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cppdraft_translate/cppdraft/iostreams/base.md
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2025-10-25 03:02:53 +03:00

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[iostreams.base]

31 Input/output library [input.output]

31.5 Iostreams base classes [iostreams.base]

31.5.1 Header synopsis [ios.syn]

🔗

#include // see [iosfwd.syn]namespace std {// [stream.types], typesusing streamoff = implementation-defined; using streamsize = implementation-defined; // [fpos], class template fpostemplate class fpos; // [ios.base], class ios_baseclass ios_base; // [ios], class template basic_iostemplate<class charT, class traits = char_traits>class basic_ios; // [std.ios.manip], manipulators ios_base& boolalpha (ios_base& str); ios_base& noboolalpha(ios_base& str);

ios_base& showbase (ios_base& str); ios_base& noshowbase (ios_base& str);

ios_base& showpoint (ios_base& str); ios_base& noshowpoint(ios_base& str);

ios_base& showpos (ios_base& str); ios_base& noshowpos (ios_base& str);

ios_base& skipws (ios_base& str); ios_base& noskipws (ios_base& str);

ios_base& uppercase (ios_base& str); ios_base& nouppercase(ios_base& str);

ios_base& unitbuf (ios_base& str); ios_base& nounitbuf (ios_base& str); // [adjustfield.manip], adjustfield ios_base& internal (ios_base& str); ios_base& left (ios_base& str); ios_base& right (ios_base& str); // [basefield.manip], basefield ios_base& dec (ios_base& str); ios_base& hex (ios_base& str); ios_base& oct (ios_base& str); // [floatfield.manip], floatfield ios_base& fixed (ios_base& str); ios_base& scientific (ios_base& str); ios_base& hexfloat (ios_base& str); ios_base& defaultfloat(ios_base& str); // [error.reporting], error reportingenum class io_errc {stream = 1}; template<> struct is_error_code_enum<io_errc> : public true_type { }; error_code make_error_code(io_errc e) noexcept; error_condition make_error_condition(io_errc e) noexcept; const error_category& iostream_category() noexcept;}

31.5.2 Class ios_base [ios.base]

31.5.2.1 General [ios.base.general]

🔗

namespace std {class ios_base {public:class failure; // see below// [ios.fmtflags], fmtflagsusing fmtflags = T1; static constexpr fmtflags boolalpha = unspecified; static constexpr fmtflags dec = unspecified; static constexpr fmtflags fixed = unspecified; static constexpr fmtflags hex = unspecified; static constexpr fmtflags internal = unspecified; static constexpr fmtflags left = unspecified; static constexpr fmtflags oct = unspecified; static constexpr fmtflags right = unspecified; static constexpr fmtflags scientific = unspecified; static constexpr fmtflags showbase = unspecified; static constexpr fmtflags showpoint = unspecified; static constexpr fmtflags showpos = unspecified; static constexpr fmtflags skipws = unspecified; static constexpr fmtflags unitbuf = unspecified; static constexpr fmtflags uppercase = unspecified; static constexpr fmtflags adjustfield = see below; static constexpr fmtflags basefield = see below; static constexpr fmtflags floatfield = see below; // [ios.iostate], iostateusing iostate = T2; static constexpr iostate badbit = unspecified; static constexpr iostate eofbit = unspecified; static constexpr iostate failbit = unspecified; static constexpr iostate goodbit = see below; // [ios.openmode], openmodeusing openmode = T3; static constexpr openmode app = unspecified; static constexpr openmode ate = unspecified; static constexpr openmode binary = unspecified; static constexpr openmode in = unspecified; static constexpr openmode noreplace = unspecified; static constexpr openmode out = unspecified; static constexpr openmode trunc = unspecified; // [ios.seekdir], seekdirusing seekdir = T4; static constexpr seekdir beg = unspecified; static constexpr seekdir cur = unspecified; static constexpr seekdir end = unspecified; class Init; // [fmtflags.state], fmtflags state fmtflags flags() const; fmtflags flags(fmtflags fmtfl); fmtflags setf(fmtflags fmtfl); fmtflags setf(fmtflags fmtfl, fmtflags mask); void unsetf(fmtflags mask);

streamsize precision() const; streamsize precision(streamsize prec); streamsize width() const; streamsize width(streamsize wide); // [ios.base.locales], locales locale imbue(const locale& loc); locale getloc() const; // [ios.base.storage], storagestatic int xalloc(); long& iword(int idx); void*& pword(int idx); // destructorvirtual ~ios_base(); // [ios.base.callback], callbacksenum event { erase_event, imbue_event, copyfmt_event }; using event_callback = void (*)(event, ios_base&, int idx); void register_callback(event_callback fn, int idx);

ios_base(const ios_base&) = delete; ios_base& operator=(const ios_base&) = delete; static bool sync_with_stdio(bool sync = true); protected: ios_base(); private:static int index; // exposition onlylong* iarray; // exposition onlyvoid** parray; // exposition only};}

