Cargo.toml

[dependencies.windows]
version = "0.52"
features = [
    "Win32_Foundation",
    "Win32_System_LibraryLoader",
]

main.rs

use windows::{core::*, Win32::Foundation::*, Win32::System::LibraryLoader::*};

pub unsafe fn delay_load<T>(library: PCSTR, function: PCSTR) -> Option<T> {
    let library = LoadLibraryExA(library, None, LOAD_LIBRARY_SEARCH_DEFAULT_DIRS);

    let Ok(library) = library else {
        return None;
    };

    let address = GetProcAddress(library, function);

    if address.is_some() {
        return Some(std::mem::transmute_copy(&address));
    }

    _ = FreeLibrary(library);
    None
}

fn main() {
    unsafe {
        if let Some(api) = delay_load::<ShellMessageBoxW>(s!("shlwapi.dll"), s!("ShellMessageBoxW"))
        {
            api(0, 0, w!("text"), w!("title"), 16384);
        } else {
            println!("Can't find API");
        }
    }
}

type ShellMessageBoxW = unsafe extern "cdecl" fn(
    happinst: usize,
    hwnd: usize,
    lpctext: PCWSTR,
    lpctitle: PCWSTR,
    fustyle: u32,
    ...
) -> i32;