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std::basic_ios::tie

From cppreference.com
< cpp‎ | io‎ | basic ios
std::basic_ostream<CharT,Traits>* tie() const;
(1)
std::basic_ostream<CharT,Traits>* tie( std::basic_ostream<CharT,Traits>* str );
(2)

Manages the tied stream. A tied stream is an output stream which is synchronized with the sequence controlled by the stream buffer (rdbuf()), that is, flush() is called on the tied stream before any input/output operation on *this.

1) Returns the current tied stream. If there is no tied stream, NULL is returned.
2) Sets the current tied stream to str. Returns the tied stream before the operation. If there is no tied stream, NULL is returned.

Contents

[edit] Parameters

str - an output stream to set as the tied stream

[edit] Return value

The tied stream, or NULL if there was no tied stream.

[edit] Exceptions

(none)

[edit] Notes

By default, the standard streams cin and cerr are tied to cout. Similarly, their wide counterparts wcin and wcerr are tied to wcout.

[edit] Example

#include <iostream>
#include <fstream>
#include <string>
 
int main()
{
    std::ofstream os("test.txt");
    std::ifstream is("test.txt");
    std::string value("0");
 
    os << "Hello";
    is >> value;
 
    std::cout << "Result before tie(): \"" << value << "\"\n";
    is.clear();
    is.tie(&os);
 
    is >> value;
 
    std::cout << "Result after tie(): \"" << value << "\"\n";
}

Output:

Result before tie(): "0"
Result after tie(): "Hello"