rust-loadlibrary.rs

use std::ffi::c_void;
use std::ptr;

type Error = u32;
type FnMessageBox = extern "stdcall" fn(hWnd: *const c_void, lpText: *const u16, lpCaption: *const u16, uType: u32) -> i32;

#[link(name = "kernel32")]
#[no_mangle]
extern "stdcall" {
    fn GetLastError() -> Error;
    fn LoadLibraryExW(lpLibFileName: *const u16, hFile: *const c_void, dwFlags: u32) -> *const c_void;
    fn FreeLibrary(hLibModule: *const c_void) -> i32;
    fn GetProcAddress(hModule: *const c_void, lpProcName: *const u8) -> *const c_void;
}

fn main() {
    unsafe {
        let h = LoadLibraryExW("user32.dll".to_nullterminated_u16().as_ptr(),
                               ptr::null(),
                               0x800).to_result().unwrap();

        let p = GetProcAddress(h, "MessageBoxW\0".as_ptr()).to_result().unwrap();
        let fn_message_box = std::mem::transmute::<_, FnMessageBox>(p);

        fn_message_box(ptr::null(),
                       "Hello, Rust!".to_nullterminated_u16().as_ptr(),
                       "MessageBox".to_nullterminated_u16().as_ptr(),
                       0);

        FreeLibrary(h);
    }
}


trait ToResult: Sized {
    fn to_result(&self) -> Result<Self, Error>;
}

impl ToResult for *const c_void {
    fn to_result(&self) -> Result<*const c_void, Error> {
        if *self == ptr::null() {
            unsafe {
                Err(GetLastError())
            }
        } else {
            Ok(*self)
        }
    }
}

trait IntoNullTerminatedU16 {
    fn to_nullterminated_u16(&self) -> Vec<u16>;
}

impl IntoNullTerminatedU16 for str {
    fn to_nullterminated_u16(&self) -> Vec<u16> {
        self.encode_utf16().chain(Some(0)).collect()
    }
}