1

#

ios_base defines several member types:

a type failure, defined as either a class derived fromsystem_error or a synonym for a class derived from system_error;

a class Init;

three bitmask types, fmtflags, iostate, and openmode;

an enumerated type, seekdir.

2

#

It maintains several kinds of data:

state information that reflects the integrity of the stream buffer;

control information that influences how to interpret (format) input sequences and how to generate (format) output sequences;

additional information that is stored by the program for its private use.

3

#

[Note 1:

For the sake of exposition, the maintained data is presented here as:

static int index, specifies the next available unique index for the integer or pointer arrays maintained for the private use of the program, initialized to an unspecified value;

long* iarray, points to the first element of an arbitrary-lengthlong array maintained for the private use of the program;

void** parray, points to the first element of an arbitrary-length pointer array maintained for the private use of the program.

— end note]

31.5.2.2 Types [ios.types]

31.5.2.2.1 Class ios_base​::​failure [ios.failure]

🔗

namespace std {class ios_base::failure : public system_error {public:explicit failure(const string& msg, const error_code& ec = io_errc::stream); explicit failure(const char* msg, const error_code& ec = io_errc::stream); };}

1

#

An implementation is permitted to define ios_base​::​failure as a synonym for a class with equivalent functionality to class ios_base​::​failure shown in this subclause.

[Note 1:

When ios_base​::​failure is a synonym for another type, that type needs to provide a nested type failure to emulate the injected-class-name.

— end note]

The classfailure defines the base class for the types of all objects thrown as exceptions, by functions in the iostreams library, to report errors detected during stream buffer operations.

2

#

When throwing ios_base​::​failure exceptions, implementations should provide values of ec that identify the specific reason for the failure.

[Note 2:

Errors arising from the operating system would typically be reported assystem_category() errors with an error value of the error number reported by the operating system.

Errors arising from within the stream library would typically be reported as error_code(io_errc​::​stream, iostream_category()).

— end note]

🔗

explicit failure(const string& msg, const error_code& ec = io_errc::stream);

3

#

Effects: Constructs the base class with msg and ec.

🔗

explicit failure(const char* msg, const error_code& ec = io_errc::stream);

4

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Effects: Constructs the base class with msg and ec.

31.5.2.2.2 Type ios_base​::​fmtflags [ios.fmtflags]

🔗

using fmtflags = T1;

1

#

The typefmtflags is a bitmask type ([bitmask.types]).

Setting its elements has the effects indicated in Table 136.

Table 136 — fmtflags effects [tab:ios.fmtflags]

🔗
Element		 Effect(s) if set
🔗
boolalpha		 insert and extract bool type in alphabetic format
🔗
dec		 converts integer input or generates integer output in decimal base
🔗
fixed		 generate floating-point output in fixed-point notation
🔗
hex		 converts integer input or generates integer output in hexadecimal base
🔗
internal		 adds fill characters at a designated internal point in certain generated output, or identical to right if no such point is designated
🔗
left		 adds fill characters on the right (final positions) of certain generated output
🔗
oct		 converts integer input or generates integer output in octal base
🔗
right		 adds fill characters on the left (initial positions) of certain generated output
🔗
scientific		 generates floating-point output in scientific notation
🔗
showbase		 generates a prefix indicating the numeric base of generated integer output
🔗
showpoint		 generates a decimal-point character unconditionally in generated floating-point output
🔗
showpos		 generates a + sign in non-negative generated numeric output
🔗
skipws		 skips leading whitespace before certain input operations
🔗
unitbuf		 flushes output after each output operation
🔗
uppercase		 replaces certain lowercase letters with their uppercase equivalents in generated output

2

#

Typefmtflags also defines the constants indicated in Table 137.

