cpp/io/basic istream/sync

Synchronizes the input buffer with the associated data source.

Behaves as, except that gcount is not affected. After constructing and checking the sentry object,

If rdbuf is a null pointer, returns.

Otherwise, calls. If that function returns, calls and returns. Otherwise, returns.

Parameters
(none)

Return value
on success, on failure or if the stream does not support this operation (is unbuffered).