Thursday, December 04, 2008

Accessing the Windows Registry

Source :


What is the Registry?

It is where Windows stores many of its configuration options and also allows applications to access this data as well as save their own data.

If you want to take a look at the registry, just execute the REGEDIT.EXE application located in the Windows directory. Be careful not to change anything or you could end up ruining your installation! Now, the data in the registry is stored in a tree structure. There are many roots (many trees):

Each root can have values and keys. The values are data stored under item names (right panel of RegEdit). Keys can have values and other keys, forming a tree structure (left panel of RegEdit).


The TRegistry class is declared in the Registry unit, so you will have to add this unit to the uses clause of the unit or program where you want to use it. To access a value in the registry first you should create an object of this class, assign the root to its RootKey property (the values are defined in the Windows unit) and then try to open a key with the OpenKey function method, which will return True if successful. Then you can read (with the ReadXxxx functions) or write (with the WriteXxxx procedures) the values of the open key and, after that, you should close the key with CloseKey. When you are done with the registry, you should free the registry object you created.

Let's see an example of how to obtain the name of the processor in our computer:

uses Registry, Windows, Dialogs;  procedure TForm1.Button1Click(Sender: TObject); begin   with TRegistry.Create do     try       RootKey := HKEY_LOCAL_MACHINE;       if OpenKey('\Hardware\Description\System'           + '\CentralProcessor\0', False) then begin         ShowMessage(ReadString('Identifier'));         CloseKey;       end;     finally       Free;     end; end;

You can see another example in the article Determining the associated application.

Of course, there are many more things you can do with the registry, like creating and deleting keys and values...

The TRegistryIniFile class makes it simpler for applications to write and read their configuration information to and from the registry, while TRegistry operates at a lower level.



To simplify reading a data value from the registry you can use the following function that can read any data type from the registry and returns it as a variant (string or integer). The function performs exception handling.

uses Registry, Windows, SysUtils;  function GetRegistryData(RootKey: HKEY; Key, Value: string): variant; var   Reg: TRegistry;   RegDataType: TRegDataType;   DataSize, Len: integer;   s: string; label cantread; begin   Reg := nil;   try     Reg := TRegistry.Create(KEY_QUERY_VALUE);     Reg.RootKey := RootKey;     if Reg.OpenKeyReadOnly(Key) then begin       try         RegDataType := Reg.GetDataType(Value);         if (RegDataType = rdString) or            (RegDataType = rdExpandString) then           Result := Reg.ReadString(Value)         else if RegDataType = rdInteger then           Result := Reg.ReadInteger(Value)         else if RegDataType = rdBinary then begin           DataSize := Reg.GetDataSize(Value);           if DataSize = -1 then goto cantread;           SetLength(s, DataSize);           Len := Reg.ReadBinaryData(Value, PChar(s)^, DataSize);           if Len <> DataSize then goto cantread;           Result := s;         end else cantread:           raise Exception.Create(SysErrorMessage(ERROR_CANTREAD));       except         s := ''; // Deallocates memory if allocated         Reg.CloseKey;         raise;       end;       Reg.CloseKey;     end else       raise Exception.Create(SysErrorMessage(GetLastError));   except     Reg.Free;     raise;   end;   Reg.Free; end;

Sample Call

ShowMessage(GetRegistryData(HKEY_LOCAL_MACHINE,   '\Hardware\Description\System\CentralProcessor\0', 'Identifier'));


To simplify writing a data value to the registry you can use the following procedure that can write any data type to the registry. The procedure performs exception handling.

uses Registry, Windows, SysUtils;  procedure SetRegistryData(RootKey: HKEY; Key, Value: string;   RegDataType: TRegDataType; Data: variant); var   Reg: TRegistry;   s: string; begin   Reg := TRegistry.Create(KEY_WRITE);   try     Reg.RootKey := RootKey;     if Reg.OpenKey(Key, True) then begin       try         if RegDataType = rdUnknown then           RegDataType := Reg.GetDataType(Value);         if RegDataType = rdString then           Reg.WriteString(Value, Data)         else if RegDataType = rdExpandString then           Reg.WriteExpandString(Value, Data)         else if RegDataType = rdInteger then           Reg.WriteInteger(Value, Data)         else if RegDataType = rdBinary then begin           s := Data;           Reg.WriteBinaryData(Value, PChar(s)^, Length(s));         end else           raise Exception.Create(SysErrorMessage(ERROR_CANTWRITE));       except         Reg.CloseKey;         raise;       end;       Reg.CloseKey;     end else       raise Exception.Create(SysErrorMessage(GetLastError));   finally     Reg.Free;   end; end;

Sample Call

SetRegistryData(HKEY_LOCAL_MACHINE,   '\Software\Microsoft\Windows\CurrentVersion',   'RegisteredOrganization', rdString, 'Latium Software');

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