Winreg

Opening keys:

use winreg::enums::*;
use winreg::{HKCU, HKLM};

// Open with KEY_READ (default)
let key = HKCU.open_subkey("Software\\MyProduct")?;

// Open with custom permissions
let key = HKLM.open_subkey_with_flags("SOFTWARE\\Microsoft", KEY_READ)?;

Creating keys:

let (key, disp) = HKCU.create_subkey("Software\\MyProduct\\Settings")?;
match disp {
    REG_CREATED_NEW_KEY => println!("Created new key"),
    REG_OPENED_EXISTING_KEY => println!("Opened existing key"),
}

Reading values:

let server: String = key.get_value("Server")?;
let port: u32 = key.get_value("Port")?;
let raw: RegValue = key.get_raw_value("Data")?;

Writing values:

key.set_value("Server", &"example.com")?;
key.set_value("Port", &8080u32)?;
key.set_raw_value("Data", &RegValue { vtype: REG_BINARY, bytes: vec![1,2,3].into() })?;

Iterating:

for name in key.enum_keys().map(|x| x.unwrap()) {
    println!("Subkey: {}", name);
}
for (name, value) in key.enum_values().map(|x| x.unwrap()) {
    println!("{} = {:?}", name, value);
}

Deleting:

key.delete_value("OldValue")?;
HKCU.delete_subkey("Software\\MyProduct\\OldSubkey")?;
HKCU.delete_subkey_all("Software\\MyProduct")?;  // recursive

RegValue

Raw registry value with vtype: RegType and bytes: Cow<[u8]>.

RegKeyMetadata

Returned by key.query_info(). Contains subkey/value counts and last write time.

Predefined Keys

HKCR, HKCU, HKLM, HKU, HKCC — shorthand constants for RegKey::predef(HKEY_*).

Enums (winreg::enums)

RegDisposition

• REG_CREATED_NEW_KEY — key was created
• REG_OPENED_EXISTING_KEY — key already existed

RegType

Registry value types: REG_SZ, REG_DWORD, REG_QWORD, REG_BINARY, REG_MULTI_SZ, REG_EXPAND_SZ, etc.

Permission Flags

Common Patterns

Read system info:

let cur_ver = HKLM.open_subkey("SOFTWARE\\Microsoft\\Windows\\CurrentVersion")?;
let program_files: String = cur_ver.get_value("ProgramFilesDir")?;

Check key disposition:

let (_key, disp) = HKCU.create_subkey("Software\\MyApp")?;
if disp == REG_CREATED_NEW_KEY { /* first run */ }

Multi-string values:

key.set_value("Paths", &vec!["C:\\a", "C:\\b"])?;
let paths: Vec<String> = key.get_value("Paths")?;

Serde serialization (feature serialization-serde):

use serde_derive::{Serialize, Deserialize};

#[derive(Serialize, Deserialize)]
struct Settings { width: u32, height: u32 }

let s = Settings { width: 800, height: 600 };
key.encode(&s)?;               // preserve existing subkeys
key.encode_destructive(&s)?;   // wipe before writing
let loaded: Settings = key.decode()?;

Error Handling

All methods return io::Result<T>. Common errors:

• NotFound — key or value does not exist
• PermissionDenied — insufficient registry permissions

Documentation

• docs.rs/winreg
• crates.io/winreg
• GitHub