std::ios_base::sync_with_stdio

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 C++ and the C streams use the same buffer, and therefore, can be mixed freely. 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.

It is implementation-defined if this function has any effect if called after some I/O occurred on the standard stream.

Parameters

Return value

synchronization state before the call to the function.

Example

#include <iostream>
#include <cstdio>
 
int main()
{
    std::cout.sync_with_stdio(false);
    std::cout << "a\n";
    std::printf("b\n");
    std::cout << "c\n";
}

b
a
c

See also