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std::filesy...te_hard_link(3) C++ Standard Libarystd::filesy...te_hard_link(3)

NAME
       std::filesystem::create_hard_link - std::filesystem::create_hard_link

Synopsis
	  Defined in header <filesystem>
	  void create_hard_link( const std::filesystem::path& target,

	  const	std::filesystem::path& link );
	  void	create_hard_link( const	std::filesystem::path& target,	(since
       C++17)
	  const	std::filesystem::path& link,

	  std::error_code& ec )	noexcept;

	  Creates a hard link link with	its target set	to  target  as	if  by
       POSIX link(): the
	  pathname target must exist.

	  Once	created,  link	and target are two logical names that refer to
       the same	file
	  (they	are equivalent). Even if the original name target is  deleted,
       the file
	  continues to exist and is accessible as link.

Parameters
	  target - path	of the file or directory to link to
	  link	 - path	of the new hard	link
	  ec	 - out-parameter for error reporting in	the non-throwing over-
       load

Return value
	  (none)

Exceptions
	  The overload that does not take a std::error_code& parameter throws
	  filesystem::filesystem_error	on  underlying	OS  API	 errors,  con-
       structed	with target as
	  the first path argument, link	as the second path argument,  and  the
       OS error	code as
	  the  error code argument. The	overload taking	a std::error_code& pa-
       rameter sets it to
	  the OS API error  code  if  an  OS  API  call	 fails,	 and  executes
       ec.clear() if no	errors
	  occur.  Any overload not marked noexcept may throw std::bad_alloc if
       memory
	  allocation fails.

Notes
	  Some operating systems do not	support	hard links at all  or  support
       them only for
	  regular files.

	  Some	file systems do	not support hard links regardless of the oper-
       ating system: the
	  FAT file system used on memory cards and flash drives, for example.

	  Some file systems limit the number of	links per file.

	  Hardlinking to directories is	typically restricted to	the superuser.

	  Hard links typically cannot cross filesystem boundaries.

	  The special pathname dot (".") is a hard link	to its	parent	direc-
       tory. The special
	  pathname  dot-dot  ".."  is a	hard link to the directory that	is the
       parent of its
	  parent.

Example
       // Run this code

	#include <iostream>
	#include <fstream>
	#include <filesystem>
	namespace fs = std::filesystem;

	int main()
	{
	    fs::create_directories("sandbox/subdir");
	    std::ofstream("sandbox/a").put('a'); // create regular file
	    fs::create_hard_link("sandbox/a", "sandbox/b");
	    fs::remove("sandbox/a");
	    // read from the original file via surviving hard link
	    char c = std::ifstream("sandbox/b").get();
	    std::cout << c << '\n';
	    fs::remove_all("sandbox");
	}

Output:
	a

See also
	  create_symlink
	  create_directory_symlink creates a symbolic link
	  (C++17)		   (function)
	  (C++17)
	  hard_link_count	   returns the number of hard links  referring
       to the specific
	  (C++17)		   file
				   (function)

http://cppreference.com		  2022.07.31	 std::filesy...te_hard_link(3)

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