Struct `VaList`

struct VaList<'a> { ... }

A variable argument list, ABI-compatible with va_list in C.

This type is created in c-variadic functions when ... is desugared. A VaList is automatically initialized (equivalent to calling va_start in C).

#![feature(c_variadic)]

use std::ffi::VaList;

/// # Safety
/// Must be passed at least `count` arguments of type `i32`.
unsafe extern "C" fn my_func(count: u32, ap: ...) -> i32 {
    unsafe { vmy_func(count, ap) }
}

/// # Safety
/// Must be passed at least `count` arguments of type `i32`.
unsafe fn vmy_func(count: u32, mut ap: VaList<'_>) -> i32 {
    let mut sum = 0;
    for _ in 0..count {
        sum += unsafe { ap.arg::<i32>() };
    }
    sum
}

assert_eq!(unsafe { my_func(1, 42i32) }, 42);
assert_eq!(unsafe { my_func(3, 42i32, -7i32, 20i32) }, 55);

The VaList::arg method can be used to read an argument from the list. This method automatically advances the VaList to the next argument. The C equivalent is va_arg.

Cloning a VaList performs the equivalent of C va_copy, producing an independent cursor that arguments can be read from without affecting the original. Dropping a VaList performs the equivalent of C va_end.

This can be used across an FFI boundary, and fully matches the platform's va_list.

Implementations

`impl<'f> VaList<'f>`

unsafe const fn arg<T: VaArgSafe>(self: &mut Self) -> T

Read an argument from the variable argument list, and advance to the next argument.

Only types that implement VaArgSafe can be read from a variable argument list.

Safety

This function is only sound to call when there is another argument to read, and that argument is a properly initialized value of the type T.

Calling this function with an incompatible type, an invalid value, or when there are no more variable arguments, is unsound.

`impl Debug for VaList<'_>`

fn fmt(self: &Self, f: &mut Formatter<'_>) -> Result

`impl<'a> Freeze for VaList<'a>`

`impl<'a> RefUnwindSafe for VaList<'a>`

`impl<'a> Send for VaList<'a>`

`impl<'a> Sync for VaList<'a>`

`impl<'a> Unpin for VaList<'a>`

`impl<'a> UnsafeUnpin for VaList<'a>`

`impl<'a> UnwindSafe for VaList<'a>`

`impl<'f> Clone for VaList<'f>`

fn clone(self: &Self) -> Self

`impl<'f> Drop for VaList<'f>`

fn drop(self: &mut Self)

`impl<T> Any for VaList<'a>`

fn type_id(self: &Self) -> TypeId

`impl<T> Borrow for VaList<'a>`

fn borrow(self: &Self) -> &T

`impl<T> BorrowMut for VaList<'a>`

fn borrow_mut(self: &mut Self) -> &mut T

`impl<T> CloneToUninit for VaList<'a>`

unsafe fn clone_to_uninit(self: &Self, dest: *mut u8)

`impl<T> From for VaList<'a>`

fn from(t: T) -> T: Returns the argument unchanged.

`impl<T, U> Into for VaList<'a>`

fn into(self: Self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of [From]<T> for U chooses to do.

`impl<T, U> TryFrom for VaList<'a>`

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

`impl<T, U> TryInto for VaList<'a>`

fn try_into(self: Self) -> Result<U, <U as TryFrom<T>>::Error>