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 specifiers indicate the type, storage class or other properties of
  the objects, functions or typedefs being  declared.   The  declarators
  specify  the  names  of  these  objects,  functions  or  typedefs, and
  (optionally) 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 id-expression
                  ::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
                  direct-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 "integer," "pointer to integer," "array of

  3 pointers to integers," "pointer to array of 3  integers,"  "function
  taking  no  parameters and returning pointer to integer," and "pointer
  to a function taking one parameter of type  double  and  returning  an
  integer."  ]

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(int x)  {
                  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 _parm)) { }
                             // not: void f(int C);

          int g(C);

          void foo() {
                  f1(1);   // error: cannot convert 1 to function ptr
                  f1(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  (_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 of a function,
  variable, or class member of a namespace 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  declaration  shall  refer  to a previously declared member of the
  class or namespace to which the qualifier refers.  [Note: if the qual­
  ifier  is  the  global :: scope resolution operator, the declarator-id
  refers to a name declared in the global namespace scope.  ]  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.

2 Thus, a declaration of a particular identifier has the form
          T D
  where T is a decl-specifier-seq and D is a declarator.  The  following
  subclauses  give a recursive procedure for determining the type speci­
  fied for the contained declarator-id by such a declaration.

3 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_).  ]

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

5 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-
  unqualified pointer later, for example:
          *ppc = &ci;  // okay, 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 There can be no pointers to references (_dcl.ref_) or pointers to bit-
  fields (_class.bit_).

  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".
  ] 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  references  to  bit-
  fields (_class.bit_), no arrays of references, and no pointers to ref­
  erences.  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_) declara­
  tion  within a class declaration, or is the declaration of a parameter
  or a return type (_dcl.fct_); see _basic.def_.  A reference  shall  be
  initialized to refer to a valid object or function.  [Note: in partic­
  ular, 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  unde­
  fined behavior.  ]

  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,  an  incomplete  type,  a  function  type  or  an

  abstract  class  type.   If  the constant-expression (_expr.const_) is
  present, its value shall be greater than zero.  The  constant  expres­
  sion 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."  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  incomplete  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-qualifier-seq T," and  similarly
  for "array of unknown bound of T."  An object of array type contains a
  contiguously allocated non-empty set  of  N  sub-objects  of  type  T.
          typedef int A[5], AA[2][3];
          const A x;      // type is ``array of 5 const int''
          const AA y;     // type is ``array of 2 array of 3 const int''
   --end example]

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-
  expression  can  also be omitted when the declarator is followed by an
  initializer (_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
  3×5×7.  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 i×j×...×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 3×5 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) As indicated by the syntax, cv-qualifiers are a significant  compo­
  nent in function return types.

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 (_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 parameters;
  the presence or absence of the ellipsis  is  considered  part  of  the
  function type.  The type of a function is determined using the follow­
  ing 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,  sev­
  eral  transformations  take  place  upon  these types to determine the
  function  type.   Any  cv-qualifier  modifying  a  parameter  type  is
  deleted;  e.g.,  the type void(const int) becomes void(int).  Such cv-
  qualifiers only affect the definition 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;
  e.g.,  register  char*  becomes  char*.  Such storage-class-qualifiers
  affect only the definition of the parameter within  the  body  of  the
  function; they do not affect the function type.  The resulting list of
  transformed parameter types is the function's parameter type list.   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.  ]

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

5 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.

6 A typedef of function type may be used to declare a function but shall
  not be used to define a function.  [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]

7 An identifier can optionally be provided as a parameter name; if  pre­
  sent  in  a  function definition (_dcl.fct.def_), it names a parameter
  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.

  (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_).  ]

8 [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-
  declaration-clause,  it  shall  not  occur  within  a  declarator   or
  abstract-declarator of a parameter-declaration.4)
  4)  This  means  that default arguments cannot appear, for example, in

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
          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] Declarations of a given function in different transla­
  tion units shall specify the same default arguments  (the  accumulated
  sets of default arguments at the end of the translation units shall be
  the same); see _basic.def.odr_.

5 Default argument expressions have their names bound  and  their  types
  checked at the point of declaration.  [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))
  declarations of pointers to functions,  references  to  functions,  or
  typedef declarations.

   --end example]

6 In member function declarations, names in default argument expressions
  are  looked up in the scope of the class like names in member function
  bodies (_basic.lookup.unqual_).  The default  arguments  in  a  member
  function  definition  that appears outside of the class definition are
  added to the set of default arguments provided by the member  function
  declaration in the class definition.  [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  at each point of call before entry
  into a function.  The order of evaluation  of  function  arguments  is
  unspecified.  Consequently, parameters of a function shall not be used
  in default argument 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

  following 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 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 _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();      // fine, 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 imported as well.

