Import headers from c++ library in swift - c++

Question

I am learning how to communicate between swift and c++ for ios. As a first step I have looked on this example:
https://github.com/leetal/ios-cmake
There is an example-app that I have managed to compile and run. Took some time to get it to work. That is an objective-c project.
The next step is to create a new swift project and try and import the compiled library and use the headers in swift instead.
I have not managed to do that. I think the current problem is that I cannot include the header HelloWorldIOS.h.
import SwiftUI
import HelloWorldIOS.h <- No such module found
struct ContentView: View {
var body: some View {
Text(sayHello())
.padding()
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
I have tried to create a bridging file example-Bridging-Header.h as suggested here: https://developer.apple.com/documentation/swift/importing-objective-c-into-swift
It looks like:
//
// example-Bridging-Header.h
// example-swift
//
#ifndef example_Bridging_Header_h
#define example_Bridging_Header_h
#import "HelloWorldIOS.h"
#endif /* example_Bridging_Header_h */
I have also added the path to the headers in Target - Build Settings - Header Search Paths
The Objective-C Bridging Header looks like example-swift/example-Bridging-Header.h.
Are there any good instructions for how to call c++ code from a compiled library? I hoped this example I found would be easy to get to work.
The comment below helped me plus that I had to link to libc++.tbd.

Answer 1

You don't import anything in your Swift code when Objective-C headers are imported in the bridging header.
All public interfaces available from the imported files get available in the entire Swift module by default after that.
Sample listing
TDWObject.h
#import <Foundation/Foundation.h>
NS_ASSUME_NONNULL_BEGIN
#interface TDWObject : NSObject
- (void)someCPPCode;
#end
NS_ASSUME_NONNULL_END
TDWObject.mm
#include <iostream>
#import "TDWObject.h"
#implementation TDWObject
- (void)someCPPCode {
std::cout << "Hello from CPP cout" << std::endl;
}
#end
Some-Bridging-Header.h
#import "TDWObject.h"
main.swift
TDWObject().someCPPCode()
Provided the main.swift file is the entry point of the program, it will print Hello from CPP cout.

Answer 2

You can use Scapix Language Bridge to automatically bridge C++ to Swift (among other languages). Bridge code automatically generated on the fly directly from C++ header files. Here is an example:
C++:
#include <scapix/bridge/object.h>
class contact : public scapix::bridge::object<contact>
{
public:
std::string name();
void send_message(const std::string& msg, std::shared_ptr<contact> from);
void add_tags(const std::vector<std::string>& tags);
void add_friends(std::vector<std::shared_ptr<contact>> friends);
void notify(std::function<bool(std::shared_ptr<contact>)> callback);
};
Swift:
class ViewController: UIViewController {
func send(friend: Contact) {
let contact = Contact()
contact.sendMessage("Hello", friend)
contact.addTags(["a","b","c"])
contact.addFriends([friend])
contact.notify() {
(c: Contact) in
//...
return true
}
}
}
Disclaimer: I am the author of Scapix Language Bridge.