[swift-users] UnsafePointer<Int8> and C-String

[Rien]

Thanks Jeremy & Ole,

That was indeed my expectation, but I had not thought of looking in the source code!

Regards,
Rien

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> On 03 Jan 2017, at 16:31, Ole Begemann <ole at oleb.net> wrote:
> 
>> What I cannot find though is the guarantee that the buffer where the
>> String is converted to an UTF8 sequence is always null-terminated.
>> 
>> I very much suspect it is, and all my tests did find a null-terminated
>> string.
>> 
>> Question: Does anybody know for sure that the buffer is always
>> null-terminated? (a link to where I can check this would be most
>> appreciated)
> 
> I'm not 100% certain, but I think the compiler uses this function to convert a String argument to a pointer:
> 
> /// Derive a UTF-8 pointer argument from a value string parameter.
> public // COMPILER_INTRINSIC
> func _convertConstStringToUTF8PointerArgument<
>  ToPointer : _Pointer
> >(_ str: String) -> (AnyObject?, ToPointer) {
>  let utf8 = Array(str.utf8CString)
>  return _convertConstArrayToPointerArgument(utf8)
> }
> 
> Source: Pointer.swift [1]
> 
> This in turn calls `String.utf8CString` [2], which indeed returns a null-terminated string.
> 
> [1]: https://github.com/apple/swift/blob/master/stdlib/public/core/Pointer.swift#L85-L92
> [2]: https://github.com/apple/swift/blob/master/stdlib/public/core/StringUTF8.swift#L383-L405
>