Table 137 — fmtflags constants [tab:ios.fmtflags.const]

🔗
Constant		 Allowable values
🔗
adjustfield		 left
🔗
basefield		 dec
🔗
floatfield		 scientific

31.5.2.2.3 Type ios_base​::​iostate [ios.iostate]

🔗

using iostate = T2;

1

#

The typeiostate is a bitmask type ([bitmask.types]) that contains the elements indicated in Table 138.

Table 138 — iostate effects [tab:ios.iostate]

🔗
Element		 Effect(s) if set
🔗
badbit		 indicates a loss of integrity in an input or output sequence (such as an irrecoverable read error from a file);
🔗
eofbit		 indicates that an input operation reached the end of an input sequence;
🔗
failbit		 indicates that an input operation failed to read the expected characters, or that an output operation failed to generate the desired characters.

2

#

Typeiostate also defines the constant:

goodbit, the value zero.

31.5.2.2.4 Type ios_base​::​openmode [ios.openmode]

🔗

using openmode = T3;

1

#

The typeopenmode is a bitmask type ([bitmask.types]).

It contains the elements indicated in Table 139.

Table 139 — openmode effects [tab:ios.openmode]

🔗
Element		 Effect(s) if set
🔗
app		 seek to end before each write
🔗
ate		 open and seek to end immediately after opening
🔗
binary		 perform input and output in binary mode (as opposed to text mode)
🔗
in		 open for input
🔗
noreplace		 open in exclusive mode
🔗
out		 open for output
🔗
trunc		 truncate an existing stream when opening

31.5.2.2.5 Type ios_base​::​seekdir [ios.seekdir]

🔗

using seekdir = T4;

1

#

The typeseekdir is an enumerated type ([enumerated.types]) that contains the elements indicated in Table 140.

Table 140 — seekdir effects [tab:ios.seekdir]

🔗
Element		 Meaning
🔗
beg		 request a seek (for subsequent input or output) relative to the beginning of the stream
🔗
cur		 request a seek relative to the current position within the sequence
🔗
end		 request a seek relative to the current end of the sequence

31.5.2.2.6 Class ios_base​::​Init [ios.init]

🔗

namespace std {class ios_base::Init {public: Init(); Init(const Init&) = default; ~Init(); Init& operator=(const Init&) = default; };}

1

#

The class Init describes an object whose construction ensures the construction of the eight objects declared in ([iostream.objects]) that associate file stream buffers with the standard C streams provided for by the functions declared in.

🔗

Init();

2

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Effects: Constructs and initializes the objects cin, cout, cerr,clog, wcin, wcout, wcerr, and wclog if they have not already been constructed and initialized.

🔗

~Init();

3

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Effects: If there are no other instances of the class still in existence, callscout.flush(),cerr.flush(),clog.flush(),wcout.flush(),wcerr.flush(),wclog.flush().

31.5.2.3 State functions [fmtflags.state]

🔗

fmtflags flags() const;

1

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Returns: The format control information for both input and output.

🔗

fmtflags flags(fmtflags fmtfl);

2

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Postconditions: fmtfl == flags().

3

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Returns: The previous value offlags().

🔗

fmtflags setf(fmtflags fmtfl);

4

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Effects: Sets fmtfl inflags().

5

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Returns: The previous value offlags().

🔗

fmtflags setf(fmtflags fmtfl, fmtflags mask);

6

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Effects: Clears mask inflags(), setsfmtfl & mask inflags().

7

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Returns: The previous value offlags().

🔗

void unsetf(fmtflags mask);

8

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Effects: Clears mask inflags().

🔗

streamsize precision() const;

9

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Returns: The precision to generate on certain output conversions.

🔗

streamsize precision(streamsize prec);

10

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Postconditions: prec == precision().

11

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Returns: The previous value ofprecision().

🔗

streamsize width() const;

12

#

Returns: The minimum field width (number of characters) to generate on certain output conversions.

🔗

streamsize width(streamsize wide);

13

#

Postconditions: wide == width().

14

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Returns: The previous value ofwidth().

31.5.2.4 Functions [ios.base.locales]

🔗

locale imbue(const locale& loc);

1

#

Effects: Calls each registered callback pair(fn, idx) ([ios.base.callback]) as(*fn)(imbue_event, *this, idx) at such a time that a call toios_base​::​getloc() from withinfn returns the new locale valueloc.

2

#

Postconditions: loc == getloc().

3

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Returns: The previous value ofgetloc().

🔗

locale getloc() const;

4

#

Returns: If no locale has been imbued, a copy of the global C++ locale,locale(), in effect at the time of construction.

