# withVaList(_:_:) Invokes the given closure with a C `va_list` argument derived from the given array of arguments. ``` func withVaList(_ args: [any CVarArg], _ body: (CVaListPointer) -> R) -> R ``` ## Parameters `args` An array of arguments to convert to a C `va_list` pointer. `body` A closure with a `CVaListPointer` parameter that references the arguments passed as `args`. If `body` has a return value, that value is also used as the return value for the `withVaList(_:)` function. The pointer argument is valid only for the duration of the function’s execution. ## Return Value The return value, if any, of the `body` closure parameter. ## Discussion The pointer passed as an argument to `body` is valid only during the execution of `withVaList(_:_:)`. Do not store or return the pointer for later use. If you need to pass an optional pointer as a `CVarArg` argument, use the `Int(bitPattern:)` initializer to interpret the optional pointer as an `Int` value, which has the same C variadic calling conventions as a pointer on all supported platforms. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)