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%!TEX root = std.tex
\normannex{depr}{Compatibility features}
\newcommand{\requires}{\Fundesc{Requires}}
\rSec1[depr.general]{General}
\pnum
This Annex describes features of the \Cpp{} Standard that are specified for compatibility with
existing implementations.
\pnum
These are deprecated features, where
\term{deprecated}
is defined as:
Normative for the current revision of \Cpp{},
but having been identified as a candidate for removal from future revisions.
An implementation may declare library names and entities described in this Clause with the
\tcode{deprecated} attribute\iref{dcl.attr.deprecated}.
\rSec1[depr.arith.conv.enum]{Arithmetic conversion on enumerations}
\pnum
The ability to apply the usual arithmetic conversions\iref{expr.arith.conv}
on operands where one is of enumeration type
and the other is of a different enumeration type
or a floating-point type
is deprecated.
\begin{note}
Three-way comparisons\iref{expr.spaceship} between such operands are ill-formed.
\end{note}
\begin{example}
\begin{codeblock}
enum E1 { e };
enum E2 { f };
bool b = e <= 3.7; // deprecated
int k = f - e; // deprecated
auto cmp = e <=> f; // error
\end{codeblock}
\end{example}
\rSec1[depr.capture.this]{Implicit capture of \tcode{*this} by reference}
\pnum
For compatibility with prior revisions of \Cpp{},
a \grammarterm{lambda-expression} with \grammarterm{capture-default}
\tcode{=}\iref{expr.prim.lambda.capture} may implicitly capture
\tcode{*this} by reference.
\begin{example}
\begin{codeblock}
struct X {
int x;
void foo(int n) {
auto f = [=]() { x = n; }; // deprecated: \tcode{x} means \tcode{this->x}, not a copy thereof
auto g = [=, this]() { x = n; }; // recommended replacement
}
};
\end{codeblock}
\end{example}
\rSec1[depr.array.comp]{Array comparisons}
\pnum
Equality and relational comparisons\iref{expr.eq,expr.rel}
between two operands of array type
are deprecated.
\begin{note}
Three-way comparisons\iref{expr.spaceship} between such operands are ill-formed.
\end{note}
\begin{example}
\begin{codeblock}
int arr1[5];
int arr2[5];
bool same = arr1 == arr2; // deprecated, same as \tcode{\&arr1[0] == \&arr2[0]},
// does not compare array contents
auto cmp = arr1 <=> arr2; // error
\end{codeblock}
\end{example}
\rSec1[depr.volatile.type]{Deprecated \tcode{volatile} types}
\pnum
Postfix \tcode{++} and \tcode{--} expressions\iref{expr.post.incr} and
prefix \tcode{++} and \tcode{--} expressions\iref{expr.pre.incr}
of volatile-qualified arithmetic and pointer types are deprecated.
\begin{example}
\begin{codeblock}
volatile int velociraptor;
++velociraptor; // deprecated
\end{codeblock}
\end{example}
\pnum
Certain assignments
where the left operand is a volatile-qualified non-class type
are deprecated; see~\ref{expr.ass}.
\begin{example}
\begin{codeblock}
int neck, tail;
volatile int brachiosaur;
brachiosaur = neck; // OK
tail = brachiosaur; // OK
tail = brachiosaur = neck; // deprecated
brachiosaur += neck; // deprecated
brachiosaur = brachiosaur + neck; // OK
\end{codeblock}
\end{example}
\pnum
A function type\iref{dcl.fct}
with a parameter with volatile-qualified type or
with a volatile-qualified return type is deprecated.
\begin{example}
\begin{codeblock}
volatile struct amber jurassic(); // deprecated
void trex(volatile short left_arm, volatile short right_arm); // deprecated
void fly(volatile struct pterosaur* pteranodon); // OK
\end{codeblock}
\end{example}
\pnum
A structured binding\iref{dcl.struct.bind} of a volatile-qualified type
is deprecated.
\begin{example}
\begin{codeblock}
struct linhenykus { short forelimb; };
void park(linhenykus alvarezsauroid) {
volatile auto [what_is_this] = alvarezsauroid; // deprecated
// ...
}
\end{codeblock}
\end{example}
\rSec1[depr.static.constexpr]{Redeclaration of \tcode{static constexpr} data members}
\pnum
For compatibility with prior revisions of \Cpp{}, a \keyword{constexpr}
static data member may be redundantly redeclared outside the class with no initializer.
