Android Studio中的命名空间‘std’中没有名为'variant‘的模板

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

android {
    ...
    defaultConfig {
        ...
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++17"
            }
        }
    }
    ...
}

gcc --version
clang --version

cmake_minimum_required(VERSION 3.10.2)

project("mycppproject")

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

add_library(
    mycppproject
    SHARED
    src/main/cpp/native-lib.cpp
)

find_library(
    log-lib
    log
)

target_link_libraries(
    mycppproject
    ${log-lib}
)

apply plugin: 'com.android.application'

android {
    compileSdkVersion 30
    defaultConfig {
        applicationId "com.example.mycppproject"
        minSdkVersion 21
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        externalNativeBuild {
            cmake {
                cppFlags "-std=c++17"
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
}

dependencies {
    implementation fileTree(dir: "libs", include: ["*.jar"])
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.3.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    testImplementation 'junit:junit:4.13.1'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}

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

extern "C" JNIEXPORT jstring JNICALL
Java_com_example_mycppproject_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::variant<int, std::string> myVariant = "Hello from C++17";
    return env->NewStringUTF(std::get<std::string>(myVariant).c_str());
}