std::basic_fstream::is_open

From cppreference.com
< cpplrm; | iolrm; | basic fstream

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)