Rust中extern fn和extern“C”fn有什么区别？

Question

I've tried reading various github issues trying to track down what the difference is and just ended up confused.

#[no_mangle]
pub extern fn foo() {
   ...
}

vs.

#[no_mangle]
pub extern "C" fn foo() {
   ...
}

Answer 1

There is no difference because, as the reference says:

By default external blocks assume that the library they are calling uses the standard C ABI on the specific platform.

extern "C" -- This is the same as extern fn foo(); whatever the default your C compiler supports.

An issue was created to always require explicitly stating extern "C" but the RFC has been refused .

There is an issue in fmt-rfcs about "should we format extern "C" fn as that or extern fn ?".