This usage is deprecated.
\begin{example}
\begin{codeblock}
struct A {
static constexpr int n = 5; // definition (declaration in \CppXIV{})
};
constexpr int A::n; // redundant declaration (definition in \CppXIV{})
\end{codeblock}
\end{example}
\rSec1[depr.local]{Non-local use of TU-local entities}
\pnum
A declaration of a non-TU-local entity that is an exposure\iref{basic.link}
is deprecated.
\begin{note}
Such a declaration in an importable module unit is ill-formed.
\end{note}
\begin{example}
\begin{codeblock}
namespace {
struct A {
void f() {}
};
}
A h(); // deprecated: not internal linkage
inline void g() {A().f();} // deprecated: inline and not internal linkage
\end{codeblock}
\end{example}
\rSec1[depr.impldec]{Implicit declaration of copy functions}
\pnum
The implicit definition of a copy constructor\iref{class.copy.ctor}
as defaulted is deprecated if the class has
a user-declared copy assignment operator or
a user-declared destructor\iref{class.dtor}.
The implicit definition of a copy assignment operator\iref{class.copy.assign}
as defaulted is deprecated if the class has
a user-declared copy constructor or
a user-declared destructor.
It is possible that future versions of \Cpp{} will specify
that these implicit definitions are deleted\iref{dcl.fct.def.delete}.
\rSec1[depr.template.template]{\tcode{template} keyword before qualified names}
\pnum
The use of the keyword \keyword{template}
before the qualified name of a class or alias template
without a template argument list is deprecated.
\rSec1[depr.res.on.required]{Requires paragraph}
\pnum
In addition to the elements specified in \ref{structure.specifications},
descriptions of function semantics may also contain a \requires element
to denote the preconditions for calling a function.
\pnum
\indextext{restriction}%
Violation of any preconditions specified in a function's \requires element
results in undefined behavior
unless the function's \throws element
specifies throwing an exception when the precondition is violated.
\rSec1[depr.relops]{Relational operators}%
\indexlibraryglobal{rel_ops}%
\pnum
The header \libheaderref{utility} has the following additions:
\begin{codeblock}
namespace std::rel_ops {
template<class T> bool operator!=(const T&, const T&);
template<class T> bool operator> (const T&, const T&);
template<class T> bool operator<=(const T&, const T&);
template<class T> bool operator>=(const T&, const T&);
}
\end{codeblock}
\pnum
To avoid redundant definitions of \tcode{operator!=} out of \tcode{operator==}
and operators \tcode{>}, \tcode{<=}, and \tcode{>=} out of \tcode{operator<},
the library provides the following:
\indexlibrary{\idxcode{operator"!=}}%
\begin{itemdecl}
template<class T> bool operator!=(const T& x, const T& y);
\end{itemdecl}
\begin{itemdescr}
\pnum
\requires
Type \tcode{T} is \oldconcept{EqualityComparable} (\tref{cpp17.equalitycomparable}).
\pnum
\returns
\tcode{!(x == y)}.
\end{itemdescr}
\indexlibraryglobal{operator>}%
\begin{itemdecl}
template<class T> bool operator>(const T& x, const T& y);
\end{itemdecl}
\begin{itemdescr}
\pnum
\requires
Type \tcode{T} is \oldconcept{LessThanComparable} (\tref{cpp17.lessthancomparable}).
\pnum
\returns
\tcode{y < x}.
\end{itemdescr}
\indexlibrary{\idxcode{operator<=}}%
\begin{itemdecl}
template<class T> bool operator<=(const T& x, const T& y);
\end{itemdecl}
\begin{itemdescr}
\pnum
\requires
Type \tcode{T} is \oldconcept{LessThanComparable} (\tref{cpp17.lessthancomparable}).
\pnum
\returns
\tcode{!(y < x)}.
\end{itemdescr}
\indexlibrary{\idxcode{operator>=}}%
\begin{itemdecl}
template<class T> bool operator>=(const T& x, const T& y);
\end{itemdecl}
\begin{itemdescr}
\pnum
\requires
Type \tcode{T} is \oldconcept{LessThanComparable} (\tref{cpp17.lessthancomparable}).
\pnum
\returns
\tcode{!(x < y)}.
