compiler/rustc_error_codes/src/error_codes/E0060.md

   1 External C functions are allowed to be variadic. However, a variadic function
   2 takes a minimum number of arguments. For example, consider C's variadic `printf`
   3 function:
   4
   5 ```compile_fail,E0060
   6 use std::os::raw::{c_char, c_int};
   7
   8 extern "C" {
   9     fn printf(_: *const c_char, ...) -> c_int;
  10 }
  11
  12 unsafe { printf(); } // error!
  13 ```
  14
  15 Using this declaration, it must be called with at least one argument, so
  16 simply calling `printf()` is invalid. But the following uses are allowed:
  17
  18 ```
  19 # use std::os::raw::{c_char, c_int};
  20 # #[cfg_attr(all(windows, target_env = "msvc"),
  21 #            link(name = "legacy_stdio_definitions",
  22 #                 kind = "static", modifiers = "-bundle"))]
  23 # extern "C" { fn printf(_: *const c_char, ...) -> c_int; }
  24 # fn main() {
  25 unsafe {
  26     use std::ffi::CString;
  27
  28     let fmt = CString::new("test\n").unwrap();
  29     printf(fmt.as_ptr());
  30
  31     let fmt = CString::new("number = %d\n").unwrap();
  32     printf(fmt.as_ptr(), 3);
  33
  34     let fmt = CString::new("%d, %d\n").unwrap();
  35     printf(fmt.as_ptr(), 10, 5);
  36 }
  37 # }
  38 ```