withVaList(_:_:)

Invokes the given closure with a C va_list argument derived from the given array of arguments.

Declaration

func withVaList<R>(_ 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.

Mentioned in

Using Imported C Functions in Swift

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.