Annex D (normative) Compatibility features [depr]

This Clause describes features of the C++ Standard that are specified for compatibility with existing implementations.
These are deprecated features, where deprecated is defined as: Normative for the current edition of this International Standard, but having been identified as a candidate for removal from future revisions.
An implementation may declare library names and entities described in this section with the deprecated attribute.

D.1 Redeclaration of static constexpr data members [depr.static_constexpr]

For compatibility with prior C++ International Standards, a constexpr static data member may be redundantly redeclared outside the class with no initializer.
This usage is deprecated.
[Example
:
struct A {
  static constexpr int n = 5;  // definition (declaration in C++ 2014)
};

constexpr int A::n;  // redundant declaration (definition in C++ 2014)
end example
]

D.2 Implicit declaration of copy functions [depr.impldec]

The implicit definition of a copy constructor as defaulted is deprecated if the class has a user-declared copy assignment operator or a user-declared destructor.
The implicit definition of a copy assignment operator as defaulted is deprecated if the class has a user-declared copy constructor or a user-declared destructor ([class.dtor], [class.copy]).
In a future revision of this International Standard, these implicit definitions could become deleted ([dcl.fct.def]).

D.3 Deprecated exception specifications [depr.except.spec]

The noexcept-specifier throw() is deprecated.

D.4 C++standard library headers [depr.cpp.headers]

For compatibility with prior C++International Standards, the C++standard library provides headers <ccomplex> ([depr.ccomplex.syn]), <cstdalign> ([depr.cstdalign.syn]), <cstdbool> ([depr.cstdbool.syn]), and <ctgmath> ([depr.ctgmath.syn]).
The use of these headers is deprecated.

D.4.1 Header <ccomplex> synopsis [depr.ccomplex.syn]

#include <complex>
The header <ccomplex> behaves as if it simply includes the header <complex> ([complex.syn]).

D.4.2 Header <cstdalign> synopsis [depr.cstdalign.syn]

#define __alignas_­is_­defined 1
The contents of the header <cstdalign> are the same as the C standard library header <stdalign.h>, with the following changes: The header <cstdalign> and the header <stdalign.h> shall not define a macro named alignas.
See also: ISO C 7.
15

D.4.3 Header <cstdbool> synopsis [depr.cstdbool.syn]

#define __bool_­true_­false_­are_­defined 1
The contents of the header <cstdbool> are the same as the C standard library header <stdbool.h>, with the following changes: The header <cstdbool> and the header <stdbool.h> shall not define macros named bool, true, or false.
See also: ISO C 7.
18

D.4.4 Header <ctgmath> synopsis [depr.ctgmath.syn]

#include <complex>
#include <cmath>
The header <ctgmath> simply includes the headers <complex> ([complex.syn]) and <cmath> ([cmath.syn]).
[Note
:
The overloads provided in C by type-generic macros are already provided in <complex> and <cmath> by “sufficient” additional overloads.
end note
]

D.5 C standard library headers [depr.c.headers]

For compatibility with the C standard library, the C++ standard library provides the C headers shown in Table 141.
Table 141 — C headers
<assert.h>
<inttypes.h>
<signal.h>
<stdio.h>
<wchar.h>
<complex.h>
<iso646.h>
<stdalign.h>
<stdlib.h>
<wctype.h>
<ctype.h>
<limits.h>
<stdarg.h>
<string.h>
<errno.h>
<locale.h>
<stdbool.h>
<tgmath.h>
<fenv.h>
<math.h>
<stddef.h>
<time.h>
<float.h>
<setjmp.h>
<stdint.h>
<uchar.h>
The header <complex.h> behaves as if it simply includes the header <ccomplex>.
The header <tgmath.h> behaves as if it simply includes the header <ctgmath>.
Every other C header, each of which has a name of the form name.h, behaves as if each name placed in the standard library namespace by the corresponding cname header is placed within the global namespace scope, except for the functions described in [sf.cmath], the declaration of std​::​byte ([cstddef.syn]), and the functions and function templates described in [support.types.byteops].
It is unspecified whether these names are first declared or defined within namespace scope ([basic.scope.namespace]) of the namespace std and are then injected into the global namespace scope by explicit using-declarations.
[Example
:
The header <cstdlib> assuredly provides its declarations and definitions within the namespace std.
It may also provide these names within the global namespace.
The header <stdlib.h> assuredly provides the same declarations and definitions within the global namespace, much as in the C Standard.
It may also provide these names within the namespace std.
end example
]

D.6 char* streams [depr.str.strstreams]

The header <strstream> defines three types that associate stream buffers with character array objects and assist reading and writing such objects.

D.6.1 Class strstreambuf [depr.strstreambuf]

namespace std {
  class strstreambuf : public basic_streambuf<char> {
  public:
    explicit strstreambuf(streamsize alsize_arg = 0);
    strstreambuf(void* (*palloc_arg)(size_t), void (*pfree_arg)(void*));
    strstreambuf(char* gnext_arg, streamsize n, char* pbeg_arg = nullptr);
    strstreambuf(const char* gnext_arg, streamsize n);

    strstreambuf(signed char* gnext_arg, streamsize n,
                 signed char* pbeg_arg = nullptr);
    strstreambuf(const signed char* gnext_arg, streamsize n);
    strstreambuf(unsigned char* gnext_arg, streamsize n,
                 unsigned char* pbeg_arg = nullptr);
    strstreambuf(const unsigned char* gnext_arg, streamsize n);

    virtual ~strstreambuf();

    void  freeze(bool freezefl = true);
    char* str();
    int   pcount();

  protected:
    int_type overflow (int_type c = EOF) override;
    int_type pbackfail(int_type c = EOF) override;
    int_type underflow() override;
    pos_type seekoff(off_type off, ios_base::seekdir way,
                     ios_base::openmode which
                      = ios_base::in | ios_base::out) override;
    pos_type seekpos(pos_type sp,
                     ios_base::openmode which
                      = ios_base::in | ios_base::out) override;
    streambuf* setbuf(char* s, streamsize n) override;

