std::basic_ios<CharT,Traits>::tie

 

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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, a null pointer is returned.

2) Sets the current tied stream to str. Returns the tied stream before the operation. If there is no tied stream, a null pointer is returned.

Parameters

str

-

an output stream to set as the tied stream

Return value

The tied stream, or a null pointer if there was no tied stream.

Exceptions

May throw implementation-defined exceptions.

Notes

By default, the standard stream cout is tied to cin and cerr. Similarly, its wide counterpart wcout is tied to wcin and wcerr.

Example

Run this code

#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"