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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,  (1)
       (since C++17)
				 const std::filesystem::path& link );
	  void create_hard_link( const std::filesystem::path& target,

				 const	std::filesystem::path&	 link,	   (2)
       (since C++17)

				 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
	  Any overload not marked noexcept may throw std::bad_alloc if	memory
       allocation
	  fails.

	  1) Throws std::filesystem::filesystem_error on underlying OS API er-
       rors, constructed
	  with	target as the first path argument, link	as the second path ar-
       gument, and the OS
	  error	code as	the error code argument.
	  2) Sets a std::error_code& parameter to the OS API error code	if  an
       OS API call
	  fails, and executes ec.clear() if no errors occur.

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 <filesystem>
	#include <fstream>
	#include <iostream>
	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		  2024.06.10	 std::filesy...te_hard_link(3)

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