[istream.unformatted]

# 31 Input/output library [[input.output]](./#input.output)

## 31.7 Formatting and manipulators [[iostream.format]](iostream.format#istream.unformatted)

### 31.7.5 Input streams [[input.streams]](input.streams#istream.unformatted)

#### 31.7.5.4 Unformatted input functions [istream.unformatted]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5035)

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[.](#1.sentence-1)

It then creates an object of classsentry with the default argumentnoskipws (second) argumenttrue[.](#1.sentence-2)

If thesentry object returnstrue,
when converted to a value of typebool,
the function endeavors
to obtain the requested input[.](#1.sentence-3)

Otherwise, if the sentry constructor exits by throwing an exception or if
the sentry object produces false, when converted to a value of typebool,
the function returns without attempting to obtain any input[.](#1.sentence-4)

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 (usingcharT())
in the first location of the array[.](#1.sentence-5)

If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits​::​eof(), thenios_base​::​eofbit is set in the local error state and
the input function stops trying to obtain the requested input[.](#1.sentence-6)

If an exception is thrown during input thenios_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[.](#1.sentence-7)

If no exception has been thrown it
stores the number of characters extracted
in a member object[.](#1.sentence-8)

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[.](#1.sentence-9)

In any event thesentry object
is destroyed before leaving the unformatted input function[.](#1.sentence-10)

[ð](#lib:gcount,basic_istream)

`streamsize gcount() const;
`

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5087)

*Effects*: None[.](#2.sentence-1)

This member function does not behave as an unformatted
input function (as described above)[.](#2.sentence-2)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5093)

*Returns*: The number of characters
extracted by the last unformatted input member function called for the object[.](#3.sentence-1)

If the number cannot be represented,
returns numeric_limits<streamsize>​::​max()[.](#3.sentence-2)

[ð](#lib:get,basic_istream)

`int_type get();
`

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5107)

*Effects*: Behaves as an unformatted input function
(as described above)[.](#4.sentence-1)

After constructing a sentry object, extracts
a character c, if one is available[.](#4.sentence-2)

Otherwise,ios_base​::​failbit is set in the input function's local error state
before setstate is called[.](#4.sentence-3)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5117)

*Returns*: c if available,
otherwisetraits​::​eof()[.](#5.sentence-1)

[ð](#lib:get,basic_istream_)

`basic_istream& get(char_type& c);
`

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5130)

*Effects*: Behaves as an unformatted input function
(as described above)[.](#6.sentence-1)

After constructing a sentry object, extracts
a character, if one is available, and assigns it to c[.](#6.sentence-2)[276](#footnote-276 "Note that this function is not overloaded on types signed char and unsigned char.")

Otherwise,ios_base​::​failbit is set in the input function's local error state
before setstate is called[.](#6.sentence-3)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5147)

*Returns*: *this[.](#7.sentence-1)

[ð](#lib:get,basic_istream__)

`basic_istream& get(char_type* s, streamsize n, char_type delim);
`

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5158)

*Effects*: Behaves as an unformatted input function
(as described above)[.](#8.sentence-1)

After constructing a sentry object, extracts
characters and stores them
into successive locations of an array whose first element is designated bys[.](#8.sentence-2)[277](#footnote-277 "Note that this function is not overloaded on types signed char and unsigned char.")

Characters are extracted and stored until any of the following occurs:

- [(8.1)](#8.1)

n is less than one or n - 1 characters are stored;

- [(8.2)](#8.2)

end-of-file occurs on the input sequence;

- [(8.3)](#8.3)

traits​::​eq(c, delim) for the next available input
character c (in which case c is not extracted)[.](#8.sentence-3)

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5186)

If the function stores no characters,ios_base​::​failbit is set in the input function's local error state
before setstate is called[.](#9.sentence-1)

In any case, if n is greater than zero it then stores a null character
into the next successive location of the array[.](#9.sentence-2)

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5193)

*Returns*: *this[.](#10.sentence-1)

[ð](#lib:get,basic_istream___)

`basic_istream& get(char_type* s, streamsize n);
`

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5204)

*Effects*: Callsget(s, n, widen('\n'))[.](#11.sentence-1)

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5209)

*Returns*: Value returned by the call[.](#12.sentence-1)

