Attribute Macro windows_dll::dll

#[dll]

Dynamically load functions from a windows dll

Works on extern blocks containing only functions, e.g:

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

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, e.g:

#[dll("user32.dll")]
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, e.g:

#[dll("uxtheme.dll")]
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, e.g:

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> To better integrate with the ? operator, Just put a #[fallible] attribute on the function declaration, e.g:

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