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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

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Filesystem library (C++17)

Regular expressions library (C++11)

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Technical specifications

Symbols index

External libraries

 

Input/output library

I/O manipulators

Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (deprecated in C++98)

basic_syncbuf (C++20)

Streams

Abstractions

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

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (deprecated in C++98)

ostrstream (deprecated in C++98)

strstream (deprecated in C++98)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

std::basic_ifstream

Member functions

basic_ifstream::basic_ifstream

basic_ifstream::operator= (C++11)

basic_ifstream::swap (C++11)

basic_ifstream::rdbuf

basic_ifstream::native_handle (C++26)

File operations

basic_ifstream::is_open

basic_ifstream::open

basic_ifstream::close

Non-member functions

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

 

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 <string>
#include <fstream>
#include <iostream>
 
// this file is called main.cpp
 
bool file_exists(const std::string& str)
{
    std::ifstream fs(str);
    return fs.is_open();
}
 
int main()
{
    std::boolalpha(std::cout);
    std::cout << file_exists("main.cpp")  << '\n'
              << file_exists("strange_file") << '\n';
}

Possible output:

true
false

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)