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.

Parameters

Return value

Synchronization state before the call to the function.

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";
}

b
a
c

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also