std::basic_fstream::is_open

C++

Language

Headers

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Named requirements

Language support library

Concepts library (C++20)

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Numerics library

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Regular expressions library (C++11)

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Technical Specifications

Input/output library

I/O manipulators

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

strstreambuf (deprecated)

basic_syncbuf (C++20)

Streams

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ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

File I/O

basic_ifstream

basic_ofstream

basic_fstream

String I/O

basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

istrstream (deprecated)

ostrstream (deprecated)

strstream (deprecated)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

std::basic_fstream

Member functions

basic_fstream::basic_fstream

basic_fstream::operator= (C++11)

basic_fstream::swap (C++11)

basic_fstream::rdbuf

File operations

basic_fstream::is_open

basic_fstream::open

basic_fstream::close

Non-member functions

basic_fstream::swap(std::basic_fstream) (C++11)

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

Run this code

#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

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