std::basic_ostream::operator<< - cppreference.com

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# std::basic_ostream::operator<<

From cppreference.com
< cpp‎ | io‎ | basic ostream

basic_ostream& operator<<( short value ); basic_ostream& operator<<( unsigned short value ); | (1) |
basic_ostream& operator<<( int value ); basic_ostream& operator<<( unsigned int value ); | (2) |
basic_ostream& operator<<( long value ); basic_ostream& operator<<( unsigned long value ); | (3) |
basic_ostream& operator<<( long long value ); basic_ostream& operator<<( unsigned long long value ); | (4) | (since C++11)
basic_ostream& operator<<( float value ); basic_ostream& operator<<( double value ); basic_ostream& operator<<( long double value ); | (5) |
basic_ostream& operator<<( bool value ); | (6) |
basic_ostream& operator<<( const void* value ); | (7) |
basic_ostream& operator<<( std::basic_streambuf<CharT, Traits>* sb); | (8) |
| (9) |
basic_ostream& operator<<( std::ios_base& (*func)(std::ios_base&) ); |  |
basic_ostream& operator<<( std::basic_ios<CharT,Traits>& (*func)(std::basic_ios<CharT,Traits>&) ); |  |
basic_ostream& operator<<( std::basic_ostream& (*func)(std::basic_ostream&) ); |  |

Inserts data into the stream.

1-2) Behaves as an `FormattedOutputFunction`. After constructing and checking the sentry object, if `value` is short or int, then casts it to unsigned short or unsigned int if ios_base::flags() & ios_base::basefield is ios_base::oct or ios_base::hex. After that, casts to long in any case and outputs as in (3). If `value` is unsigned short or unsigned int, casts to unsigned long and outputs as in (3).
3-7) Behaves as an `FormattedOutputFunction`. After constructing and checking the sentry object, inserts an integer, floating point, boolean or generic pointer value by calling `num_put::put()`. If the end of file condition was encountered during output (put().failed() == true), sets ios::badbit.
8) Behaves as an `UnformattedOutputFunction`. After constructing and checking the sentry object, checks if `sb` is a null pointer. If it is, executes setstate(badbit) and exits. Otherwise, extracts characters from the input sequence controlled by `sb` and inserts them into *this until 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).

If no characters were inserted, executes setstate(badbit). If an exception was thrown while extracting, sets failbit
9) Calls func(*this);. This overload is used to implement output I/O manipulators such as std::endl.

### [edit] Parameters

value | - | integer, floating-point, boolean, or pointer value to insert
func | - | function to call
sb | - | pointer to the streambuffer to read the data from

### [edit] Return value

*this

### [edit] Notes

There are no overload for pointers to volatile or function pointers (other than the ones with signatures accepted by the (9) overload). Attempting to output such objects invokes implicit conversion to bool, and, for any non-null pointer value, the value 1 is printed (unless boolalpha was set).

### [edit] Example

Run this code

    #include <iostream>
    #include <iomanip>
    #include <sstream>
    int main()
    {
        std::istringstream input(" \"Some text.\" ");
        volatile int n = 42;
        double f = 3.14;
        bool b = true;;
        std::cout << n   // int overload
                  << ' ' // non-member overload
                  << std::boolalpha << b // bool overload
                  << " " // non-member overload
                  << std::fixed << f // double overload
                  << input.rdbuf() // streambuf overload
                  << &n // bool overload
                  << std::endl; // function overload
    }

Output:

    42 true 3.140000 "Some text." true

### [edit] See also

operator<<(std::basic_ostream) | inserts character data (function) [edit]
operator<<operator>> | performs stream I/O of strings (function template)
operator<<operator>> | performs stream input and output of bitsets (function)
operator<<operator>> | serializes and deserializes a complex number (function template)
operator<<operator>> | performs stream input and output on pseudo-random number engine (function) [edit]
operator<<operator>> | performs stream input and output on pseudo-random number distribution (function) [edit]
put | inserts a character (public member function) [edit]
write | inserts blocks of characters (public member function) [edit]

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