How to Open, Create, and Close Registry Keys

How to Open, Create, and Close Registry Keys?

Before an application can add data to the registry, it must create or open a key.

Note: Incorrectly editing the registry may severely damage your system. Before making changes to the registry, you should back up any valued data on your computer including your registry (See, How to backup Registry?).

To create or open a key, an application always refers to the key as a subkey of a currently open key (See, How to Fix application path problems?). The following predefined keys are always open: HKEY_LOCAL_MACHINE, HKEY_CLASSES_ROOT, HKEY_USERS, and HKEY_CURRENT_USER.

Opening, Creating, and Closing Keys

An application uses the RegOpenKeyEx function to open a key and the RegCreateKeyEx function to create a key. A registry tree can be 512 levels deep. You can create up to 32 levels at a time through a single registry API call.

An application can use the RegCloseKey function to close a key and write the data it contains into the registry. RegCloseKey does not necessarily write the data to the registry before returning; it can take as much as several seconds for the cache to be flushed to the hard disk. If an application must explicitly write registry data to the hard disk, it can use the RegFlushKey function. RegFlushKey, however, uses many system resources and should be called only when absolutely necessary.

RegOpenKeyEx Function - Opens the specified registry key. Note that key names are not case sensitive.

RegCreateKeyEx Function - Creates the specified registry key. If the key already exists, the function opens it. Note that key names are not case sensitive.

RegCloseKey Function - Closes a handle to the specified registry key.

RegFlushKey Function - Writes all the attributes of the specified open registry key into the registry.

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