]

1 A  char  array (whether plain char, signed char, or unsigned char) can
  be initialized by a string-literal (optionally enclosed in braces);  a
  wchar_t  array can be initialized by a wide string-literal (optionally
  enclosed in braces); successive characters of the string-literal  ini-
  tialize the members of the array.  [Example:
  char msg[] = "Syntax error on line %s\n";
  shows  a  character array whose members are initialized with a string-
  literal.  Note that because '\n' is a single character and  because  a
  trailing '\0' is appended, sizeof(msg) is 25.  ]

2 There  shall  not  be more initializers than there are array elements.
  char cv[4] = "asdf";            // error
  is ill-formed since there is no space for the implied  trailing  '\0'.

  8.5.3  References                                       [dcl.init.ref]

1 A  variable  declared  to  be  a  T&,  that  is  "reference to type T"
  (_dcl.ref_), shall be initialized by an object, or function, of type T
  or by an object that can be converted into a T.  [Example:

  int g(int);
  void f()
      int i;
      int& r = i;                 // r refers to i
      r = 1;                      // the value of i becomes 1
      int* p = &r;                // p points to i
      int& rr = r;                // rr refers to what r refers to,
                                  // that is, to i
      int (&rg)(int) = g;         // rg refers to the function g
      rg(i);                      // calls function g
      int a[3];
      int (&ra)[3] = a;           // ra refers to the array a
      ra[1] = i;                  // modifies a[1]
   --end example]

2 A  reference  cannot  be changed to refer to another object after ini-
  tialization.  Note that initialization of a reference is treated  very
  differently from assignment to it.  Argument passing (_expr.call_) and
  function value return (_stmt.return_) are initializations.

3 The initializer can be omitted for a reference  only  in  a  parameter
  declaration (_dcl.fct_), in the declaration of a function return type,
  in the declaration of a class  member  within  its  class  declaration
  (_class.mem_),  and  where  the  extern  specifier is explicitly used.
  int& r1;                        // error: initializer missing
  extern int& r2;                 // OK
   --end example]

4 Given types "cv1 T1" and "cv2 T2," "cv1 T1"  is  reference-related  to
  "cv2 T2"  if  T1  is the same type as T2, or T1 is a base class of T2.
  "cv1 T1" is reference-compatible with "cv2 T2"  if  T1  is  reference-
  related  to T2 and cv1 is the same cv-qualification as, or greater cv-
  qualification than, cv2.  For purposes of overload  resolution,  cases
  for  which  cv1 is greater cv-qualification than cv2 are identified as
  reference-compatible with added qualification  (see  _over.ics.rank_).
  In all cases where the reference-related or reference-compatible rela-
  tionship of two types is used to establish the validity of a reference
  binding,  and  T1  is  a base class of T2, a program that necessitates
  such a  binding  is  ill-formed  if  T1  is  an  inaccessible  (clause
  _class.access_) or ambiguous (_class.member.lookup_) base class of T2.

5 A reference to type "cv1 T1" is initialized by an expression  of  type
  "cv2 T2" as follows:

  --If the initializer expression

    --is  an lvalue (but not an lvalue for a bit-field), and "cv1 T1" is
      reference-compatible with "cv2 T2," or

    --has a class type (i.e., T2 is a class type) and can be  implicitly

      converted  to an lvalue of type "cv3 T3," where "cv1 T1" is refer-
      ence-compatible  with  "cv3 T3" 8) (this conversion is selected by
      enumerating the applicable conversion functions (_over.match.ref_)
      and   choosing   the   best   one   through   overload  resolution
      (_over.match_)), then

7   the reference is bound directly to the initializer expression lvalue
    in  the  first case, and the reference is bound to the lvalue result
    of the conversion in the second case.  In these cases the  reference
    is  said to bind directly to the initializer expression.  [Note: the
    usual     lvalue-to-rvalue      (_conv.lval_),      array-to-pointer
    (_conv.array_),  and function-to-pointer (_conv.func_) standard con-
    versions are not needed, and therefore  are  suppressed,  when  such
    direct bindings to lvalues are done.  ] [Example:
      double d = 2.0;
      double& rd = d;                 // rd refers to d
      const double& rcd = d;          // rcd refers to d

      struct A { };
      struct B : public A { } b;
      A& ra = b;                      // ra refers to A sub-object in b
      const A& rca = b;               // rca refers to A sub-object in b
     --end example]

  --Otherwise,  the  reference  shall  be  to  a non-volatile const type
    (i.e., cv1 shall be const).  [Example:
      double& rd2 = 2.0;              // error: not an lvalue and reference
                                      //   not const
      int  i = 2;
      double& rd3 = i;                // error: type mismatch and reference
                                      //   not const
     --end example]

    --If the initializer expression is an rvalue, with T2 a class  type,
      and  "cv1 T1" is reference-compatible with "cv2 T2," the reference
      is bound in one of the following ways (the choice  is  implementa-

      --The  reference  is bound to the object represented by the rvalue
        (see _basic.lval_) or to a sub-object within that object.

      --A temporary of type "cv1 T2" [sic] is created, and a constructor
        is  called  to copy the entire rvalue object into the temporary.
        The reference is bound to  the  temporary  or  to  a  sub-object
        within the temporary.9)
  8) This requires a conversion function (_class.conv.fct_) returning  a
  reference type.
  9) Clearly, if the reference initialization being processed is one for
  the first argument of a copy constructor call, an implementation  must
  eventually  choose  the first alternative (binding without copying) to
  avoid infinite recursion.

9     The constructor that would be used  to  make  the  copy  shall  be
      callable whether or not the copy is actually done.  [Example:
          struct A { };
          struct B : public A { } b;
          extern B f();
          const A& rca = f();             // Either bound to the A sub-object of the
                                          //   B rvalue, or the entire B object is copied
                                          //   and the reference is bound to the
                                          //   A sub-object of the copy
       --end example]

    --Otherwise, a temporary of type "cv1 T1" is created and initialized
      from the initializer expression using the rules for  a  non-refer-
      ence  copy  initialization  (_dcl.init_).   The  reference is then
      bound to the temporary.  If T1 is  reference-related  to  T2,  cv1
      must  be the same cv-qualification as, or greater cv-qualification
      than, cv2; otherwise, the program is ill-formed.  [Example:
          const double& rcd2 = 2;         // rcd2 refers to temporary
                                          // with value 2.0
          const volatile int cvi = 1;
          const int& r = cvi;             // error: type qualifiers dropped
       --end example]

11  [Note: _class.temporary_ describes the lifetime of temporaries bound
    to references.  ]