CODEWITHSUNDEEP
javajava-native-interface
Marcos Vasconcelos
Marcos Vasconcelos

Reputation: 18276

How convert unsigned char to jbyteArray

How do I convert a unsigned char buffer to a jbyteArray? I need get a C++ buffer and returns to Java through JNI.

This is my current code to do that.

JNIEXPORT jbyteArray JNICALL Java_com_rmsdk_wrapper_RMServices_getImageBuffer(JNIEnv *env, jobject thiso,
    jint w, jint h) {
    emh::PNGSurface * surface = services->getImageBuffer(w,h);
jbyteArray * buffer = (jbyteArray*)malloc(sizeof(jbyteArray)*surface->getBufferSize());
    unsigned char * imgBuff = surface->getBuffer();

    for(int i = 0; i < surface->getBufferSize();i++){
        buffer = imgBuff;
        buffer++;
        imgBuff++;
    }
    return *buffer;
};

I got the following error when compiling.

Compile++ thumb  : rmsdk <= RMSDK_Wrapper_JNI.cpp
/home/marcos/dev/workspace/rmsdk.native.wraper/jni/RMSDK_Wrapper_JNI.cpp: In function '_jbyteArray* Java_com_rmsdk_wrapper_RMServices_getImageBuffer(JNIEnv*, _jobject*, jint, jint)':
/home/marcos/dev/workspace/rmsdk.native.wraper/jni/RMSDK_Wrapper_JNI.cpp:37: error: cannot convert 'unsigned char*' to '_jbyteArray**' in assignment
make: *** [/home/marcos/dev/workspace/rmsdk.native.wraper/obj/local/armeabi/objs/rmsdk/RMSDK_Wrapper_JNI.o] Error 1

Ty.

Upvotes: 4

Views: 8782

Answers (1)

Andy Thomas
Andy Thomas

Reputation: 86419

See these JNI array operations, particularly:

  • NewByteArray
  • GetArrayElements
  • ReleaseArrayElements

If you know a maximum size for the array beforehand, you can avoid the NewByteArray call.

If you call this infrequently, you might find it easier to use JNA.

Upvotes: 6

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