Registry API Reference

This section provides detailed documentation for the Windows Registry API, which allows applications to access and manipulate the system's registry. The registry is a hierarchical database that stores configuration settings and options for the operating system, hardware, and applications.

Overview

The Windows Registry is organized as a tree of keys and values. Each key can contain subkeys and values, similar to a file system. Applications can use the registry API to:

  • Create, open, and close registry keys.
  • Set, retrieve, and delete registry values.
  • Enumerate subkeys and values within a key.
  • Manage security and permissions for registry keys.
Important: Incorrect manipulation of the registry can cause serious system instability or failure. Always exercise caution and back up the registry before making significant changes.

Key Functions

The following are some of the most commonly used functions for interacting with the Windows Registry:

Key Management

  • RegCreateKeyEx: Creates a new registry key or opens an existing one.
  • RegOpenKeyEx: Opens an existing registry key.
  • RegCloseKey: Closes an open registry key handle.
  • RegDeleteKeyEx: Deletes a registry key and its subkeys.
  • RegEnumKeyEx: Enumerates the subkeys of a registry key.

Value Management

  • RegSetValueEx: Sets the data and type for a specified registry value.
  • RegQueryValueEx: Retrieves the type and data for a specified registry value.
  • RegDeleteValue: Deletes a specified registry value.
  • RegEnumValue: Enumerates the values of a registry key.

Registry Hives and Root Keys

The registry is composed of several root keys, often referred to as hives. Common root keys include:

  • HKEY_CLASSES_ROOT: File associations and COM object information.
  • HKEY_CURRENT_USER: User-specific settings for the currently logged-in user.
  • HKEY_LOCAL_MACHINE: System-wide hardware and software configuration.
  • HKEY_USERS: Settings for all user profiles on the system.
  • HKEY_CURRENT_CONFIG: Hardware profile information for the system.

Example Usage

Here's a basic C++ example demonstrating how to create a registry key and set a string value:


#include <windows.h>
#include <iostream>

int main() {
    HKEY hKey;
    DWORD dwDisposition;
    LPCWSTR subKeyPath = L"Software\\MyApplication\\Settings";
    LPCWSTR valueName = L"DefaultPath";
    WCHAR valueData[] = L"C:\\Program Files\\MyApplication\\Data";

    LONG result = RegCreateKeyExW(
        HKEY_CURRENT_USER,
        subKeyPath,
        0,
        NULL,
        REG_OPTION_NON_VOLATILE,
        KEY_WRITE,
        NULL,
        &hKey,
        &dwDisposition
    );

    if (result == ERROR_SUCCESS) {
        result = RegSetValueExW(
            hKey,
            valueName,
            0,
            REG_SZ,
            (LPBYTE)valueData,
            sizeof(valueData)
        );

        if (result == ERROR_SUCCESS) {
            std::wcout << L"Registry value '" << valueName << L"' set successfully." << std::endl;
        } else {
            std::wcerr << L"Failed to set registry value. Error code: " << result << std::endl;
        }
        RegCloseKey(hKey);
    } else {
        std::wcerr << L"Failed to create or open registry key. Error code: " << result << std::endl;
    }

    return 0;
}
Tip: For managing complex registry settings, consider using the Windows Registry Editor (regedit.exe) to explore existing keys and values.

Further Reading