Issue description:

• I’m new to Xcode and I’m making a “Hello world” in C++.
• I created an empty “static library” project in Xcode and added main.cpp, main.h and Bridging-Header.h.
• I created an empty “app” project to display the text output of the above static library (in the iOS simulator) and I included it as the only dependency.
• Calling testC() produces text output in the app, so everything works up to this point.
• But calling testCpp() fails at std::string part.
• It seems that std (C++ standard library) is not accessible in the “static library” project. Does anyone know how to fix it?

What I tried:

• I produced a separate CommandLine project and the same testCpp() works in that project.
• I tried modifying “Build Settings” to include standard library (via -stdlib=libc++ and -std=c++17) in “Other linker flags” and in “Other C++ flags” but that didn’t help.

Xcode: 15.4

macOS: 14.6.1

MyStaticLib/main.h:

#include <stdio.h>

#ifdef __cplusplus
extern "C" {
#endif

const char* testC();
const char* testCpp();

#ifdef __cplusplus
}
#endif

MyStaticLib/main.cpp:

#include "main.h"
#include <iostream>
#include <string>

// This function fully works.
const char* testC() {
    return "testC(): Hello from C!";
}

// This doesn't work.
const char* testCpp() {
    static const std::string message = "testCpp(): Hello from C++!";
    return message.c_str();
}

MyStaticLib/Bridging-Header.h:

#include "main.h"

MyStaticLib/MyClass.swift:

public class MyClass {
    public init() {}
    public func ExampleMethod() {
        print("Static library works.");
        
        let message = String(cString: testCpp()); // This fails.
        
        print(message);
    }
}

TestApp/TestAppMain.swift:

import Foundation
import SwiftUI
import MyStaticLib

@main
struct TestAppMain: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
                .onAppear(perform: customFunction)
        }
    }
    
    func customFunction() {
        let instance = MyStaticLib.MyClass();
        
        instance.ExampleMethod();
    }
}

The error is this:

Undefined symbol: std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>::__init(char const*, unsigned long)
Undefined symbol: std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>::~basic_string()
Undefined symbol: std::terminate()
Undefined symbol: ___cxa_begin_catch
[...]
Linker command failed with exit code 1 (use -v to see invocation)