JNI IMU 代码未编译 "base operand of ‘->’ has non-pointer type ‘JNIEnv’"

Question

我正在开发一个本机模块以允许在 java 中使用 RPI 感应帽，但我的本机无法编译：目前我只是想 return 将数据作为字符串，如果您有更简单的方法请告诉我。这是源文件（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));
}

完整的错误是：

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

JNIEnv 对于 C 和 C++ 的声明略有不同，请参阅 jni.h 了解详细信息。在 C 语言中，我们使用

(*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。

JNI IMU 代码未编译 "base operand of ‘->’ has non-pointer type ‘JNIEnv’"

JNI IMU code not compiling "base operand of ‘->’ has non-pointer type ‘JNIEnv’"

c

c++

java

java-native-interface

native