  private:
    using strstate = T1;              // exposition only
    static const strstate allocated;  // exposition only
    static const strstate constant;   // exposition only
    static const strstate dynamic;    // exposition only
    static const strstate frozen;     // exposition only
    strstate strmode;                 // exposition only
    streamsize alsize;                // exposition only
    void* (*palloc)(size_t);          // exposition only
    void (*pfree)(void*);             // exposition only
  };
}
The class strstreambuf associates the input sequence, and possibly the output sequence, with an object of some character array type, whose elements store arbitrary values.
The array object has several attributes.
[Note
:
For the sake of exposition, these are represented as elements of a bitmask type (indicated here as T1) called strstate.
The elements are:
  • allocated, set when a dynamic array object has been allocated, and hence should be freed by the destructor for the strstreambuf object;
  • constant, set when the array object has const elements, so the output sequence cannot be written;
  • dynamic, set when the array object is allocated (or reallocated) as necessary to hold a character sequence that can change in length;
  • frozen, set when the program has requested that the array object not be altered, reallocated, or freed.
end note
]
[Note
:
For the sake of exposition, the maintained data is presented here as:
  • strstate strmode, the attributes of the array object associated with the strstreambuf object;
  • int alsize, the suggested minimum size for a dynamic array object;
  • void* (*palloc)(size_­t), points to the function to call to allocate a dynamic array object;
  • void (*pfree)(void*), points to the function to call to free a dynamic array object.
end note
]
Each object of class strstreambuf has a seekable area, delimited by the pointers seeklow and seekhigh.
If gnext is a null pointer, the seekable area is undefined.
Otherwise, seeklow equals gbeg and seekhigh is either pend, if pend is not a null pointer, or gend.

D.6.1.1 strstreambuf constructors [depr.strstreambuf.cons]

explicit strstreambuf(streamsize alsize_arg = 0);
Effects: Constructs an object of class strstreambuf, initializing the base class with streambuf().
The postconditions of this function are indicated in Table 142.
Table 142strstreambuf(streamsize) effects
Element
Value
strmode
dynamic
alsize
alsize_­arg
palloc
a null pointer
pfree
a null pointer
strstreambuf(void* (*palloc_arg)(size_t), void (*pfree_arg)(void*));
Effects: Constructs an object of class strstreambuf, initializing the base class with streambuf().
The postconditions of this function are indicated in Table 143.
Table 143strstreambuf(void* (*)(size_­t), void (*)(void*)) effects
Element
Value
strmode
dynamic
alsize
an unspecified value
palloc
palloc_­arg
pfree
pfree_­arg
strstreambuf(char* gnext_arg, streamsize n, char* pbeg_arg = nullptr); strstreambuf(signed char* gnext_arg, streamsize n, signed char* pbeg_arg = nullptr); strstreambuf(unsigned char* gnext_arg, streamsize n, unsigned char* pbeg_arg = nullptr);
Effects: Constructs an object of class strstreambuf, initializing the base class with streambuf().
The postconditions of this function are indicated in Table 144.
Table 144strstreambuf(charT*, streamsize, charT*) effects
Element
Value
strmode
0
alsize
an unspecified value
palloc
a null pointer
pfree
a null pointer
gnext_­arg shall point to the first element of an array object whose number of elements N is determined as follows:
  • If n > 0, N is n.
  • If n == 0, N is std​::​strlen(gnext_­arg).
  • If n < 0, N is INT_­MAX.331
If pbeg_­arg is a null pointer, the function executes:
setg(gnext_arg, gnext_arg, gnext_arg + N);
Otherwise, the function executes:
setg(gnext_arg, gnext_arg, pbeg_arg);
setp(pbeg_arg,  pbeg_arg + N);
strstreambuf(const char* gnext_arg, streamsize n); strstreambuf(const signed char* gnext_arg, streamsize n); strstreambuf(const unsigned char* gnext_arg, streamsize n);
Effects: Behaves the same as strstreambuf((char*)gnext_­arg,n), except that the constructor also sets constant in strmode.
virtual ~strstreambuf();
Effects: Destroys an object of class strstreambuf.
The function frees the dynamically allocated array object only if (strmode & allocated) != 0 and (strmode & frozen) == 0.
([depr.strstreambuf.virtuals] describes how a dynamically allocated array object is freed.)
The function signature strlen(const char*) is declared in <cstring>.
The macro INT_­MAX is defined in <climits>.

D.6.1.2 Member functions [depr.strstreambuf.members]

void freeze(bool freezefl = true);
Effects: If strmode & dynamic is nonzero, alters the freeze status of the dynamic array object as follows:
  • If freezefl is true, the function sets frozen in strmode.
  • Otherwise, it clears frozen in strmode.
char* str();
Effects: Calls freeze(), then returns the beginning pointer for the input sequence, gbeg.
Remarks: The return value can be a null pointer.
int pcount() const;
Effects: If the next pointer for the output sequence, pnext, is a null pointer, returns zero.
Otherwise, returns the current effective length of the array object as the next pointer minus the beginning pointer for the output sequence, pnext - pbeg.

D.6.1.3 strstreambuf overridden virtual functions [depr.strstreambuf.virtuals]

