basic_ostream&operator<<(boolvalue); (1) basic_ostream&operator<<(longvalue); (2)basic_ostream&operator<<(unsignedlongvalue); (3) basic_ostream&operator<<(longlongvalue); (4) (since C++11)basic_ostream&operator<<(unsignedlonglongvalue); (5) (since C++11)basic_ostream&operator<<(doublevalue); (6) basic_ostream&operator<<(longdoublevalue); (7) basic_ostream&operator<<(constvoid*value); (8)basic_ostream&operator<<(constvolatilevoid*value); (9) (since C++23)basic_ostream&operator<<(std::nullptr_t); (10) (since C++17)basic_ostream&operator<<(shortvalue); (11)basic_ostream&operator<<(intvalue); (12) basic_ostream&operator<<(unsignedshortvalue); (13) basic_ostream&operator<<(unsignedintvalue); (14) basic_ostream&operator<<(floatvalue); (15) basic_ostream&operator<<(/* extended-floating-point-type */value); (16) (since C++23)basic_ostream&operator<<(std::basic_streambuf<CharT,Traits>*sb); (17) basic_ostream&operator<<(std::ios_base&(*func)(std::ios_base&)); (18)basic_ostream&operator<<(std::basic_ios<CharT,Traits>&(*func)(std::basic_ios<CharT,Traits>&)); (19) basic_ostream&operator<<(std::basic_ostream<CharT,Traits>&(*func)(std::basic_ostream<CharT,Traits>&)); (20) Inserts data into the stream.
1-8) Inserts value.
This function behaves as a
. After constructing and checking the sentry object, inserts a value by calling
. If the end of file condition was encountered during output (put().failed()==true), sets badbit.
9) Equivalent to returnoperator<<(const_cast<constvoid*>(p));.
10) Equivalent to return*this<<s;, where s is an implementation-defined null-terminated character type string.
11) Inserts a value from shortvalue.
This function behaves as a
. After constructing and checking the sentry object, inserts a long value lval as in (2), where lval is
static_cast<long>(static_cast<unsignedshort>(value)), if flags()&std::ios_base::basefield is
or
, or
static_cast<long>(value) otherwise.
12) Inserts a value from intvalue.
This function behaves as a
. After constructing and checking the sentry object, inserts a long value lval as in (2), where lval is
static_cast<long>(static_cast<unsignedint>(value)), if flags()&std::ios_base::basefield is
or
, or
static_cast<long>(value) otherwise.
13,14) Inserts a value from unsignedshort or unsignedintvalue.
This function behaves as a
. After constructing and checking the sentry object, inserts static_cast<unsignedlong>(value) as in (3).
15) Inserts a value from floatvalue.
This function behaves as a
. After constructing and checking the sentry object, inserts static_cast<double>(value) as in (6).
16) Inserts a value from value. The library provides overloads for all cv-unqualified
as the type of the parameter value.
This function behaves as a
. After constructing and checking the sentry object, checks the
floating-point conversion rank
of /* extended-floating-point-type */:
If the rank is less than or equal to that of double, inserts static_cast<double>(value) as in (6).
Otherwise, if the rank is less than or equal to that of longdouble, inserts static_cast<longdouble>(value) as in (7).
Otherwise, an invocation of this overload is conditionally supported with implementation-defined semantics.
17) This function behaves as an
. 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
, rethrows the exception.
18-20) Calls func(*this). These overloads are used to implement output I/O manipulators such as
.
Parameters
value - integer, floating-point, boolean, or pointer value to insert func - function to call sb - pointer to the stream buffer to read the data from Return value
1-19)*this
20)func(*this)
Notes
There are no overloads for pointers to non-static members, pointers to volatiles,(until C++23) or function pointers (other than the ones with signatures accepted by the (
) 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 constchar*) are handled by the
of operator<<.
Attempting to output a character using the member function call syntax (e.g., std::cout.operator<<('c');) will call one of the overloads in (
) or (
) and output the numerical value.
Attempting to output a character string using the member function call syntax will call overload (8) and print the pointer value instead.
Overload (10) was added by the resolution of
, but it is never implemented in any standard library implementation under C++11/14 modes.
Example
Run this code
#include<iomanip>#include<iostream>#include<sstream>intfun(){return42;}intmain(){std::istringstreaminput(" \"Some text.\" ");doublef=3.14;boolb=true;std::cout<<fun()// int overload (12)<<' '// non-member overload<<std::boolalpha// function overload (18)<<b// bool overload (1)<<" "// non-member overload<<std::fixed// function overload (18) again<<f// double overload (6)<<input.rdbuf()// streambuf overload<<fun// bool overload (1): there's no overload for int(*)()<<std::endl;// function overload (18) againintx=0;int*p1=&x;volatileint*p2=&x;std::cout<<"p1: "<<p1<<'\n'// `const void*` overload, prints address<<"p2: "<<p2<<'\n';// before C++23 (P1147): bool overload :), because// operator<<(const void*) is not a match, as it discards the `volatile`// qualifier. To fix this, C++23 adds `const volatile void*` overload (9),// that prints the address as expected.}Possible output:
42 true 3.140000 "Some text." true p1: 0x7ffcea766600 p2: 0x7ffcea766600 Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++98 overloads (1-8,11-15) delegated the insertion to
, but it does not have overloads for short,
unsignedshort, int, unsignedint, and floatthey are converted
before being passed
to num_put::put
C++98 overload (17) behaved as a
because of the resolution of
it behaves as an
See also
operator<<(std::basic_ostream)
inserts character data or insert into rvalue stream
(function template)
performs stream input and output on strings
(function template)
(C++17)
performs stream output on string views
(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)
inserts a character
(public member function)
inserts blocks of characters
(public member function)
(C++17)
converts an integer or floating-point value to a character sequence
(function)