31 Input/output library [input.output]

31.7 Formatting and manipulators [iostream.format]

31.7.1 Header <istream> synopsis [istream.syn]

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namespace std { template<class charT, class traits = char_traits<charT>> class basic_istream; using istream = basic_istream<char>; using wistream = basic_istream<wchar_t>; template<class charT, class traits = char_traits<charT>> class basic_iostream; using iostream = basic_iostream<char>; using wiostream = basic_iostream<wchar_t>; template<class charT, class traits> basic_istream<charT, traits>& ws(basic_istream<charT, traits>& is); template<class Istream, class T> Istream&& operator>>(Istream&& is, T&& x); }

31.7.2 Header <ostream> synopsis [ostream.syn]

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namespace std { template<class charT, class traits = char_traits<charT>> class basic_ostream; using ostream = basic_ostream<char>; using wostream = basic_ostream<wchar_t>; template<class charT, class traits> basic_ostream<charT, traits>& endl(basic_ostream<charT, traits>& os); template<class charT, class traits> basic_ostream<charT, traits>& ends(basic_ostream<charT, traits>& os); template<class charT, class traits> basic_ostream<charT, traits>& flush(basic_ostream<charT, traits>& os); template<class charT, class traits> basic_ostream<charT, traits>& emit_on_flush(basic_ostream<charT, traits>& os); template<class charT, class traits> basic_ostream<charT, traits>& noemit_on_flush(basic_ostream<charT, traits>& os); template<class charT, class traits> basic_ostream<charT, traits>& flush_emit(basic_ostream<charT, traits>& os); template<class Ostream, class T> Ostream&& operator<<(Ostream&& os, const T& x); // [ostream.formatted.print], print functions template<class... Args> void print(ostream& os, format_string<Args...> fmt, Args&&... args); template<class... Args> void println(ostream& os, format_string<Args...> fmt, Args&&... args); void vprint_unicode(ostream& os, string_view fmt, format_args args); void vprint_nonunicode(ostream& os, string_view fmt, format_args args); }

31.7.3 Header <iomanip> synopsis [iomanip.syn]

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namespace std { unspecified resetiosflags(ios_base::fmtflags mask); unspecified setiosflags (ios_base::fmtflags mask); unspecified setbase(int base); template<class charT> unspecified setfill(charT c); unspecified setprecision(int n); unspecified setw(int n); template<class moneyT> unspecified get_money(moneyT& mon, bool intl = false); template<class moneyT> unspecified put_money(const moneyT& mon, bool intl = false); template<class charT> unspecified get_time(tm* tmb, const charT* fmt); template<class charT> unspecified put_time(const tm* tmb, const charT* fmt); template<class charT> unspecified quoted(const charT* s, charT delim = charT('"'), charT escape = charT('\\')); template<class charT, class traits, class Allocator> unspecified quoted(const basic_string<charT, traits, Allocator>& s, charT delim = charT('"'), charT escape = charT('\\')); template<class charT, class traits, class Allocator> unspecified quoted(basic_string<charT, traits, Allocator>& s, charT delim = charT('"'), charT escape = charT('\\')); template<class charT, class traits> unspecified quoted(basic_string_view<charT, traits> s, charT delim = charT('"'), charT escape = charT('\\')); }

31.7.4 Header <print> synopsis [print.syn]

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namespace std { // [print.fun], print functions template<class... Args> void print(format_string<Args...> fmt, Args&&... args); template<class... Args> void print(FILE* stream, format_string<Args...> fmt, Args&&... args); template<class... Args> void println(format_string<Args...> fmt, Args&&... args); template<class... Args> void println(FILE* stream, format_string<Args...> fmt, Args&&... args); void vprint_unicode(string_view fmt, format_args args); void vprint_unicode(FILE* stream, string_view fmt, format_args args); void vprint_nonunicode(string_view fmt, format_args args); void vprint_nonunicode(FILE* stream, string_view fmt, format_args args); }

31.7.5 Input streams [input.streams]

31.7.5.1 General [input.streams.general]

1
#
The header <istream> defines two class templates and a function template that control input from a stream buffer, along with a function template that extracts from stream rvalues.

31.7.5.2 Class template basic_istream [istream]

31.7.5.2.1 General [istream.general]

1
#
When a function is specified with a type placeholder of extended-floating-point-type, the implementation provides overloads for all cv-unqualified extended floating-point types ([basic.fundamental]) in lieu of extended-floating-​point-type.
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namespace std { template<class charT, class traits = char_traits<charT>> class basic_istream : virtual public basic_ios<charT, traits> { public: // types (inherited from basic_ios) using char_type = charT; using int_type = typename traits::int_type; using pos_type = typename traits::pos_type; using off_type = typename traits::off_type; using traits_type = traits; // [istream.cons], constructor/destructor explicit basic_istream(basic_streambuf<charT, traits>* sb); virtual ~basic_istream(); // [istream.sentry], prefix/suffix class sentry; // [istream.formatted], formatted input basic_istream& operator>>(basic_istream& (*pf)(basic_istream&)); basic_istream& operator>>(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&)); basic_istream& operator>>(ios_base& (*pf)(ios_base&)); basic_istream& operator>>(bool& n); basic_istream& operator>>(short& n); basic_istream& operator>>(unsigned short& n); basic_istream& operator>>(int& n); basic_istream& operator>>(unsigned int& n); basic_istream& operator>>(long& n); basic_istream& operator>>(unsigned long& n); basic_istream& operator>>(long long& n); basic_istream& operator>>(unsigned long long& n); basic_istream& operator>>(float& f); basic_istream& operator>>(double& f); basic_istream& operator>>(long double& f); basic_istream& operator>>(extended-floating-point-type& f); basic_istream& operator>>(void*& p); basic_istream& operator>>(basic_streambuf<char_type, traits>* sb); // [istream.unformatted], unformatted input streamsize gcount() const; int_type get(); basic_istream& get(char_type& c); basic_istream& get(char_type* s, streamsize n); basic_istream& get(char_type* s, streamsize n, char_type delim); basic_istream& get(basic_streambuf<char_type, traits>& sb); basic_istream& get(basic_streambuf<char_type, traits>& sb, char_type delim); basic_istream& getline(char_type* s, streamsize n); basic_istream& getline(char_type* s, streamsize n, char_type delim); basic_istream& ignore(streamsize n = 1, int_type delim = traits::eof()); int_type peek(); basic_istream& read (char_type* s, streamsize n); streamsize readsome(char_type* s, streamsize n); basic_istream& putback(char_type c); basic_istream& unget(); int sync(); pos_type tellg(); basic_istream& seekg(pos_type); basic_istream& seekg(off_type, ios_base::seekdir); protected: // [istream.cons], copy/move constructor basic_istream(const basic_istream&) = delete; basic_istream(basic_istream&& rhs); // [istream.assign], assignment and swap basic_istream& operator=(const basic_istream&) = delete; basic_istream& operator=(basic_istream&& rhs); void swap(basic_istream& rhs); }; // [istream.extractors], character extraction templates template<class charT, class traits> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&, charT&); template<class traits> basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, unsigned char&); template<class traits> basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, signed char&); template<class charT, class traits, size_t N> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&, charT(&)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, unsigned char(&)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, signed char(&)[N]); }
2
#
The class template basic_istream defines a number of member function signatures that assist in reading and interpreting input from sequences controlled by a stream buffer.
3
#
Two groups of member function signatures share common properties: the formatted input functions (or extractors) and the unformatted input functions. Both groups of input functions are described as if they obtain (or extract) input characters by calling rdbuf()->sbumpc() or rdbuf()->sgetc().
They may use other public members of istream.

31.7.5.2.2 Constructors [istream.cons]

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explicit basic_istream(basic_streambuf<charT, traits>* sb);
1
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Effects: Initializes the base class subobject with basic_ios​::​init(sb) ([basic.ios.cons]).
2
#
Postconditions: gcount() == 0.
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basic_istream(basic_istream&& rhs);
3
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Effects: Default constructs the base class, copies the gcount() from rhs, calls basic_ios<charT, traits>​::​move(rhs) to initialize the base class, and sets the gcount() for rhs to 0.
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virtual ~basic_istream();
4
#
Remarks: Does not perform any operations of rdbuf().

