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.
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
b a c
| writes to the standard C output stream stdout|
| writes to the standard C error stream stderr, unbuffered|
| writes to the standard C error stream stderr|