std::basic_istream<CharT,Traits>::operator>>

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Input/output library
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(C++23)
(deprecated in C++98)
(C++20)
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(C++23)
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(C++20)
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(C++11)
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std::basic_istream
 
basic_istream& operator>>( short& value );
basic_istream& operator>>( unsigned short& value );
 (1)
basic_istream& operator>>( int& value );
basic_istream& operator>>( unsigned int& value );
 (2)
basic_istream& operator>>( long& value );
basic_istream& operator>>( unsigned long& value );
 (3)
basic_istream& operator>>( long long& value );
basic_istream& operator>>( unsigned long long& value );
 (4) (since C++11)
basic_istream& operator>>( float& value );

basic_istream& operator>>( double& value );

basic_istream& operator>>( long double& value );
 (5)
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>&
                                (*func)(std::basic_ios<CharT,Traits>&) );
 (9)
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 failure set to zero or minimum/maximum values

See also

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