int_type overflow(int_type c = EOF) override;
Effects: Appends the character designated by c to the output sequence, if possible, in one of two ways:
  • If c != EOF and if either the output sequence has a write position available or the function makes a write position available (as described below), assigns c to *pnext++.
    Returns (unsigned char)c.
  • If c == EOF, there is no character to append.
    Returns a value other than EOF.
Returns EOF to indicate failure.
Remarks: The function can alter the number of write positions available as a result of any call.
To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements n to hold the current array object (if any), plus at least one additional write position.
How many additional write positions are made available is otherwise unspecified.
332 If palloc is not a null pointer, the function calls (*palloc)(n) to allocate the new dynamic array object.
Otherwise, it evaluates the expression new charT[n].
In either case, if the allocation fails, the function returns EOF.
Otherwise, it sets allocated in strmode.
To free a previously existing dynamic array object whose first element address is p: If pfree is not a null pointer, the function calls (*pfree)(p).
Otherwise, it evaluates the expression delete[]p.
If (strmode & dynamic) == 0, or if (strmode & frozen) != 0, the function cannot extend the array (reallocate it with greater length) to make a write position available.
int_type pbackfail(int_type c = EOF) override;
Puts back the character designated by c to the input sequence, if possible, in one of three ways:
  • If c != EOF, if the input sequence has a putback position available, and if (char)c == gnext[-1], assigns gnext - 1 to gnext.
    Returns c.
  • If c != EOF, if the input sequence has a putback position available, and if strmode & constant is zero, assigns c to *--gnext.
    Returns c.
  • If c == EOF and if the input sequence has a putback position available, assigns gnext - 1 to gnext.
    Returns a value other than EOF.
Returns EOF to indicate failure.
Remarks: If the function can succeed in more than one of these ways, it is unspecified which way is chosen.
The function can alter the number of putback positions available as a result of any call.
int_type underflow() override;
Effects: Reads a character from the input sequence, if possible, without moving the stream position past it, as follows:
  • If the input sequence has a read position available, the function signals success by returning (unsigned char)​*gnext.
  • Otherwise, if the current write next pointer pnext is not a null pointer and is greater than the current read end pointer gend, makes a read position available by assigning to gend a value greater than gnext and no greater than pnext.
    Returns (unsigned char)*gnext.
Returns EOF to indicate failure.
Remarks: The function can alter the number of read positions available as a result of any call.
pos_type seekoff(off_type off, seekdir way, openmode which = in | out) override;
Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table 145.
Table 145seekoff positioning
Conditions
Result
(which & ios​::​in) != 0
positions the input sequence
(which & ios​::​out) != 0
positions the output sequence
(which & (ios​::​in |
ios​::​out)) == (ios​::​in |
ios​::​out)) and
way == either
ios​::​beg or
ios​::​end
positions both the input and the output sequences
Otherwise
the positioning operation fails.
For a sequence to be positioned, if its next pointer is a null pointer, the positioning operation fails.
Otherwise, the function determines newoff as indicated in Table 146.
Table 146newoff values
Condition
newoff Value
way == ios​::​beg
0
way == ios​::​cur
the next pointer minus the beginning pointer (xnext - xbeg).
way == ios​::​end
seekhigh minus the beginning pointer (seekhigh - xbeg).
If (newoff + off) < (seeklow - xbeg) or (seekhigh - xbeg) < (newoff + off), the positioning operation fails.
Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext.
Returns: pos_­type(newoff), constructed from the resultant offset newoff (of type off_­type), that stores the resultant stream position, if possible.
If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_­type(off_­type(-1)).
pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;
Effects: Alters the stream position within one of the controlled sequences, if possible, to correspond to the stream position stored in sp (as described below).
  • If (which & ios​::​in) != 0, positions the input sequence.
  • If (which & ios​::​out) != 0, positions the output sequence.
  • If the function positions neither sequence, the positioning operation fails.
For a sequence to be positioned, if its next pointer is a null pointer, the positioning operation fails.
Otherwise, the function determines newoff from sp.offset():
  • If newoff is an invalid stream position, has a negative value, or has a value greater than (seekhigh - seeklow), the positioning operation fails
  • Otherwise, the function adds newoff to the beginning pointer xbeg and stores the result in the next pointer xnext.
Returns: pos_­type(newoff), constructed from the resultant offset newoff (of type off_­type), that stores the resultant stream position, if possible.
If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_­type(off_­type(-1)).
streambuf<char>* setbuf(char* s, streamsize n) override;
Effects: Implementation defined, except that setbuf(0, 0) has no effect.
An implementation should consider alsize in making this decision.

D.6.2 Class istrstream [depr.istrstream]

namespace std {
  class istrstream : public basic_istream<char> {
  public:
    explicit istrstream(const char* s);
    explicit istrstream(char* s);
    istrstream(const char* s, streamsize n);
    istrstream(char* s, streamsize n);
    virtual ~istrstream();

    strstreambuf* rdbuf() const;
    char* str();
  private:
    strstreambuf sb;  // exposition only
  };
}
The class istrstream supports the reading of objects of class strstreambuf.
It supplies a strstreambuf object to control the associated array object.
For the sake of exposition, the maintained data is presented here as:
  • sb, the strstreambuf object.

D.6.2.1 istrstream constructors [depr.istrstream.cons]

explicit istrstream(const char* s); explicit istrstream(char* s);
Effects: Constructs an object of class istrstream, initializing the base class with istream(&sb) and initializing sb with strstreambuf(s,0).
s shall designate the first element of an ntbs.
istrstream(const char* s, streamsize n); istrstream(char* s, streamsize n);
Effects: Constructs an object of class istrstream, initializing the base class with istream(&sb) and initializing sb with strstreambuf(s,n).
s shall designate the first element of an array whose length is n elements, and n shall be greater than zero.

D.6.2.2 Member functions [depr.istrstream.members]

strstreambuf* rdbuf() const;
Returns: const_­cast<strstreambuf*>(&sb).
char* str();
Returns: rdbuf()->str().

D.6.3 Class ostrstream [depr.ostrstream]

namespace std {
  class ostrstream : public basic_ostream<char> {
  public:
    ostrstream();
    ostrstream(char* s, int n, ios_base::openmode mode = ios_base::out);
    virtual ~ostrstream();

    strstreambuf* rdbuf() const;
    void freeze(bool freezefl = true);
    char* str();
    int pcount() const;
  private:
    strstreambuf sb;  // exposition only
  };
}
The class ostrstream supports the writing of objects of class strstreambuf.
It supplies a strstreambuf object to control the associated array object.
For the sake of exposition, the maintained data is presented here as:
  • sb, the strstreambuf object.