31.7.5.2.3 Assignment and swap [istream.assign]

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basic_istream& operator=(basic_istream&& rhs);
1
#
Effects: Equivalent to swap(rhs).
2
#
Returns: *this.
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void swap(basic_istream& rhs);
3
#
Effects: Calls basic_ios<charT, traits>​::​swap(rhs).
Exchanges the values returned by gcount() and rhs.gcount().

31.7.5.2.4 Class basic_istream​::​sentry [istream.sentry]

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namespace std { template<class charT, class traits> class basic_istream<charT, traits>::sentry { bool ok_; // exposition only public: explicit sentry(basic_istream& is, bool noskipws = false); ~sentry(); explicit operator bool() const { return ok_; } sentry(const sentry&) = delete; sentry& operator=(const sentry&) = delete; }; }
1
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The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.
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explicit sentry(basic_istream& is, bool noskipws = false);
2
#
Effects: If is.good() is false, calls is.setstate(failbit).
Otherwise, prepares for formatted or unformatted input.
First, if is.tie() is not a null pointer, the function calls is.tie()->flush() to synchronize the output sequence with any associated external C stream.
Except that this call can be suppressed if the put area of is.tie() is empty.
Further an implementation is allowed to defer the call to flush until a call of is.rdbuf()->underflow() occurs.
If no such call occurs before the sentry object is destroyed, the call to flush may be eliminated entirely.281
If noskipws is zero and is.flags() & ios_base​::​skipws is nonzero, the function extracts and discards each character as long as the next available input character c is a whitespace character.
If is.rdbuf()->sbumpc() or is.rdbuf()->sgetc() returns traits​::​eof(), the function calls setstate(failbit | eofbit) (which may throw ios_base​::​failure).
3
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Remarks: The constructor explicit sentry(basic_istream& is, bool noskipws = false) uses the currently imbued locale in is, to determine whether the next input character is whitespace or not.
4
#
To decide if the character c is a whitespace character, the constructor performs as if it executes the following code fragment: const ctype<charT>& ctype = use_facet<ctype<charT>>(is.getloc()); if (ctype.is(ctype.space, c) != 0) // c is a whitespace character.
5
#
If, after any preparation is completed, is.good() is true, ok_ != false otherwise, ok_ == false.
During preparation, the constructor may call setstate(failbit) (which may throw ios_base​::​​failure ([iostate.flags])).282
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~sentry();
6
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Effects: None.
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explicit operator bool() const;
7
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Returns: ok_.
281)281)
This will be possible only in functions that are part of the library.
The semantics of the constructor used in user code is as specified.
282)282)
The sentry constructor and destructor can also perform additional implementation-dependent operations.

31.7.5.3 Formatted input functions [istream.formatted]

31.7.5.3.1 Common requirements [istream.formatted.reqmts]

1
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Each formatted input function begins execution by constructing an object of type ios_base​::​iostate, termed the local error state, and initializing it to ios_base​::​goodbit.
It then creates an object of class sentry with the noskipws (second) argument false.
If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input.
Otherwise, if the sentry constructor exits by throwing an exception or if the sentry object produces false when converted to a value of type bool, the function returns without attempting to obtain any input.
If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits​::​eof(), then ios_base​::​eofbit is set in the local error state and the input function stops trying to obtain the requested input.
If an exception is thrown during input then ios_base​::​badbit is set in the local error state, *this's error state is set to the local error state, and the exception is rethrown if (exceptions() & badbit) != 0.
After extraction is done, the input function calls setstate, which sets *this's error state to the local error state, and may throw an exception.
In any case, the formatted input function destroys the sentry object.
If no exception has been thrown, it returns *this.

31.7.5.3.2 Arithmetic extractors [istream.formatted.arithmetic]

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basic_istream& operator>>(unsigned short& val); basic_istream& operator>>(unsigned int& val); basic_istream& operator>>(long& val); basic_istream& operator>>(unsigned long& val); basic_istream& operator>>(long long& val); basic_istream& operator>>(unsigned long long& val); basic_istream& operator>>(float& val); basic_istream& operator>>(double& val); basic_istream& operator>>(long double& val); basic_istream& operator>>(bool& val); basic_istream& operator>>(void*& val);
1
#
As in the case of the inserters, these extractors depend on the locale's num_get<> object to perform parsing the input stream data.
These extractors behave as formatted input functions (as described in [istream.formatted.reqmts]).
After a sentry object is constructed, the conversion occurs as if performed by the following code fragment, where state represents the input function's local error state: using numget = num_get<charT, istreambuf_iterator<charT, traits>>; use_facet<numget>(loc).get(*this, 0, *this, state, val);
In the above fragment, loc stands for the private member of the basic_ios class.
[Note 1: 
The first argument provides an object of the istreambuf_iterator class which is an iterator pointed to an input stream.
It bypasses istreams and uses streambufs directly.
— end note]
Class locale relies on this type as its interface to istream, so that it does not need to depend directly on istream.
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basic_istream& operator>>(short& val);
2
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The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment): using numget = num_get<charT, istreambuf_iterator<charT, traits>>; long lval; use_facet<numget>(loc).get(*this, 0, *this, state, lval); if (lval < numeric_limits<short>::min()) { state |= ios_base::failbit; val = numeric_limits<short>::min(); } else if (numeric_limits<short>::max() < lval) { state |= ios_base::failbit; val = numeric_limits<short>::max(); } else val = static_cast<short>(lval);
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basic_istream& operator>>(int& val);
3
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The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment): using numget = num_get<charT, istreambuf_iterator<charT, traits>>; long lval; use_facet<numget>(loc).get(*this, 0, *this, state, lval); if (lval < numeric_limits<int>::min()) { state |= ios_base::failbit; val = numeric_limits<int>::min(); } else if (numeric_limits<int>::max() < lval) { state |= ios_base::failbit; val = numeric_limits<int>::max(); } else val = static_cast<int>(lval);
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basic_istream& operator>>(extended-floating-point-type& val);
4
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If the floating-point conversion rank of extended-floating-point-type is not less than or equal to that of long double, then an invocation of the operator function is conditionally supported with implementation-defined semantics.
5
#
Otherwise, let FP be a standard floating-point type:
  • (5.1)
    if the floating-point conversion rank of extended-floating-point-type is less than or equal to that of float, then FP is float,
  • (5.2)
    otherwise, if the floating-point conversion rank of extended-floating-point-type is less than or equal to that of double, then FP is double,
  • (5.3)
    otherwise, FP is long double.
6
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The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment): using numget = num_get<charT, istreambuf_iterator<charT, traits>>; FP fval; use_facet<numget>(loc).get(*this, 0, *this, state, fval); if (fval < -numeric_limits<extended-floating-point-type>::max()) { state |= ios_base::failbit; val = -numeric_limits<extended-floating-point-type>::max(); } else if (numeric_limits<extended-floating-point-type>::max() < fval) { state |= ios_base::failbit; val = numeric_limits<extended-floating-point-type>::max(); } else { val = static_cast<extended-floating-point-type>(fval); }
[Note 2: 
When the extended floating-point type has a floating-point conversion rank that is not equal to the rank of any standard floating-point type, then double rounding during the conversion can result in inaccurate results.
from_chars can be used in situations where maximum accuracy is important.
— end note]

31.7.5.3.3 basic_istream​::​operator>> [istream.extractors]

