std::filesystem::create_hard_link

Since C++17

Header: <filesystem>

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

# Declarations

void create_hard_link( const std::filesystem::path& target,
const std::filesystem::path& link );

(since C++17)

void create_hard_link( const std::filesystem::path& target,
const std::filesystem::path& link,
std::error_code& ec ) noexcept;

(since C++17)

# 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 overload

# Return value

(none)

# 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 operating 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 directory. The special pathname dot-dot “..” is a hard link to the directory that is the parent of its parent.

# Example

#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");
}