未定义对Android NDK功能的引用

Question

我试图用现有的使用OpenCV的c++代码构建Android应用程序。但Android NDK表示，"未定义对‘TestMath:：getHello（）’的引用"

这是我的Android.mk:

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
#opencv
OPENCVROOT := /mypath/OpenCV-android-sdk
OPENCV_CAMERA_MODULES := off
OPENCV_INSTALL_MODULES := off
OPENCV_LIB_TYPE := SHARED
include ${OPENCVROOT}/sdk/native/jni/OpenCV.mk
LOCAL_MODULE := CrossMath
LOCAL_SRC_FILES := com_testapp_recognition_TestMath.cpp
LOCAL_SHARED_LIBRARIES := -lopencv_java3
include $(BUILD_SHARED_LIBRARY)

Application.mk:

APP_ABI := all
APP_CPPFLAGS := -frtti -fexceptions -std=c++11
APP_STL := gnustl_static
APP_PLATFORM := android-16

com_testap_agnition_TestMath.hpp:

#include <jni.h>
#include "CrossMath/TestMath.hpp"
#ifndef _Included_com_testapp_recognition_TestMath
#define _Included_com_testapp_recognition_TestMath
#ifdef __cplusplus
extern "C" {
#endif
JNIEXPORT jint JNICALL Java_com_testapp_recognition_TestMath_recognize(JNIEnv *, jobject, cv::Mat& originalImage);
#ifdef __cplusplus
}
#endif
#endif

com_testap_agnition_TestMath.cpp:

#include "com_testapp_recognition_TestMath.hpp"
JNIEXPORT jint JNICALL Java_com_testapp_recognition_TestMath_recognize(JNIEnv *, jobject, cv::Mat& originalImage) {
     return TestMath::getHello().size();
}

最后是位于子文件夹CrossMath:中的TestMath.cpp

#include "TestMath.hpp"
namespace TestMath {
     string getHello() {
         return "Hello";
     }
}

TestMath.hpp:

#ifndef TestMath_hpp
#define TestMath_hpp
#include <stdio.h>
#include <iostream>
#include "opencv2/core/core_c.h"
#include "opencv2/opencv.hpp"
#include "opencv2/highgui.hpp"
namespace TestMath {
    string getHello();
}

Java类和其他人员定义，我检查了路径并包含在文件中。

错误：

Error:(13) undefined reference to `TestMath::getHello()'

Answer 1

您的LOCAL_SRC_FILES中缺少CrossMath/TestMath.cpp。

除此之外，如果您在代码中引用的string应该是std::string，则需要在TestMath.hpp中包含<string>，并将类型更改为std::string。

Answer 2

错误消息"对'TestMath:：getHello（）'的未定义引用"表示NDK工具找不到TestMath::getHello()的实现。

请尝试以下com_testap_activation_TestMath.cpp:

#include "TestMath.hpp"
namespace TestMath {
    string getHello() {
        return "Hello";
    }
}
#include "com_testapp_recognition_TestMath.hpp"
    JNIEXPORT jint JNICALL Java_com_testapp_recognition_TestMath_recognize(JNIEnv *, jobject, cv::Mat& originalImage) {
    return TestMath::getHello().size();
}