Variadic Functions

• Declared variadic by specifying ... as the last argument

Examples

use std::ffi::*;

extern "C" {
    /// print formatted output
    fn printf(format: *const c_char, ...) -> c_int;
}

fn main() {
    let format = CString::new("Hello, %s!").unwrap();
    let arg = CString::new("RustBLR").unwrap();
    assert_eq!(unsafe { printf(format.as_ptr(), arg.as_ptr()) }, 15);
}

Caveats

• Needs least one parameter before variadic parameter
• Normal Rust functions can not be variadic

References

• https://doc.rust-lang.org/stable/reference/items/external-blocks.html#variadic-functions
• https://doc.rust-lang.org/nomicon/ffi.html#variadic-functions