D.6.3.1 ostrstream constructors [depr.ostrstream.cons]

ostrstream();
Effects: Constructs an object of class ostrstream, initializing the base class with ostream(&sb) and initializing sb with strstreambuf().
ostrstream(char* s, int n, ios_base::openmode mode = ios_base::out);
Effects: Constructs an object of class ostrstream, initializing the base class with ostream(&sb), and initializing sb with one of two constructors:
  • If (mode & app) == 0, then s shall designate the first element of an array of n elements.
    The constructor is strstreambuf(s, n, s).
  • If (mode & app) != 0, then s shall designate the first element of an array of n elements that contains an ntbs whose first element is designated by s.
    The constructor is strstreambuf(s, n, s + std​::​strlen(s)).333
The function signature strlen(const char*) is declared in <cstring>.

D.6.3.2 Member functions [depr.ostrstream.members]

strstreambuf* rdbuf() const;
Returns: (strstreambuf*)&sb.
void freeze(bool freezefl = true);
Effects: Calls rdbuf()->freeze(freezefl).
char* str();
Returns: rdbuf()->str().
int pcount() const;
Returns: rdbuf()->pcount().

D.6.4 Class strstream [depr.strstream]

namespace std {
  class strstream
    : public basic_iostream<char> {
  public:
    // Types
    using char_type = char;
    using int_type  = char_traits<char>::int_type;
    using pos_type  = char_traits<char>::pos_type;
    using off_type  = char_traits<char>::off_type;

    // constructors/destructor
    strstream();
    strstream(char* s, int n,
              ios_base::openmode mode = ios_base::in|ios_base::out);
    virtual ~strstream();

    // Members:
    strstreambuf* rdbuf() const;
    void freeze(bool freezefl = true);
    int pcount() const;
    char* str();

  private:
  strstreambuf sb;  // exposition only
  };
}
The class strstream supports reading and writing from objects of class strstreambuf.
It supplies a strstreambuf object to control the associated array object.
For the sake of exposition, the maintained data is presented here as:
  • sb, the strstreambuf object.

D.6.4.1 strstream constructors [depr.strstream.cons]

strstream();
Effects: Constructs an object of class strstream, initializing the base class with iostream(&sb).
strstream(char* s, int n, ios_base::openmode mode = ios_base::in|ios_base::out);
Effects: Constructs an object of class strstream, initializing the base class with iostream(&sb) and initializing sb with one of the two constructors:
  • If (mode & app) == 0, then s shall designate the first element of an array of n elements.
    The constructor is strstreambuf(s,n,s).
  • If (mode & app) != 0, then s shall designate the first element of an array of n elements that contains an ntbs whose first element is designated by s.
    The constructor is strstreambuf(s,n,s + std​::​strlen(s)).

D.6.4.2 strstream destructor [depr.strstream.dest]

virtual ~strstream();
Effects: Destroys an object of class strstream.

D.6.4.3 strstream operations [depr.strstream.oper]

strstreambuf* rdbuf() const;
Returns: &sb.
void freeze(bool freezefl = true);
Effects: Calls rdbuf()->freeze(freezefl).
char* str();
Returns: rdbuf()->str().
int pcount() const;
Returns: rdbuf()->pcount().

D.7 uncaught_­exception [depr.uncaught]

The header <exception> has the following addition:
namespace std {
  bool uncaught_exception() noexcept;
}
bool uncaught_exception() noexcept;
Returns: uncaught_­exceptions() > 0.

D.8 Old adaptable function bindings [depr.func.adaptor.binding]

D.8.1 Weak result types [depr.weak.result_type]

If it does, the type of its member type result_­type is based on the type T of the wrapper's target object:
  • if T is a pointer to function type, result_­type shall be a synonym for the return type of T;
  • if T is a pointer to member function, result_­type shall be a synonym for the return type of T;
  • if T is a class type and the qualified-id T​::​result_­type is valid and denotes a type ([temp.deduct]), then result_­type shall be a synonym for T​::​result_­type;
  • otherwise result_­type shall not be defined.

D.8.2 Typedefs to support function binders [depr.func.adaptor.typedefs]

To enable old function adaptors to manipulate function objects that take one or two arguments, many of the function objects in this International Standard correspondingly provide typedef-names argument_­type and result_­type for function objects that take one argument and first_­argument_­type, second_­argument_­type, and result_­type for function objects that take two arguments.
The following member names are defined in addition to names specified in Clause [function.objects]:
namespace std {
  template<class T> struct owner_less<shared_ptr<T>> {
    using result_type          = bool;
    using first_argument_type  = shared_ptr<T>;
    using second_argument_type = shared_ptr<T>;
  };

  template<class T> struct owner_less<weak_ptr<T>> {
    using result_type          = bool;
    using first_argument_type  = weak_ptr<T>;
    using second_argument_type = weak_ptr<T>;
  };

  template <class T> class reference_wrapper {
  public:
    using result_type          = see below; // not always defined
    using argument_type        = see below; // not always defined
    using first_argument_type  = see below; // not always defined
    using second_argument_type = see below; // not always defined
  };

  template <class T> struct plus {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct minus {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct multiplies {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct divides {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct modulus {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct negate {
    using argument_type = T;
    using result_type   = T;
  };

  template <class T> struct equal_to {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct not_equal_to {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct greater {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct less {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct greater_equal {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct less_equal {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct logical_and {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct logical_or {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct logical_not {
    using argument_type = T;
    using result_type   = bool;
  };

  template <class T> struct bit_and {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct bit_or {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct bit_xor {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct bit_not {
    using argument_type = T;
    using result_type   = T;
  };

  template<class R, class T1> class function<R(T1)> {
  public:
    using argument_type = T1;
  };

