Attribute Macro windows_dll::dll

#[dll]

Dynamically load functions from a windows dll

Works on extern blocks containing only functions:

use windows_dll::dll;

#[dll("user32.dll")]
extern "system" {
    #[allow(non_snake_case)]
    fn SetWindowCompositionAttribute(h_wnd: HWND, data: *mut WINDOWCOMPOSITIONATTRIBDATA) -> BOOL;
}

The .dll file extension can be omitted if the dll name has no path:

use windows_dll::dll;

#[dll("user32")]
extern "system" {
    // ...
}

if the dll name is a valid rust identifier, you can also omit the quotes:

use windows_dll::dll;

#[dll(user32)]
extern "system" {
    // ...
}

For each function declaration, an unsafe rust wrapper function will be generated which dynamically loads the original function from the dll.

Rename

If you need to give the rust function a different name you can manually specify the dll symbol to load, Just put the dll symbol name in a #[link_name] attribute:

use windows_dll::dll;

#[dll(user32)]
extern "system" {
    #[link_name = "SetWindowCompositionAttribute"]
    fn set_window_composition_attribute(h_wnd: HWND, data: *mut WINDOWCOMPOSITIONATTRIBDATA) -> BOOL;
}

Ordinal exports

If you need to load a function that is exported by ordinal you can put the ordinal in a #[link_ordinal] attribute:

use windows_dll::dll;

#[dll(uxtheme)]
extern "system" {
    #[link_ordinal = 133]
    fn allow_dark_mode_for_window(hwnd: HWND, allow: BOOL) -> BOOL;
}

Error handling

By default the generated functions panic when the dll function cannot be loaded you can check if they exist by calling function_name::exists() which returns a bool:

unsafe {
    if allow_dark_mode_for_window::exists() {
        allow_dark_mode_for_window(hwnd, allow);
    }
}

You can also generate a wrapper function which returns a Result<T, windows_dll::Error<function_name>> To better integrate with the ? operator, Just put a #[fallible] attribute on the function declaration:

use std::error::Error;
use windows_dll::dll;

#[dll(user32)]
extern "system" {
    #[allow(non_snake_case)]
    #[fallible]
    fn SetWindowCompositionAttribute(h_wnd: HWND, data: *mut WINDOWCOMPOSITIONATTRIBDATA) -> BOOL;
}
fn main() -> Result<(), Box<dyn Error>> {
    // ...
    let result: Result<BOOL, windows_dll::Error<SetWindowCompositionAttribute>> = unsafe { SetWindowCompositionAttribute(hwnd, &mut data) };
    let result = result?;
    // ...
}

LoadLibraryExW flags

This library uses the Win32 API function LoadLibraryExW internally. You can pass flags to the dwFlags parameter by passing a second argument to the #[dll] attribute:

use windows_dll::{dll, flags::*};

#[dll(bcrypt, LOAD_LIBRARY_SEARCH_SYSTEM32)]
extern "system" {
    #[link_name = "BCryptAddContextFunction"]
    fn bcrypt_add_context_function(dw_table: ULONG, psz_context: LPCWSTR, dw_interface: ULONG, psz_function: LPCWSTR, dw_position: ULONG) -> BOOL;
}

Available flags are re-exported from the flags module