Mega Code Archive
Hardlinks and Shortcuts
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Title: Hardlinks and Shortcuts
Question: How do you create Hardlinks and Shortcuts ? What is the difference between both ?
Answer:
Shortcuts or *.lnk files are usually found on desktops
and are useful to reference something else. But they
have a drawback: the target object of a shortcut may
change over time. If it is moved, deleted, or simply
renamed, the shortcut becomes invalid.
Since Windows 2000, Hardlinks are available. Hardlinks
are capable of adapting themselves to these changes,
due to some form of inner magic of the NFTS file system.
If the original target object is moved, deleted or renamed,
the hardlink is still valid.
Hardlinks look like a true copy of the file, but the necessary
disk space is allocated only once. They are useful if you
have to copy a large part of a huge number of files without
allocation of further disk space.
It is easy to create Hardlinks. In the Command Shell
("DOS-Box") you can use the fsutil command :
fsutil hardlink create Hardlink_FileName Existing_FileName
In a Delphi application, you can call directly the
API function CreateHardLink(). The function CreateHardLink
can be found in kernel32.dll (for Windows XP or Windows 2000)
and is already defined in Windows.pas as part of the Windows API.
function CreateHardLink(lpFileName, lpExistingFileName: PChar;
lpSecurityAttributes: PSecurityAttributes): BOOL; stdcall;
A simple example:
if CreateHardLink(PChar('C:\Data\Projects\HardLink\hardlink_1.png'),
PChar('C:\Data\Projects\HardLink\1.png'),
nil) then
ShowMessage('HardLink created');
Creating a shortcut is a bit more complicated and requires
in the Age of .NET still ugly COM programming:
uses ShlObj, ActiveX, ComObj;
procedure CreateShortCut(Filename,Arguments,TargetDir : string);
var
MyObject : IUnknown;
MySLink : IShellLink;
MyPFile : IPersistFile;
WFileName : WideString;
Filepath : string;
begin
Filepath := ExtractFilePath(Filename);
Filename := ExtractFileName(Filename);
MyObject := CreateComObject(CLSID_ShellLink);
MySLink := MyObject as IShellLink;
MyPFile := MyObject as IPersistFile;
with MySLink do
begin
SetArguments(PChar(Arguments));
SetPath(PChar(IncludeTrailingPathDelimiter(Filepath) + Filename));
SetWorkingDirectory(PChar(FilePath));
end;
Filename:=ChangeFileExt(Filename,'.lnk');
WFileName := IncludeTrailingPathDelimiter(TargetDir) + Filename;
MyPFile.Save(PWChar(WFileName), False);
end;
Reference:
A Programmer's Perspective on NTFS 2000 Part 1: Stream and Hard Link
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnfiles/html/ntfs5.asp
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