Otherwise, returns the imbued locale, to be used to perform locale-dependent input and output operations.

31.5.2.5 Static members [ios.members.static]

🔗

static bool sync_with_stdio(bool sync = true);

1

#

Effects: If any input or output operation has occurred using the standard streams prior to the call, the effect isimplementation-defined.

Otherwise, called with a false argument, it allows the standard streams to operate independently of the standard C streams.

2

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Returns: true if the previous state of the standard iostream objects was synchronized and otherwise returnsfalse.

The first time it is called, the function returnstrue.

3

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Remarks: When a standard iostream object str issynchronized with a standard stdio stream f, the effect of inserting a character c byfputc(f, c); is the same as the effect ofstr.rdbuf()->sputc(c); for any sequences of characters; the effect of extracting a character c byc = fgetc(f); is the same as the effect ofc = str.rdbuf()->sbumpc(); for any sequences of characters; and the effect of pushing back a character c byungetc(c, f); is the same as the effect ofstr.rdbuf()->sputbackc(c); for any sequence of characters.259

259)259)

This implies that operations on a standard iostream object can be mixed arbitrarily with operations on the corresponding stdio stream.

In practical terms, synchronization usually means that a standard iostream object and a standard stdio object share a buffer.

31.5.2.6 Storage functions [ios.base.storage]

🔗

static int xalloc();

1

#

Returns: index++.

2

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Remarks: Concurrent access to this function by multiple threads does not result in adata race.

🔗

long& iword(int idx);

3

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Preconditions: idx is a value obtained by a call to xalloc.

4

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Effects: If iarray is a null pointer, allocates an array oflong of unspecified size and stores a pointer to its first element iniarray.

The function then extends the array pointed at byiarray as necessary to include the elementiarray[idx].

Each newly allocated element of the array is initialized to zero.

The reference returned is invalid after any other operation on the object.260

However, the value of the storage referred to is retained, so that until the next call tocopyfmt, callingiword with the same index yields another reference to the same value.

If the function fails261 and*this is a base class subobject of abasic_ios<> object or subobject, the effect is equivalent to callingbasic_ios<>​::​setstate(badbit) on the derived object (which may throwfailure).

5

#

Returns: On successiarray[idx].

On failure, a validlong& initialized to 0.

🔗

void*& pword(int idx);

6

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Preconditions: idx is a value obtained by a call to xalloc.

7

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Effects: If parray is a null pointer, allocates an array of pointers to void of unspecified size and stores a pointer to its first element in parray.

The function then extends the array pointed at by parray as necessary to include the elementparray[idx].

Each newly allocated element of the array is initialized to a null pointer.

The reference returned is invalid after any other operation on the object.

However, the value of the storage referred to is retained, so that until the next call tocopyfmt, callingpword with the same index yields another reference to the same value.

If the function fails262 and*this is a base class subobject of abasic_ios<> object or subobject, the effect is equivalent to callingbasic_ios<>​::​setstate(badbit) on the derived object (which may throwfailure).

8

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Returns: On successparray[idx].

On failure a validvoid*& initialized to 0.

9

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Remarks: After a subsequent call topword(int) for the same object, the earlier return value may no longer be valid.

260)260)

An implementation is free to implement both the integer array pointed at by iarray and the pointer array pointed at byparray as sparse data structures, possibly with a one-element cache for each.

261)261)

For example, because it cannot allocate space.

262)262)

For example, because it cannot allocate space.

31.5.2.7 Callbacks [ios.base.callback]

🔗

void register_callback(event_callback fn, int idx);

1

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Preconditions: The functionfn does not throw exceptions.

2

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Effects: Registers the pair(fn, idx) such that during calls toimbue() ([ios.base.locales]),copyfmt(), or~ios_base() ([ios.base.cons]), the functionfn is called with argumentidx.

Functions registered are called when an event occurs, in opposite order of registration.

Functions registered while a callback function is active are not called until the next event.

3

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Remarks: Identical pairs are not merged.

A function registered twice will be called twice.

31.5.2.8 Constructors and destructor [ios.base.cons]

🔗

ios_base();

1

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Effects: Eachios_base member has an indeterminate value after construction.

The object's members shall be initialized by callingbasic_ios​::​init before the object's first use or before it is destroyed, whichever comes first; otherwise the behavior is undefined.

