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std::basic_fstream::open(3)   C++ Standard Libary  std::basic_fstream::open(3)

NAME
       std::basic_fstream::open	- std::basic_fstream::open

Synopsis
	  void open( const char	*filename,				(1)
	  ios_base::openmode mode = ios_base::in|ios_base::out );
	  void	open(  const  std::filesystem::path::value_type	*filename, (2)
       (since C++17)
	  ios_base::openmode mode = ios_base::in|ios_base::out );
	  void open( const  std::string	 &filename,			   (3)
       (since C++11)
	  ios_base::openmode mode = ios_base::in|ios_base::out );
	  void	open(  const  std::filesystem::path &filename,		   (4)
       (since C++17)
	  ios_base::openmode mode = ios_base::in|ios_base::out );

	  Opens	and associates the file	 with  name  filename  with  the  file
       stream.

	  Calls	setstate(failbit) on failure.

	  Calls	clear()	on success. (since C++11)

	  1-2)	Effectively calls rdbuf()->open(filename, mode). (see std::ba-
       sic_filebuf::open
	  for the details on the effects of that call).
	  Overload (2) is only provided	 if  std::filesystem::path::value_type
       is not char.
	  (since C++17)
	  3-4) Effectively calls (1-2) as if by	open(filename.c_str(), mode).

Parameters
	  filename - the name of the file to be	opened
		     specifies	stream open mode. It is	bitmask	type, the fol-
       lowing constants
		     are defined:

		     Constant Explanation
	  mode	   - app      seek to the end of stream	before each write
		     binary   open in binary mode
		     in	      open for reading
		     out      open for writing
		     trunc    discard the contents of the stream when opening
		     ate      seek to the end of stream	immediately after open

Return value
	  (none)

Example
       // Run this code

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

	int main()
	{
	    std::string	filename = "example.123";

	    std::fstream fs;

	    fs.open(filename);

	    if(!fs.is_open())
	    {
	       fs.clear();
	       fs.open(filename, std::ios::out); //Create file.
	       fs.close();
	       fs.open(filename);
	    }

	    std::cout << std::boolalpha;
	    std::cout << "fs.is_open() = " << fs.is_open() << '\n';
	    std::cout << "fs.good() = "	<< fs.good() <<	'\n';
	}

See also
	  is_open checks if the	stream has an associated file
		  (public member function)
	  close	  closes the associated	file
		  (public member function)
	  open	  opens	a file and configures it as the	 associated  character
       sequence
		  (public member function of std::basic_filebuf<CharT,Traits>)

http://cppreference.com		  2022.07.31	   std::basic_fstream::open(3)

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