CreateHardLink Function (Windows)

CreateHardLink Function

CreateHardLink Function

Establishes a hard link between an existing file and a new file. This function is only supported on the NTFS file system, and only for files, not directories.

To perform this operation as a transacted operation, use the CreateHardLinkTransacted function.

Syntax

C++

BOOL WINAPI CreateHardLink(
  __in        LPCTSTR lpFileName,
  __in        LPCTSTR lpExistingFileName,
  __reserved  LPSECURITY_ATTRIBUTES lpSecurityAttributes
);

Parameters

lpFileName [in]

The name of the new file.

This parameter cannot specify the name of a directory.

lpExistingFileName [in]

The name of the existing file.

This parameter cannot specify the name of a directory.

lpSecurityAttributes

Reserved; must be NULL.

Return Value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero (0). To get extended error information, call GetLastError.

The maximum number of hard links that can be created with this function is 1023 per file. If more than 1023 links are created for a file, an error results.

Remarks

Any directory entry for a file that is created with CreateFile or CreateHardLink is a hard link to an associated file. An additional hard link that is created with the CreateHardLink function allows you to have multiple directory entries for a file, that is, multiple hard links to the same file, which can be different names in the same directory, or the same or different names in different directories. However, all hard links to a file must be on the same volume.

Because hard links are only directory entries for a file, many changes to that file are instantly visible to applications that access it through the hard links that reference it. However, the directory entry size and attribute information is updated only for the link through which the change was made.

The security descriptor belongs to the file to which a hard link points. The link itself is only a directory entry, and does not have a security descriptor. Therefore, when you change the security descriptor of a hard link, you a change the security descriptor of the underlying file, and all hard links that point to the file allow the newly specified access. You cannot give a file different security descriptors on a per-hard-link basis.

This function does not modify the security descriptor of the file to be linked to, even if security descriptor information is passed in the lpSecurityAttributes parameter.

Use DeleteFile to delete hard links. You can delete them in any order regardless of the order in which they are created.

Flags, attributes, access, and sharing that are specified in CreateFile operate on a per-file basis. That is, if you open a file that does not allow sharing, another application cannot share the file by creating a new hard link to the file.

When you create a hard link on the NTFS file system, the file attribute information in the directory entry is refreshed only when the file is opened, or when GetFileInformationByHandle is called with the handle of a specific file.

To compile an application that uses this function, define the _WIN32_WINNT macro as 0x0500 or later. For more information, see Using the Windows Headers.

Symbolic link behavior—If the path points to a symbolic link, the function creates a hard link to the target.

Examples

The following code snippet shows you how to call CreateHardLink so that it does not modify the security descriptor of a file. The pszExistingFileName parameter can be the original file name, or any existing link to a file. After this code is executed, pszNewLinkName refers to the file.

	BOOL fCreatedLink = CreateHardLink( pszNewLinkName, 
								        pszExistingFileName, 
								        NULL // reserved, must be NULL
                                      ); 
	if ( fCreatedLink == FALSE )
    {
        ;// handle error condition
    }

Requirements