NAME¶

std::basic_fstream::is_open - std::basic_fstream::is_open

Synopsis¶

bool is_open() const;

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¶

// Run this code

#include <fstream>
#include <iostream>
#include <string>

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

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 365 C++98 is_open was not declared with const qualifier declared with const
qualifier

See also¶

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