🔗

~ios_base();

2

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Effects: Calls each registered callback pair(fn, idx) ([ios.base.callback]) as(*fn)(​erase_event, *this, idx) at such time that anyios_base member function called from withinfn has well-defined results.

Then, any memory obtained is deallocated.

31.5.3 Class template fpos [fpos]

31.5.3.1 General [fpos.general]

🔗

namespace std {template class fpos {public:// [fpos.members], members stateT state() const; void state(stateT); private: stateT st; // exposition only};}

31.5.3.2 Members [fpos.members]

🔗

void state(stateT s);

1

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Effects: Assigns s to st.

🔗

stateT state() const;

2

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Returns: Current value of st.

31.5.3.3 Requirements [fpos.operations]

1

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An fpos type specifies file position information.

It holds a state object whose type is equal to the template parameter stateT.

Type stateT shall meet the Cpp17DefaultConstructible (Table 30),Cpp17CopyConstructible (Table 32),Cpp17CopyAssignable (Table 34), andCpp17Destructible (Table 35) requirements.

If is_trivially_copy_constructible_v is true, then fpos has a trivial copy constructor.

If is_trivially_copy_assignable_v is true, then fpos has a trivial copy assignment operator.

If is_trivially_destructible_v is true, then fpos has a trivial destructor.

All specializations of fpos meet the Cpp17DefaultConstructible,Cpp17CopyConstructible,Cpp17CopyAssignable,Cpp17Destructible, and Cpp17EqualityComparable (Table 28) requirements.

In addition, the expressions shown in Table 141 are valid and have the indicated semantics.

In that table,

P refers to a specialization of fpos,

p and q refer to values of type P or const P,

pl and ql refer to modifiable lvalues of type P,

O refers to type streamoff, and

o and o2 refer to values of type streamoff or const streamoff.

Table 141 — Position type requirements [tab:fpos.operations]

🔗
Expression		 Return type Operational Assertion/note
🔗 semantics pre-/post-condition
🔗
P(o)		 P converts from offset Effects: Value-initializes the state object.
🔗
P p(o); P p = o;		 Effects: Value-initializes the state object.
Postconditions: p == P(o) is true.
🔗
P()		 P P(0)
🔗
P p;		 P p(0);
🔗
O(p)		 streamoff converts to offset P(O(p)) == p
🔗
p == q		 bool Remarks: For any two values o and o2, if p is obtained from o converted to P or from a copy of such P value and if q is obtained from o2 converted to P or from a copy of such P value, then p == q is true only if o == o2 is true.
🔗
p != q		 bool !(p == q)
🔗
p + o		 P + offset Remarks: With ql = p + o;, then: ql - o == p
🔗
pl += o		 P& += offset Remarks: With ql = pl; before the +=, then: pl - o == ql
🔗
p - o		 P - offset Remarks: With ql = p - o;, then: ql + o == p
🔗
pl -= o		 P& -= offset Remarks: With ql = pl; before the -=, then: pl + o == ql
🔗
o + p		 convertible to P p + o P(o + p) == p + o
🔗
p - q		 streamoff distance p == q + (p - q)

2

#

Stream operations that return a value of typetraits​::​pos_type returnP(O(-1)) as an invalid value to signal an error.

If this value is used as an argument to anyistream,ostream, orstreambuf member that accepts a value of typetraits​::​pos_type then the behavior of that function is undefined.

31.5.4 Class template basic_ios [ios]

31.5.4.1 Overview [ios.overview]

🔗

namespace std {template<class charT, class traits = char_traits>class basic_ios : public ios_base {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; // [iostate.flags], flags functionsexplicit operator bool() const; bool operator!() const; iostate rdstate() const; void clear(iostate state = goodbit); void setstate(iostate state); bool good() const; bool eof() const; bool fail() const; bool bad() const;

iostate exceptions() const; void exceptions(iostate except); // [basic.ios.cons], constructor/destructorexplicit basic_ios(basic_streambuf<charT, traits>* sb); virtual ~basic_ios(); // [basic.ios.members], members basic_ostream<charT, traits>* tie() const; basic_ostream<charT, traits>* tie(basic_ostream<charT, traits>* tiestr);

basic_streambuf<charT, traits>* rdbuf() const; basic_streambuf<charT, traits>* rdbuf(basic_streambuf<charT, traits>* sb);

basic_ios& copyfmt(const basic_ios& rhs);

char_type fill() const; char_type fill(char_type ch);

locale imbue(const locale& loc); char narrow(char_type c, char dfault) const; char_type widen(char c) const;

basic_ios(const basic_ios&) = delete; basic_ios& operator=(const basic_ios&) = delete; protected: basic_ios(); void init(basic_streambuf<charT, traits>* sb); void move(basic_ios& rhs); void move(basic_ios&& rhs); void swap(basic_ios& rhs) noexcept; void set_rdbuf(basic_streambuf<charT, traits>* sb); };}

31.5.4.2 Constructors [basic.ios.cons]

🔗

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

1

#

Effects: Assigns initial values to its member objects by callinginit(sb).

