In previous part of this article we learned how we can read a value from windows registry. In this part of article we will see how we can write or update setting values from registry database. Following functions are sample codes for writing and updating a value in windows registry from a global character string  variable "gSerial". void UpdateSerKey() { TRegistry *Reg = new TRegistry(); AnsiString temp; Reg->RootKey = HKEY_LOCAL_MACHINE; if(Reg->KeyExists("SOFTWARE\\TestSoftware")) { try { if(Reg->OpenKey("Software\\TestSoftware",FALSE)) { Reg->WriteString("SERIAL",gSerial); Reg->CloseKey(); } else ShowMessage("Can not open program serial key ."); Reg->CloseKey(); } catch(ERegistryException &E) { ShowMessage(E.Message); delete Reg; return; } } delete Reg; } void MakeSerKey() { TRegistry *Reg = new TRegistry(); AnsiString temp; Reg->RootKey = HKEY_LOCAL_MACHINE; if(!Reg->KeyExists("SOFTWARE\\TestSoftware")) { if(!Reg->CreateKey("Software\\TestSoftware")) { Application->MessageBox ("Can not Make Serial Key","Error",MB_OK); return; } try { if(Reg->OpenKey("Software\\TestSoftware",FALSE)) { Reg->WriteString("SERIAL",gSerial); Reg->CloseKey(); } else ShowMessage("Registry RootDir error"); Reg->CloseKey(); } catch(ERegistryException &E) { ShowMessage(E.Message); delete Reg; return; } } delete Reg; } 1- First of all we must create a Registry object in memory  using "new" command. 2- Registry database has five root keys. Five trees grow  from these five root keys. Root keys are: HKEY_CLASSES_ROOT HKEY_CURRENT_USER HKEY_LOCAL_MACHINE HKEY_USERS HKEY_CURRENT_CONFIG Before starting to work we must determine one of root keys  as starting point for the tree that our key is on it. In  this example our key is located on HKEY_LOCAL_MACHINE. Complete address of our key is:  HKEY_LOCAL_MACHINE\Software\TestSoftware  i.e. our key is TestSoftware. We have chosen the name  exactly as our software name. This will ease finding the  key. 3-Now we test to see if the key we want to write a value  inside it exists. If the key exists we start writing or updating setting values, otherwise we delete registry  object we created when starting this function and leave the function. This is done using "exists" method of  registry object. 4- if the key exists we can open. We use try...catch to  prevent exceptions. We can open the key using "OpenKey"  method of registry object. 5- If opening the key was successful then we can use  "WriteString" method of registry object to write the value  "SERIAL" to registry key. 6- After all we will close the key. And before exit we must  delete registry key.  If you have any question about this article you can post your message in our message boards. http://op.htmsoft.com/forums/