Attempted to pass an invalid type of variable into a variadic function.
Erroneous code example:
extern "C" {
fn printf(format: *const c_char, ...) -> c_int;
}
unsafe {
printf("%f\n\0".as_ptr() as _, 0f32);
// error: cannot pass an `f32` to variadic function, cast to `c_double`
}Certain Rust types must be cast before passing them to a variadic function,
because of arcane ABI rules dictated by the C standard. To fix the error,
cast the value to the type specified by the error message (which you may need
to import from std::os::raw).
In this case, c_double has the same size as f64 so we can use it directly:
unsafe {
printf("%f\n\0".as_ptr() as _, 0f64); // ok!
}