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basic_istream& operator>>(basic_istream& (*pf)(basic_istream&));
1
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Effects: None.
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
2
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Returns: pf(*this).
283
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basic_istream& operator>>(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
3
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Effects: Calls pf(*this).
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
4
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Returns: *this.
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basic_istream& operator>>(ios_base& (*pf)(ios_base&));
5
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Effects: Calls pf(*this).284
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
6
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Returns: *this.
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template<class charT, class traits, size_t N> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& in, charT (&s)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in, unsigned char (&s)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in, signed char (&s)[N]);
7
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Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in.
After a sentry object is constructed, operator>> extracts characters and stores them into s.
If width() is greater than zero, n is min(size_t(width()), N).
Otherwise n is N.
n is the maximum number of characters stored.
8
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Characters are extracted and stored until any of the following occurs:
  • (8.1)
    n-1 characters are stored;
  • (8.2)
    end of file occurs on the input sequence;
  • (8.3)
    letting ct be use_facet<ctype<charT>>(in.getloc()), ct.is(ct.space, c) is true.
9
#
operator>> then stores a null byte (charT()) in the next position, which may be the first position if no characters were extracted.
operator>> then calls width(0).
10
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If the function extracted no characters, ios_base​::​failbit is set in the input function's local error state before setstate is called.
11
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Returns: in.
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template<class charT, class traits> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& in, charT& c); template<class traits> basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in, unsigned char& c); template<class traits> basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in, signed char& c);
12
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Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in.
A character is extracted from in, if one is available, and stored in c.
Otherwise, ios_base​::​failbit is set in the input function's local error state before setstate is called.
13
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Returns: in.
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basic_istream& operator>>(basic_streambuf<charT, traits>* sb);
14
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Effects: Behaves as an unformatted input function.
If sb is null, calls setstate(failbit), which may throw ios_base​::​failure ([iostate.flags]).
After a sentry object is constructed, extracts characters from *this and inserts them in the output sequence controlled by sb.
Characters are extracted and inserted until any of the following occurs:
  • (14.1)
    end-of-file occurs on the input sequence;
  • (14.2)
    inserting in the output sequence fails (in which case the character to be inserted is not extracted);
  • (14.3)
    an exception occurs (in which case the exception is caught).
15
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If the function inserts no characters, ios_base​::​failbit is set in the input function's local error state before setstate is called.
16
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Returns: *this.
283)283)
See, for example, the function signature ws(basic_istream&) ([istream.manip]).
284)284)
See, for example, the function signature dec(ios_base&) ([basefield.manip]).

31.7.5.4 Unformatted input functions [istream.unformatted]

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Each unformatted input function begins execution by constructing an object of type ios_base​::​iostate, termed the local error state, and initializing it to ios_base​::​goodbit.
It then creates an object of class sentry with the default argument noskipws (second) argument true.
If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input.
Otherwise, if the sentry constructor exits by throwing an exception or if the sentry object produces false, when converted to a value of type bool, the function returns without attempting to obtain any input.
In either case the number of extracted characters is set to 0; unformatted input functions taking a character array of nonzero size as an argument shall also store a null character (using charT()) in the first location of the array.
If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits​::​eof(), then ios_base​::​eofbit is set in the local error state and the input function stops trying to obtain the requested input.
If an exception is thrown during input then ios_base​::​badbit is set in the local error state, *this's error state is set to the local error state, and the exception is rethrown if (exceptions() & badbit) != 0.
If no exception has been thrown it stores the number of characters extracted in a member object.
After extraction is done, the input function calls setstate, which sets *this's error state to the local error state, and may throw an exception.
In any event the sentry object is destroyed before leaving the unformatted input function.
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streamsize gcount() const;
2
#
Effects: None.
This member function does not behave as an unformatted input function (as described above).
3
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Returns: The number of characters extracted by the last unformatted input member function called for the object.
If the number cannot be represented, returns numeric_limits<streamsize>​::​max().
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int_type get();
4
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Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts a character c, if one is available.
Otherwise, ios_base​::​failbit is set in the input function's local error state before setstate is called.
5
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Returns: c if available, otherwise traits​::​eof().
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basic_istream& get(char_type& c);
6
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Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts a character, if one is available, and assigns it to c.285
Otherwise, ios_base​::​failbit is set in the input function's local error state before setstate is called.
7
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Returns: *this.
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basic_istream& get(char_type* s, streamsize n, char_type delim);
8
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Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts characters and stores them into successive locations of an array whose first element is designated by s.286
Characters are extracted and stored until any of the following occurs:
  • (8.1)
    n is less than one or n - 1 characters are stored;
  • (8.2)
    end-of-file occurs on the input sequence;
  • (8.3)
    traits​::​eq(c, delim) for the next available input character c (in which case c is not extracted).
9
#
If the function stores no characters, ios_base​::​failbit is set in the input function's local error state before setstate is called.
In any case, if n is greater than zero it then stores a null character into the next successive location of the array.
10
#
Returns: *this.
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basic_istream& get(char_type* s, streamsize n);
11
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Effects: Calls get(s, n, widen('\n')).
12
#
Returns: Value returned by the call.
🔗
basic_istream& get(basic_streambuf<char_type, traits>& sb, char_type delim);
13
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts characters and inserts them in the output sequence controlled by sb.
Characters are extracted and inserted until any of the following occurs:
  • (13.1)
    end-of-file occurs on the input sequence;
  • (13.2)
    inserting in the output sequence fails (in which case the character to be inserted is not extracted);
  • (13.3)
    traits​::​eq(c, delim) for the next available input character c (in which case c is not extracted);
  • (13.4)
    an exception occurs (in which case, the exception is caught but not rethrown).
14
#
If the function inserts no characters, ios_base​::​failbit is set in the input function's local error state before setstate is called.
15
#
Returns: *this.
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basic_istream& get(basic_streambuf<char_type, traits>& sb);
16
#
Effects: Calls get(sb, widen('\n')).
17
#
Returns: Value returned by the call.
🔗
basic_istream& getline(char_type* s, streamsize n, char_type delim);
18
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts characters and stores them into successive locations of an array whose first element is designated by s.287
Characters are extracted and stored until one of the following occurs:
1.end-of-file occurs on the input sequence;
2.traits​::​eq(c, delim) for the next available input character c (in which case the input character is extracted but not stored);288
3.n is less than one or n - 1 characters are stored (in which case the function calls setstate(​failbit)).
19
#
These conditions are tested in the order shown.289
20
#
If the function extracts no characters, ios_base​::​failbit is set in the input function's local error state before setstate is called.290
21
#
In any case, if n is greater than zero, it then stores a null character (using charT()) into the next successive location of the array.
22
#
Returns: *this.
23
#
[Example 1: #include <iostream> int main() { using namespace std; const int line_buffer_size = 100; char buffer[line_buffer_size]; int line_number = 0; while (cin.getline(buffer, line_buffer_size, '\n') || cin.gcount()) { int count = cin.gcount(); if (cin.eof()) cout << "Partial final line"; // cin.fail() is false else if (cin.fail()) { cout << "Partial long line"; cin.clear(cin.rdstate() & ~ios_base::failbit); } else { count--; // Don't include newline in count cout << "Line " << ++line_number; } cout << " (" << count << " chars): " << buffer << endl; } } — end example]
🔗
basic_istream& getline(char_type* s, streamsize n);
24
#
Returns: getline(s, n, widen('\n'))
🔗
basic_istream& ignore(streamsize n = 1, int_type delim = traits::eof());
25
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts characters and discards them.
Characters are extracted until any of the following occurs:
  • (25.1)
    n != numeric_limits<streamsize>​::​max()numeric.limits and n characters have been extracted so far
  • (25.2)
    end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit), which may throw ios_base​::​failure ([iostate.flags]));
  • (25.3)
    traits​::​eq_int_type(traits​::​to_int_type(c), delim) for the next available input character c (in which case c is extracted).
[Note 1: 
The last condition will never occur if traits​::​eq_int_type(delim, traits​::​eof()).
— end note]
26
#
Returns: *this.
🔗
int_type peek();
27
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, reads but does not extract the current input character.
28
#
Returns: traits​::​eof() if good() is false.
Otherwise, returns rdbuf()->sgetc().
🔗
basic_istream& read(char_type* s, streamsize n);
29
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return.
Otherwise extracts characters and stores them into successive locations of an array whose first element is designated by s.291
Characters are extracted and stored until either of the following occurs:
  • (29.1)
    n characters are stored;
  • (29.2)
    end-of-file occurs on the input sequence (in which case the function calls setstate(failbit | eofbit), which may throw ios_base​::​failure ([iostate.flags])).
30
#
Returns: *this.
🔗
streamsize readsome(char_type* s, streamsize n);
31
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return.
Otherwise extracts characters and stores them into successive locations of an array whose first element is designated by s.
If rdbuf()->in_avail() == -1, calls setstate(eofbit) (which may throw ios_base​::​failure ([iostate.flags])), and extracts no characters;
  • (31.1)
    If rdbuf()->in_avail() == 0, extracts no characters
  • (31.2)
    If rdbuf()->in_avail() > 0, extracts min(rdbuf()->in_avail(), n)).
32
#
Returns: The number of characters extracted.
🔗
basic_istream& putback(char_type c);
33
#
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit.
After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return.
If rdbuf() is not null, calls rdbuf()->sputbackc(c).
If rdbuf() is null, or if sputbackc returns traits​::​eof(), calls setstate(badbit) (which may throw ios_base​::​failure ([iostate.flags])).
[Note 2: 
This function extracts no characters, so the value returned by the next call to gcount() is 0.
— end note]
34
#
Returns: *this.
🔗
basic_istream& unget();
35
#
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit.
After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return.
If rdbuf() is not null, calls rdbuf()->sungetc().
If rdbuf() is null, or if sungetc returns traits​::​eof(), calls setstate(badbit) (which may throw ios_base​::​failure ([iostate.flags])).
[Note 3: 
This function extracts no characters, so the value returned by the next call to gcount() is 0.
— end note]
36
#
Returns: *this.
🔗
int sync();
37
#
Effects: Behaves as an unformatted input function (as described above), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount().
After constructing a sentry object, if rdbuf() is a null pointer, returns -1.
Otherwise, calls rdbuf()->pubsync() and, if that function returns -1 calls setstate(badbit) (which may throw ios_base​::​failure ([iostate.flags]), and returns -1.
Otherwise, returns zero.
🔗
pos_type tellg();
38
#
Effects: Behaves as an unformatted input function (as described above), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount().
39
#
Returns: After constructing a sentry object, if fail() != false, returns pos_type(-1) to indicate failure.
Otherwise, returns rdbuf()->pubseekoff(0, cur, in).
🔗
basic_istream& seekg(pos_type pos);
40
#
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit, it does not count the number of characters extracted, and it does not affect the value returned by subsequent calls to gcount().
After constructing a sentry object, if fail() != true, executes rdbuf()->pubseekpos(pos, ios_base​::​in).
In case of failure, the function calls setstate(failbit) (which may throw ios_base​::​failure).
41
#
Returns: *this.
🔗
basic_istream& seekg(off_type off, ios_base::seekdir dir);
42
#
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit, does not count the number of characters extracted, and does not affect the value returned by subsequent calls to gcount().
After constructing a sentry object, if fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base​::​in).
In case of failure, the function calls setstate(​failbit) (which may throw ios_base​::​failure).
43
#
Returns: *this.
285)285)
Note that this function is not overloaded on types signed char and unsigned char.
286)286)
Note that this function is not overloaded on types signed char and unsigned char.
287)287)
Note that this function is not overloaded on types signed char and unsigned char.
288)288)
Since the final input character is “extracted”, it is counted in the gcount(), even though it is not stored.
289)289)
This allows an input line which exactly fills the buffer, without setting failbit.
This is different behavior than the historical AT&T implementation.
290)290)
This implies an empty input line will not cause failbit to be set.
291)291)
Note that this function is not overloaded on types signed char and unsigned char.

