std::endl - cppreference.com (original) (raw)

Inserts a newline character into the output sequence os and flushes it as if by calling os.put(os.widen('\n')) followed by os.flush().

This is an output-only I/O manipulator, it may be called with an expression such as out << std::endl for any out of type std::basic_ostream.

[edit] Notes

This manipulator may be used to produce a line of output immediately, e.g. when displaying output from a long-running process, logging activity of multiple threads or logging activity of a program that may crash unexpectedly. An explicit flush of std::cout is also necessary before a call to std::system, if the spawned process performs any screen I/O. In most other usual interactive I/O scenarios, std::endl is redundant when used with std::cout because any input from std::cin, output to std::cerr, or program termination forces a call to std::cout.flush(). Use of std::endl in place of '\n', encouraged by some sources, may significantly degrade output performance.

In many implementations, standard output is line-buffered, and writing '\n' causes a flush anyway, unless std::ios::sync_with_stdio(false) was executed. In those situations, unnecessary endl only degrades the performance of file output, not standard output.

The code samples on this wiki follow Bjarne Stroustrup and The C++ Core Guidelines in flushing the standard output only where necessary.

When an incomplete line of output needs to be flushed, the std::flush manipulator may be used.

When every character of output needs to be flushed, the std::unitbuf manipulator may be used.

[edit] Parameters

[edit] Return value

os (reference to the stream after manipulation).

[edit] Example

With '\n' instead of endl, the output would be the same, but may not appear in real time.

Possible output:

566ms passed 1133ms passed 1699ms passed 2262ms passed 2829ms passed

[edit] See also

| | controls whether output is flushed after each operation (function) [edit] | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | flushes the output stream (function template) [edit] | | | synchronizes with the underlying storage device (public member function of std::basic_ostream<CharT,Traits>) [edit] |