Inserts data into the stream.

[edit]Parameters

[edit]Return value

[edit]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(18-20) overloads).

• Attempting to output such objects invokes implicit conversion tobool, and, for any non-null pointer value, the value1 is printed (unlessboolalpha was set, in which casetrue is printed).

Character and character string arguments (e.g., of typechar orconstchar*) are handled by thenon-member overloads ofoperator<<.

• Attempting to output a character using the member function call syntax (e.g.,std::cout.operator<<('c');) will call one of the overloads in(2-5) or(11-14) 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 ofLWG issue 2221, but it is never implemented in any standard library implementation under C++11/14 modes.

[edit]Example

#include <iomanip>#include <iostream>#include <sstream> int fun(){return42;} int main(){std::istringstream input("\"Some text.\" ");double f=3.14;bool b=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) again int x=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.}

42 true 3.140000 "Some text." truep1: 0x7ffcea766600p2: 0x7ffcea766600

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit]See also

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