31.7.5.5 Standard basic_istream manipulators [istream.manip]

1
#
Each instantiation of the function template specified in this subclause is a designated addressable function ([namespace.std]).
🔗
template<class charT, class traits> basic_istream<charT, traits>& ws(basic_istream<charT, traits>& is);
2
#
Effects: Behaves as an unformatted input function, except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to is.gcount().
After constructing a sentry object extracts characters as long as the next available character c is whitespace or until there are no more characters in the sequence.
Whitespace characters are distinguished with the same criterion as used by sentry​::​sentry.
If ws stops extracting characters because there are no more available it sets eofbit, but not failbit.
3
#
Returns: is.

31.7.5.6 Rvalue stream extraction [istream.rvalue]

🔗
template<class Istream, class T> Istream&& operator>>(Istream&& is, T&& x);
1
#
Constraints: The expression is >> std​::​forward<T>(x) is well-formed when treated as an unevaluated operand and Istream is publicly and unambiguously derived from ios_base.
2
#
Effects: Equivalent to: is >> std::forward<T>(x); return std::move(is);

31.7.5.7 Class template basic_iostream [iostreamclass]

31.7.5.7.1 General [iostreamclass.general]

🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_iostream : public basic_istream<charT, traits>, public basic_ostream<charT, traits> { public: using char_type = charT; using int_type = typename traits::int_type; using pos_type = typename traits::pos_type; using off_type = typename traits::off_type; using traits_type = traits; // [iostream.cons], constructor explicit basic_iostream(basic_streambuf<charT, traits>* sb); // [iostream.dest], destructor virtual ~basic_iostream(); protected: // [iostream.cons], constructor basic_iostream(const basic_iostream&) = delete; basic_iostream(basic_iostream&& rhs); // [iostream.assign], assignment and swap basic_iostream& operator=(const basic_iostream&) = delete; basic_iostream& operator=(basic_iostream&& rhs); void swap(basic_iostream& rhs); }; }
1
#
The class template basic_iostream inherits a number of functions that allow reading input and writing output to sequences controlled by a stream buffer.

31.7.5.7.2 Constructors [iostream.cons]

🔗
explicit basic_iostream(basic_streambuf<charT, traits>* sb);
1
#
Effects: Initializes the base class subobjects with basic_istream<charT, traits>(sb) ([istream]) and basic_ostream<charT, traits>(sb).
2
#
Postconditions: rdbuf() == sb and gcount() == 0.
🔗
basic_iostream(basic_iostream&& rhs);
3
#
Effects: Move constructs from the rvalue rhs by constructing the basic_istream base class with std​::​move(rhs).

31.7.5.7.3 Destructor [iostream.dest]

🔗
virtual ~basic_iostream();
1
#
Remarks: Does not perform any operations on rdbuf().

31.7.5.7.4 Assignment and swap [iostream.assign]

🔗
basic_iostream& operator=(basic_iostream&& rhs);
1
#
Effects: Equivalent to swap(rhs).
🔗
void swap(basic_iostream& rhs);
2
#
Effects: Calls basic_istream<charT, traits>​::​swap(rhs).

31.7.6 Output streams [output.streams]

31.7.6.1 General [output.streams.general]

1
#
The header <ostream> defines a class template and several function templates that control output to a stream buffer, along with a function template that inserts into stream rvalues.

31.7.6.2 Class template basic_ostream [ostream]

31.7.6.2.1 General [ostream.general]

1
#
When a function has a parameter type extended-floating-point-type, the implementation provides overloads for all cv-unqualified extended floating-point types ([basic.fundamental]).
🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_ostream : virtual public basic_ios<charT, traits> { public: // types (inherited from basic_ios) using char_type = charT; using int_type = typename traits::int_type; using pos_type = typename traits::pos_type; using off_type = typename traits::off_type; using traits_type = traits; // [ostream.cons], constructor/destructor explicit basic_ostream(basic_streambuf<char_type, traits>* sb); virtual ~basic_ostream(); // [ostream.sentry], prefix/suffix class sentry; // [ostream.formatted], formatted output basic_ostream& operator<<(basic_ostream& (*pf)(basic_ostream&)); basic_ostream& operator<<(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&)); basic_ostream& operator<<(ios_base& (*pf)(ios_base&)); basic_ostream& operator<<(bool n); basic_ostream& operator<<(short n); basic_ostream& operator<<(unsigned short n); basic_ostream& operator<<(int n); basic_ostream& operator<<(unsigned int n); basic_ostream& operator<<(long n); basic_ostream& operator<<(unsigned long n); basic_ostream& operator<<(long long n); basic_ostream& operator<<(unsigned long long n); basic_ostream& operator<<(float f); basic_ostream& operator<<(double f); basic_ostream& operator<<(long double f); basic_ostream& operator<<(extended-floating-point-type f); basic_ostream& operator<<(const void* p); basic_ostream& operator<<(const volatile void* p); basic_ostream& operator<<(nullptr_t); basic_ostream& operator<<(basic_streambuf<char_type, traits>* sb); // [ostream.unformatted], unformatted output basic_ostream& put(char_type c); basic_ostream& write(const char_type* s, streamsize n); basic_ostream& flush(); // [ostream.seeks], seeks pos_type tellp(); basic_ostream& seekp(pos_type); basic_ostream& seekp(off_type, ios_base::seekdir); protected: // [ostream.cons], copy/move constructor basic_ostream(const basic_ostream&) = delete; basic_ostream(basic_ostream&& rhs); // [ostream.assign], assignment and swap basic_ostream& operator=(const basic_ostream&) = delete; basic_ostream& operator=(basic_ostream&& rhs); void swap(basic_ostream& rhs); }; // [ostream.inserters.character], character inserters template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&, charT); template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&, char); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, signed char); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, unsigned char); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, wchar_t) = delete; template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char8_t) = delete; template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char16_t) = delete; template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char32_t) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<<(basic_ostream<wchar_t, traits>&, char8_t) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<<(basic_ostream<wchar_t, traits>&, char16_t) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<<(basic_ostream<wchar_t, traits>&, char32_t) = delete; template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&, const charT*); template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&, const char*); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const char*); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const signed char*); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const unsigned char*); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const wchar_t*) = delete; template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const char8_t*) = delete; template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const char16_t*) = delete; template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const char32_t*) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<<(basic_ostream<wchar_t, traits>&, const char8_t*) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<<(basic_ostream<wchar_t, traits>&, const char16_t*) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<<(basic_ostream<wchar_t, traits>&, const char32_t*) = delete; }
2
#
The class template basic_ostream defines a number of member function signatures that assist in formatting and writing output to output sequences controlled by a stream buffer.
3
#
Two groups of member function signatures share common properties: the formatted output functions (or inserters) and the unformatted output functions. Both groups of output functions generate (or insert) output characters by actions equivalent to calling rdbuf()->sputc(int_type).
They may use other public members of basic_ostream except that they shall not invoke any virtual members of rdbuf() except overflow(), xsputn(), and sync().
4
#
If one of these called functions throws an exception, then unless explicitly noted otherwise the output function sets badbit in the error state.
If badbit is set in exceptions(), the output function rethrows the exception without completing its actions, otherwise it does not throw anything and proceeds as if the called function had returned a failure indication.
5
#
[Note 1: 
The deleted overloads of operator<< prevent formatting characters as integers and strings as pointers.
— end note]

