static bool sync_with_stdio( bool sync = true ); |
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.
sync | - | the new synchronization setting |
synchronization state before the call to the function.
#include <iostream> #include <cstdio> 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
writes to the standard C output stream stdout (global object) |
|
writes to the standard C error stream stderr , unbuffered(global object) |
|
writes to the standard C error stream stderr (global object) |
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