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 fundamental type, storage class, or other
  properties of the objects and functions being declared.  The  declara­
  tors specify the names of these objects and functions and (optionally)
  modify the type 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)

4 Declarators have the syntax
                  ptr-operator declarator
  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 one declarator  modifies  the  name  environment
  used by a following declarator, 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

                  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
                  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
  having no parameters and returning pointer to integer,"  and  "pointer
  to function of double 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, it surfaces  as  a  choice
  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 statements, the resolution
  is to consider any construct that could possibly be  a  declaration  a
  declaration.   A declaration can be explicitly disambiguated by a non­
  function-style cast or a = to indicate initialization.  [Example:
          struct S {
          void foo(double a)
              S x(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 many different contexts.  The ambigu­
  ity surfaces 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]

  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.  A declara­
  tor-id shall be a simple identifier, except for the  following  cases:
  the declaration of some special functions (_class.conv_, _class.dtor_,
  _over.oper_), the definition of a member function (_class.mfct_),  the
  definition  of  a static data member (_class.static_), the declaration
  of  a  friend  function  that   is   a   member   of   another   class
  (_class.friend_).   An auto, static, extern, register, 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
  subsections give an inductive procedure for determining the type spec­
  ified 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 dec­
          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 volatile specifiers are handled similarly.

4 See also _expr.ass_ and _dcl.init_.

5 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." At all times during the
  determination of a type, any type of the form "cv-qualifier-seq refer­
  ence to T" is adjusted to be "reference to T".  [Example: in
          typedef int& A;
          const A aref = 3;
  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.  In particular,

  null references are prohibited; no diagnostic is required.

  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:
  There  is  no   "reference-to-member"   type   in   C++.    See   also
  _expr.mptr.oper_ and _expr.unary_.  ]

  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  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 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 numbered 0 to N-1, and the type of the  identifier  of  D  is
  "derived-declarator-type-list  array  of N T." If the constant expres­
  sion 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_.   At  all  times  during  the
  determination  of a type, 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" [Example:
          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 types2)
  (except void), from a pointer, from a pointer to member, from a class,
  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,
  2) The enumeration types are included in the fundamental types.

  subscripting 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  cv-qualifier-seqopt  function  with
  parameters  of  type  parameter-declaration-clause and returning T"; a
  type of this form is a function type3).
                  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

  3) 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.  If  the
  parameter-declaration-clause  terminates  with an ellipsis, the number
  of arguments shall be equal to or greater than the number  of  parame­
  ters  specified; if it 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).  Where syntacti­
  cally  correct, ", ..." is synonymous with "...".  [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 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 the types.  Any cv-qualifier mod­
  ifying a parameter type is deleted; e.g.,  the  type  void(const  int)
  becomes  void(int).   Such cv-qualifiers affect only the definition of
  the parameter within the body of the function.  If the  storage-class-
  specifier  register  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.  The resulting list of transformed parameter types is
  the function's parameter type list.  The return type and the parameter
  type list, but not the default arguments (_dcl.fct.default_) or excep­
  tion specification (_except.spec_), are part of the function type.  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.4) A cv-qualifier-seq can only be part of a
  declaration or definition of a nonstatic member  function,  and  of  a
  pointer  to  a  member  function; see _class.this_.  It is part of the
  function type.

4 Functions shall not return arrays  or  functions,  although  they  can
  return  pointers  and  references  to  such things.  There shall be no
  arrays of functions, although there can be arrays of pointers to func­

  4) 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.

5 Types shall not be defined in return or parameter types.

6 [Note:  the  parameter-declaration-clause is used to check and convert
  arguments in calls and  to  check  pointer-to-function,  reference-to-
  function,  and  pointer-to-member-function assignments and initializa­
  tions.  ]

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
  (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 an identifier is present in a function dec­
  laration, it cannot be used since it goes out of scope at the  end  of
  the function declarator (_basic.scope_); ]

8 [Note: The exception-specification is described in _except.spec_ .  ]

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.

10Typedefs  are  sometimes convenient when the return type of a function
  is complex.  For another example, the function fpif above  could  have
  been declared
          typedef int  IFUNC(int);
          IFUNC*  fpif(int);

11The declaration
          int fseek(FILE*, long, int);
  declares a function taking three arguments of the specified types, and
  returning int (_dcl.type_).  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*.

12 --end example]

  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.5)

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

  5) 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] Declarations of a given nonmember function in  differ­
  ent  translation  units  need  not specify the same default arguments.
  Declarations of a  given  member  function  in  different  translation
  units,  however, shall specify the same default arguments (the accumu­
  lated sets of default arguments at the end of  the  translation  units
  shall be the same).

  +-------                      BEGIN BOX 1                     -------+
  This  was decided on the basis of guesses regarding the One Definition
  Rule and should be reviewed once that section is finished.
  +-------                       END BOX 1                      -------+

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))
   --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 (_class.scope0_).  The  default  arguments  in  an  out-of-line
  function 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
  implementation-defined.   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 argu­
  ment 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 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 2                     -------+
  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 2                      -------+

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->A::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 constants 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 or pointer-to-member type, 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 nonstatic data  mem­
    ber 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,  the  default  constructor  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.

  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.6)

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,
  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);

11The 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
  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_.

  --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
      versions  that can convert from the source type to the destination
      type are enumerated (_over.match.user_), and the best one is  cho­
      sen  through overload resolution (_over.match_).  The user-defined
      conversion so  selected  is  called  to  convert  the  initializer
      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.7) In certain cases,  an  implementa­
      tion  is  permitted to eliminate the temporary by initializing 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.

  7) 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.

              int a;
              const int b = a;
              int c = b;
     --end note]

12If T is a scalar type, then a declaration of the form
          T x = { a };
  is equivalent to
          T x = a;

  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 non-static members of reference type, no
  non-static const members, no base classes  (_class.derived_),  and  no
  virtual functions (_class.virtual_).8)

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.8)

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

  8) 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
  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 When 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.  ]

10Braces 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

11All  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.  ]

12[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_.  ]

13When an aggregate is initialized with  a  brace-enclosed  initializer-
  list,  if  some  members are initialized with constant expressions and
  other members are initialized with  non-constant  expressions,  it  is
  unspecified  whether  the  initialization  of  members  with  constant
  expressions takes place during the static phase or during the  dynamic
  phase of initialization (_basic.start.init_).

14The  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]

  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  to  an
      lvalue  of  type  "cv3 T1," where cv3 is the same cv-qualification
      as, or lesser cv-qualification than, cv1, 9) then

7   the  reference  is  bound  directly  to  the  initializer expression
    lvalue.  [Note: the usual lvalue-to-rvalue (_conv.lval_),  array-to-
    pointer  (_conv.array_), and function-to-pointer (_conv.func_) stan­
    dard 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'
  9) This requires a conversion function (_class.conv.fct_) returning  a
  reference type, and therefore applies only when T2 is a class type.

     --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
        temporary.  The reference is bound to the temporary or to a sub-
        object within the temporary.10)

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 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]
  10) 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  infi­
  nite recursion.

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