  template<class R, class T1, class T2> class function<R(T1, T2)> {
  public:
    using first_argument_type  = T1;
    using second_argument_type = T2;
  };
}
reference_­wrapper<T> has a weak result type.
If T is a function type, result_­type shall be a synonym for the return type of T.
The template specialization reference_­wrapper<T> shall define a nested type named argument_­type as a synonym for T1 only if the type T is any of the following:
  • a function type or a pointer to function type taking one argument of type T1
  • a pointer to member function R T0​::​f() cv (where cv represents the member function's cv-qualifiers); the type T1 is cv T0*
  • a class type where the qualified-id T​::​argument_­type is valid and denotes a type ([temp.deduct]); the type T1 is T​::​argument_­type.
The template instantiation reference_­wrapper<T> shall define two nested types named first_­argument_­type and second_­argument_­type as synonyms for T1 and T2, respectively, only if the type T is any of the following:
  • a function type or a pointer to function type taking two arguments of types T1 and T2
  • a pointer to member function R T0​::​f(T2) cv (where cv represents the member function's cv-qualifiers); the type T1 is cv T0*
  • a class type where the qualified-ids T​::​first_­argument_­type and T​::​second_­argument_­type are both valid and both denote types ([temp.deduct]); the type T1 is T​::​first_­argument_­type and the type T2 is T​::​second_­argument_­type.
All enabled specializations hash<Key> of hash ([unord.hash]) provide two nested types, result_­type and argument_­type, which shall be synonyms for size_­t and Key, respectively.
The forwarding call wrapper g returned by a call to bind(f, bound_­args...) ([func.bind.bind]) shall have a weak result type.
The forwarding call wrapper g returned by a call to bind<R>(f, bound_­args...) ([func.bind.bind]) shall have a nested type result_­type defined as a synonym for R.
The simple call wrapper returned from a call to mem_­fn(pm) shall have a nested type result_­type that is a synonym for the return type of pm when pm is a pointer to member function.
The simple call wrapper returned from a call to mem_­fn(pm) shall define two nested types named argument_­type and result_­type as synonyms for cv T* and Ret, respectively, when pm is a pointer to member function with cv-qualifier cv and taking no arguments, where Ret is pm's return type.
The simple call wrapper returned from a call to mem_­fn(pm) shall define three nested types named first_­argument_­type, second_­argument_­type, and result_­type as synonyms for cv T*, T1, and Ret, respectively, when pm is a pointer to member function with cv-qualifier cv and taking one argument of type T1, where Ret is pm's return type.
The following member names are defined in addition to names specified in Clause [containers]:
namespace std {
  template <class Key, class T, class Compare, class Allocator>
  class map<Key, T, Compare, Allocator>::value_compare {
  public:
    using result_type          = bool;
    using first_argument_type  = value_type;
    using second_argument_type = value_type;
  };

  template <class Key, class T, class Compare, class Allocator>
  class multimap<Key, T, Compare, Allocator>::value_compare {
  public:
    using result_type          = bool;
    using first_argument_type  = value_type;
    using second_argument_type = value_type;
  };
}

D.8.3 Negators [depr.negators]

The header <functional> has the following additions:
namespace std {
  template <class Predicate> class unary_negate;
  template <class Predicate>
    constexpr unary_negate<Predicate> not1(const Predicate&);
  template <class Predicate> class binary_negate;
  template <class Predicate>
    constexpr binary_negate<Predicate> not2(const Predicate&);
}
Negators not1 and not2 take a unary and a binary predicate, respectively, and return their logical negations ([expr.unary.op]).
template <class Predicate>
class unary_negate {
public:
  constexpr explicit unary_negate(const Predicate& pred);
  constexpr bool operator()(const typename Predicate::argument_type& x) const;
  using argument_type = typename Predicate::argument_type;
  using result_type   = bool;
};
constexpr bool operator()(const typename Predicate::argument_type& x) const;
Returns: !pred(x).
template <class Predicate> constexpr unary_negate<Predicate> not1(const Predicate& pred);
Returns: unary_­negate<Predicate>(pred).
template <class Predicate>
class binary_negate {
public:
  constexpr explicit binary_negate(const Predicate& pred);
  constexpr bool operator()(const typename Predicate::first_argument_type& x,
                            const typename Predicate::second_argument_type& y) const;
  using first_argument_type  = typename Predicate::first_argument_type;
  using second_argument_type = typename Predicate::second_argument_type;
  using result_type          = bool;

};
constexpr bool operator()(const typename Predicate::first_argument_type& x, const typename Predicate::second_argument_type& y) const;
Returns: !pred(x,y).
template <class Predicate> constexpr binary_negate<Predicate> not2(const Predicate& pred);
Returns: binary_­negate<Predicate>(pred).

D.9 The default allocator [depr.default.allocator]

The following members and explicit class template specialization are defined in addition to those specified in [default.allocator]:
namespace std {
  // specialize for void:
  template <> class allocator<void> {
  public:
    using value_type    = void;
    using pointer       = void*;
    using const_pointer = const void*;
    // reference-to-void members are impossible.

    template <class U> struct rebind { using other = allocator<U>; };
  };

  template <class T> class allocator {
   public:
    using size_type       = size_t;
    using difference_type = ptrdiff_t;
    using pointer         = T*;
    using const_pointer   = const T*;
    using reference       = T&;
    using const_reference = const T&;
    template <class U> struct rebind { using other = allocator<U>; };

    T* address(T& x) const noexcept;
    const T* address(const T& x) const noexcept;

    T* allocate(size_t n, const void* hint);

    template<class U, class... Args>
      void construct(U* p, Args&&... args);
    template <class U>
      void destroy(U* p);

    size_t max_size() const noexcept;
  };
}
T* address(T& x) const noexcept; const T* address(const T& x) const noexcept;
Returns: addressof(x).
T* allocate(size_t n, const void* hint);
Returns: A pointer to the initial element of an array of storage of size n * sizeof(T), aligned appropriately for objects of type T.
It is implementation-defined whether over-aligned types are supported ([basic.align]).
Remarks: The storage is obtained by calling ​::​operator new(std​::​size_­t) ([new.delete]), but it is unspecified when or how often this function is called.
Throws: bad_­alloc if the storage cannot be obtained.
template <class U, class... Args> void construct(U* p, Args&&... args);
Effects: As if by: ​::​new((void *)p) U(std​::​forward<Args>(args)...);
template <class U> void destroy(U* p);
Effects: As if by p->~U().
size_t max_size() const noexcept;
Returns: The largest value N for which the call allocate(N, 0) might succeed.