\end{itemdescr}
\rSec1[depr.str.strstreams]{\tcode{char*} streams}
\rSec2[depr.strstream.syn]{Header \tcode{<strstream>} synopsis}
\pnum
The header \libheaderdef{strstream}
defines types that associate stream buffers with
character array objects and assist reading and writing such objects.
\begin{codeblock}
namespace std {
class strstreambuf;
class istrstream;
class ostrstream;
class strstream;
}
\end{codeblock}
\rSec2[depr.strstreambuf]{Class \tcode{strstreambuf}}
\rSec3[depr.strstreambuf.general]{General}
\indexlibraryglobal{strstreambuf}%
\begin{codeblock}
namespace std {
class strstreambuf : public basic_streambuf<char> {
public:
strstreambuf() : strstreambuf(0) {}
explicit strstreambuf(streamsize alsize_arg);
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; // \expos
static const strstate allocated; // \expos
static const strstate constant; // \expos
static const strstate dynamic; // \expos
static const strstate frozen; // \expos
strstate strmode; // \expos
streamsize alsize; // \expos
void* (*palloc)(size_t); // \expos
void (*pfree)(void*); // \expos
};
}
\end{codeblock}
\pnum
The class
\tcode{strstreambuf}
associates the input sequence, and possibly the output sequence, with an object of some
\textit{character}
array type, whose elements store arbitrary values.
The array object has several attributes.
\pnum
\begin{note}
For the sake of exposition, these are represented as elements of a bitmask type
(indicated here as \tcode{T1}) called \tcode{strstate}.
The elements are:
\begin{itemize}
\item
\tcode{allocated}, set when a dynamic array object has been
allocated, and hence will be freed by the destructor for the
\tcode{strstreambuf} object;
\item
\tcode{constant}, set when the array object has
\keyword{const} elements, so the output sequence cannot be written;
\item
\tcode{dynamic}, set when the array object is allocated
(or reallocated)
as necessary to hold a character sequence that can change in length;
\item
\tcode{frozen}, set when the program has requested that the
array object not be altered, reallocated, or freed.
\end{itemize}
\end{note}
\pnum
\begin{note}
For the sake of exposition, the maintained data is presented here as:
\begin{itemize}
\item
\tcode{strstate strmode}, the attributes of the array object
associated with the \tcode{strstreambuf} object;
\item
\tcode{int alsize}, the suggested minimum size for a
dynamic array object;
\item
\tcode{void* (*palloc)(size_t)}, points to the function
to call to allocate a dynamic array object;
\item
\tcode{void (*pfree)(void*)}, points to the function to
call to free a dynamic array object.
\end{itemize}
\end{note}
\pnum
Each object of class
\tcode{strstreambuf}
has a
\term{seekable area},
delimited by the pointers \tcode{seeklow} and \tcode{seekhigh}.
If \tcode{gnext} is a null pointer, the seekable area is undefined.
Otherwise, \tcode{seeklow} equals \tcode{gbeg} and
\tcode{seekhigh} is either \tcode{pend},
if \tcode{pend} is not a null pointer, or \tcode{gend}.
\rSec3[depr.strstreambuf.cons]{\tcode{strstreambuf} constructors}
\indexlibraryctor{strstreambuf}%
\begin{itemdecl}
explicit strstreambuf(streamsize alsize_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Initializes the base class with \tcode{streambuf()}.
The postconditions of this function are indicated in \tref{depr.strstreambuf.cons.sz}.
\end{itemdescr}
\begin{libtab2}{\tcode{strstreambuf(streamsize)} effects}{depr.strstreambuf.cons.sz}
{ll}
{Element}{Value}
\tcode{strmode} & \tcode{dynamic} \\
\tcode{alsize} & \tcode{alsize_arg} \\
\tcode{palloc} & a null pointer \\
\tcode{pfree} & a null pointer \\
\end{libtab2}
\indexlibraryctor{strstreambuf}%
\begin{itemdecl}
strstreambuf(void* (*palloc_arg)(size_t), void (*pfree_arg)(void*));
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Initializes the base class with \tcode{streambuf()}.
The postconditions of this function are indicated in \tref{depr.strstreambuf.cons.alloc}.
\begin{libtab2}{\tcode{strstreambuf(void* (*)(size_t), void (*)(void*))} effects}
{depr.strstreambuf.cons.alloc}
{ll}
{Element}{Value}
\tcode{strmode} & \tcode{dynamic} \\
\tcode{alsize} & an unspecified value \\
\tcode{palloc} & \tcode{palloc_arg} \\
\tcode{pfree} & \tcode{pfree_arg} \\
\end{libtab2}
\end{itemdescr}
\indextext{unspecified}%
\indexlibraryctor{strstreambuf}%
\begin{itemdecl}
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);
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Initializes the base class with \tcode{streambuf()}.