🔗

basic_ios();

2

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Effects: Leaves its member objects uninitialized.

The object shall be initialized by callingbasic_ios​::​init before its first use or before it is destroyed, whichever comes first; otherwise the behavior is undefined.

🔗

~basic_ios();

3

#

Remarks: The destructor does not destroyrdbuf().

🔗

void init(basic_streambuf<charT, traits>* sb);

4

#

Postconditions: The postconditions of this function are indicated in Table 142.

Table 142 — basic_ios​::​init() effects [tab:basic.ios.cons]

🔗
Element		 Value
🔗
rdbuf()		 sb
🔗
tie()		 0
🔗
rdstate()		 goodbit if sb is not a null pointer, otherwise badbit.
🔗
exceptions()		 goodbit
🔗
flags()		 skipws
🔗
width()		 0
🔗
precision()		 6
🔗
fill()		 widen(' ')
🔗
getloc()		 a copy of the value returned by locale()
🔗
iarray		 a null pointer
🔗
parray		 a null pointer

31.5.4.3 Member functions [basic.ios.members]

🔗

basic_ostream<charT, traits>* tie() const;

1

#

Returns: An output sequence that istied to (synchronized with) the sequence controlled by the stream buffer.

🔗

basic_ostream<charT, traits>* tie(basic_ostream<charT, traits>* tiestr);

2

#

Preconditions: If tiestr is not null, tiestr is not reachable by traversing the linked list of tied stream objects starting fromtiestr->tie().

3

#

Postconditions: tiestr == tie().

4

#

Returns: The previous value oftie().

🔗

basic_streambuf<charT, traits>* rdbuf() const;

5

#

Returns: A pointer to thestreambuf associated with the stream.

🔗

basic_streambuf<charT, traits>* rdbuf(basic_streambuf<charT, traits>* sb);

6

#

Effects: Callsclear().

7

#

Postconditions: sb == rdbuf().

8

#

Returns: The previous value ofrdbuf().

🔗

locale imbue(const locale& loc);

9

#

Effects: Callsios_base​::​imbue(loc) and ifrdbuf() != 0 thenrdbuf()->pubimbue(loc).

10

#

Returns: The prior value ofios_base​::​imbue().

🔗

char narrow(char_type c, char dfault) const;

11

#

Returns: use_facet<ctype<char_type>>(getloc()).narrow(c, dfault).

🔗

char_type widen(char c) const;

12

#

Returns: use_facet<ctype<char_type>>(getloc()).widen(c).

🔗

char_type fill() const;

13

#

Returns: The character used to pad (fill) an output conversion to the specified field width.

🔗

char_type fill(char_type fillch);

14

#

Postconditions: traits​::​eq(fillch, fill()).

15

#

Returns: The previous value offill().

🔗

basic_ios& copyfmt(const basic_ios& rhs);

16

#

Effects: If(this == addressof(rhs)) is true does nothing.

Otherwise assigns to the member objects of*this the corresponding member objects of rhs as follows:

calls each registered callback pair (fn, idx) as(*fn)(erase_event, *this, idx);

then, assigns to the member objects of *this the corresponding member objects ofrhs, except that

rdstate(), rdbuf(), and exceptions() are left unchanged;

the contents of arrays pointed at by pword and iword are copied, not the pointers themselves;263 and

if any newly stored pointer values in *this point at objects stored outside the object rhs and those objects are destroyed when rhs is destroyed, the newly stored pointer values are altered to point at newly constructed copies of the objects;

then, calls each callback pair that was copied from rhs as(*fn)(copyfmt_event, *this, idx);

then, calls exceptions(rhs.exceptions()).

17

#

[Note 1:

The second pass through the callback pairs permits a copied pword value to be zeroed, or to have its referent deep copied or reference counted, or to have other special action taken.

— end note]

18

#

Postconditions: The postconditions of this function are indicated in Table 143.

