How do I convert wchar_t array to Swift String?

Question

trudnai OP

Created Jul ’20

Replies 3

Boosts 0

Views 1.1k

Participants 2

I have a C module with a unicode string like this:

Code Block wchar_t * helloWorld = L"Hello World";

I have all the bridging header and all, Swift sees the C variable, no problem with that part. However, how do I get this converted to a String in Swift? I was trying to do something like this:

Code Block let hw = String(cString: helloWorld, encoding: .unicode)

Swift came back with an ugly error:

Code Block Cannot convert value of type 'UnsafeMutablePointer<wchar_t>?' (aka 'Optional<UnsafeMutablePointer<Int32>>') to expected argument type 'UnsafePointer<CChar>' (aka 'UnsafePointer<Int8>')

Any idea how it is done? I could not find anything useful on Google. Thanks.

Answered by OOPer in 624456022

wchar_t is a system dependent type in C, I assume it used under the default settings of Apple's platform, meaning 32-bit wide.
Under the assumption, an L-prefixed string literal is made of Unicode Code Points, 32-bit each.
Unfortunately, Swift.String does not have an initializer taking a pointer to wchar_t.

You may need to write something like this:

Code Block let byteSize = wcslen(helloWorld) * MemoryLayout<wchar_t>.stride
let data = Data(bytes: helloWorld, count: byteSize)
let encoding: String.Encoding = (1.littleEndian == 1) ? .utf32LittleEndian : .utf32BigEndian
let str = String(data: data, encoding: encoding)!

Boost

Answer 1

OOPer OP

Jul ’20

Accepted Answer

wchar_t is a system dependent type in C, I assume it used under the default settings of Apple's platform, meaning 32-bit wide.
Under the assumption, an L-prefixed string literal is made of Unicode Code Points, 32-bit each.
Unfortunately, Swift.String does not have an initializer taking a pointer to wchar_t.

You may need to write something like this:

Code Block let byteSize = wcslen(helloWorld) * MemoryLayout<wchar_t>.stride
let data = Data(bytes: helloWorld, count: byteSize)
let encoding: String.Encoding = (1.littleEndian == 1) ? .utf32LittleEndian : .utf32BigEndian
let str = String(data: data, encoding: encoding)!

1

Answer 2

trudnai OP

Jul ’20

Thanks @OOPer, it works. But good grief, why is it so complicated in Swift? :-)

0

Answer 3

OOPer OP

Jul ’20

Happy to hear that it works for your project.

why is it so complicated in Swift?

In fact, Swift.String has some initializers work with UTF-8 bytes, UTF-16 code units and Unicode Scalars.
And they make similar conversions more simple.

You should better send a feedback to Apple, or join the discussion in the Evolution category of forums.swift.org.
Here's a thread for example:
Additional String Processing APIs

0