31.7.6.2.2 Constructors [ostream.cons]

🔗
explicit basic_ostream(basic_streambuf<charT, traits>* sb);
1
#
Effects: Initializes the base class subobject with basic_ios<charT, traits>​::​init(sb) ([basic.ios.cons]).
2
#
Postconditions: rdbuf() == sb.
🔗
basic_ostream(basic_ostream&& rhs);
3
#
Effects: Move constructs from the rvalue rhs.
This is accomplished by default constructing the base class and calling basic_ios<charT, traits>​::​move(rhs) to initialize the base class.
🔗
virtual ~basic_ostream();
4
#
Remarks: Does not perform any operations on rdbuf().

31.7.6.2.3 Assignment and swap [ostream.assign]

🔗
basic_ostream& operator=(basic_ostream&& rhs);
1
#
Effects: Equivalent to swap(rhs).
2
#
Returns: *this.
🔗
void swap(basic_ostream& rhs);
3
#
Effects: Calls basic_ios<charT, traits>​::​swap(rhs).

31.7.6.2.4 Class basic_ostream​::​sentry [ostream.sentry]

🔗
namespace std { template<class charT, class traits> class basic_ostream<charT, traits>::sentry { bool ok_; // exposition only public: explicit sentry(basic_ostream& os); ~sentry(); explicit operator bool() const { return ok_; } sentry(const sentry&) = delete; sentry& operator=(const sentry&) = delete; }; }
1
#
The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.
🔗
explicit sentry(basic_ostream& os);
2
#
If os.good() is nonzero, prepares for formatted or unformatted output.
If os.tie() is not a null pointer, calls os.tie()->flush().292
3
#
If, after any preparation is completed, os.good() is true, ok_ == true otherwise, ok_ == false.
During preparation, the constructor may call setstate(failbit) (which may throw ios_base​::​​failure ([iostate.flags])).293
🔗
~sentry();
4
#
If (os.flags() & ios_base​::​unitbuf) && !uncaught_exceptions() && os.good() is true, calls os.rdbuf()->pubsync().
If that function returns , sets badbit in os.rdstate() without propagating an exception.
🔗
explicit operator bool() const;
5
#
Effects: Returns ok_.
292)292)
The call os.tie()->flush() does not necessarily occur if the function can determine that no synchronization is necessary.
293)293)
The sentry constructor and destructor can also perform additional implementation-dependent operations.

31.7.6.2.5 Seek members [ostream.seeks]

1
#
Each seek member function begins execution by constructing an object of class sentry.
It returns by destroying the sentry object.
🔗
pos_type tellp();
2
#
Returns: If fail() != false, returns pos_type(-1) to indicate failure.
Otherwise, returns rdbuf()->​pubseekoff(​0, cur, out).
🔗
basic_ostream& seekp(pos_type pos);
3
#
Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_base​::​out).
In case of failure, the function calls setstate(failbit) (which may throw ios_base​::​failure).
4
#
Returns: *this.
🔗
basic_ostream& seekp(off_type off, ios_base::seekdir dir);
5
#
Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base​::​out).
In case of failure, the function calls setstate(failbit) (which may throw ios_base​::​failure).
6
#
Returns: *this.

31.7.6.3 Formatted output functions [ostream.formatted]

31.7.6.3.1 Common requirements [ostream.formatted.reqmts]

1
#
Each formatted output function begins execution by constructing an object of class sentry.
If that object returns true when converted to a value of type bool, the function endeavors to generate the requested output.
If the generation fails, then the formatted output function does setstate(ios_base​::​failbit), which can throw an exception.
If an exception is thrown during output, then ios_base​::​badbit is set294 in *this's error state.
If (exceptions()&badbit) != 0 then the exception is rethrown.
Whether or not an exception is thrown, the sentry object is destroyed before leaving the formatted output function.
If no exception is thrown, the result of the formatted output function is *this.
2
#
The descriptions of the individual formatted output functions describe how they perform output and do not mention the sentry object.
3
#
If a formatted output function of a stream os determines padding, it does so as follows.
Given a charT character sequence seq where charT is the character container type of the stream, if the length of seq is less than os.width(), then enough copies of os.fill() are added to this sequence as necessary to pad to a width of os.width() characters.
If (os.flags() & ios_base​::​adjustfield) == ios_base​::​left is true, the fill characters are placed after the character sequence; otherwise, they are placed before the character sequence.
294)294)
This is done without causing an ios_base​::​failure to be thrown.

31.7.6.3.2 Arithmetic inserters [ostream.inserters.arithmetic]

🔗
basic_ostream& operator<<(bool val); basic_ostream& operator<<(short val); basic_ostream& operator<<(unsigned short val); basic_ostream& operator<<(int val); basic_ostream& operator<<(unsigned int val); basic_ostream& operator<<(long val); basic_ostream& operator<<(unsigned long val); basic_ostream& operator<<(long long val); basic_ostream& operator<<(unsigned long long val); basic_ostream& operator<<(float val); basic_ostream& operator<<(double val); basic_ostream& operator<<(long double val); basic_ostream& operator<<(const void* val);
1
#
Effects: The classes num_get<> and num_put<> handle locale-dependent numeric formatting and parsing.
These inserter functions use the imbued locale value to perform numeric formatting.
When val is of type bool, long, unsigned long, long long, unsigned long long, double, long double, or const void*, the formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet< num_put<charT, ostreambuf_iterator<charT, traits>> >(getloc()).put(*this, *this, fill(), val).failed();
When val is of type short the formatting conversion occurs as if it performed the following code fragment: ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield; bool failed = use_facet< num_put<charT, ostreambuf_iterator<charT, traits>> >(getloc()).put(*this, *this, fill(), baseflags == ios_base::oct || baseflags == ios_base::hex ? static_cast<long>(static_cast<unsigned short>(val)) : static_cast<long>(val)).failed();
When val is of type int the formatting conversion occurs as if it performed the following code fragment: ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield; bool failed = use_facet< num_put<charT, ostreambuf_iterator<charT, traits>> >(getloc()).put(*this, *this, fill(), baseflags == ios_base::oct || baseflags == ios_base::hex ? static_cast<long>(static_cast<unsigned int>(val)) : static_cast<long>(val)).failed();
When val is of type unsigned short or unsigned int the formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet< num_put<charT, ostreambuf_iterator<charT, traits>> >(getloc()).put(*this, *this, fill(), static_cast<unsigned long>(val)).failed();
When val is of type float the formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet< num_put<charT, ostreambuf_iterator<charT, traits>> >(getloc()).put(*this, *this, fill(), static_cast<double>(val)).failed();
2
#
The first argument provides an object of the ostreambuf_iterator<> class which is an iterator for class basic_ostream<>.
It bypasses ostreams and uses streambufs directly.
Class locale relies on these types as its interface to iostreams, since for flexibility it has been abstracted away from direct dependence on ostream.
The second parameter is a reference to the base class subobject of type ios_base.
It provides formatting specifications such as field width, and a locale from which to obtain other facets.
If failed is true then does setstate(badbit), which may throw an exception, and returns.
3
#
Returns: *this.
🔗
basic_ostream& operator<<(const volatile void* p);
4
#
Effects: Equivalent to: return operator<<(const_cast<const void*>(p));
🔗
basic_ostream& operator<<(extended-floating-point-type val);
5
#
Effects: If the floating-point conversion rank of extended-floating-point-type is less than or equal to that of double, the formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet< num_put<charT, ostreambuf_iterator<charT, traits>> >(getloc()).put(*this, *this, fill(), static_cast<double>(val)).failed();
Otherwise, if the floating-point conversion rank of extended-floating-point-type is less than or equal to that of long double, the formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet< num_put<charT, ostreambuf_iterator<charT, traits>> >(getloc()).put(*this, *this, fill(), static_cast<long double>(val)).failed();
Otherwise, an invocation of the operator function is conditionally supported with implementation-defined semantics.
If failed is true then does setstate(badbit), which may throw an exception, and returns.
6
#
Returns: *this.

