Import headers from c++ library in swift

August 16, 2022

I am learning how to communicate between swift and c++ for ios. As a first step I have looked on this example:

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.

>Solution :

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.
Pay attention that Objective-C implementation file has to be of mm extension. Otherwise the compiler would not recognise C++ code in it