475. (Android) [Android Native Library] [NDK] [JNI] [cpp] 안드로이드 에서 C 코드 사용 방법 - CMake 모듈 생성 방법

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[개발 환경 설정]

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개발 툴 : AndroidStudio

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[방법 설명]

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[C_Test.h : 소스 코드]

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//
// Created by KGH on 2023-02-12.
//

#ifndef MY_APPLICATION_C_TEST_H
#define MY_APPLICATION_C_TEST_H

// -------------------------------------------------
#include <stdio.h>

// -------------------------------------------------

// TODO [헤더 파일 소스 코드 작성 실시]

struct book
{

    char title[30];

    char author[30];

    int price;

};

// -------------------------------------------------

#endif //MY_APPLICATION_C_TEST_H

 

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[C_Test.c : 소스 코드]

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//
// Created by KGH on 2023-02-12.
//

// -------------------------------------------------
// TODO [헤더 파일 import]

#include "C_Test.h"

// -------------------------------------------------


// -------------------------------------------------
// TODO [구현부 소스 코드 작성]

int add (int a, int b) {
    return a+b;
}

// -------------------------------------------------

 

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[CMakeLists.txt : 소스 코드]

 

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.18.1)

# Declares and names the project.

project("nativelib")

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

# -------------------------------------------------

# TODO [생성된 파일 빌드를 수행하기 위해 헤더파일 및 구현부 추가 실시]

add_library( # Sets the name of the library.
        nativelib

        # Sets the library as a shared library.
        SHARED

        # Provides a relative path to your source file(s).
        nativelib.cpp

        C_Test.c)

# -------------------------------------------------

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
        log-lib

        # Specifies the name of the NDK library that
        # you want CMake to locate.
        log)

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
        nativelib

        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

 

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[nativelib.cpp : 소스 코드]

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#include <jni.h>
#include <string>


// -------------------------------------------------
// TODO [Test 파일 import]
#include "C_Test.h"
#include "C_Test.c"
// -------------------------------------------------


// -------------------------------------------------
// TODO [기존 : 결과 반환 소스 코드 작성 실시]
extern "C" JNIEXPORT jstring JNICALL
Java_com_example_nativelib_NativeLib_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}
// -------------------------------------------------


// -------------------------------------------------
// TODO [커스텀 : 결과 반환 소스 코드 작성 실시]
// [기본 경로 [패키지 및 클래스 명칭] : Java_com_example_nativelib_NativeLib_]
// [커스텀 설정 명칭] : Test]
extern "C" JNIEXPORT jstring JNICALL
Java_com_example_nativelib_NativeLib_Test(
        JNIEnv* env,
        jobject /* this */) {

    struct book my_book = {"HTML과 CSS", "홍길동", 28000};
    int value = add(10,20);

    std::string result = std::to_string(my_book.price);
    std::string result2 = std::to_string(value);

    return env->NewStringUTF(result2.c_str());
}
// -------------------------------------------------

 

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[NativeLib : 소스 코드]

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package com.example.nativelib;

public class NativeLib {

    // Used to load the 'nativelib' library on application startup.
    static {
        System.loadLibrary("nativelib");
    }

    /**
     * A native method that is implemented by the 'nativelib' native library,
     * which is packaged with this application.
     */

    public native String stringFromJNI();


    // -------------------------------------------------
    // TODO [커스텀 : 결과 반환 함수 등록]
    // -------------------------------------------------
    public native String Test();
    // -------------------------------------------------
}

 

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[호출 소스 코드]

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        // -------------------------------------------------------------
        // TODO [메인 프로젝트에서 >> 모듈에 정의된 함수 호출 수행 실시]
        NativeLib nativeLib = new NativeLib();
        String result = nativeLib.Test();

        Log.i("---","---");
        Log.d("//===========//","================================================");
        Log.i("","\n"+"[MainActivity >> NativeLib :: 함수 호출 수행 결과]");
        Log.i("","\n"+"[result :: "+String.valueOf(result)+"]");
        Log.d("//===========//","================================================");
        Log.i("---","---");
        // -------------------------------------------------------------

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[Module build gradle : 소스 코드]

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plugins {
    id 'com.android.library'
}

android {
    namespace 'com.example.nativelib'
    compileSdk 32

    defaultConfig {
        minSdk 21
        targetSdk 32

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        consumerProguardFiles "consumer-rules.pro"
        externalNativeBuild {
            cmake {
                //arguments "-DANDROID_STL=c++_static"
                //cppFlags "-std=c++11 -fexceptions"

                cppFlags ""
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
            version "3.18.1"
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.6.0'
    implementation 'com.google.android.material:material:1.8.0'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.5'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
}

 

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[Main build gradle : 소스 코드]

 

    // ---------------------------------------------
    // TODO [메인 build.gradle 에 모듈 추가 실시]
    implementation project(':nativelib')
    // ---------------------------------------------

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[결과 출력]

 

D///===========//: ================================================
I/: [MainActivity >> NativeLib :: 함수 호출 수행 결과]
I/: [result :: 30]
D///===========//: ================================================

---

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