std::ostream::operator<<

(1) arithmetic types

Generates a sequence of characters with the representation of val, properly formatted according to the locale and other formatting settings selected in the stream, and inserts them into the output stream.
Internally, the function accesses the output sequence by first constructing a sentry object. Then (if good), it calls num_put::put (using the stream's selected locale) to perform both the formatting and the insertion operations, adjusting the stream's internal state flags accordingly. Finally, it destroys the sentry object before returning.

(2) stream buffers

Retrieves as many characters as possible from the input sequence controlled by the stream buffer object pointed by sb (if any) and inserts them into the stream, until either the input sequence is exhausted or the function fails to insert into the stream.
Internally, the function accesses the output sequence by first constructing a sentry object. Then (if good), it inserts characters into its associated stream buffer object as if calling its member function sputc, and finally destroys the sentry object before returning.

(3) manipulators

Calls pf(*this), where pf may be a manipulator.
Manipulators are functions specifically designed to be called when used with this operator.
This operation has no effect on the output sequence and inserts no characters (unless the manipulator itself does, like endl or ends do).

Parameters

val

Value to be formatted and inserted into the stream.
Notice that the type of this argument (along with the stream's format flags) influences the format of the representation inserted.

sb

Pointer to a streambuf object from whose controlled input sequence the characters are copied.

pf

A function that takes and returns a stream object. It generally is a manipulator function.
The standard manipulators which have an effect when used on standard ostream objects are:

manipulator	Effect
endl	Inserts a new-line character and flushes the stream.
ends	Inserts a null character.
flush	Flushes the stream.
boolalpha / noboolalpha	Activates/deactivates the insertion of bool values as their alphanumerical representations.
showbase / noshowbase	Activates/deactivates the insertion of base prefixes in the representations of integer values.
showpoint / noshowpoint	Activates/deactivates the requirement that the decimal point is always written on the representations of floating-point values.
showpos / noshowpos	Activates/deactivates the requirement that positive values are preceded with a plus sign (+).
unitbuf / nounitbuf	Activates/deactivates automatic flushing after each insertion operation.
uppercase / nouppercase	Activates/deactivates the use of uppercase letters for characters used in the representations of arithmetic types.
dec / hex / oct	basefield setting: Sets that base used to represent integral numerical values.
fixed / scientific / hexfloat / defaultfloat	floatfield setting: Format used to represent floating-point values.
internal / left / right	adjustfield setting: Position where fill characters are inserted to adjust the field to the field width.

The following extended manipulators can also be applied to istream objects (these take additional arguments and require the explicit inclusion of the <iomanip> header):

manipulator	Effect
setbase	Sets the numerical base used to represent integral numerical values .
setfill	Sets the fill character used to adjust fields to the field width.
setprecision	Sets the decimal precision used to represent floating-point values.
setw	Sets the field width used by the next formatted insertion.
setiosflags/resetiosflags	Set/reset format flags.

Return Value

Example

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// example on insertion
#include <iostream>     // std::cout, std::right, std::endl
#include <iomanip>      // std::setw
int main () {
  int val = 65;
  std::cout << std::right;       // right-adjusted (manipulator)
  std::cout << std::setw(10);    // set width (extended manipulator)
  std::cout << val << std::endl; // multiple insertions
  return 0;
}

        65

Data races

Exception safety

See also

operator<< (ostream)

Insert characters (public member function)

ostream::put

Put character (public member function)

ostream::write

Write block of data (public member function)

istream::operator>>

Extract formatted input (public member function)