#[ctor]
Expand description
Marks a function or static variable as a library/executable constructor. This uses OS-specific linker sections to call a specific function at load time.
Multiple startup functions/statics are supported, but the invocation order is not guaranteed.
Examples
Print a startup message:
#[ctor]
fn foo() {
println!("Hello, world!");
}
println!("main()");
Make changes to static
variables:
static INITED: AtomicBool = AtomicBool::new(false);
#[ctor]
fn foo() {
INITED.store(true, Ordering::SeqCst);
}
Initialize a HashMap
at startup time:
#[ctor]
static STATIC_CTOR: HashMap<u32, String> = {
let mut m = HashMap::new();
for i in 0..100 {
m.insert(i, format!("x*100={}", i*100));
}
m
};
Details
The #[ctor]
macro makes use of linker sections to ensure that a
function is run at startup time.
The above example translates into the following Rust code (approximately):
#[used]
#[cfg_attr(any(target_os = "linux", target_os = "android"), link_section = ".init_array")]
#[cfg_attr(target_os = "freebsd", link_section = ".init_array")]
#[cfg_attr(target_os = "netbsd", link_section = ".init_array")]
#[cfg_attr(target_os = "openbsd", link_section = ".init_array")]
#[cfg_attr(target_os = "illumos", link_section = ".init_array")]
#[cfg_attr(any(target_os = "macos", target_os = "ios"), link_section = "__DATA,__mod_init_func")]
#[cfg_attr(target_os = "windows", link_section = ".CRT$XCU")]
static FOO: extern fn() = {
#[cfg_attr(any(target_os = "linux", target_os = "android"), link_section = ".text.startup")]
extern fn foo() { /* ... */ };
foo
};