cppdraft_translate/cppdraft/ostream.md

[ostream]

31 Input/output library [input.output]

31.7 Formatting and manipulators [iostream.format]

31.7.6 Output streams [output.streams]

31.7.6.2 Class template basic_ostream [ostream]

31.7.6.2.1 General [ostream.general]

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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]).

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namespace std {template<class charT, class traits = char_traits>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/destructorexplicit basic_ostream(basic_streambuf<char_type, traits>* sb); virtual ~basic_ostream(); // [ostream.sentry], prefix/suffixclass 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 inserterstemplate<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 basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char); template basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, signed char); template basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, unsigned char); template basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, wchar_t) = delete; template basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char8_t) = delete; template basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char16_t) = delete; template basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char32_t) = delete; template basic_ostream<wchar_t, traits>&operator<<(basic_ostream<wchar_t, traits>&, char8_t) = delete; template basic_ostream<wchar_t, traits>&operator<<(basic_ostream<wchar_t, traits>&, char16_t) = delete; template 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 basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const char*); template basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const signed char*); template basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const unsigned char*); template basic_ostream<char, traits>&operator<<(basic_ostream<char, traits>&, const wchar_t*) = delete; template basic_ostream<char, traits>&operator<<(basic_ostream<char, traits>&, const char8_t*) = delete; template basic_ostream<char, traits>&operator<<(basic_ostream<char, traits>&, const char16_t*) = delete; template basic_ostream<char, traits>&operator<<(basic_ostream<char, traits>&, const char32_t*) = delete; template basic_ostream<wchar_t, traits>&operator<<(basic_ostream<wchar_t, traits>&, const char8_t*) = delete; template basic_ostream<wchar_t, traits>&operator<<(basic_ostream<wchar_t, traits>&, const char16_t*) = delete; template basic_ostream<wchar_t, traits>&operator<<(basic_ostream<wchar_t, traits>&, const char32_t*) = delete;}

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The class templatebasic_ostream defines a number of member function signatures that assist in formatting and writing output to output sequences controlled by a stream buffer.

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Two groups of member function signatures share common properties: theformatted output functions (orinserters) and theunformatted output functions. Both groups of output functions generate (orinsert) outputcharacters by actions equivalent to callingrdbuf()->sputc(int_type).

They may use other public members ofbasic_ostream except that they shall not invoke any virtual members ofrdbuf() exceptoverflow(),xsputn(), andsync().

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If one of these called functions throws an exception, then unless explicitly noted otherwise the output function setsbadbit in the error state.

Ifbadbit is set inexceptions(), 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.

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[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]

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explicit basic_ostream(basic_streambuf<charT, traits>* sb);

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Effects: Initializes the base class subobject withbasic_ios<charT, traits>​::​init(sb) ([basic.ios.cons]).

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Postconditions: rdbuf() == sb.

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basic_ostream(basic_ostream&& rhs);

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Effects: Move constructs from the rvalue rhs.

This is accomplished by default constructing the base class and callingbasic_ios<charT, traits>​::​move(rhs) to initialize the base class.

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virtual ~basic_ostream();

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Remarks: Does not perform any operations onrdbuf().

31.7.6.2.3 Assignment and swap [ostream.assign]

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basic_ostream& operator=(basic_ostream&& rhs);

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Effects: Equivalent to swap(rhs).

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Returns: *this.

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void swap(basic_ostream& rhs);

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Effects: Calls basic_ios<charT, traits>​::​swap(rhs).

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

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namespace std {template<class charT, class traits>class basic_ostream<charT, traits>::sentry {bool ok_; // exposition onlypublic:explicit sentry(basic_ostream& os); ~sentry(); explicit operator bool() const { return ok_; } sentry(const sentry&) = delete; sentry& operator=(const sentry&) = delete; };}

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The classsentry defines a class that is responsible for doing exception safe prefix and suffix operations.

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explicit sentry(basic_ostream& os);

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Ifos.good() is nonzero, prepares for formatted or unformatted output.

Ifos.tie() is not a null pointer, callsos.tie()->flush().283

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If, after any preparation is completed,os.good() istrue,ok_ == true otherwise,ok_ == false.

During preparation, the constructor may callsetstate(failbit) (which may throwios_base​::​​failure ([iostate.flags])).284

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~sentry();

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If(os.flags() & ios_base​::​unitbuf) && !uncaught_exceptions()&& os.good() istrue, callsos.rdbuf()->pubsync().

If that function returns −1 or exits via an exception, sets badbit inos.rdstate() without propagating an exception.

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explicit operator bool() const;

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Effects: Returnsok_.

283)283)

The callos.tie()->flush() does not necessarily occur if the function can determine that no synchronization is necessary.

284)284)

Thesentry constructor and destructor can also perform additionalimplementation-dependent operations.

31.7.6.2.5 Seek members [ostream.seeks]

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Each seek member function begins execution by constructing an object of class sentry.

It returns by destroying the sentry object.

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pos_type tellp();

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Returns: Iffail() != false, returnspos_type(-1) to indicate failure.

Otherwise, returnsrdbuf()->​pubseekoff(​0, cur, out).

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basic_ostream& seekp(pos_type pos);

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Effects: Iffail() != true, executesrdbuf()->pubseekpos(pos, ios_base​::​out).

In case of failure, the function callssetstate(failbit) (which may throwios_base​::​failure).

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Returns: *this.

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basic_ostream& seekp(off_type off, ios_base::seekdir dir);

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Effects: Iffail() != true, executesrdbuf()->pubseekoff(off, dir, ios_base​::​out).

In case of failure, the function calls setstate(failbit) (which may throw ios_base​::​failure).

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Returns: *this.