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

Checks if the file stream has an associated file.

# Declarations

bool is_open() const;

# Return value

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

# Example

#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';
    }
}

# Defect reports

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
close