std::basic_ostream<CharT,Traits>::operator<< - cppreference.com (original) (raw)

Inserts data into the stream.

1-8) Inserts value.

This function behaves as a FormattedOutputFunction. After constructing and checking the sentry object, inserts a value by calling

std::num_put::put()

. If the end of file condition was encountered during output (put().failed() == true), sets badbit.

1. Equivalent to return operator<<(const_cast<const void*>(p));.

2. Equivalent to return *this << s;, where s is an implementation-defined null-terminated character type string.

3. Inserts a value from short value.

4. Inserts a value from int value.

13,14) Inserts a value from unsigned short or unsigned int value.

This function behaves as a FormattedOutputFunction. After constructing and checking the sentry object, inserts static_cast<unsigned long>(value) as in (3).

1. Inserts a value from float value.

This function behaves as a FormattedOutputFunction. After constructing and checking the sentry object, inserts static_cast<double>(value) as in (6).

1. Inserts a value from value. The library provides overloads for all cv-unqualified extended floating-point types as the type of the parameter value.

This function behaves as a FormattedOutputFunction. 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 long double, inserts static_cast<long double>(value) as in (7).
• Otherwise, an invocation of this overload is conditionally supported with implementation-defined semantics.

1. This function 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.

18-20) Calls func(*this). These overloads are used to implement output I/O manipulators such as std::endl.

[edit] Parameters

[edit] Return value

1-19) *this

1. func(*this)

[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 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 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 of LWG issue 2221, but it is never implemented in any standard library implementation under C++11/14 modes.

[edit] Example

#include #include #include   int fun() { return 42; }   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; volatile int* 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

[edit] Defect reports

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

[edit] See also