Reference

public member function
<ios> <iostream>

std::basic_ios::tie

get (1)
basic_ostream<char_type,traits_type>* tie() const;
set (2)
basic_ostream<char_type,traits_type>* tie (basic_ostream<char_type,traits_type>* tiestr);
Get/set tied stream
The first form (1) returns a pointer to the tied output stream.

The second form (2) ties the object to tiestr and returns a pointer to the stream tied before the call, if any.

The tied stream is an output stream object which is flushed before each i/o operation in this stream object.

By default, cin is tied to cout , and wcin to wcout . Library implementations may tie other standard streams on initialization.
By default, the standard narrow streams cin and cerr are tied to cout , and their wide character counterparts (wcin and wcerr ) to wcout . Library implementations may also tie clog and wclog .

Parameters

tiestr
An output stream object.
char_type and traits_type are member types defined as aliases of the first and second class template parameters, respectively (see basic_ios types).

Return Value

A pointer to the stream object tied before the call, or a null pointer in case the stream was not tied.

Example

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// redefine tied object
#include <iostream> // std::ostream, std::cout, std::cin
#include <fstream> // std::ofstream
int main () {
 std::ostream *prevstr;
 std::ofstream ofs;
 ofs.open ("test.txt");
 std::cout << "tie example:\n";
 *std::cin.tie() << "This is inserted into cout";
 prevstr = std::cin.tie (&ofs);
 *std::cin.tie() << "This is inserted into the file";
 std::cin.tie (prevstr);
 ofs.close();
 return 0;
}

Output:

tie example:
This is inserted into cout


Data races

Accesses (1) or modifies (2) the stream object.
Concurrent access to the same stream object may cause data races.

Exception safety

Basic guarantee: if an exception is thrown, the stream is in a valid state.

basic_ios::rdbuf
Get/set stream buffer (public member function)

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