xcode ios project , how to import cpp code files from other directory?

Question

I tried to put the CPP codes in a folder for unified management,
and provide them for Android and iOS platforms to compile and use together.

I've searched the Internet for several examples ,
but none of them provide detailed steps .

---

The directory structure for my experiment is as follows :

TestCppCrossPlatorm
 |---AndroidDemo     // for AndroidStudio to create a AndroidDemo
 |
 |---CommonCPP       // cpp files 
   |---Core.h
   |---Core.cpp
   |---myMath
     |---NumAdd.h
     |---NumAdd.cpp 
 |
 |---iOS_Demo       // for Xcode to create a iOS project

---

AndroidDemo
 |---app
    |---src
      |---main
         |---cpp
            |---CMakeLists.txt
            |---native-lib.cpp
         |---java
         |---res

A demo project created by AndroidStudio, I configure in CMakeFiles.txt to add CommonCPP code files as follow :

include_directories(../../../../../CommonCPP)


add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             native-lib.cpp
            ../../../../../CommonCPP/Core.h
            ../../../../../CommonCPP/Core.cpp

            ../../../../../CommonCPP/myMath/NumAdd.h
            ../../../../../CommonCPP/myMath/NumAdd.cpp
        )

Edit native-lib.cpp :

#include "Core.h"            // test cpp code : Core.h
#include "myMath/NumAdd.h"   // test cpp code : NumAdd.h

extern "C" JNIEXPORT jstring JNICALL
Java_sodino_demo_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {

    // code to try :  it's ok!
    std::string addResult = std::to_string(add(2, 3));
    const char* result = concatenateMyStringWithCppString(addResult.c_str());
//    std::string hello = "Hello from C++";
    return env->NewStringUTF(result);
}

The code is working fine, and the demo is also running OK.

---

There are some problems with the configuration of the iOS project

A iOS demo project is created in the folder iOS_Demo by Xcode,

First, I add a static library named CommonCPP for iOS_Demo by the path Build Settings -> Targets -> Add ,

Second, click CommonCPP target, select Build Phases -> Compile Sources -> Add , add CommonCPP folder, as follow :

Edit ViewController.mm to add include Core.h and myMath/NumAdd.h ,

It failed ... 'myMath/NumAdd.h' file not found

Question 1 :
Why is all cpp files displayed in the Xcode below Demo_iOS instead of the CommonCPP target?

Question 2 :
Why Core.h can be include ok, but myMath/NumAdd.h failed? and how to fixed it?

---

examples without detailed steps : How to use C++ for Cross-Platform Development

CMAKE is a good choice But now, I'm more concerned about how to do it step by step, and right .

---

Core.h

#ifndef __HelloCpp__Core__
#define __HelloCpp__Core__

#include <iostream>

const char *concatenateMyStringWithCppString(const char *myString);

#endif /* defined(__HelloCpp__Core__) */

Core.cpp

#include <string.h>
#include "Core.h"
#include "myMath/NumAdd.h"

const char *CPP_BASE_STRING = "cpp says hello to %s";

const char *concatenateMyStringWithCppString(const char *myString) {
    char *concatenatedString = new char[strlen(CPP_BASE_STRING) + strlen(myString)];
    sprintf(concatenatedString, CPP_BASE_STRING, myString);


    return concatenatedString;
}

myMath/NumAdd.h

//
// Created by sodino on 2021/7/18.
//

#ifndef ANDROIDDEMO_NUMADD_H
#define ANDROIDDEMO_NUMADD_H

int add(int a, int b);


#endif //ANDROIDDEMO_NUMADD_H

myMath/NumAdd.cpp

//
// Created by sodino on 2021/7/18.
//

#include "NumAdd.h"
int add(int a, int b) {
    return a + b;
}

Answer 1

Your problem is that you need to define the proper header path location for your libraries which will probably be something like ../CommonCPP .

You'll want to add it to Header Search Paths . You can use non-recursive based on the way you are including your files. Note I did add an Objective C++ file after I did the screenshot to verify it would build.

Note this is what the directory structure looks like:

You can adjust your path accordingly based on your Xcode project directory. But if it looks like mine, you can use the ../CommonCPP .