Table 143 — basic_ios​::​copyfmt() effects [tab:basic.ios.copyfmt]

🔗
Element		 Value
🔗
rdbuf()		 unchanged
🔗
tie()		 rhs.tie()
🔗
rdstate()		 unchanged
🔗
exceptions()		 rhs.exceptions()
🔗
flags()		 rhs.flags()
🔗
width()		 rhs.width()
🔗
precision()		 rhs.precision()
🔗
fill()		 rhs.fill()
🔗
getloc()		 rhs.getloc()

19

#

Returns: *this.

🔗

void move(basic_ios& rhs); void move(basic_ios&& rhs);

20

#

Postconditions: *this has the state thatrhs had before the function call, except thatrdbuf() returns nullptr.

rhs is in a valid but unspecified state, except that rhs.rdbuf() returns the same value as it returned before the function call, andrhs.tie() returns nullptr.

🔗

void swap(basic_ios& rhs) noexcept;

21

#

Effects: The states of *this and rhs are exchanged, except that rdbuf() returns the same value as it returned before the function call, and rhs.rdbuf() returns the same value as it returned before the function call.

🔗

void set_rdbuf(basic_streambuf<charT, traits>* sb);

22

#

Preconditions: sb != nullptr is true.

23

#

Effects: Associates the basic_streambuf object pointed to by sb with this stream without callingclear().

24

#

Postconditions: rdbuf() == sb is true.

25

#

Throws: Nothing.

263)263)

This suggests an infinite amount of copying, but the implementation can keep track of the maximum element of the arrays that is nonzero.

31.5.4.4 Flags functions [iostate.flags]

🔗

explicit operator bool() const;

1

#

Returns: !fail().

🔗

bool operator!() const;

2

#

Returns: fail().

🔗

iostate rdstate() const;

3

#

Returns: The error state of the stream buffer.

🔗

void clear(iostate state = goodbit);

4

#

Effects: If ((state | (rdbuf() ? goodbit : badbit)) & exceptions()) == 0, returns.

Otherwise, the function throws an object of classios_base​::​failure ([ios.failure]), constructed withimplementation-defined argument values.

5

#

Postconditions: Ifrdbuf() != 0 thenstate == rdstate(); otherwiserdstate() == (state | ios_base​::​badbit).

🔗

void setstate(iostate state);

6

#

Effects: Callsclear(rdstate() | state) (which may throwios_base​::​failure ([ios.failure])).

🔗

bool good() const;

7

#

Returns: rdstate() == 0.

🔗

bool eof() const;

8

#

Returns: true ifeofbit is set inrdstate().

🔗

bool fail() const;

9

#

Returns: true iffailbit orbadbit is set inrdstate().264

🔗

bool bad() const;

10

#

Returns: true ifbadbit is set inrdstate().

🔗

iostate exceptions() const;

11

#

Returns: A mask that determines what elements set inrdstate() cause exceptions to be thrown.

🔗

void exceptions(iostate except);

12

#

Effects: Callsclear(rdstate()).

13

#

Postconditions: except == exceptions().

264)264)

Checkingbadbit also forfail() is historical practice.

31.5.5 ios_base manipulators [std.ios.manip]

31.5.5.1 fmtflags manipulators [fmtflags.manip]

1

#

Each function specified in this subclause is a designated addressable function ([namespace.std]).

🔗

ios_base& boolalpha(ios_base& str);

2

#

Effects: Callsstr.setf(ios_base​::​boolalpha).

3

#

Returns: str.

🔗

ios_base& noboolalpha(ios_base& str);

4

#

Effects: Callsstr.unsetf(ios_base​::​boolalpha).

5

#

Returns: str.

🔗

ios_base& showbase(ios_base& str);

6

#

Effects: Callsstr.setf(ios_base​::​showbase).

7

#

Returns: str.

🔗

ios_base& noshowbase(ios_base& str);

8

#

Effects: Callsstr.unsetf(ios_base​::​showbase).

9

#

Returns: str.

🔗

ios_base& showpoint(ios_base& str);

10

#

Effects: Callsstr.setf(ios_base​::​showpoint).

11

#

Returns: str.

🔗

ios_base& noshowpoint(ios_base& str);

12

#

Effects: Callsstr.unsetf(ios_base​::​showpoint).

13

#

Returns: str.

🔗

ios_base& showpos(ios_base& str);

14

#

Effects: Callsstr.setf(ios_base​::​showpos).

