problem with using the library

[sadeghhosseini]

I am using this library in my android app. The cpp/CMakeLists.txt's content is:

cmake_minimum_required(VERSION 3.4.1)
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)
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)
add_library(
    curl
    SHARED
    IMPORTED
)
set_target_properties(
    curl
    PROPERTIES IMPORTED_LOCATION
    ${CMAKE_SOURCE_DIR}/curl-android-ios/prebuilt-with-ssl/android/${ANDROID_ABI}/libcurl.a
)
include_directories(
    ${CMAKE_SOURCE_DIR}/curl-android-ios/prebuilt-with-ssl/android/include/
)
find_library(
    zlib
    z
)
message("***********************" ${zlib})
target_link_libraries( # Specifies the target library.
        native-lib
        curl
        z
        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

And this is my cpp/native-lib.cpp file:

#include <jni.h>
#include <string>
#include <curl/curl.h>
#include <stdio.h>
#include <iostream>
#include <android/log.h>
#define LOGI(...) ((void)__android_log_print(ANDROID_LOG_INFO, "native-lib", __VA_ARGS__))
size_t WriteCallback(char *contents, size_t size, size_t nmemb, void *userp)
{
    ((std::string*)userp)->append((char*)contents, size * nmemb);
    return size * nmemb;
}


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

    curl_global_init(CURL_GLOBAL_ALL);

    CURL* easyhandle = curl_easy_init();
    std::string readBuffer;

    curl_easy_setopt(easyhandle, CURLOPT_URL, "https://google.com");
    curl_easy_setopt(easyhandle, CURLOPT_VERBOSE, 1L);
//    curl_easy_setopt(easyhandle, CURLOPT_PROXY, "http://my.proxy.net");   // replace with your actual proxy
//    curl_easy_setopt(easyhandle, CURLOPT_PROXYPORT, 8080L);
    curl_easy_setopt(easyhandle, CURLOPT_WRITEFUNCTION, WriteCallback);
    curl_easy_setopt(easyhandle, CURLOPT_WRITEDATA, &readBuffer);

    curl_easy_perform(easyhandle);


    __android_log_print(ANDROID_LOG_DEBUG, "LOG_TAG", "\n this is log messge \n");
//    std::cout << readBuffer << std::endl;
    std::string result = "here: " + readBuffer;
    std::string hello = "hello";
    return env->NewStringUTF(result.c_str());
}

But nothing is shown in the textview in android.
Would you please help me fix this?