std::basic_ostream::operator<<

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::nullptr_t );	(8)	(since C++17)
basic_ostream& operator<<( std::basic_streambuf<CharT, Traits>* sb);	(9)
basic_ostream& operator<<( std::ios_base& (*func)(std::ios_base&) );	(10)
basic_ostream& operator<<( std::basic_ios<CharT,Traits>& (*func)(std::basic_ios<CharT,Traits>&) );	(11)
basic_ostream& operator<<( std::basic_ostream<CharT,Traits>& (*func)(std::basic_ostream<CharT,Traits>&) );	(12)

Inserts data into the stream.

1-2) Behaves as a 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 a 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) Outputs an implementation-defined string as if by *this << s, where s is a null-terminated character type string.

9) 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(failbit). If an exception was thrown while extracting, sets failbit and, if failbit is set in exceptions(), rethrows the exception.

10-12) Calls func(*this). These overloads are used to implement output I/O manipulators such as std::endl.

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

Return value

1-11) *this

12) func(*this)

Notes

There are no overload for pointers to non-static member, pointers to volatile, or function pointers (other than the ones with signatures accepted by the (10-12) overloads). 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, in which case true is printed).

Character and character string arguments (e.g., of type char or const char*) are handled by the non-member overloads of operator<<. Attempting to output a character using the member function call syntax (e.g., std::cout.operator<<('c');) will call one of overloads (2-4) and output the numerical value. Attempting to output a character string using the member function call syntax will call overload (7) and print the pointer value instead.

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: volatile int* doesn't convert to const void*
              << std::endl; // function overload
}

Output:

42 true 3.140000 "Some text." true

Language
Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

I/O manipulators
C-style I/O
Buffers
basic_streambuf
basic_filebuf
basic_stringbuf
strstreambuf (deprecated)
basic_syncbuf (C++20)
Streams
Abstractions
ios_base
basic_ios
basic_istream
basic_ostream
basic_iostream
File I/O
basic_ifstream
basic_ofstream
basic_fstream
String I/O
basic_istringstream
basic_ostringstream
basic_stringstream
Array I/O
istrstream (deprecated)
ostrstream (deprecated)
strstream (deprecated)
Synchronized Output
basic_osyncstream (C++20)
Types
streamoff
streamsize
fpos
Error category interface
iostream_category (C++11)
io_errc (C++11)

operator<<(std::basic_ostream)	inserts character data (function template)
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 template)
operator<<operator>>	performs stream input and output on pseudo-random number distribution (function template)
put	inserts a character (public member function)
write	inserts blocks of characters (public member function)
to_chars (C++17)	converts an integer or floating-point value to a character sequence (function)

std::basic_ostream::operator<<

Parameters

Return value

Notes

Example

See also