std::unitbuf, std::nounitbuf
| I/O manipulators | ||||
| Print functions (C++23) | ||||
| C-style I/O | ||||
| Buffers | ||||
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(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) |
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| Whitespace processing | |||||||||||||||||||||||||||||||
| Output flushing | |||||||||||||||||||||||||||||||
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| Status flags manipulation | |||||||||||||||||||||||||||||||
| Time and money I/O | |||||||||||||||||||||||||||||||
| Quoted manipulator | |||||||||||||||||||||||||||||||
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| Defined in header <ios>
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| std::ios_base& unitbuf( std::ios_base& str ); |
(1) | |
| std::ios_base& nounitbuf( std::ios_base& str ); |
(2) | |
Enables or disables automatic flushing of the output stream after any output operation. Has no effect on input.
This is an I/O manipulator, it may be called with an expression such as out << std::unitbuf for any out of type std::basic_ostream or with an expression such as in >> std::unitbuf for any in of type std::basic_istream.
Contents |
[edit] Notes
Flushing is performed in the destructor of the std::basic_ostream::sentry object, which calls str.rdbuf()->pubsync() if str.flags() & std::ios_base::unitbuf is true.
The standard output objects std::cerr and std::wcerr have their unitbuf bit set by default.
[edit] Parameters
| str | - | reference to I/O stream |
[edit] Return value
str (reference to the stream after manipulation).
[edit] Example
Without std::unitbuf or another explicit flush, the output is the same, but does 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) << " ... "; } int main() { volatile int sink = 0; std::cout << std::unitbuf; / enable automatic flushing const auto start = 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 work log_progress(std::chrono::high_resolution_clock::now() - start); } std::cout << '\n'; }
Output:
571ms ... 1146ms ... 1722ms ... 2294ms ... 2865ms ...
[edit] See also
| flushes the output stream (function template) [edit] | |
| outputs '\n' and flushes the output stream (function template) [edit] |
