E0724 - Error codes index
Description: Book listing all Rust error codes

# Error code E0724

#### Note: this error code is no longer emitted by the compiler.

`#[ffi_returns_twice]` was used on something other than a foreign function declaration.

Erroneous code example:

    #![allow(unused)]
    #![feature(ffi_returns_twice)]
    #![crate_type = "lib"]

    fn main() {
    #[ffi_returns_twice] // error!
    pub fn foo() {}
    }

`#[ffi_returns_twice]` can only be used on foreign function declarations. For example, we might correct the previous example by declaring the function inside of an `extern` block.

    #![allow(unused)]
    #![feature(ffi_returns_twice)]

    fn main() {
    extern "C" {
       #[ffi_returns_twice] // ok!
       pub fn foo();
    }
    }