31.7.6.3.3 basic_ostream​::​operator<< [ostream.inserters]

🔗
basic_ostream& operator<<(basic_ostream& (*pf)(basic_ostream&));
1
#
Effects: None.
Does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
2
#
Returns: pf(*this).295
🔗
basic_ostream& operator<<(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
3
#
Effects: Calls pf(*this).
This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
4
#
Returns: *this.296
🔗
basic_ostream& operator<<(ios_base& (*pf)(ios_base&));
5
#
Effects: Calls pf(*this).
This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
6
#
Returns: *this.
🔗
basic_ostream& operator<<(basic_streambuf<charT, traits>* sb);
7
#
Effects: Behaves as an unformatted output function ([ostream.unformatted]).
After the sentry object is constructed, if sb is null calls setstate(badbit) (which may throw ios_base​::​failure).
8
#
Gets characters from sb and inserts them in *this.
Characters are read from sb and inserted until any of the following occurs:
  • (8.1)
    end-of-file occurs on the input sequence;
  • (8.2)
    inserting in the output sequence fails (in which case the character to be inserted is not extracted);
  • (8.3)
    an exception occurs while getting a character from sb.
9
#
If the function inserts no characters, it calls setstate(failbit) (which may throw ios_base​::​​failure ([iostate.flags])).
If an exception was thrown while extracting a character, the function sets failbit in the error state, and if failbit is set in exceptions() the caught exception is rethrown.
10
#
Returns: *this.
🔗
basic_ostream& operator<<(nullptr_t);
11
#
Effects: Equivalent to: return *this << s; where s is an implementation-defined NTCTS.
295)295)
See, for example, the function signature endl(basic_ostream&) ([ostream.manip]).
296)296)
See, for example, the function signature dec(ios_base&) ([basefield.manip]).

31.7.6.3.4 Character inserter function templates [ostream.inserters.character]

🔗
template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out, charT c); template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out, char c); // specialization template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, char c); // signed and unsigned template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, signed char c); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, unsigned char c);
1
#
Effects: Behaves as a formatted output function of out.
Constructs a character sequence seq.
If c has type char and the character container type of the stream is not char, then seq consists of out.widen(c); otherwise seq consists of c.
Determines padding for seq as described in [ostream.formatted.reqmts].
Inserts seq into out.
Calls os.width(0).
2
#
Returns: out.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out, const charT* s); template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out, const char* s); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, const char* s); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, const signed char* s); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, const unsigned char* s);
3
#
Preconditions: s is not a null pointer.
4
#
Effects: Behaves like a formatted inserter (as described in [ostream.formatted.reqmts]) of out.
Creates a character sequence seq of n characters starting at s, each widened using out.widen() ([basic.ios.members]), where n is the number that would be computed as if by:
  • (4.1)
    traits​::​length(s) for the overload where the first argument is of type basic_ostream<charT, traits>& and the second is of type const charT*, and also for the overload where the first argument is of type basic_ostream<char, traits>& and the second is of type const char*,
  • (4.2)
    char_traits<char>​::​length(s) for the overload where the first argument is of type basic_ostream<charT, traits>& and the second is of type const char*,
  • (4.3)
    traits​::​length(reinterpret_cast<const char*>(s)) for the other two overloads.
Determines padding for seq as described in [ostream.formatted.reqmts].
Inserts seq into out.
Calls width(0).
5
#
Returns: out.

31.7.6.3.5 Print [ostream.formatted.print]

🔗
template<class... Args> void print(ostream& os, format_string<Args...> fmt, Args&&... args);
1
#
Effects: If the ordinary literal encoding ([lex.charset]) is UTF-8, equivalent to: vprint_unicode(os, fmt.str, make_format_args(args...));
Otherwise, equivalent to: vprint_nonunicode(os, fmt.str, make_format_args(args...));
🔗
template<class... Args> void println(ostream& os, format_string<Args...> fmt, Args&&... args);
2
#
Effects: Equivalent to: print(os, "{}\n", format(fmt, std::forward<Args>(args)...));
🔗
void vprint_unicode(ostream& os, string_view fmt, format_args args); void vprint_nonunicode(ostream& os, string_view fmt, format_args args);
3
#
Effects: Behaves as a formatted output function ([ostream.formatted.reqmts]) of os, except that:
  • (3.1)
    failure to generate output is reported as specified below, and
  • (3.2)
    any exception thrown by the call to vformat is propagated without regard to the value of os.exceptions() and without turning on ios_base​::​badbit in the error state of os.
After constructing a sentry object, the function initializes an automatic variable via string out = vformat(os.getloc(), fmt, args);
If the function is vprint_unicode and os is a stream that refers to a terminal capable of displaying Unicode which is determined in an implementation-defined manner, writes out to the terminal using the native Unicode API; if out contains invalid code units, the behavior is undefined and implementations are encouraged to diagnose it.
If the native Unicode API is used, the function flushes os before writing out.
Otherwise (if os is not such a stream or the function is vprint_nonunicode), inserts the character sequence [out.begin(), out.end()) into os.
If writing to the terminal or inserting into os fails, calls os.setstate(ios_base​::​badbit) (which may throw ios_base​::​failure).
4
#
Recommended practice: For vprint_unicode, if invoking the native Unicode API requires transcoding, implementations should substitute invalid code units with U+fffd replacement character per the Unicode Standard, Chapter 3.9 U+fffd Substitution in Conversion.

31.7.6.4 Unformatted output functions [ostream.unformatted]

1
#
Each unformatted output function begins execution by constructing an object of class sentry.
If that object returns true, while converting to a value of type bool, the function endeavors to generate the requested output.
If an exception is thrown during output, then ios_base​::​badbit is set297 in *this's error state.
If (exceptions() & badbit) != 0 then the exception is rethrown.
In any case, the unformatted output function ends by destroying the sentry object, then, if no exception was thrown, returning the value specified for the unformatted output function.
🔗
basic_ostream& put(char_type c);
2
#
Effects: Behaves as an unformatted output function (as described above).
After constructing a sentry object, inserts the character c, if possible.298
3
#
Otherwise, calls setstate(badbit) (which may throw ios_base​::​failure ([iostate.flags])).
4
#
Returns: *this.
🔗
basic_ostream& write(const char_type* s, streamsize n);
5
#
Effects: Behaves as an unformatted output function (as described above).
After constructing a sentry object, obtains characters to insert from successive locations of an array whose first element is designated by s.299
Characters are inserted until either of the following occurs:
  • (5.1)
    n characters are inserted;
  • (5.2)
    inserting in the output sequence fails (in which case the function calls setstate(badbit), which may throw ios_base​::​failure ([iostate.flags])).
6
#
Returns: *this.
🔗
basic_ostream& flush();
7
#
Effects: Behaves as an unformatted output function (as described above).
If rdbuf() is not a null pointer, constructs a sentry object.
If that object returns true when converted to a value of type bool the function calls rdbuf()->pubsync().
If that function returns calls setstate(badbit) (which may throw ios_base​::​failure ([iostate.flags])).
Otherwise, if the sentry object returns false, does nothing.
8
#
Returns: *this.
297)297)
This is done without causing an ios_base​::​failure to be thrown.
298)298)
Note that this function is not overloaded on types signed char and unsigned char.
299)299)
Note that this function is not overloaded on types signed char and unsigned char.

