不编译“‘->’基操作数‘有非指针类型’JNIEnv‘的JNI IMU代码

Question

我正在开发一个本机模块，以允许在java中使用RPI感知帽子，而我的本机不会编译:目前，我只是尝试以字符串的形式返回数据，如果您有更简单的方法，请告诉我。下面是源文件(SenseHat.cpp)：

#include <jni.h>
#include <stdio.h>
#include "SenseHat.h"
#include "RTIMULib.h"


RTIMU *imu;
RTPressure *pressure;
RTHumidity *humidity;

JNIEXPORT void JNICALL Java_SenseHat_init(JNIEnv *env, jobject thisObj) {

    RTIMUSettings *settings = new RTIMUSettings("RTIMULib");

    imu = RTIMU::createIMU(settings);
    pressure = RTPressure::createPressure(settings);
    humidity = RTHumidity::createHumidity(settings);

    if ((imu == NULL) || (imu->IMUType() == RTIMU_TYPE_NULL)) {
        printf("No IMU found\n");
        exit(1);
    }

    //  This is an opportunity to manually override any settings before the call IMUInit

    //  set up IMU

    imu->IMUInit();

    //  this is a convenient place to change fusion parameters

    imu->setSlerpPower(0.02);
    imu->setGyroEnable(true);
    imu->setAccelEnable(true);
    imu->setCompassEnable(true);

    //  set up pressure sensor

    if (pressure != NULL)
        pressure->pressureInit();

    //  set up humidity sensor

    if (humidity != NULL)
        humidity->humidityInit();

}

JNIEXPORT jstring JNICALL Java_SenseHat_getTemperature(JNIEnv *env, jobject thisObj) {
   RTIMU_DATA imuData = imu->getIMUData();
   if (humidity != NULL)
      humidity->humidityRead(imuData);
   return ((*env)->NewStringUTF(env,imuData.temperature));
}

JNIEXPORT jstring JNICALL Java_SenseHat_getHumidity(JNIEnv *env, jobject thisObj) {
   RTIMU_DATA imuData = imu->getIMUData();
   if (humidity != NULL)
      humidity->humidityRead(imuData);
   return ((*env)->NewStringUTF(env,imuData.humidity));

}

JNIEXPORT jstring JNICALL Java_SenseHat_getOrientation(JNIEnv *env, jobject thisObj) {
   RTIMU_DATA imuData = imu->getIMUData();
   return ((*env)->NewStringUTF(env,imuData.fusionPose));
}

全部错误是：

SenseHat.cpp: In function ‘_jstring* Java_SenseHat_getTemperature(JNIEnv*, jobject)’:
SenseHat.cpp:53:18: error: base operand of ‘->’ has non-pointer type ‘JNIEnv’
    return ((*env)->NewStringUTF(env,imuData.temperature));
                  ^
SenseHat.cpp: In function ‘_jstring* Java_SenseHat_getHumidity(JNIEnv*, jobject)’:
SenseHat.cpp:60:18: error: base operand of ‘->’ has non-pointer type ‘JNIEnv’
    return ((*env)->NewStringUTF(env,imuData.humidity));
                  ^
SenseHat.cpp: In function ‘_jstring* Java_SenseHat_getOrientation(JNIEnv*, jobject)’:
SenseHat.cpp:66:18: error: base operand of ‘->’ has non-pointer type ‘JNIEnv’
    return ((*env)->NewStringUTF(env,imuData.fusionPose));

^

编译代码：

gcc -I /usr/lib/jvm/jdk-8-oracle-arm32-vfp-hflt/include/ -I /usr/lib/jvm/jdk-8-oracle-arm32-vfp-hflt/include/linux/ -shared -o libSenseHat.so SenseHat.cpp

Answer 1

对于C和C++，JNIEnv声明有一点不同，详细信息请参见jni.h。在C语言中，我们用几个词

(*env)->NewStringUTF(env,imuData.temperature);

在C++中，应该是

env->NewStringUTF(imuData.temperature);

如您所见，C++版本不需要env取消引用，并将其作为第一个参数传递给JNI函数。