Error code E0060
External C functions are allowed to be variadic. However, a variadic function
takes a minimum number of arguments. For example, consider C's variadic printf
function:
#![allow(unused)] fn main() { use std::os::raw::{c_char, c_int}; extern "C" { fn printf(_: *const c_char, ...) -> c_int; } unsafe { printf(); } // error! }
Using this declaration, it must be called with at least one argument, so
simply calling printf()
is invalid. But the following uses are allowed:
use std::os::raw::{c_char, c_int}; #[cfg_attr(all(windows, target_env = "msvc"), link(name = "legacy_stdio_definitions", kind = "static", modifiers = "-bundle"))] extern "C" { fn printf(_: *const c_char, ...) -> c_int; } fn main() { unsafe { use std::ffi::CString; let fmt = CString::new("test\n").unwrap(); printf(fmt.as_ptr()); let fmt = CString::new("number = %d\n").unwrap(); printf(fmt.as_ptr(), 3); let fmt = CString::new("%d, %d\n").unwrap(); printf(fmt.as_ptr(), 10, 5); } }