[ð](#lib:get,basic_istream____)

`basic_istream& get(basic_streambuf<char_type, traits>& sb, char_type delim);
`

[13](#13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5220)

*Effects*: Behaves as an unformatted input function
(as described above)[.](#13.sentence-1)

After constructing a sentry object, extracts
characters and inserts them
in the output sequence controlled bysb[.](#13.sentence-2)

Characters are extracted and inserted until any of the following occurs:

- [(13.1)](#13.1)

end-of-file occurs on the input sequence;

- [(13.2)](#13.2)

inserting in the output sequence fails
(in which case the character to be inserted is not extracted);

- [(13.3)](#13.3)

traits​::​eq(c, delim) for the next available input
character c (in which case c is not extracted);

- [(13.4)](#13.4)

an exception occurs
(in which case, the exception is caught but not rethrown)[.](#13.sentence-3)

[14](#14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5244)

If the function inserts no characters,ios_base​::​failbit is set in the input function's local error state
before setstate is called[.](#14.sentence-1)

[15](#15)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5249)

*Returns*: *this[.](#15.sentence-1)

[ð](#lib:get,basic_istream_____)

`basic_istream& get(basic_streambuf<char_type, traits>& sb);
`

[16](#16)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5260)

*Effects*: Callsget(sb, widen('\n'))[.](#16.sentence-1)

[17](#17)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5265)

*Returns*: Value returned by the call[.](#17.sentence-1)

[ð](#lib:getline,basic_istream)

`basic_istream& getline(char_type* s, streamsize n, char_type delim);
`

[18](#18)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5276)

*Effects*: Behaves as an unformatted input function
(as described above)[.](#18.sentence-1)

After constructing a sentry object, extracts
characters and stores them
into successive locations of an array whose first element is designated bys[.](#18.sentence-2)[278](#footnote-278 "Note that this function is not overloaded on types signed char and unsigned char.")

Characters are extracted and stored until one of the following occurs:

| [1.](#18.1) | end-of-file occurs on the input sequence; |
| --- | --- |
| [2.](#18.2) | traits​::​eq(c, delim) for the next available input character c (in which case the input character is extracted but not stored);[279](#footnote-279 "Since the final input character is âextractedâ, it is counted in the gcount(), even though it is not stored.") |
| [3.](#18.3) | n is less than one or n - 1 characters are stored (in which case the function calls setstate(​failbit))[.](#18.sentence-3) |

[19](#19)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5313)

These conditions are tested in the order shown[.](#19.sentence-1)[280](#footnote-280 "This allows an input line which exactly fills the buffer, without setting failbit. This is different behavior than the historical AT&amp;T implementation.")

[20](#20)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5322)

If the function extracts no characters,ios_base​::​failbit is set in the input function's local error state
before setstate is called[.](#20.sentence-1)[281](#footnote-281 "This implies an empty input line will not cause failbit to be set.")

[21](#21)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5333)

In any case, if n is greater than zero, it then stores a null character
(usingcharT())
into the next successive location of the array[.](#21.sentence-1)

[22](#22)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5339)

*Returns*: *this[.](#22.sentence-1)

[23](#23)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5343)

[*Example [1](#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 falseelse 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; }} â *end example*]

[ð](#lib:getline,basic_istream_)

`basic_istream& getline(char_type* s, streamsize n);
`

[24](#24)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5378)

*Returns*: getline(s, n, widen('\n'))[.](#24.sentence-1)

[ð](#lib:ignore,basic_istream)

`basic_istream& ignore(streamsize n = 1, int_type delim = traits::eof());
`

[25](#25)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5389)

*Effects*: Behaves as an unformatted input function
(as described above)[.](#25.sentence-1)

After constructing a sentry object, extracts
characters and discards them[.](#25.sentence-2)

Characters are extracted until any of the following occurs:

- [(25.1)](#25.1)

n != [numeric_limits<streamsize>​::​max()](numeric.limits.members#lib:numeric_limits,max "17.3.5.2 numeric_­limits members [numeric.limits.members]")numeric.limits andn characters have been extracted so far;

- [(25.2)](#25.2)

end-of-file occurs on the input sequence
(in which case the function callssetstate(eofbit),
which may throwios_base​::​failure ([[iostate.flags]](iostate.flags "31.5.4.4 Flags functions")));