D.10 Raw storage iterator [depr.storage.iterator]

The header <memory> has the following addition:
namespace std {
  template <class OutputIterator, class T>
  class raw_storage_iterator {
  public:
    using iterator_category = output_iterator_tag;
    using value_type        = void;
    using difference_type   = void;
    using pointer           = void;
    using reference         = void;

    explicit raw_storage_iterator(OutputIterator x);

    raw_storage_iterator& operator*();
    raw_storage_iterator& operator=(const T& element);
    raw_storage_iterator& operator=(T&& element);
    raw_storage_iterator& operator++();
    raw_storage_iterator  operator++(int);
    OutputIterator base() const;
  };
}
raw_­storage_­iterator is provided to enable algorithms to store their results into uninitialized memory.
The template parameter OutputIterator is required to have its operator* return an object for which operator& is defined and returns a pointer to T, and is also required to satisfy the requirements of an output iterator.
explicit raw_storage_iterator(OutputIterator x);
Effects: Initializes the iterator to point to the same value to which x points.
raw_storage_iterator& operator*();
Returns: *this
raw_storage_iterator& operator=(const T& element);
Requires: T shall be CopyConstructible.
Effects: Constructs a value from element at the location to which the iterator points.
Returns: A reference to the iterator.
raw_storage_iterator& operator=(T&& element);
Requires: T shall be MoveConstructible.
Effects: Constructs a value from std​::​move(element) at the location to which the iterator points.
Returns: A reference to the iterator.
raw_storage_iterator& operator++();
Effects: Pre-increment: advances the iterator and returns a reference to the updated iterator.
raw_storage_iterator operator++(int);
Effects: Post-increment: advances the iterator and returns the old value of the iterator.
OutputIterator base() const;
Returns: An iterator of type OutputIterator that points to the same value as *this points to.

D.11 Temporary buffers [depr.temporary.buffer]

The header <memory> has the following additions:
namespace std {
  template <class T>
    pair<T*, ptrdiff_t> get_temporary_buffer(ptrdiff_t n) noexcept;
  template <class T>
    void return_temporary_buffer(T* p);
}
template <class T> pair<T*, ptrdiff_t> get_temporary_buffer(ptrdiff_t n) noexcept;
Effects: Obtains a pointer to uninitialized, contiguous storage for N adjacent objects of type T, for some non-negative number N.
It is implementation-defined whether over-aligned types are supported ([basic.align]).
Remarks: Calling get_­temporary_­buffer with a positive number n is a non-binding request to return storage for n objects of type T.
In this case, an implementation is permitted to return instead storage for a non-negative number N of such objects, where N != n (including N == 0).
[Note
:
The request is non-binding to allow latitude for implementation-specific optimizations of its memory management.
end note
]
Returns: If n <= 0 or if no storage could be obtained, returns a pair P such that P.first is a null pointer value and P.second == 0; otherwise returns a pair P such that P.first refers to the address of the uninitialized storage and P.second refers to its capacity N (in the units of sizeof(T)).
template <class T> void return_temporary_buffer(T* p);
Effects: Deallocates the storage referenced by p.
Requires: p shall be a pointer value returned by an earlier call to get_­temporary_­buffer that has not been invalidated by an intervening call to return_­temporary_­buffer(T*).
Throws: Nothing.

D.12 Deprecated type traits [depr.meta.types]

The header <type_­traits> has the following addition:
namespace std {
  template <class T> struct is_literal_type;

  template <class T> constexpr bool is_literal_type_v = is_literal_type<T>::value;

  template <class> struct result_of; // not defined
  template <class Fn, class... ArgTypes> struct result_of<Fn(ArgTypes...)>;

  template <class T> using result_of_t = typename result_of<T>::type;
}
Requires: For is_­literal_­type, remove_­all_­extents_­t<T> shall be a complete type or cv void.
For result_­of<Fn(ArgTypes...)>, Fn and all types in the parameter pack ArgTypes shall be complete types, cv void, or arrays of unknown bound.
is_­literal_­type<T> is a UnaryTypeTrait ([meta.rqmts]) with a base characteristic of true_­type if T is a literal type, and false_­type otherwise.
The partial specialization result_­of<Fn(ArgTypes...)> is a TransformationTrait whose member typedef type is defined if and only if invoke_­result<Fn, ArgTypes...>​::​type is defined.
If type is defined, it names the same type as invoke_­result_­t<Fn, ArgTypes...>.
The behavior of a program that adds specializations for is_­literal_­type or is_­literal_­type_­v is undefined.

D.13 Deprecated iterator primitives [depr.iterator.primitives]

D.13.1 Basic iterator [depr.iterator.basic]

The header <iterator> has the following addition:
namespace std {
  template<class Category, class T, class Distance = ptrdiff_t,
    class Pointer = T*, class Reference = T&>
  struct iterator {
    using iterator_category = Category;
    using value_type        = T;
    using difference_type   = Distance;
    using pointer           = Pointer;
    using reference         = Reference;
  };
}
The iterator template may be used as a base class to ease the definition of required types for new iterators.
[Note
:
If the new iterator type is a class template, then these aliases will not be visible from within the iterator class's template definition, but only to callers of that class.
end note
]
[Example
:
If a C++ program wants to define a bidirectional iterator for some data structure containing double and such that it works on a large memory model of the implementation, it can do so with:
class MyIterator :
  public iterator<bidirectional_iterator_tag, double, long, T*, T&> {
  // code implementing ++, etc.
};
end example
]

D.14 Deprecated shared_­ptr observers [depr.util.smartptr.shared.obs]

The following member is defined in addition to those members specified in [util.smartptr.shared]:
namespace std {
  template<class T> class shared_ptr {
  public:
    bool unique() const noexcept;
  };
}
bool unique() const noexcept;
Returns: use_­count() == 1.

D.15 Deprecated standard code conversion facets [depr.locale.stdcvt]

The header <codecvt> provides code conversion facets for various character encodings.