31.7.6.5 Standard manipulators [ostream.manip]

1
#
Each instantiation of any of the function templates specified in this subclause is a designated addressable function ([namespace.std]).
🔗
template<class charT, class traits> basic_ostream<charT, traits>& endl(basic_ostream<charT, traits>& os);
2
#
Effects: Calls os.put(os.widen('\n')), then os.flush().
3
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& ends(basic_ostream<charT, traits>& os);
4
#
Effects: Inserts a null character into the output sequence: calls os.put(charT()).
5
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& flush(basic_ostream<charT, traits>& os);
6
#
Effects: Calls os.flush().
7
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& emit_on_flush(basic_ostream<charT, traits>& os);
8
#
Effects: If os.rdbuf() is a basic_syncbuf<charT, traits, Allocator>*, called buf for the purpose of exposition, calls buf->set_emit_on_sync(true).
Otherwise this manipulator has no effect.
[Note 1: 
To work around the issue that the Allocator template argument cannot be deduced, implementations can introduce an intermediate base class to basic_syncbuf that manages its emit_on_sync flag.
— end note]
9
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& noemit_on_flush(basic_ostream<charT, traits>& os);
10
#
Effects: If os.rdbuf() is a basic_syncbuf<charT, traits, Allocator>*, called buf for the purpose of exposition, calls buf->set_emit_on_sync(false).
Otherwise this manipulator has no effect.
11
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& flush_emit(basic_ostream<charT, traits>& os);
12
#
Effects: Calls os.flush().
Then, if os.rdbuf() is a basic_syncbuf<charT, traits, Allocator>*, called buf for the purpose of exposition, behaves as an unformatted output function ([ostream.unformatted]) of os.
After constructing a sentry object, calls buf->emit().
If that call returns false, calls os.setstate(ios_base​::​badbit).
13
#
Returns: os.

31.7.6.6 Rvalue stream insertion [ostream.rvalue]

🔗
template<class Ostream, class T> Ostream&& operator<<(Ostream&& os, const T& x);
1
#
Constraints: The expression os << x is well-formed when treated as an unevaluated operand and Ostream is publicly and unambiguously derived from ios_base.
2
#
Effects: As if by: os << x;
3
#
Returns: std​::​move(os).

31.7.7 Standard manipulators [std.manip]

1
#
The header <iomanip> defines several functions that support extractors and inserters that alter information maintained by class ios_base and its derived classes.
🔗
unspecified resetiosflags(ios_base::fmtflags mask);
2
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << resetiosflags(mask) behaves as if it called f(out, mask), or if in is an object of type basic_istream<charT, traits> then the expression in >> resetiosflags(​mask) behaves as if it called f(in, mask), where the function f is defined as:300 void f(ios_base& str, ios_base::fmtflags mask) { // reset specified flags str.setf(ios_base::fmtflags(0), mask); }
The expression out << resetiosflags(mask) has type basic_ostream<charT, traits>& and value out.
The expression in >> resetiosflags(mask) has type basic_istream<charT, traits>& and value in.
🔗
unspecified setiosflags(ios_base::fmtflags mask);
3
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << setiosflags(mask) behaves as if it called f(out, mask), or if in is an object of type basic_istream<charT, traits> then the expression in >> setiosflags(mask) behaves as if it called f(in, mask), where the function f is defined as:
🔗
void f(ios_base& str, ios_base::fmtflags mask) { // set specified flags str.setf(mask); }
The expression out << setiosflags(mask) has type basic_ostream<charT, traits>& and value out.
The expression in >> setiosflags(mask) has type basic_istream<charT, traits>& and value in.
🔗
unspecified setbase(int base);
4
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << setbase(base) behaves as if it called f(out, base), or if in is an object of type basic_istream<charT, traits> then the expression in >> setbase(base) behaves as if it called f(in, base), where the function f is defined as: void f(ios_base& str, int base) { // set basefield str.setf(base == 8 ? ios_base::oct : base == 10 ? ios_base::dec : base == 16 ? ios_base::hex : ios_base::fmtflags(0), ios_base::basefield); }
The expression out << setbase(base) has type basic_ostream<charT, traits>& and value out.
The expression in >> setbase(base) has type basic_istream<charT, traits>& and value in.
🔗
unspecified setfill(char_type c);
5
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> and c has type charT then the expression out << setfill(c) behaves as if it called f(out, c), where the function f is defined as: template<class charT, class traits> void f(basic_ios<charT, traits>& str, charT c) { // set fill character str.fill(c); }
The expression out << setfill(c) has type basic_ostream<charT, traits>& and value out.
🔗
unspecified setprecision(int n);
6
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << setprecision(n) behaves as if it called f(out, n), or if in is an object of type basic_istream<charT, traits> then the expression in >> setprecision(n) behaves as if it called f(in, n), where the function f is defined as: void f(ios_base& str, int n) { // set precision str.precision(n); }
The expression out << setprecision(n) has type basic_ostream<charT, traits>& and value out.
The expression in >> setprecision(n) has type basic_istream<charT, traits>& and value in.
🔗
unspecified setw(int n);
7
#
Returns: An object of unspecified type such that if out is an instance of basic_ostream<charT, traits> then the expression out << setw(n) behaves as if it called f(out, n), or if in is an object of type basic_istream<charT, traits> then the expression in >> setw(n) behaves as if it called f(in, n), where the function f is defined as: void f(ios_base& str, int n) { // set width str.width(n); }
The expression out << setw(n) has type basic_ostream<charT, traits>& and value out.
The expression in >> setw(n) has type basic_istream<charT, traits>& and value in.
300)300)
The expression cin >> resetiosflags(ios_base​::​skipws) clears ios_base​::​skipws in the format flags stored in the basic_istream<charT, traits> object cin (the same as cin >> noskipws), and the expression cout << resetiosflags(ios_base​::​showbase) clears ios_base​::​showbase in the format flags stored in the basic_ostream<charT, traits> object cout (the same as cout << noshowbase).