- [(25.3)](#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)[.](#25.sentence-3)

[*Note [1](#note-1)*:

The last condition will never occur iftraits​::​eq_int_type(delim, traits​::​eof())[.](#25.sentence-4)

â *end note*]

[26](#26)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5417)

*Returns*: *this[.](#26.sentence-1)

[ð](#lib:ignore,basic_istream_)

`basic_istream& ignore(streamsize n, char_type delim);
`

[27](#27)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5428)

*Constraints*: is_same_v<char_type, char> is true[.](#27.sentence-1)

[28](#28)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5432)

*Effects*: Equivalent to: return ignore(n, traits​::​to_int_type(delim));

[ð](#lib:peek,basic_istream)

`int_type peek();
`

[29](#29)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5443)

*Effects*: Behaves as an unformatted input function
(as described above)[.](#29.sentence-1)

After constructing a sentry object, reads but does not extract
the current input character[.](#29.sentence-2)

[30](#30)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5450)

*Returns*: traits​::​eof() ifgood() isfalse[.](#30.sentence-1)

Otherwise, returnsrdbuf()->sgetc()[.](#30.sentence-2)

[ð](#lib:read,basic_istream)

`basic_istream& read(char_type* s, streamsize n);
`

[31](#31)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5467)

*Effects*: Behaves as an unformatted input function (as described above)[.](#31.sentence-1)

After constructing
a sentry object, if!good() callssetstate(failbit) which may throw an exception,
and return[.](#31.sentence-2)

Otherwise extracts characters and stores them
into successive locations of an array whose first element is designated bys[.](#31.sentence-3)[282](#footnote-282 "Note that this function is not overloaded on types signed char and unsigned char.")

Characters are extracted and stored until either of the following occurs:

- [(31.1)](#31.1)

n characters are stored;

- [(31.2)](#31.2)

end-of-file occurs on the input sequence
(in which case the function callssetstate(failbit | eofbit),
which may throwios_base​::​failure ([[iostate.flags]](iostate.flags "31.5.4.4 Flags functions")))[.](#31.sentence-4)

[32](#32)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5498)

*Returns*: *this[.](#32.sentence-1)

[ð](#lib:readsome,basic_istream)

`streamsize readsome(char_type* s, streamsize n);
`

[33](#33)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5509)

*Effects*: Behaves as an unformatted input function (as described above)[.](#33.sentence-1)

After constructing
a sentry object, if!good() callssetstate(failbit) which may throw an exception,
and return[.](#33.sentence-2)

Otherwise extracts characters and stores them
into successive locations of an array whose first element is designated bys[.](#33.sentence-3)

Ifrdbuf()->in_avail() == -1,
callssetstate(eofbit) (which may throwios_base​::​failure ([[iostate.flags]](iostate.flags "31.5.4.4 Flags functions"))),
and extracts no characters;

- [(33.1)](#33.1)

Ifrdbuf()->in_avail() == 0,
extracts no characters

- [(33.2)](#33.2)

Ifrdbuf()->in_avail() > 0,
extractsmin(rdbuf()->in_avail(), n))[.](#33.sentence-4)

[34](#34)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5541)

*Returns*: The number of characters extracted[.](#34.sentence-1)

[ð](#lib:putback,basic_istream)

`basic_istream& putback(char_type c);
`

[35](#35)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5552)

*Effects*: Behaves as an unformatted input function (as described above), except that the function first clears eofbit[.](#35.sentence-1)

After constructing
a sentry object, if!good() callssetstate(failbit) which may throw an exception,
and return[.](#35.sentence-2)

Ifrdbuf() is not null, callsrdbuf()->sputbackc(c)[.](#35.sentence-3)

Ifrdbuf() is null, or ifsputbackc returnstraits​::​eof(),
callssetstate(badbit) (which may throwios_base​::​failure ([[iostate.flags]](iostate.flags "31.5.4.4 Flags functions")))[.](#35.sentence-4)

[*Note [2](#note-2)*:

This
function extracts no characters, so the value returned by the next call togcount() is 0[.](#35.sentence-5)

â *end note*]

[36](#36)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5583)

*Returns*: *this[.](#36.sentence-1)

[ð](#lib:unget,basic_istream)

