Reading and Writing the Registry in .NET

• By Scott Loban
• May 24, 2002
• Article is provided courtesy of New Riders

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This article introduces the classes and syntax used to store and retrieve information from the Windows Registry. Before proceeding, please note that a damaged Registry can make applications—or even the entire computer system—unstable or completely unusable. Before attempting to programmatically read or write the Registry, back up the system state, ensuring that you have a way to restore an unbootable system.

Windows Registry

The Windows Registry is a data repository that exists on each computer in Windows 95 and later systems. Both the system and application programs use this repository to store information needed at runtime. For example, the system stores file associations (the applications or command lines associated with each known file extension) in the Registry. Applications often use the Registry to store information such as users' option settings and data file pathnames.

The system reads the Registry into memory at bootup. This memory image then serves as a working copy for the system. When the system is shut down, it persists the current Registry to disk. The Registry is stored in several files. The location and organization of these files depends on the version of Windows. For example, in Windows 2000, the Registry is stored in a number of files located in the \%SystemRoot%\System32\Config folder, whereas in Windows 95, the Registry is contained in user.dat and system.dat, which are hidden system files in the Windows folder. In all cases, these files must not be edited directly. Changes to the Registry can be made only programmatically or by using a special Registry editor application.

Structure of the Registry

The Registry has a hierarchical structure, like the folders on a disk volume. The root is not used directly, but instead holds six top-level branches, or hives. The hives are HKEY_CLASSES_ROOT, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, HKEY_USERS, HKEY_CURRENT_CONFIG, and HKEY_DYN_DATA. These hives are described in Table 1.

Table 1—Registry Hives

Each hive contains a number of keys (see Figure 1). Registry keys are the basic data structure for the Registry. A Registry key acts like a subfolder, holding additional levels of subkeys, as well as values—name/value pairs that are used to hold the actual information.

Figure 1 The organization of the Registry.

Registry Data Types

The data that is stored in a Registry value can be represented by one of a number of data types. The most common are number, text string, and direct binary data. These are implemented through five data types: REG_DWORD, REG_BINARY, REG_SZ, REG_MULTI_SZ, or REG_EXPAND_SZ. These data types are described further in Table 2.

Table 2—Registry Data Types