| 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 | |||||||||||||||||||||||||||||||
| Boolean formatting | |||||||||||||||||||||||||||||||
| Field width and fill control | |||||||||||||||||||||||||||||||
| Other formatting | |||||||||||||||||||||||||||||||
| Whitespace processing | |||||||||||||||||||||||||||||||
| Output flushing | |||||||||||||||||||||||||||||||
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| Status flags manipulation | |||||||||||||||||||||||||||||||
| Time and money I/O | |||||||||||||||||||||||||||||||
| Quoted manipulator | |||||||||||||||||||||||||||||||
(C++14) | |||||||||||||||||||||||||||||||
Defined in header <ostream> | ||
template<class CharT,class Traits> std::basic_ostream<CharT, Traits>& flush(std::basic_ostream<CharT, Traits>& os); | ||
Flushes the output sequenceos as if by callingos.flush().
This is an output-only I/O manipulator, it may be called with an expression such asout<< std::flush for anyout of typestd::basic_ostream.
Contents |
This manipulator may be used to produce an incomplete 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 ofstd::cout is also necessary before a call tostd::system, if the spawned process performs any screen I/O (a common example isstd::system("pause") on Windows). In most other usual interactive I/O scenarios,std::endl is redundant when used withstd::cout because any input fromstd::cin, output tostd::cerr, or program termination forces a call tostd::cout.flush().
When a complete line of output needs to be flushed, thestd::endl manipulator may be used.
When every output operation needs to be flushed, thestd::unitbuf manipulator may be used.
| os | - | reference to output stream |
os (reference to the stream after manipulation).
Withoutstd::flush, 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)<<" ... "<< std::flush;} int main(){volatileint sink=0; auto t1=std::chrono::high_resolution_clock::now();for(int j=0; j<5;++j){for(int n=0; n<10000;++n)for(int m=0; m<20000;++m) sink+= m* n;// do some workauto now=std::chrono::high_resolution_clock::now(); log_progress(now- t1);}std::cout<<'\n';}
Possible output:
567ms ... 1137ms ... 1707ms ... 2269ms ... 2842ms ...
| controls whether output is flushed after each operation (function)[edit] | |
| outputs'\n' and flushes the output stream (function template)[edit] | |
| synchronizes with the underlying storage device (public member function of std::basic_ostream<CharT,Traits>)[edit] |