The postconditions of this function are indicated in \tref{depr.strstreambuf.cons.ptr}.
\begin{libtab2}{\tcode{strstreambuf(charT*, streamsize, charT*)} effects}
{depr.strstreambuf.cons.ptr}
{ll}
{Element}{Value}
\tcode{strmode} & 0 \\
\tcode{alsize} & an unspecified value \\
\tcode{palloc} & a null pointer \\
\tcode{pfree} & a null pointer \\
\end{libtab2}
\pnum
\tcode{gnext_arg} shall point to the first element of an array
object whose number of elements \tcode{N} is determined as follows:
\begin{itemize}
\item
If
\tcode{n > 0},
\tcode{N} is \tcode{n}.
\item
If
\tcode{n == 0},
\tcode{N} is
\tcode{std::strlen(gnext_arg)}.
\indexlibraryglobal{strlen}%
\item
If
\tcode{n < 0},
\tcode{N} is
\tcode{INT_MAX}.
\begin{footnote}
The function signature
\indexlibraryglobal{strlen}%
\tcode{strlen(const char*)}
is declared in \libheaderref{cstring}.
The macro \tcode{INT_MAX} is defined in \libheaderref{climits}.
\end{footnote}
\end{itemize}
\pnum
If \tcode{pbeg_arg} is a null pointer, the function executes:
\begin{codeblock}
setg(gnext_arg, gnext_arg, gnext_arg + N);
\end{codeblock}
\pnum
Otherwise, the function executes:
\begin{codeblock}
setg(gnext_arg, gnext_arg, pbeg_arg);
setp(pbeg_arg, pbeg_arg + N);
\end{codeblock}
\end{itemdescr}
\indexlibraryctor{strstreambuf}%
\begin{itemdecl}
strstreambuf(const char* gnext_arg, streamsize n);
strstreambuf(const signed char* gnext_arg, streamsize n);
strstreambuf(const unsigned char* gnext_arg, streamsize n);
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Behaves the same as
\tcode{strstreambuf((char*)gnext_arg,n)},
except that the constructor also sets \tcode{constant} in \tcode{strmode}.
\end{itemdescr}
\indexlibrarydtor{strstreambuf}%
\begin{itemdecl}
virtual ~strstreambuf();
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Destroys an object of class
\tcode{strstreambuf}.
The function frees the dynamically allocated array object only if
\tcode{(strmode \& allocated) != 0}
and
\tcode{(strmode \& frozen) == 0}.
(\ref{depr.strstreambuf.virtuals} describes how a dynamically allocated array object is freed.)
\end{itemdescr}
\rSec3[depr.strstreambuf.members]{Member functions}
\indexlibrarymember{freeze}{strstreambuf}%
\begin{itemdecl}
void freeze(bool freezefl = true);
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
If \tcode{strmode \& dynamic} is nonzero, alters the
freeze status of the dynamic array object as follows:
\begin{itemize}
\item
If \tcode{freezefl} is
\tcode{true},
the function sets \tcode{frozen} in \tcode{strmode}.
\item
Otherwise, it clears \tcode{frozen} in \tcode{strmode}.
\end{itemize}
\end{itemdescr}
\indexlibrarymember{str}{strstreambuf}%
\begin{itemdecl}
char* str();
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Calls
\tcode{freeze()},
then returns the beginning pointer for the input sequence, \tcode{gbeg}.
\pnum
\remarks
The return value can be a null pointer.
\end{itemdescr}
\indexlibrarymember{pcount}{strstreambuf}%
\begin{itemdecl}
int pcount() const;
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
If the next pointer for the output sequence, \tcode{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, \tcode{pnext - pbeg}.
\end{itemdescr}
\rSec3[depr.strstreambuf.virtuals]{\tcode{strstreambuf} overridden virtual functions}
\indexlibrarymember{overflow}{strstreambuf}%
\begin{itemdecl}
int_type overflow(int_type c = EOF) override;
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Appends the character designated by \tcode{c} to the output
sequence, if possible, in one of two ways:
\begin{itemize}
\item
If
\tcode{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 \tcode{c} to
\tcode{*pnext++}.
Returns
\tcode{(unsigned char)c}.