15

#

Returns: str.

🔗

ios_base& noshowpos(ios_base& str);

16

#

Effects: Callsstr.unsetf(ios_base​::​showpos).

17

#

Returns: str.

🔗

ios_base& skipws(ios_base& str);

18

#

Effects: Callsstr.setf(ios_base​::​skipws).

19

#

Returns: str.

🔗

ios_base& noskipws(ios_base& str);

20

#

Effects: Callsstr.unsetf(ios_base​::​skipws).

21

#

Returns: str.

🔗

ios_base& uppercase(ios_base& str);

22

#

Effects: Callsstr.setf(ios_base​::​uppercase).

23

#

Returns: str.

🔗

ios_base& nouppercase(ios_base& str);

24

#

Effects: Callsstr.unsetf(ios_base​::​uppercase).

25

#

Returns: str.

🔗

ios_base& unitbuf(ios_base& str);

26

#

Effects: Callsstr.setf(ios_base​::​unitbuf).

27

#

Returns: str.

🔗

ios_base& nounitbuf(ios_base& str);

28

#

Effects: Callsstr.unsetf(ios_base​::​unitbuf).

29

#

Returns: str.

31.5.5.2 adjustfield manipulators [adjustfield.manip]

1

#

Each function specified in this subclause is a designated addressable function ([namespace.std]).

🔗

ios_base& internal(ios_base& str);

2

#

Effects: Callsstr.setf(ios_base​::​internal, ios_base​::​adjustfield).

3

#

Returns: str.

🔗

ios_base& left(ios_base& str);

4

#

Effects: Callsstr.setf(ios_base​::​left, ios_base​::​adjustfield).

5

#

Returns: str.

🔗

ios_base& right(ios_base& str);

6

#

Effects: Callsstr.setf(ios_base​::​right, ios_base​::​adjustfield).

7

#

Returns: str.

31.5.5.3 basefield manipulators [basefield.manip]

1

#

Each function specified in this subclause is a designated addressable function ([namespace.std]).

🔗

ios_base& dec(ios_base& str);

2

#

Effects: Callsstr.setf(ios_base​::​dec, ios_base​::​basefield).

3

#

Returns: str.265

🔗

ios_base& hex(ios_base& str);

4

#

Effects: Callsstr.setf(ios_base​::​hex, ios_base​::​basefield).

5

#

Returns: str.

🔗

ios_base& oct(ios_base& str);

6

#

Effects: Callsstr.setf(ios_base​::​oct, ios_base​::​basefield).

7

#

Returns: str.

265)265)

The function signaturedec(ios_base&) can be called by the function signaturebasic_ostream& stream​::​operator<<(ios_base& (*)(ios_base&)) to permit expressions of the formcout << dec to change the format flags stored incout.

31.5.5.4 floatfield manipulators [floatfield.manip]

1

#

Each function specified in this subclause is a designated addressable function ([namespace.std]).

🔗

ios_base& fixed(ios_base& str);

2

#

Effects: Callsstr.setf(ios_base​::​fixed, ios_base​::​floatfield).

3

#

Returns: str.

🔗

ios_base& scientific(ios_base& str);

4

#

Effects: Callsstr.setf(ios_base​::​scientific, ios_base​::​floatfield).

5

#

Returns: str.

🔗

ios_base& hexfloat(ios_base& str);

6

#

Effects: Calls str.setf(ios_base​::​fixed | ios_base​::​scientific, ios_base​::​floatfield).

7

#

Returns: str.

8

#

[Note 1:

ios_base​::​hex cannot be used to specify a hexadecimal floating-point format, because it is not part of ios_base​::​floatfield (Table 137).

— end note]

🔗

ios_base& defaultfloat(ios_base& str);

9

#

Effects: Calls str.unsetf(ios_base​::​floatfield).

10

#

Returns: str.

31.5.6 Error reporting [error.reporting]

🔗

error_code make_error_code(io_errc e) noexcept;

1

#

Returns: error_code(static_cast(e), iostream_category()).

🔗

error_condition make_error_condition(io_errc e) noexcept;

2

#

Returns: error_condition(static_cast(e), iostream_category()).

🔗

const error_category& iostream_category() noexcept;

3

#

Returns: A reference to an object of a type derived from classerror_category.

4

#

The object's default_error_condition and equivalent virtual functions shall behave as specified for the class error_category.

The object's name virtual function shall return a pointer to the string "iostream".