  +-------                      BEGIN BOX 1                     -------+
  Can additional default arguments be added to the  function  thereafter
  by  way  of redeclarations of the function?  Can the function be rede­
  clared in the namespace with added default arguments, and if  so,  are
  those  added arguments visible to those who have imported the function
  via using?
  +-------                       END BOX 1                      -------+

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 The  parameters  are  in the scope of the outermost block of the func­

3 [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.  ]

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

5 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.

6 [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
  this  subclause (_dcl.init_) applies also to initializations specified
  by other syntactic contexts, such as the  initialization  of  function
  parameters  with argument expressions (_expr.call_) or the initializa­
  tion 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  member  (which
    must not be static (_class.union_)) is zero-initialized;

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

  --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 (_class_), the default constructor  for
    T is called (and the initialization is ill-formed if T has no acces­
    sible default constructor);

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

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

  Default-initialization  uses   the   direct-initialization   semantics
  described below.

6 The  memory occupied by any object of static storage duration shall be
  zero-initialized.  Furthermore, if no initializer is explicitly speci­
  fied  in  the  declaration  of the object and the object is of non-POD
  class type (or array thereof), then default  initialization  shall  be
  performed.   If  no  initializer is specified for an object with auto­
  matic or dynamic storage duration, the object and its  subobjects,  if
  any, have an indeterminate initial value.5)

7 An  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]

8 The 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.

9 [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_).  ]

10The initialization that occurs in argument passing,  function  return,
  throwing   an   exception   (_except.throw_),  handling  an  exception
  (_except.handle_),    and     brace-enclosed     initializer     lists
  5) This does not apply to aggregate objects with automatic storage du­
  ration initialized with an incomplete brace-enclosed initializer-list;
  see _dcl.init.aggr_.

  (_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);

11If T is a scalar type, then a declaration of the form
          T x = { a };
  is equivalent to
          T x = a;

12The 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
  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), a
      temporary of the destination type is created.   User-defined  con­
      version  sequences  that  can  convert from the source type to the
      destination type are enumerated (_over.match.user_), and the  best
      one  is  chosen  through  overload resolution (_over.match_).  The
      user-defined conversion so selected is called to convert the  ini­
      tializer  expression into the temporary.  If the conversion cannot
      be done or is ambiguous, the initialization  is  ill-formed.   The
      object  being  initialized  is  then  direct-initialized  from the

      temporary according to the rules above.6)  In  certain  cases,  an
      implementation is permitted to eliminate the temporary by initial­
      izing the object directly; 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.user_), 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 (_class_) with no user-declared
  constructors (_class.ctor_), no private or protected  non-static  data
  members  (_class.access_),  no  base classes (_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_.
  6) Because the type of the temporary is the same as the  type  of  the
  object  being initialized, this direct-initialization, if well-formed,
  will use a copy constructor (_class.copy_) to copy the temporary.

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:
          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
  initialized  with  a value of the form T() (_expr.type.conv_), where T
  represents the type of the uninitialized member.  [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.

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

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:
          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-
  separated list of initializers initializes the members of a  subaggre­
  gate;  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  type conversions (_over.match.user_) are considered when initial­
  izing the aggregate member with an initializer  from  an  initializer-
  list.   If the initializer can initialize a member, the member is ini­
  tialized.  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 is initialized with  a  brace-enclosed  initializer-
  list,  if  all the member initializer expressions are constant expres­
  sions, 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  initialization  of  members
  with  constant expressions takes place during the static phase or dur­
  ing the dynamic phase of initialization.

15The initializer for a  union  with  no  user-declared  constructor  is
  either  a single expression of the same type, or a brace-enclosed ini­
  tializer 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, or unsigned) can be initial­
  ized  by a string; a wchar_t array can be initialized by a wide string
  literal; successive characters of the string initialize 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.
  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 (_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

    --the initializer expression can be implicitly converted (_conv_) to
      an lvalue of type "cv3 T1," where cv3 is the same cv-qualification
      as, or lesser cv-qualification than, cv1, 8) 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.  [Note: the  usual  lvalue-to-
    rvalue (_conv.lval_), array-to-pointer (_conv.array_), and function-
    to-pointer (_conv.func_) standard conversions 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 directly 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  copy  con­
        structor  is  called  to  copy the entire rvalue object into the
  8)  This requires a conversion function (_class.conv.fct_) returning a
  reference type, and therefore applies only when T2 is a class type.

        temporary.  The reference is bound to the temporary or to a sub-
        object within the temporary.9)

9     The appropriate copy constructor must 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 directly 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-
      reference  direct  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.
                  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.  ]

  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 direct-binding alternative to avoid infinite re­