Windows Registry Reference

The Windows Registry is a hierarchical database that stores low-level settings for the Microsoft Windows operating system and for applications that opt to use the registry. It contains information such as user profiles, installed hardware, software configuration, and operating system settings.

This section provides detailed documentation for the Core APIs related to interacting with the Windows Registry. These APIs allow developers to programmatically read, write, and manage registry keys and values.

Key Registry Functions

`RegOpenKeyEx()`

Opens an existing key in the registry. If the key is not in the current computer's registry, the function supplies the information for the non-existent key.

Syntax:

LONG RegOpenKeyEx(
  HKEY hKey,
  LPCSTR lpSubKey,
  DWORD ulOptions,
  REGSAM samDesired,
  PHKEY phkResult
);

Parameters:

Name	Type	Description
`hKey`	`HKEY`	A handle to an open key in the registry.
`lpSubKey`	`LPCSTR`	The name of the subkey to open.
`ulOptions`	`DWORD`	This parameter is reserved and must be zero.
`samDesired`	`REGSAM`	A bitmask that specifies the desired access rights to the key.
`phkResult`	`PHKEY`	A pointer to a variable that receives a handle to the opened key.

Return Value:

`LONG`

If the function succeeds, the return value is ERROR_SUCCESS. If the function fails, the return value is a system-defined error code.

`RegCreateKeyEx()`

Creates the specified registry key. If the key already exists, the function opens it and returns a handle to it. The key is created under the parent key indicated by the hKey parameter.

Syntax:

LONG RegCreateKeyEx(
  HKEY hKey,
  LPCSTR lpSubKey,
  DWORD Reserved,
  LPSTR lpClass,
  DWORD dwOptions,
  REGSAM samDesired,
  LPSECURITY_ATTRIBUTES lpSecurityAttributes,
  PHKEY phkResult,
  LPDWORD lpDisposition
);

Parameters:

Name	Type	Description
`hKey`	`HKEY`	A handle to an open key in the registry.
`lpSubKey`	`LPCSTR`	The name of the subkey to create or open.
`Reserved`	`DWORD`	This parameter is reserved and must be zero.
`lpClass`	`LPSTR`	The user-defined class type of the key being created.
`dwOptions`	`DWORD`	Specifies the options for the key.
`samDesired`	`REGSAM`	A bitmask that specifies the desired access rights to the key.
`lpSecurityAttributes`	`LPSECURITY_ATTRIBUTES`	A pointer to a SECURITY_ATTRIBUTES structure.
`phkResult`	`PHKEY`	A pointer to a variable that receives a handle to the opened or created key.
`lpDisposition`	`LPDWORD`	A pointer to a variable that receives a value indicating whether the key was created or opened.

Return Value:

`LONG`

If the function succeeds, the return value is ERROR_SUCCESS. If the function fails, the return value is a system-defined error code.

`RegSetValueEx()`

Sets the data for a specified registry value under an open key.

Syntax:

LONG RegSetValueEx(
  HKEY hKey,
  LPCSTR lpValueName,
  DWORD Reserved,
  DWORD Type,
  const BYTE* lpData,
  DWORD cbData
);

Parameters:

Name	Type	Description
`hKey`	`HKEY`	A handle to an open key in the registry.
`lpValueName`	`LPCSTR`	The name of the registry value to set.
`Reserved`	`DWORD`	This parameter is reserved and must be zero.
`Type`	`DWORD`	The type of data to be stored.
`lpData`	`const BYTE*`	A pointer to the buffer that contains the data to be stored.
`cbData`	`DWORD`	The size, in bytes, of the data.

Return Value:

`LONG`

If the function succeeds, the return value is ERROR_SUCCESS. If the function fails, the return value is a system-defined error code.

`RegGetValue()`

Retrieves the type and data for the specified registry value. This function supports local and remote retrieval of registry values.

Syntax:

LONG RegGetValue(
  HKEY hkey,
  PCSTR lpSubKey,
  PCSTR lpValue,
  DWORD dwFlags,
  LPDWORD pdwType,
  PVOID pvData,
  LPDWORD pcbData
);

Parameters:

Name	Type	Description
`hkey`	`HKEY`	A handle to an open key in the registry, or any of the predefined HKEY_ constants.
`lpSubKey`	`PCSTR`	The path to the subkey that contains the value.
`lpValue`	`PCSTR`	The name of the value to retrieve.
`dwFlags`	`DWORD`	Flags that specify how the data is to be read.
`pdwType`	`LPDWORD`	A pointer to a variable that receives the type of the data.
`pvData`	`PVOID`	A pointer to a buffer that receives the value's data.
`pcbData`	`LPDWORD`	A pointer to a variable that receives the size of the data.

Return Value:

`LONG`

If the function succeeds, the return value is ERROR_SUCCESS. If the function fails, the return value is a system-defined error code.

Important Considerations

Registry operations can have a significant impact on system stability. Always ensure you have proper error handling and understand the implications of modifying registry values. Back up the registry before making critical changes.

Registry Data Types

The Windows Registry supports various data types. Common types include:

REG_SZ: A null-terminated string.
REG_DWORD: A 32-bit unsigned integer.
REG_BINARY: Binary data.
REG_MULTI_SZ: An array of null-terminated strings, terminated by two null characters.
REG_EXPAND_SZ: A null-terminated string that contains unexpanded references to environment variables.

For a complete list of registry data types and more advanced registry operations, please refer to the Advanced Registry Operations page.