\item
If
\tcode{c == EOF},
there is no character to append.
Returns a value other than \tcode{EOF}.
\end{itemize}
\pnum
Returns
\tcode{EOF}
to indicate failure.
\pnum
\remarks
The function can alter the number of write positions available as a
result of any call.
\pnum
To make a write position available, the function reallocates
(or initially allocates)
an array object with a sufficient number of elements
\tcode{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.%
\indextext{unspecified}%
If \tcode{palloc} is not a null pointer, the function calls
\tcode{(*palloc)(n)}
to allocate the new dynamic array object.
Otherwise, it evaluates the expression
\tcode{new charT[n]}.
In either case, if the allocation fails, the function returns
\tcode{EOF}.
Otherwise, it sets \tcode{allocated} in \tcode{strmode}.
\pnum
To free a previously existing dynamic array object whose first
element address is \tcode{p}:
If \tcode{pfree} is not a null pointer,
the function calls
\tcode{(*pfree)(p)}.
Otherwise, it evaluates the expression \tcode{delete[]p}.
\pnum
If
\tcode{(strmode \& dynamic) == 0},
or if
\tcode{(strmode \& frozen) != 0},
the function cannot extend the array (reallocate it with greater length) to make a write position available.
\pnum
\recommended
An implementation should consider \tcode{alsize} in making the
decision how many additional write positions to make available.
\end{itemdescr}
\indexlibrarymember{pbackfail}{strstreambuf}%
\begin{itemdecl}
int_type pbackfail(int_type c = EOF) override;
\end{itemdecl}
\begin{itemdescr}
\pnum
Puts back the character designated by \tcode{c} to the input
sequence, if possible, in one of three ways:
\begin{itemize}
\item
If
\tcode{c != EOF},
if the input sequence has a putback position available, and if
\tcode{(char)c == gnext[-1]},
assigns
\tcode{gnext - 1}
to \tcode{gnext}.
Returns \tcode{c}.
\item
If
\tcode{c != EOF},
if the input sequence has a putback position available, and if
\tcode{strmode \& constant} is zero,
assigns \tcode{c} to
\tcode{*--gnext}.
Returns
\tcode{c}.
\item
If
\tcode{c == EOF}
and if the input sequence has a putback position available,
assigns
\tcode{gnext - 1}
to \tcode{gnext}.
Returns a value other than
\tcode{EOF}.
\end{itemize}
\pnum
Returns
\tcode{EOF}
to indicate failure.
\pnum
\remarks
If the function can succeed in more than one of these ways, it is
unspecified which way is chosen.
\indextext{unspecified}%
The function can alter the number of putback
positions available as a result of any call.
\end{itemdescr}
\indexlibrarymember{underflow}{strstreambuf}%
\begin{itemdecl}
int_type underflow() override;
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Reads a character from the
\term{input sequence},
if possible, without moving the stream position past it, as follows:
\begin{itemize}
\item
If the input sequence has a read position available, the function
signals success by returning
\tcode{(unsigned char)\brk*gnext}.
\item
Otherwise, if
the current write next pointer \tcode{pnext} is not a null pointer and
is greater than the current read end pointer \tcode{gend},
makes a
\term{read position}
available by
assigning to \tcode{gend} a value greater than \tcode{gnext} and
no greater than \tcode{pnext}.
Returns \tcode{(unsigned char)*gnext}.
\end{itemize}
\pnum
Returns
\tcode{EOF}
to indicate failure.
\pnum
\remarks
The function can alter the number of read positions available as a
result of any call.
\end{itemdescr}
\indexlibrarymember{seekoff}{strstreambuf}%
\begin{itemdecl}
pos_type seekoff(off_type off, seekdir way, openmode which = in | out) override;
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Alters the stream position within one of the
controlled sequences, if possible, as indicated in \tref{depr.strstreambuf.seekoff.pos}.
\begin{libtab2}{\tcode{seekoff} positioning}{depr.strstreambuf.seekoff.pos}
{p{2.5in}l}{Conditions}{Result}
\tcode{(which \& ios::in) != 0} &
positions the input sequence \\ \rowsep
\tcode{(which \& ios::out) != 0} &
positions the output sequence \\ \rowsep
\tcode{(which \& (ios::in | ios::out)) ==}\br
\tcode{(ios::in | ios::out)} and either\br
\tcode{way == ios::beg} or \tcode{way == ios::end} &
positions both the input and the output sequences \\ \rowsep
Otherwise &
the positioning operation fails. \\
\end{libtab2}
\pnum
For a sequence to be positioned, if its next pointer is a null pointer,
the positioning operation fails.
