Registry Functions

The registry is a hierarchical database used by Microsoft Windows to store configuration settings for the operating system, hardware, and applications.

Overview

Registry functions allow applications to create, delete, query, and modify registry keys and values. These functions are part of the Windows API and are typically accessed using C or C++.

Note: Direct manipulation of the registry can be dangerous if not done correctly. Always ensure you have proper error handling and understand the implications of your changes.

Key Registry Functions

Accessing and Querying Keys

`RegOpenKeyEx`

Opens an existing registry key. If the key does not exist, the function fails. This is often the first step before performing other operations on a key.

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

Parameters:

Name	Type	Description
`hKey`	`HKEY`	A handle to an open registry key. Typically one of the predefined keys (e.g., `HKEY_CLASSES_ROOT`).
`lpSubKey`	`LPCTSTR`	The name of the subkey to open.
`ulOptions`	`DWORD`	Reserved; must be zero.
`samDesired`	`REGSAM`	An access mask that specifies the desired access rights to the key. Common values include `KEY_READ`, `KEY_WRITE`, `KEY_ALL_ACCESS`.
`phkResult`	`PHKEY`	A pointer to a variable that receives the handle to the opened key.

Return Value:

If the function succeeds, the return value is ERROR_SUCCESS. Otherwise, the return value is a system error code.

`RegQueryValueEx`

Retrieves the data and type of a specified registry value. Used to read the data associated with a specific value within a registry key.

LONG RegQueryValueEx(
        HKEY hKey,
        LPCTSTR lpValueName,
        LPDWORD lpReserved,
        LPDWORD lpType,
        LPBYTE lpData,
        LPDWORD lpcbData
    );

Parameters:

Name	Type	Description
`hKey`	`HKEY`	A handle to an open registry key.
`lpValueName`	`LPCTSTR`	The name of the registry value to query.
`lpReserved`	`LPDWORD`	Reserved; must be `NULL`.
`lpType`	`LPDWORD`	A pointer to a variable that receives the type of the value.
`lpData`	`LPBYTE`	A pointer to a buffer that receives the value's data.
`lpcbData`	`LPDWORD`	A pointer to a variable that specifies the size, in bytes, of the buffer pointed to by `lpData`.

Return Value:

If the function succeeds, the return value is ERROR_SUCCESS. Otherwise, the return value is a system error code.

Modifying and Creating Keys

`RegCreateKeyEx`

Creates a new registry key or opens an existing one. This function provides more control than RegCreateKey, allowing specification of security attributes and key state.

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

Parameters:

Name	Type	Description
`hKey`	`HKEY`	A handle to an open registry key.
`lpSubKey`	`LPCTSTR`	The name of the subkey to create or open.
`Reserved`	`DWORD`	Reserved; must be zero.
`lpClass`	`LPCTSTR`	The user-defined class type of the key. Can be `NULL`.
`dwOptions`	`DWORD`	Special options for the key. E.g., `REG_OPTION_VOLATILE`.
`samDesired`	`REGSAM`	An access mask specifying the desired access rights.
`lpSecurityAttributes`	`LPSECURITY_ATTRIBUTES`	Security attributes for the key. Can be `NULL`.
`phkResult`	`PHKEY`	Pointer to the handle of the new or opened key.
`lpDisposition`	`LPDWORD`	Receives information about whether the key was created or opened.

Return Value:

If the function succeeds, the return value is ERROR_SUCCESS. Otherwise, the return value is a system error code.

`RegSetValueEx`

Creates or updates a registry value. This function allows you to set the data and type for a registry value.

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

Parameters:

Name	Type	Description
`hKey`	`HKEY`	A handle to an open registry key.
`lpValueName`	`LPCTSTR`	The name of the registry value to set.
`Reserved`	`DWORD`	Reserved; must be zero.
`dwType`	`DWORD`	The type of data for the value. Common types include `REG_SZ`, `REG_DWORD`, `REG_BINARY`.
`lpData`	`const BYTE*`	A pointer to the buffer containing the data to be stored.
`cbData`	`DWORD`	The size, in bytes, of the data pointed to by `lpData`.

Return Value:

If the function succeeds, the return value is ERROR_SUCCESS. Otherwise, the return value is a system error code.

Deleting Keys and Values

`RegDeleteKeyEx`

Deletes a subkey and its entries from the registry. This function can only delete keys that have no subkeys.

LONG RegDeleteKeyEx(
        HKEY hKey,
        LPCTSTR lpSubKey,
        REGSAM samDesired,
        DWORD Reserved
    );

Parameters:

Name	Type	Description
`hKey`	`HKEY`	A handle to an open registry key.
`lpSubKey`	`LPCTSTR`	The name of the subkey to delete.
`samDesired`	`REGSAM`	An access mask that specifies the desired access rights to the key.
`Reserved`	`DWORD`	Reserved; must be zero.

Return Value:

If the function succeeds, the return value is ERROR_SUCCESS. Otherwise, the return value is a system error code.

`RegDeleteValue`

Deletes a registry value from a registry key.

LONG RegDeleteValue(
        HKEY hKey,
        LPCTSTR lpValueName
    );

Parameters:

Name	Type	Description
`hKey`	`HKEY`	A handle to an open registry key.
`lpValueName`	`LPCTSTR`	The name of the registry value to delete.

Return Value:

If the function succeeds, the return value is ERROR_SUCCESS. Otherwise, the return value is a system error code.

Closing Registry Keys

`RegCloseKey`

Closes a handle to an open registry key. It is important to close keys when you are finished with them to free system resources.

LONG RegCloseKey(
        HKEY hKey
    );

Parameters:

Name	Type	Description
`hKey`	`HKEY`	A handle to the registry key to close.

Return Value:

If the function succeeds, the return value is ERROR_SUCCESS. Otherwise, the return value is a system error code.

Always call RegCloseKey on handles returned by functions like RegOpenKeyEx and RegCreateKeyEx to prevent resource leaks.