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

NAME
       std::experimental::filesystem::create_hard_link	  -    std::experimen-
       tal::filesystem::create_hard_link

Synopsis
	  Defined in header <experimental/filesystem>
	  void create_hard_link( const path& target, const path& link );
	  void	create_hard_link(  const  path&	 target,  const	 path&	 link,
       (filesystem TS)
	  error_code& ec );

	  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	error_code&  parameter	throws
       filesystem_error	on
	  underlying OS	API errors, constructed	with target as the first argu-
       ment, link as the
	  second  argument,  and the OS	error code as the error	code argument.
       std::bad_alloc
	  may be thrown	if memory allocation fails. The	overload taking	a  er-
       ror_code&
	  parameter  sets it to	the OS API error code if an OS API call	fails,
       and executes
	  ec.clear() if	no errors occur. This overload has
	  noexcept specification:
	  noexcept

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 <experimental/filesystem>
	namespace fs = std::experimental::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	   creates a symbolic link
	  create_directory_symlink (function)
				   returns the number of hard links  referring
       to the specific
	  hard_link_count	   file
				   (function)

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

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