NAME¶

std::basic_istream::operator>> - std::basic_istream::operator>>

Synopsis¶

basic_istream& operator>>( short& value ); (1)
basic_istream& operator>>( unsigned short& value );
basic_istream& operator>>( int& value ); (2)
basic_istream& operator>>( unsigned int& value );
basic_istream& operator>>( long& value ); (3)
basic_istream& operator>>( unsigned long& value );
basic_istream& operator>>( long long& value ); (4) (since C++11)
basic_istream& operator>>( unsigned long long& value );
basic_istream& operator>>( float& value );

basic_istream& operator>>( double& value ); (5)

basic_istream& operator>>( long double& value );
basic_istream& operator>>( bool& value ); (6)
basic_istream& operator>>( void*& value ); (7)
basic_istream& operator>>( std::ios_base& (*func)(std::ios_base&) (8)
);
basic_istream& operator>>( std::basic_ios<CharT,Traits>& (9)
(*func)(std::basic_ios<CharT,Traits>&) );
basic_istream& operator>>( basic_istream& (*func)(basic_istream&) (10)
);
basic_istream& operator>>( std::basic_streambuf<CharT,Traits>* sb (11)
);

Extracts values from an input stream.

1-4) Extracts an integer value potentially skipping preceding whitespace. The value
is stored to a given reference value.
This function behaves as a FormattedInputFunction. After constructing and checking
the sentry object, which may skip leading whitespace, extracts an integer value by
calling std::num_get::get().
5) Extracts a floating-point value potentially skipping preceding whitespace. The
value is stored to a given reference value.
This function behaves as a FormattedInputFunction. After constructing and checking
the sentry object, which may skip leading whitespace, extracts a floating-point
value by calling std::num_get::get().
6) Extracts a boolean value potentially skipping preceding whitespace. The value is
stored to a given reference value.
This function behaves as a FormattedInputFunction. After constructing and checking
the sentry object, which may skip leading whitespace, extracts an bool value by
calling std::num_get::get().
7) Extracts a generic pointer value potentially skipping preceding whitespace. The
value is stored to a given reference value.
This function behaves as a FormattedInputFunction. After constructing and checking
the sentry object, which may skip leading whitespace, extracts a generic pointer
value by calling std::num_get::get().
8-10) Calls func(*this), where func is an I/O manipulator.
11) Behaves as an UnformattedInputFunction. After constructing and checking the
sentry object, extracts all data from the input stream and stores it to sb. The
extraction stops if one of the following conditions are met:

* end-of-file occurs on the input sequence;
* inserting in the output sequence fails (in which case the character to
be inserted is not extracted);
* an exception occurs (in which case the exception is caught, and only
rethrown if failbit is enabled in exceptions()).

In either case, stores the number of characters extracted in the member variable
accessed by subsequent calls to gcount(). If sb is a null pointer or if no
characters were inserted into sb, calls setstate(failbit) (which may throw
std::ios_base::failure if enabled).

If extraction fails (e.g. if a letter was entered where a digit is expected), zero
is written to value and failbit is set. For signed integers, if extraction results
in the value too large or too small to fit in value, std::numeric_limits<T>::max()
or std::numeric_limits<T>::min() (respectively) is written and failbit flag is set.
For unsigned integers, if extraction results in the value too large or too small to
fit in value, std::numeric_limits<T>::max() is written and failbit flag is set.

Parameters¶

value - reference to an integer or floating-point value to store the extracted value
to
func - pointer to I/O manipulator function
sb - pointer to the streambuffer to write all the data to

Return value¶

1-9,11) *this
10) func(*this)

Example¶

// Run this code

#include <iostream>
#include <iomanip>
#include <sstream>

int main()
{
std::string input = "41 3.14 false hello world";
std::istringstream stream(input);
int n;
double f;
bool b;

stream >> n >> f >> std::boolalpha >> b;
std::cout << "n = " << n << '\n'
<< "f = " << f << '\n'
<< "b = " << std::boolalpha << b << '\n';

// extract the rest using the streambuf overload
stream >> std::cout.rdbuf();
std::cout << '\n';
}

Output:¶

n = 41
f = 3.14
b = false
hello world

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 696 C++98 value was unchanged on extraction set to zero or minimum/maximum
failure values

See also¶

operator>>(std::basic_istream) extracts characters and character arrays
(function template)
operator<< performs stream input and output on strings
operator>> (function template)
operator<< performs stream input and output of bitsets
operator>> (function template)
operator<< serializes and deserializes a complex number
operator>> (function template)
operator<< performs stream input and output on pseudo-random
operator>> number engine
(C++11) (function template)
operator<< performs stream input and output on pseudo-random
operator>> number distribution
(C++11) (function template)
read extracts blocks of characters
(public member function)
readsome extracts already available blocks of characters
(public member function)
get extracts characters
(public member function)
extracts characters until the given character is
getline found
(public member function)
from_chars converts a character sequence to an integer or
(C++17) floating-point value
(function)