std::ios_base::sync_with_stdio - cppreference.com (original) (raw)

| 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:

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.

[edit] Parameters

[edit] Return value

Synchronization state before the call to the function.

[edit] Example

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

Possible output:

[edit] Defect reports

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

[edit] See also