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std::basic_...eam::is_open(3) C++ Standard Libarystd::basic_...eam::is_open(3)

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

Synopsis
	  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)

http://cppreference.com		  2022.07.31	 std::basic_...eam::is_open(3)

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<https://man.freebsd.org/cgi/man.cgi?query=std::basic_fstream::is_open&sektion=3&manpath=FreeBSD+Ports+15.0>

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