W3cubDocs

/C++

std::basic_fstream<CharT,Traits>::is_open

bool is_open();
 (until C++11) 
bool is_open() const;
 (since C++11)

Checks if the file stream has an associated file.

Effectively calls rdbuf()->is_open().

Parameters

(none).

Return value

true if the file stream has an associated file, false otherwise.

Example

#include <string>
#include <fstream>
#include <iostream>
 
int main()
{
    std::string filename = "some_file";
 
    std::fstream fs(filename, std::ios::in);
 
    std::cout << std::boolalpha;
    std::cout << "fs.is_open() = " << fs.is_open() << '\n';
 
    if(!fs.is_open())
    {
       fs.clear();
       fs.open(filename, std::ios::out);
       std::cout << "fs.is_open() = " << fs.is_open() << '\n';
    }
}

Possible output:

fs.is_open() = false
fs.is_open() = true

See also

opens a file and associates it with the stream
(public member function)
closes the associated file
(public member function)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
http://en.cppreference.com/w/cpp/io/basic_fstream/is_open