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      std::ios_base::sync_with_stdio

      From cppreference.com
      < cpp‎ | io‎ | ios base
       
      C++
       
      Input/output library
       
      std::ios_base
       
      staticbool 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:

      1)std::fputc(f, c) and str.rdbuf()->sputc(c)
      2)std::fgetc(f) and str.rdbuf()->sbumpc()
      3)std::ungetc(c, f) and str.rdbuf()->sputbackc(c)

      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.

      Contents

      [edit]Parameters

      sync - the new synchronization setting

      [edit]Return value

      synchronization state before the call to the function

      [edit]Example

      Run this code
      #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

      [edit]See also

      		 writes to the standard C output stream stdout
      (global object)[edit]
      		 writes to the standard C error stream stderr, unbuffered
      (global object)[edit]
      		 writes to the standard C error stream stderr
      (global object)[edit]
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