`basic_istream& unget();
`

[37](#37)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5594)

*Effects*: Behaves as an unformatted input function (as described above), except that the function first clears eofbit[.](#37.sentence-1)

After constructing
a sentry object, if!good() callssetstate(failbit) which may throw an exception,
and return[.](#37.sentence-2)

Ifrdbuf() is not null, callsrdbuf()->sungetc()[.](#37.sentence-3)

Ifrdbuf() is null, or ifsungetc returnstraits​::​eof(),
callssetstate(badbit) (which may throwios_base​::​failure ([[iostate.flags]](iostate.flags "31.5.4.4 Flags functions")))[.](#37.sentence-4)

[*Note [3](#note-3)*:

This
function extracts no characters, so the value returned by the next call togcount() is 0[.](#37.sentence-5)

â *end note*]

[38](#38)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5625)

*Returns*: *this[.](#38.sentence-1)

[ð](#lib:sync,basic_istream)

`int sync();
`

[39](#39)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5636)

*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 togcount()[.](#39.sentence-1)

After constructing
a sentry object, ifrdbuf() is a null pointer, returns -1[.](#39.sentence-2)

Otherwise, callsrdbuf()->pubsync() and, if that function returns -1 callssetstate(badbit) (which may throwios_base​::​failure ([[iostate.flags]](iostate.flags "31.5.4.4 Flags functions")),
and returns-1[.](#39.sentence-3)

Otherwise, returns zero[.](#39.sentence-4)

[ð](#lib:tellg,basic_istream)

`pos_type tellg();
`

[40](#40)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5664)

*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 togcount()[.](#40.sentence-1)

[41](#41)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5671)

*Returns*: After constructing a sentry object, iffail() != false,
returnspos_type(-1) to indicate failure[.](#41.sentence-1)

Otherwise, returnsrdbuf()->pubseekoff(0, cur, in)[.](#41.sentence-2)

[ð](#lib:seekg,basic_istream)

`basic_istream& seekg(pos_type pos);
`

[42](#42)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5688)

*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 togcount()[.](#42.sentence-1)

After constructing a sentry object, iffail() != true,
executesrdbuf()->pubseekpos(pos, ios_base​::​in)[.](#42.sentence-2)

In case of failure, the function callssetstate(failbit) (which may throwios_base​::​failure)[.](#42.sentence-3)

[43](#43)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5705)

*Returns*: *this[.](#43.sentence-1)

[ð](#lib:seekg,basic_istream_)

`basic_istream& seekg(off_type off, ios_base::seekdir dir);
`

[44](#44)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5716)

*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()[.](#44.sentence-1)

After constructing a sentry object, iffail() != true,
executesrdbuf()->pubseekoff(off, dir, ios_base​::​in)[.](#44.sentence-2)

In case of failure, the function calls setstate(​failbit) (which may throwios_base​::​failure)[.](#44.sentence-3)

[45](#45)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L5728)

*Returns*: *this[.](#45.sentence-1)

[276)](#footnote-276)[276)](#footnoteref-276)

Note
that this function is not overloaded on typessigned char andunsigned char[.](#footnote-276.sentence-1)

[277)](#footnote-277)[277)](#footnoteref-277)

Note that this function is not overloaded on typessigned char andunsigned char[.](#footnote-277.sentence-1)

[278)](#footnote-278)[278)](#footnoteref-278)

Note that this function is not overloaded on typessigned char andunsigned char[.](#footnote-278.sentence-1)

[279)](#footnote-279)[279)](#footnoteref-279)

Since
the final input character is âextractedâ,
it is counted in thegcount(),
even though it is not stored[.](#footnote-279.sentence-1)

[280)](#footnote-280)[280)](#footnoteref-280)

This allows an input
line which exactly fills the buffer, without settingfailbit[.](#footnote-280.sentence-1)

This is different behavior than the historical AT&T implementation[.](#footnote-280.sentence-2)

[281)](#footnote-281)[281)](#footnoteref-281)

This implies an
empty input line will not causefailbit to be set[.](#footnote-281.sentence-1)

[282)](#footnote-282)[282)](#footnoteref-282)

Note that this function is not overloaded on typessigned char andunsigned char[.](#footnote-282.sentence-1)