D.15.1 Header <codecvt> synopsis [depr.codecvt.syn]

namespace std {
  enum codecvt_mode {
    consume_header = 4,
    generate_header = 2,
    little_endian = 1
  };

  template <class Elem, unsigned long Maxcode = 0x10ffff, codecvt_mode Mode = (codecvt_mode)0>
    class codecvt_utf8 : public codecvt<Elem, char, mbstate_t> {
    public:
      explicit codecvt_utf8(size_t refs = 0);
      ~codecvt_utf8();
    };

  template <class Elem, unsigned long Maxcode = 0x10ffff, codecvt_mode Mode = (codecvt_mode)0>
    class codecvt_utf16 : public codecvt<Elem, char, mbstate_t> {
    public:
      explicit codecvt_utf16(size_t refs = 0);
      ~codecvt_utf16();
    };

  template <class Elem, unsigned long Maxcode = 0x10ffff, codecvt_mode Mode = (codecvt_mode)0>
    class codecvt_utf8_utf16 : public codecvt<Elem, char, mbstate_t> {
    public:
      explicit codecvt_utf8_utf16(size_t refs = 0);
      ~codecvt_utf8_utf16();
    };
}

D.15.2 Requirements [depr.locale.stdcvt.req]

For each of the three code conversion facets codecvt_­utf8, codecvt_­utf16, and codecvt_­utf8_­utf16:
  • Elem is the wide-character type, such as wchar_­t, char16_­t, or char32_­t.
  • Maxcode is the largest wide-character code that the facet will read or write without reporting a conversion error.
  • If (Mode & consume_­header), the facet shall consume an initial header sequence, if present, when reading a multibyte sequence to determine the endianness of the subsequent multibyte sequence to be read.
  • If (Mode & generate_­header), the facet shall generate an initial header sequence when writing a multibyte sequence to advertise the endianness of the subsequent multibyte sequence to be written.
  • If (Mode & little_­endian), the facet shall generate a multibyte sequence in little-endian order, as opposed to the default big-endian order.
For the facet codecvt_­utf8:
  • The facet shall convert between UTF-8 multibyte sequences and UCS2 or UCS4 (depending on the size of Elem) within the program.
  • Endianness shall not affect how multibyte sequences are read or written.
  • The multibyte sequences may be written as either a text or a binary file.
For the facet codecvt_­utf16:
  • The facet shall convert between UTF-16 multibyte sequences and UCS2 or UCS4 (depending on the size of Elem) within the program.
  • Multibyte sequences shall be read or written according to the Mode flag, as set out above.
  • The multibyte sequences may be written only as a binary file.
    Attempting to write to a text file produces undefined behavior.
For the facet codecvt_­utf8_­utf16:
  • The facet shall convert between UTF-8 multibyte sequences and UTF-16 (one or two 16-bit codes) within the program.
  • Endianness shall not affect how multibyte sequences are read or written.
  • The multibyte sequences may be written as either a text or a binary file.
See also: ISO/IEC 10646-1:1993.

D.16 Deprecated convenience conversion interfaces [depr.conversions]

The header <locale> has the following additions:
namespace std {
  template <class Codecvt, class Elem = wchar_t,
            class Wide_alloc = allocator<Elem>,
            class Byte_alloc = allocator<char>>
    class wstring_convert;

  template <class Codecvt, class Elem = wchar_t,
            class Tr = char_traits<Elem>>
    class wbuffer_convert;
}

D.16.1 Class template wstring_­convert [depr.conversions.string]

Class template wstring_­convert performs conversions between a wide string and a byte string.
It lets you specify a code conversion facet (like class template codecvt) to perform the conversions, without affecting any streams or locales.
[Example
:
If you want to use the code conversion facet codecvt_­utf8 to output to cout a UTF-8 multibyte sequence corresponding to a wide string, but you don't want to alter the locale for cout, you can write something like:
wstring_convert<std::codecvt_utf8<wchar_t>> myconv;
std::string mbstring = myconv.to_bytes(L"Hello\n");
std::cout << mbstring;
end example
]
namespace std {
  template <class Codecvt, class Elem = wchar_t,
            class Wide_alloc = allocator<Elem>,
            class Byte_alloc = allocator<char>>
    class wstring_convert {
    public:
      using byte_string = basic_string<char, char_traits<char>, Byte_alloc>;
      using wide_string = basic_string<Elem, char_traits<Elem>, Wide_alloc>;
      using state_type  = typename Codecvt::state_type;
      using int_type    = typename wide_string::traits_type::int_type;

      explicit wstring_convert(Codecvt* pcvt = new Codecvt);
      wstring_convert(Codecvt* pcvt, state_type state);
      explicit wstring_convert(const byte_string& byte_err,
                               const wide_string& wide_err = wide_string());
      ~wstring_convert();

      wstring_convert(const wstring_convert&) = delete;
      wstring_convert& operator=(const wstring_convert&) = delete;

      wide_string from_bytes(char byte);
      wide_string from_bytes(const char* ptr);
      wide_string from_bytes(const byte_string& str);
      wide_string from_bytes(const char* first, const char* last);

      byte_string to_bytes(Elem wchar);
      byte_string to_bytes(const Elem* wptr);
      byte_string to_bytes(const wide_string& wstr);
      byte_string to_bytes(const Elem* first, const Elem* last);

      size_t converted() const noexcept;
      state_type state() const;