31.7.8 Extended manipulators [ext.manip]

1
#
The header <iomanip> defines several functions that support extractors and inserters that allow for the parsing and formatting of sequences and values for money and time.
🔗
template<class moneyT> unspecified get_money(moneyT& mon, bool intl = false);
2
#
Mandates: The type moneyT is either long double or a specialization of the basic_string template ([strings]).
3
#
Effects: The expression in >> get_money(mon, intl) described below behaves as a formatted input function.
4
#
Returns: An object of unspecified type such that if in is an object of type basic_istream<charT, traits> then the expression in >> get_money(mon, intl) behaves as if it called f(in, mon, intl), where the function f is defined as: template<class charT, class traits, class moneyT> void f(basic_ios<charT, traits>& str, moneyT& mon, bool intl) { using Iter = istreambuf_iterator<charT, traits>; using MoneyGet = money_get<charT, Iter>; ios_base::iostate err = ios_base::goodbit; const MoneyGet& mg = use_facet<MoneyGet>(str.getloc()); mg.get(Iter(str.rdbuf()), Iter(), intl, str, err, mon); if (ios_base::goodbit != err) str.setstate(err); }
The expression in >> get_money(mon, intl) has type basic_istream<charT, traits>& and value in.
🔗
template<class moneyT> unspecified put_money(const moneyT& mon, bool intl = false);
5
#
Mandates: The type moneyT is either long double or a specialization of the basic_string template ([strings]).
6
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << put_money(mon, intl) behaves as a formatted output function that calls f(out, mon, intl), where the function f is defined as: template<class charT, class traits, class moneyT> void f(basic_ios<charT, traits>& str, const moneyT& mon, bool intl) { using Iter = ostreambuf_iterator<charT, traits>; using MoneyPut = money_put<charT, Iter>; const MoneyPut& mp = use_facet<MoneyPut>(str.getloc()); const Iter end = mp.put(Iter(str.rdbuf()), intl, str, str.fill(), mon); if (end.failed()) str.setstate(ios_base::badbit); }
The expression out << put_money(mon, intl) has type basic_ostream<charT, traits>& and value out.
🔗
template<class charT> unspecified get_time(tm* tmb, const charT* fmt);
7
#
Preconditions: The argument tmb is a valid pointer to an object of type tm, and [fmt, fmt + char_traits<charT>​::​length(fmt)) is a valid range.
8
#
Returns: An object of unspecified type such that if in is an object of type basic_istream<charT, traits> then the expression in >> get_time(tmb, fmt) behaves as if it called f(in, tmb, fmt), where the function f is defined as: template<class charT, class traits> void f(basic_ios<charT, traits>& str, tm* tmb, const charT* fmt) { using Iter = istreambuf_iterator<charT, traits>; using TimeGet = time_get<charT, Iter>; ios_base::iostate err = ios_base::goodbit; const TimeGet& tg = use_facet<TimeGet>(str.getloc()); tg.get(Iter(str.rdbuf()), Iter(), str, err, tmb, fmt, fmt + traits::length(fmt)); if (err != ios_base::goodbit) str.setstate(err); }
The expression in >> get_time(tmb, fmt) has type basic_istream<charT, traits>& and value in.
🔗
template<class charT> unspecified put_time(const tm* tmb, const charT* fmt);
9
#
Preconditions: The argument tmb is a valid pointer to an object of type tm, and [fmt, fmt + char_traits<charT>​::​length(fmt)) is a valid range.
10
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << put_time(tmb, fmt) behaves as if it called f(out, tmb, fmt), where the function f is defined as: template<class charT, class traits> void f(basic_ios<charT, traits>& str, const tm* tmb, const charT* fmt) { using Iter = ostreambuf_iterator<charT, traits>; using TimePut = time_put<charT, Iter>; const TimePut& tp = use_facet<TimePut>(str.getloc()); const Iter end = tp.put(Iter(str.rdbuf()), str, str.fill(), tmb, fmt, fmt + traits::length(fmt)); if (end.failed()) str.setstate(ios_base::badbit); }
The expression out << put_time(tmb, fmt) has type basic_ostream<charT, traits>& and value out.

31.7.9 Quoted manipulators [quoted.manip]

1
#
[Note 1: 
Quoted manipulators provide string insertion and extraction of quoted strings (for example, XML and CSV formats).
Quoted manipulators are useful in ensuring that the content of a string with embedded spaces remains unchanged if inserted and then extracted via stream I/O.
— end note]
🔗
template<class charT> unspecified quoted(const charT* s, charT delim = charT('"'), charT escape = charT('\\')); template<class charT, class traits, class Allocator> unspecified quoted(const basic_string<charT, traits, Allocator>& s, charT delim = charT('"'), charT escape = charT('\\')); template<class charT, class traits> unspecified quoted(basic_string_view<charT, traits> s, charT delim = charT('"'), charT escape = charT('\\'));
2
#
Returns: An object of unspecified type such that if out is an instance of basic_ostream with member type char_type the same as charT and with member type traits_type, which in the second and third forms is the same as traits, then the expression out << quoted(s, delim, escape) behaves as a formatted output function of out.
This forms a character sequence seq, initially consisting of the following elements:
  • (2.1)
    delim.
  • (2.2)
    Each character in s.
    If the character to be output is equal to escape or delim, as determined by traits_type​::​eq, first output escape.
  • (2.3)
    delim.
Let x be the number of elements initially in seq.
Then padding is determined for seq as described in [ostream.formatted.reqmts], seq is inserted as if by calling out.rdbuf()->sputn(seq, n), where n is the larger of out.width() and x, and out.width(0) is called.
The expression out << quoted(s, delim, escape) has type basic_ostream<charT, traits>& and value out.
🔗
template<class charT, class traits, class Allocator> unspecified quoted(basic_string<charT, traits, Allocator>& s, charT delim = charT('"'), charT escape = charT('\\'));
3
#
Returns: An object of unspecified type such that:
  • (3.1)
    If in is an instance of basic_istream with member types char_type and traits_type the same as charT and traits, respectively, then the expression in >> quoted(s, delim, escape) behaves as if it extracts the following characters from in using operator>>(basic_istream<charT, traits>&, charT&) ([istream.extractors]) which may throw ios_base​::​failure ([ios.failure]):
    • (3.1.1)
      If the first character extracted is equal to delim, as determined by traits_type​::​eq, then:
      • (3.1.1.1)
        Turn off the skipws flag.
      • (3.1.1.2)
        s.clear()
      • (3.1.1.3)
        Until an unescaped delim character is reached or !in, extract characters from in and append them to s, except that if an escape is reached, ignore it and append the next character to s.
      • (3.1.1.4)
        Discard the final delim character.
      • (3.1.1.5)
        Restore the skipws flag to its original value.
    • (3.1.2)
      Otherwise, in >> s.
  • (3.2)
    If out is an instance of basic_ostream with member types char_type and traits_type the same as charT and traits, respectively, then the expression out << quoted(s, delim, escape) behaves as specified for the const basic_string<charT, traits, Allocator>& overload of the quoted function.
  • (3.3)
    The expression in >> quoted(s, delim, escape) has type basic_istream<charT, traits>& and value in.
  • (3.4)
    The expression out << quoted(s, delim, escape) has type basic_ostream​<charT, traits>& and value out.

31.7.10 Print functions [print.fun]

🔗
template<class... Args> void print(format_string<Args...> fmt, Args&&... args);
1
#
Effects: Equivalent to: print(stdout, fmt, std::forward<Args>(args)...);
🔗
template<class... Args> void print(FILE* stream, format_string<Args...> fmt, Args&&... args);
2
#
Effects: If the ordinary literal encoding ([lex.charset]) is UTF-8, equivalent to: vprint_unicode(stream, fmt.str, make_format_args(args...));
Otherwise, equivalent to: vprint_nonunicode(stream, fmt.str, make_format_args(args...));
🔗
template<class... Args> void println(format_string<Args...> fmt, Args&&... args);
3
#
Effects: Equivalent to: println(stdout, fmt, std::forward<Args>(args)...);
🔗
template<class... Args> void println(FILE* stream, format_string<Args...> fmt, Args&&... args);
4
#
Effects: Equivalent to: print(stream, "{}\n", format(fmt, std::forward<Args>(args)...));
🔗
void vprint_unicode(string_view fmt, format_args args);
5
#
Effects: Equivalent to: vprint_unicode(stdout, fmt, args);
🔗
void vprint_unicode(FILE* stream, string_view fmt, format_args args);
6
#
Preconditions: stream is a valid pointer to an output C stream.
7
#
Effects: The function initializes an automatic variable via string out = vformat(fmt, args);
If stream refers to a terminal capable of displaying Unicode, writes out to the terminal using the native Unicode API; if out contains invalid code units, the behavior is undefined and implementations are encouraged to diagnose it.
Otherwise writes out to stream unchanged.
If the native Unicode API is used, the function flushes stream before writing out.
[Note 1: 
On POSIX and Windows, stream referring to a terminal means that, respectively, isatty(fileno(
stream)) and GetConsoleMode(_get_osfhandle(_fileno(stream)), ...) return nonzero.
— end note]
[Note 2: 
On Windows, the native Unicode API is WriteConsoleW.
— end note]
8
#
Throws: Any exception thrown by the call to vformat ([format.err.report]).
system_error if writing to the terminal or stream fails.
May throw bad_alloc.
9
#
Recommended practice: If invoking the native Unicode API requires transcoding, implementations should substitute invalid code units with U+fffd replacement character per the Unicode Standard, Chapter 3.9 U+fffd Substitution in Conversion.
🔗
void vprint_nonunicode(string_view fmt, format_args args);
10
#
Effects: Equivalent to: vprint_nonunicode(stdout, fmt, args);
🔗
void vprint_nonunicode(FILE* stream, string_view fmt, format_args args);
11
#
Preconditions: stream is a valid pointer to an output C stream.
12
#
Effects: Writes the result of vformat(fmt, args) to stream.
13
#
Throws: Any exception thrown by the call to vformat ([format.err.report]).
system_error if writing to stream fails.
May throw bad_alloc.