# Crate Features
| `proc_macro` | Enable support for the proc-macro `#[dtor]` attribute. The declarative form (`dtor!(...)`) is always available. It is recommended that crates re-exporting the `dtor` macro disable this feature and only use the declarative form. |
| `std` | Enable support for the standard library. |
# Macro Attributes
<table><tr><th>Attribute</th><th>Description</th></tr>
<tr><td><code>anonymous</code></td><td>
Make the ctor function anonymous.
</td></tr>
<tr><td><code>crate_path = ::path::to::dtor::crate</code></td><td>
Specify a custom crate path for the `dtor` crate. Used when re-exporting the dtor macro.
</td></tr>
<tr><td><code>ctor(export_name_prefix = "ctor_")</code></td><td>
Specify a custom export name prefix for the constructor function.
If specified, an export with the given prefix will be generated in the form:
`<prefix>_<unique_id>`
</td></tr>
<tr><td><code>ctor(link_section = ".ctors")</code></td><td>
Place the initialization function pointer in a custom link section.
</td></tr>
<tr><td><code>export_name_prefix = "ctor_"</code></td><td>
Specify a custom export name prefix for the destructor function.
If specified, an export with the given prefix will be generated in the form:
`<prefix>_<unique_id>`
</td></tr>
<tr><td><code>link_section = ".dtors"</code></td><td>
Place the destructor function pointer in a custom link section.
</td></tr>
<tr><td><code>method = term|unload|at_module_exit|at_binary_exit|linker</code></td><td>
Specify the dtor method.
- `term`: Run the dtor on binary termination using the platform's
[default_term_method](#default_term_method). Not recommended as code
may be unloaded before the dtor is called.
- `unload`: Run the dtor on module unload (library or binary) using the
platform's [default_unload_method](#default_unload_method).
- `at_module_exit`: Run the dtor using the platform's
[`at_module_exit`][at_module_exit] (`__cxa_atexit` on all platforms
other than Windows, `atexit` on Windows).
- `at_binary_exit`: Run the dtor using the platform's
[`at_binary_exit`][at_binary_exit] (unsupported on Windows
platforms).
- `linker`: Register the dtor using the platform's
[link_section](#link_section) or
[export_name_prefix](#export_name_prefix) (unsupported on Apple
platforms).
[at_module_exit]: crate::native::at_module_exit
[at_binary_exit]: crate::native::at_binary_exit
</td></tr>
<tr><td><code>unsafe</code></td><td>
Marks a dtor as unsafe. Required.
The `ctor` crate will warn if there is no unsafe flag in the `ctor`
annotation. This warning for a missing unsafe keyword can be hidden
by passing `RUSTFLAGS="--cfg linktime_no_fail_on_missing_unsafe"` to
Cargo.
</td></tr>
<tr><td><code>used(linker)</code></td><td>
Mark generated functions pointers `used(linker)`. Requires nightly
for the nightly-only feature `feature(used_with_arg)` (see
<https://github.com/rust-lang/rust/issues/93798>).
The can be made the default by using the `cfg` flag
`linktime_used_linker` (`RUSTFLAGS="--cfg linktime_used_linker"`).
For a crate using this macro to function correctly with and without
this flag, it is recommended to add the following line to the top of
lib.rs in the crate root:
`#![cfg_attr(linktime_used_linker, feature(used_with_arg))]`
</td></tr>
</table>
# Defaults
## `ctor_export_name_prefix`
```rust
# #[cfg(false)] {
#[cfg(target_os = "aix")]
# const _: () = { let
ctor_export_name_prefix = "__sinit80000000"
# ; };
// default
ctor_export_name_prefix = ()
# }
```
## `ctor_link_section`
```rust
# #[cfg(false)] {
#[cfg(target_vendor = "apple")]
# const _: () = { let
ctor_link_section = "__DATA,__mod_init_func,mod_init_funcs"
# ; };
#[cfg(any(target_os = "linux", target_os = "android", target_os = "freebsd",
target_os = "netbsd", target_os = "openbsd", target_os = "dragonfly",
target_os = "illumos", target_os = "haiku", target_os = "vxworks", target_os =
"nto", target_family = "wasm"))]
# const _: () = { let
ctor_link_section = ".init_array"
# ; };
#[cfg(target_os = "none")]
# const _: () = { let
ctor_link_section = ".init_array"
# ; };
#[cfg(target_arch = "xtensa")]
# const _: () = { let
ctor_link_section = ".ctors"
# ; };
#[cfg(all(target_vendor = "pc", any(target_env = "gnu", target_env = "msvc")))]
# const _: () = { let
ctor_link_section = ".CRT$XCU"
# ; };
#[cfg(all(target_vendor = "pc", not(any(target_env = "gnu", target_env = "msvc"))))]
# const _: () = { let
ctor_link_section = ".ctors"
# ; };
#[cfg(all(target_os = "aix"))]
# const _: () = { let
ctor_link_section = ()
# ; };
// default
ctor_link_section = (compile_error! ("Unsupported target for #[ctor]"))
# }
```
## `default_term_method`
```rust
# #[cfg(false)] {
#[cfg(target_vendor = "pc")]
# const _: () = { let
default_term_method = at_module_exit
# ; };
// default
default_term_method = at_binary_exit
# }
```
## `default_unload_method`
```rust
# #[cfg(false)] {
// default
default_unload_method = at_module_exit
# }
```
## `export_name_prefix`
```rust
# #[cfg(false)] {
#[cfg(target_os = "aix")]
# const _: () = { let
export_name_prefix = "__sterm80000000"
# ; };
// default
export_name_prefix = ()
# }
```
## `link_section`
```rust
# #[cfg(false)] {
#[cfg(target_vendor = "apple")]
# const _: () = { let
link_section = "__DATA,__mod_term_func,mod_term_funcs"
# ; };
#[cfg(any(target_os = "linux", target_os = "android", target_os = "freebsd",
target_os = "netbsd", target_os = "openbsd", target_os = "dragonfly",
target_os = "illumos", target_os = "haiku", target_os = "vxworks", target_os =
"nto", target_family = "wasm"))]
# const _: () = { let
link_section = ".fini_array"
# ; };
#[cfg(target_os = "none")]
# const _: () = { let
link_section = ".fini_array"
# ; };
#[cfg(target_arch = "xtensa")]
# const _: () = { let
link_section = ".dtors"
# ; };
#[cfg(all(target_vendor = "pc", any(target_env = "gnu", target_env = "msvc")))]
# const _: () = { let
link_section = ".CRT$XPU"
# ; };
#[cfg(all(target_vendor = "pc", not(any(target_env = "gnu", target_env = "msvc"))))]
# const _: () = { let
link_section = ".dtors"
# ; };
#[cfg(all(target_os = "aix"))]
# const _: () = { let
link_section = ()
# ; };
// default
link_section = (compile_error! ("Unsupported target for #[dtor]"))
# }
```
## `method`
```rust
# #[cfg(false)] {
#[cfg(target_vendor = "apple")]
# const _: () = { let
method = at_module_exit
# ; };
#[cfg(target_vendor = "pc")]
# const _: () = { let
method = at_module_exit
# ; };
// default
method = linker
# }
```
## `r#unsafe`
```rust
# #[cfg(false)] {
#[cfg(linktime_no_fail_on_missing_unsafe)]
# const _: () = { let
r#unsafe = (no_fail_on_missing_unsafe)
# ; };
// default
r#unsafe = ()
# }
```
## `used_linker`
```rust
# #[cfg(false)] {
#[cfg(linktime_used_linker)]
# const _: () = { let
used_linker = used_linker
# ; };
// default
used_linker = ()
# }
```