    private:
      byte_string byte_err_string;  // exposition only
      wide_string wide_err_string;  // exposition only
      Codecvt* cvtptr;              // exposition only
      state_type cvtstate;          // exposition only
      size_t cvtcount;              // exposition only
    };
}
The class template describes an object that controls conversions between wide string objects of class basic_­string<Elem, char_­traits<Elem>, Wide_­alloc> and byte string objects of class basic_­string<char, char_­traits<char>, Byte_­alloc>.
The class template defines the types wide_­string and byte_­string as synonyms for these two types.
Conversion between a sequence of Elem values (stored in a wide_­string object) and multibyte sequences (stored in a byte_­string object) is performed by an object of class Codecvt, which meets the requirements of the standard code-conversion facet codecvt<Elem, char, mbstate_­t>.
An object of this class template stores:
  • byte_­err_­string — a byte string to display on errors
  • wide_­err_­string — a wide string to display on errors
  • cvtptr — a pointer to the allocated conversion object (which is freed when the wstring_­convert object is destroyed)
  • cvtstate — a conversion state object
  • cvtcount — a conversion count
using byte_string = basic_string<char, char_traits<char>, Byte_alloc>;
The type shall be a synonym for basic_­string<char, char_­traits<char>, Byte_­alloc>.
size_t converted() const noexcept;
Returns: cvtcount.
wide_string from_bytes(char byte); wide_string from_bytes(const char* ptr); wide_string from_bytes(const byte_string& str); wide_string from_bytes(const char* first, const char* last);
Effects: The first member function shall convert the single-element sequence byte to a wide string.
The second member function shall convert the null-terminated sequence beginning at ptr to a wide string.
The third member function shall convert the sequence stored in str to a wide string.
The fourth member function shall convert the sequence defined by the range [first, last) to a wide string.
In all cases:
  • If the cvtstate object was not constructed with an explicit value, it shall be set to its default value (the initial conversion state) before the conversion begins.
    Otherwise it shall be left unchanged.
  • The number of input elements successfully converted shall be stored in cvtcount.
Returns: If no conversion error occurs, the member function shall return the converted wide string.
Otherwise, if the object was constructed with a wide-error string, the member function shall return the wide-error string.
Otherwise, the member function throws an object of class range_­error.
using int_type = typename wide_string::traits_type::int_type;
The type shall be a synonym for wide_­string​::​traits_­type​::​int_­type.
state_type state() const;
returns cvtstate.
using state_type = typename Codecvt::state_type;
The type shall be a synonym for Codecvt​::​state_­type.
byte_string to_bytes(Elem wchar); byte_string to_bytes(const Elem* wptr); byte_string to_bytes(const wide_string& wstr); byte_string to_bytes(const Elem* first, const Elem* last);
Effects: The first member function shall convert the single-element sequence wchar to a byte string.
The second member function shall convert the null-terminated sequence beginning at wptr to a byte string.
The third member function shall convert the sequence stored in wstr to a byte string.
The fourth member function shall convert the sequence defined by the range [first, last) to a byte string.
In all cases:
  • If the cvtstate object was not constructed with an explicit value, it shall be set to its default value (the initial conversion state) before the conversion begins.
    Otherwise it shall be left unchanged.
  • The number of input elements successfully converted shall be stored in cvtcount.
Returns: If no conversion error occurs, the member function shall return the converted byte string.
Otherwise, if the object was constructed with a byte-error string, the member function shall return the byte-error string.
Otherwise, the member function shall throw an object of class range_­error.
using wide_string = basic_string<Elem, char_traits<Elem>, Wide_alloc>;
The type shall be a synonym for basic_­string<Elem, char_­traits<Elem>, Wide_­alloc>.
explicit wstring_convert(Codecvt* pcvt = new Codecvt); wstring_convert(Codecvt* pcvt, state_type state); explicit wstring_convert(const byte_string& byte_err, const wide_string& wide_err = wide_string());
Requires: For the first and second constructors, pcvt != nullptr.
Effects: The first constructor shall store pcvt in cvtptr and default values in cvtstate, byte_­err_­string, and wide_­err_­string.
The second constructor shall store pcvt in cvtptr, state in cvtstate, and default values in byte_­err_­string and wide_­err_­string; moreover the stored state shall be retained between calls to from_­bytes and to_­bytes.
The third constructor shall store new Codecvt in cvtptr, state_­type() in cvtstate, byte_­err in byte_­err_­string, and wide_­err in wide_­err_­string.
~wstring_convert();
Effects: The destructor shall delete cvtptr.

D.16.2 Class template wbuffer_­convert [depr.conversions.buffer]

Class template wbuffer_­convert looks like a wide stream buffer, but performs all its I/O through an underlying byte stream buffer that you specify when you construct it.
Like class template wstring_­convert, it lets you specify a code conversion facet to perform the conversions, without affecting any streams or locales.
namespace std {
  template <class Codecvt, class Elem = wchar_t, class Tr = char_traits<Elem>>
    class wbuffer_convert : public basic_streambuf<Elem, Tr> {
    public:
      using state_type = typename Codecvt::state_type;

      explicit wbuffer_convert(streambuf* bytebuf = nullptr,
                               Codecvt* pcvt = new Codecvt,
                               state_type state = state_type());

      ~wbuffer_convert();

      wbuffer_convert(const wbuffer_convert&) = delete;
      wbuffer_convert& operator=(const wbuffer_convert&) = delete;

      streambuf* rdbuf() const;
      streambuf* rdbuf(streambuf* bytebuf);

      state_type state() const;

    private:
      streambuf* bufptr;            // exposition only
      Codecvt* cvtptr;              // exposition only
      state_type cvtstate;          // exposition only
  };
}
The class template describes a stream buffer that controls the transmission of elements of type Elem, whose character traits are described by the class Tr, to and from a byte stream buffer of type streambuf.
Conversion between a sequence of Elem values and multibyte sequences is performed by an object of class Codecvt, which shall meet the requirements of the standard code-conversion facet codecvt<Elem, char, mbstate_­t>.
An object of this class template stores:
  • bufptr — a pointer to its underlying byte stream buffer
  • cvtptr — a pointer to the allocated conversion object (which is freed when the wbuffer_­convert object is destroyed)
  • cvtstate — a conversion state object
state_type state() const;
Returns: cvtstate.
streambuf* rdbuf() const;
Returns: bufptr.
streambuf* rdbuf(streambuf* bytebuf);
Effects: Stores bytebuf in bufptr.
Returns: The previous value of bufptr.
using state_type = typename Codecvt::state_type;
The type shall be a synonym for Codecvt​::​state_­type.
explicit wbuffer_convert( streambuf* bytebuf = nullptr, Codecvt* pcvt = new Codecvt, state_type state = state_type());
Requires: pcvt != nullptr.
Effects: The constructor constructs a stream buffer object, initializes bufptr to bytebuf, initializes cvtptr to pcvt, and initializes cvtstate to state.
~wbuffer_convert();
Effects: The destructor shall delete cvtptr.