std::ios_base::sync_with_stdio
Sets whether the standard C++ streams are synchronized to the standard C streams after each input/output operation.
The standard C++ streams are the following: std::cin , std::cout , std::cerr , std::clog , std::wcin , std::wcout , std::wcerr and std::wclog .
The standard C streams are the following: stdin , stdout and stderr .
For a standard stream str, synchronized with the C stream f, the following pairs of functions have identical effect:
In practice, this means that the synchronized C++ streams are unbuffered, and each I/O operation on a C++ stream is immediately applied to the corresponding C stream's buffer. This makes it possible to freely mix C++ and C I/O.
In addition, synchronized C++ streams are guaranteed to be thread-safe (individual characters output from multiple threads may interleave, but no data races occur).
If the synchronization is turned off, the C++ standard streams are allowed to buffer their I/O independently, which may be considerably faster in some cases.
By default, all eight standard C++ streams are synchronized with their respective C streams.
If this function is called after I/O has occurred on the standard stream, the behavior is implementation-defined: implementations range from no effect to destroying the read buffer.
[edit] Parameters
[edit] Return value
Synchronization state before the call to the function.
[edit] Example
#include <cstdio> #include <iostream> int main() { std::ios::sync_with_stdio(false); std::cout << "a\n"; std::printf ("b\n"); std::cout << "c\n"; }
Possible output:
b a c
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 49 | C++98 | it was unspecified (1) which state is actually returned and (2) what does 'synchronized' between standard C and C++ streams mean |
both specified |