Calling C functions from Swift - is it really this difficult??

The bottom line is that I want to call UnitySendMessage() from Swift code.
It seems that I have to make a bridge from Swift to C, then call it from the C code.

I'm going crazy here. I just can't get it to work, despite setting it up based on info I've found scattered around the internet.

I've created a h and c file with the function I want to access. Here's the full code from those:
swift2c.h:

Code (C):

1. void UnitySendMessageFromSwift(char* msg);

swift2c.c:

Code (C):

1. void UnitySendMessageFromSwift(char* msg)
2. {
3.     UnitySendMessage("iOS Message Receiver", "iOSMessageReceived", msg);
4. }
5.  

I've created the "-Bridging-Header.h" file and made sure the "Objective-C Bridging Header" project setting is set to it. That includes the header from the above c file:

Code (C):

1. #include "swift2c.h"

Now to actually use the function, I created a test swift file with this:

Code (Swift):

1.  
2. import Foundation
3.  
4. class Something
5. {
6.     func doSomething()
7.     {
8.         let msg = "Something"
9.        
10.         let msg_p = UnsafeMutablePointer<CChar>(mutating: msg)
11.        
12.         UnitySendMessageFromSwift(msg_p)
13.     }
14. }
15.  

Now there's two problems here...
1. Even though Xcode's IDE shows the UnitySendMessageFromSwift() call as green, it has an error when building: "Cannot find 'UnitySendMessageFromSwift' in scope"
2. I get a warning when using the UnsafeMutablePointer function, which I don't know how to prevent: "
Initialization of 'UnsafeMutablePointer<CChar>' (aka 'UnsafeMutablePointer<Int8>') results in a dangling pointer". But apparently I can't just pass a String into the function argument. (WHY, APPLE, WHY??)

I find it very hard to believe this problem hasn't been solved by a lot of Unity developers already, but I can't seem to find anything about it online.

This article makes it look like magic. https://theswiftdev.com/how-to-call-c-code-from-swift/

 

I guess it's worth noting that I could get this to work on a new project created in Xcode (except not trying to call UnitySendMessage). Not sure why my Unity-generated project is giving this problem.

 

Ok, this seems to be related to the "Target Membership". Unity generates a project with targets for:
Unity-iPhone
Unity-iPhone Tests
UnityFramework

The plugin files all seem to need to use UnityFramework ONLY. However, if I choose UnityFramework as the Target Membership of the file that has the "Something" class, then it doesn't work. If I change the Target Membership to Unity-iPhone for the file with "Something" class, it doesn't show the error in the code, but shows an error in in the build log for Unity-iPhone:
Undefined symbol: _UnitySendMessageFromSwift

 

I found this writeup, which glosses over many of the details, but luckily it is a fully working example in the project.
The key seems to be the "module map".
https://github.com/jwtan/SwiftToUnityExample