Otherwise, the function determines \tcode{newoff} as indicated in
\tref{depr.strstreambuf.seekoff.newoff}.
\begin{libtab2}{\tcode{newoff} values}{depr.strstreambuf.seekoff.newoff}
{p{2.0in}p{2.0in}}{Condition}{\tcode{newoff} Value}
\tcode{way == ios::beg} &
0 \\ \rowsep
\tcode{way == ios::cur} &
the next pointer minus the beginning pointer (\tcode{xnext - xbeg}). \\ \rowsep
\tcode{way == ios::end} &
\tcode{seekhigh} minus the beginning pointer (\tcode{seekhigh - xbeg}). \\
\end{libtab2}
\pnum
If \tcode{(newoff + off) < (seeklow - xbeg)}
or \tcode{(seekhigh - xbeg) < (newoff + off)},
the positioning operation fails.
Otherwise, the function assigns
\tcode{xbeg + newoff + off}
to the next pointer \tcode{xnext}.
\pnum
\returns
\tcode{pos_type(newoff)},
constructed from the resultant offset
\tcode{newoff} (of type
\tcode{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
\tcode{pos_type(off_type(-1))}.
\end{itemdescr}
\indexlibrarymember{seekpos}{strstreambuf}%
\begin{itemdecl}
pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Alters the stream position within one of the
controlled sequences, if possible, to correspond to the
stream position stored in \tcode{sp}
(as described below).
\begin{itemize}
\item
If
\tcode{(which \& ios::in) != 0},
positions the input sequence.
\item
If
\tcode{(which \& ios::out) != 0},
positions the output sequence.
\item
If the function positions neither sequence, the positioning operation fails.
\end{itemize}
\pnum
For a sequence to be positioned, if its next pointer is a null pointer,
the positioning operation fails.
Otherwise, the function determines \tcode{newoff} from
\tcode{sp.offset()}:
\begin{itemize}
\item
If \tcode{newoff} is an invalid stream position,
has a negative value, or
has a value greater than (\tcode{seekhigh - seeklow}),
the positioning operation fails
\item
Otherwise, the function
adds \tcode{newoff} to the beginning pointer \tcode{xbeg} and
stores the result in the next pointer \tcode{xnext}.
\end{itemize}
\pnum
\returns
\tcode{pos_type(newoff)},
constructed from the resultant offset \tcode{newoff}
(of type
\tcode{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
\tcode{pos_type(off_type(-1))}.
\end{itemdescr}
\indexlibrarymember{setbuf}{strstreambuf}%
\begin{itemdecl}
streambuf<char>* setbuf(char* s, streamsize n) override;
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Behavior is \impldef{behavior of \tcode{strstreambuf::setbuf}},
except that
\tcode{setbuf(0, 0)}
has no effect.%
\end{itemdescr}
\rSec2[depr.istrstream]{Class \tcode{istrstream}}
\rSec3[depr.istrstream.general]{General}
\indexlibraryglobal{istrstream}%
\begin{codeblock}
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; // \expos
};
}
\end{codeblock}
\pnum
The class
\tcode{istrstream}
supports the reading of objects of class
\tcode{strstreambuf}.
It supplies a
\tcode{strstreambuf}
object to control the associated array object.
For the sake of exposition, the maintained data is presented here as:
\begin{itemize}
\item
\tcode{sb}, the \tcode{strstreambuf} object.
\end{itemize}
\rSec3[depr.istrstream.cons]{\tcode{istrstream} constructors}
\indexlibraryctor{istrstream}%
\begin{itemdecl}
explicit istrstream(const char* s);
explicit istrstream(char* s);
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Initializes the base class with \tcode{istream(\&sb)} and
\tcode{sb} with \tcode{strstreambuf(s, 0)}.
\tcode{s} shall designate the first element of an \ntbs{}.%
\indextext{NTBS@\ntbs{}}
\end{itemdescr}
\indexlibraryctor{istrstream}%
\begin{itemdecl}
istrstream(const char* s, streamsize n);
istrstream(char* s, streamsize n);
\end{itemdecl}
\begin{itemdescr}
\pnum
\effects
Initializes the base class with \tcode{istream(\&sb)}
and \tcode{sb} with \tcode{strstreambuf(s, n)}.