std::endl
| I/O manipulators | ||||
| Print functions (C++23) | ||||
| C-style I/O | ||||
| Buffers | ||||
(C++23) | ||||
(C++98/26*) | ||||
(C++20) | ||||
| Streams | ||||
| Abstractions | ||||
| File I/O | ||||
| String I/O | ||||
| Array I/O | ||||
(C++23) | ||||
(C++23) | ||||
(C++23) | ||||
(C++98/26*) | ||||
(C++98/26*) | ||||
(C++98/26*) | ||||
| Synchronized Output | ||||
(C++20) | ||||
| Types | ||||
| Error category interface | ||||
(C++11) | ||||
(C++11) |
| Floating-point formatting | |||||||||||||||||||||||||||||||
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| Integer formatting | |||||||||||||||||||||||||||||||
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| Whitespace processing | |||||||||||||||||||||||||||||||
| Output flushing | |||||||||||||||||||||||||||||||
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| Status flags manipulation | |||||||||||||||||||||||||||||||
| Time and money I/O | |||||||||||||||||||||||||||||||
| Quoted manipulator | |||||||||||||||||||||||||||||||
(C++14) | |||||||||||||||||||||||||||||||
| Defined in header <ostream>
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| template< class CharT, class Traits > std::basic_ostream<CharT, Traits>& endl( std::basic_ostream<CharT, Traits>& os ); |
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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.
Contents |
[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 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
| os | - | reference to output stream |
[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.
#include <chrono> #include <iostream> template<typename Diff> void log_progress(Diff d) { std::cout << std::chrono::duration_cast<std::chrono::milliseconds>(d) << " passed" << std::endl; } int main() { std::cout.sync_with_stdio(false); / on some platforms, stdout flushes on \n static volatile int sink{}; const auto t1 = std::chrono::high_resolution_clock::now(); for (int i = 0; i < 5; ++i) { for (int j = 0; j < 10000; ++j) for (int k = 0; k < 20000; ++k) sink += i * j * k; / do some work log_progress(std::chrono::high_resolution_clock::now() - t1); } }
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]
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