operator<<(std::basic_ostream)

Since C++11

Header: <ostream>

Inserts a character or a character string.

# Declarations

basic_ostream and character

template< class CharT, class Traits >
basic_ostream<CharT, Traits>&
operator<<( basic_ostream<CharT, Traits>& os, CharT ch );

template< class CharT, class Traits >
basic_ostream<CharT, Traits>&
operator<<( basic_ostream<CharT, Traits>& os, char ch );

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, char ch );

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, signed char ch );

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, unsigned char ch );

basic_ostream and character array

template< class CharT, class Traits >
basic_ostream<CharT, Traits>&
operator<<( basic_ostream<CharT, Traits>& os, const CharT* s );

template< class CharT, class Traits >
basic_ostream<CharT, Traits>&
operator<<( basic_ostream<CharT, Traits>& os, const char* s );

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, const char* s );

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, const signed char* s );

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, const unsigned char* s );

basic_ostream rvalue

template< class Ostream, class T >
Ostream&& operator<<( Ostream&& os, const T& value );

(since C++11)

deleted overloads for basic_ostream and UTF character/array

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, wchar_t ch ) = delete;

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, char8_t ch ) = delete;

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, char16_t ch ) = delete;

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, char32_t ch ) = delete;

template< class Traits >
basic_ostream<wchar_t, Traits>&
operator<<( basic_ostream<wchar_t, Traits>& os, char8_t ch ) = delete;

template< class Traits >
basic_ostream<wchar_t, Traits>&
operator<<( basic_ostream<wchar_t, Traits>& os, char16_t ch ) = delete;

template< class Traits >
basic_ostream<wchar_t, Traits>&
operator<<( basic_ostream<wchar_t, Traits>& os, char32_t ch ) = delete;

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, const wchar_t* s ) = delete;

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, const char8_t* s ) = delete;

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, const char16_t* s ) = delete;

template< class Traits >
basic_ostream<char, Traits>&
operator<<( basic_ostream<char, Traits>& os, const char32_t* s ) = delete;

template< class Traits >
basic_ostream<wchar_t, Traits>&
operator<<( basic_ostream<wchar_t, Traits>& os, const char8_t* s ) = delete;

template< class Traits >
basic_ostream<wchar_t, Traits>&
operator<<( basic_ostream<wchar_t, Traits>& os, const char16_t* s ) = delete;

template< class Traits >
basic_ostream<wchar_t, Traits>&
operator<<( basic_ostream<wchar_t, Traits>& os, const char32_t* s ) = delete;

# Parameters

os: output stream to insert data to
ch: reference to a character to insert
s: pointer to a character string to insert

# Notes

Before LWG issue 1203, code such as (std::ostringstream() « 1.2).str() does not compile.

# Example

#include <fstream>
#include <iostream>
 
void foo()
{
    // error: operator<< (basic_ostream<char, _Traits>&, char8_t) is deleted
//  std::cout << u8'z' << '\n';
}
 
std::ostream& operator<<(std::ostream& os, char8_t const& ch)
{
    return os << static_cast<char>(ch);
}
 
int main()
{
    std::cout << "Hello, world" // uses `const char*` overload
              << '\n';          // uses `char` overload
    std::ofstream{"test.txt"} << 1.2; // uses rvalue overload
 
    std::cout << u8'!' << '\n'; // uses program-defined operator<<(os, char8_t const&)
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 167	C++98	the number of characters inserted for alloverloads in (2) was traits::length(s)	updated the numbers for the overloadswhere CharT does not match the type of ch
LWG 1203	C++11	overload for rvalue stream returnedlvalue reference to the base class	returns rvalue referenceto the derived class
LWG 2011	C++98	padding was determined by std::num_put::do_put()	determined by the operator itself
LWG 2534	C++11	overload for rvalue stream was not constrained	constrained

operator<<(std::basic_ostream)

# Declarations

# Parameters

# Notes

# Example

# Defect reports

# See also