operator>> (std::basic_istream)

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C++
Input/output library
std::basic_istream
Defined in header <istream>
template < class CharT, class Traits >

basic_istream < CharT, Traits > &
operator >> ( basic_istream < CharT, Traits > & st, CharT & ch ) ;

template < class Traits >
basic_istream < char , Traits > &
operator >> ( basic_istream < char , Traits > & st, signed char & ch ) ;

template < class Traits >
basic_istream < char , Traits > &

operator >> ( basic_istream < char , Traits > & st, unsigned char & ch ) ;
(1)
(2)
template < class CharT, class Traits >

basic_istream < CharT, Traits > &
operator >> ( basic_istream < CharT, Traits > & st, CharT * s ) ;

template < class Traits >
basic_istream < char , Traits > &
operator >> ( basic_istream < char , Traits > & st, signed char * s ) ;

template < class Traits >
basic_istream < char , Traits > &

operator >> ( basic_istream < char , Traits > & st, unsigned char * s ) ;
(until C++20)
template < class CharT, class Traits, std:: size_t N >

basic_istream < CharT, Traits > &
operator >> ( basic_istream < CharT, Traits > & st, CharT ( & s ) [ N ] ) ;

template < class Traits, std:: size_t N >
basic_istream < char , Traits > &
operator >> ( basic_istream < char , Traits > & st, signed char ( & s ) [ N ] ) ;

template < class Traits, std:: size_t N >
basic_istream < char , Traits > &

operator >> ( basic_istream < char , Traits > & st, unsigned char ( & s ) [ N ] ) ;
(since C++20)
template < class Istream, class T >

Istream &&

operator >> ( Istream && st, T && value ) ;
(3) (since C++11)
1,2) Performs character input operations.
1) Behaves as a FormattedInputFunction . After constructing and checking the sentry object, which may skip leading whitespace, extracts a character and stores it to ch . If no character is available, sets failbit (in addition to eofbit that is set as required of a FormattedInputFunction ).
2) Behaves as a FormattedInputFunction . After constructing and checking the sentry object, which may skip leading whitespace, extracts successive characters and stores them at successive locations of a character array whose first element is pointed to by (until C++20) s . The extraction stops if any of the following conditions is met:
  • A whitespace character (as determined by the ctype<CharT> facet) is found. The whitespace character is not extracted.
  • If st. width ( ) is greater than zero, st. width ( ) - 1 characters are stored.
(until C++20)
  • n - 1 characters are stored, where n is defined as follows:
(since C++20)
  • End of file occurs in the input sequence (this also sets eofbit ).
In either case, an additional null character value CharT ( ) is stored at the end of the output. If no characters were extracted, sets failbit (the null character is still written, to the first position in the output). Finally, calls st. width ( 0 ) to cancel the effects of std::setw , if any.
3) Calls the appropriate extraction operator, given an rvalue reference to an input stream object (equivalent to st >> std:: forward < T > ( value ) ). This overload participates in overload resolution only if st >> std:: forward < T > ( value ) is well-formed and Istream is a class type publicly and unambiguously derived from std::ios_base .

Notes

Extracting a single character that is the last character of the stream does not set eofbit : this is different from other formatted input functions, such as extracting the last integer with operator >> , but this behavior matches the behavior of std::scanf with "%c" format specifier.

Parameters

st - input stream to extract the data from
ch - reference to a character to store the extracted character to
s - pointer to (until C++20) a character array to store the extracted characters to

Return value

1,2) st
3) std :: move ( st )

Example

Run this code 
#include <iomanip>
#include <iostream>
#include <sstream>
 
int main()
{
    std::string input = "n greetings";
    std::istringstream stream(input);
 
    char c;
    const int MAX = 6;
    char cstr[MAX];
 
    stream >> c >> std::setw(MAX) >> cstr;
    std::cout << "c = " << c << '\n'
              << "cstr = " << cstr << '\n';
 
    double f;
    std::istringstream("1.23") >> f; // rvalue stream extraction
    std::cout << "f = " << f << '\n';
}

Output: 

c = n
cstr = greet
f = 1.23

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 13 C++98 the definition of n mentioned a non-existing name eos replaced with CharT ( )
LWG 68 C++98 no null characters were stored at the end of the output for overload (2) stores a null character
LWG 1203 C++98 overload for rvalue stream returned lvalue reference to the base class returns rvalue reference
to the derived class
LWG 2328 C++98 overload for rvalue stream required another argument to be lvalue made to accept rvalue
LWG 2534 C++98 overload for rvalue stream was not constrained constrained

See also

extracts formatted data
(public member function)
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