Way to pass byte[] as char* from Android to C++

Kyeiv

I am developing an Android app using Qt. The app is communicating with a FTDI device via Android's USB libraries. The device sends me hex data which is stored in byte[] array on the android side. The approaches i stumbled upon require converting it to String before passing it to c++. Unfortunately this conversion ruins my hex data due to using UTF-8. So i am wandering if there is a way that could let me pass byte[] from Java and it to appear as char* in the c++ side?

Going from:

private static native void getData(String message);

    JNINativeMethod methods[] {
        {"getData", "(Ljava/lang/String;)V", reinterpret_cast<void *>(getData)}
    };

static void getData(JNIEnv *env, jobject /*thiz*/, jstring value)

to something like:

private static native void getData(byte[] message);

    JNINativeMethod methods[] {
        {"getData", "([B)V", reinterpret_cast<void *>(getData)}
    };

static void getData(JNIEnv *env, jobject /*thiz*/, jbyteArray value)

Can anyone prompt me with some ideas?

KroMignon

@Kyeiv said in Way to pass byte[] as char* from Android to C++:

i corrected it, but can you answer the question? how to cature this jbyteArray as char*

Yes I can ;)

void getData(JNIEnv *env, jobject /*thiz*/, jbyteArray value)
{
    // get array pointer and size
    jbyte *bytes = env->GetByteArrayElements(value, false);
    int arrayLength = env->GetArrayLength(value);

    // copy to local variable, for example a QByteArray 
    QByteArray b = QByteArray::fromRawData((const char*)bytes , arrayLength);

    // release memory
    env->ReleaseByteArrayElements(value, bytes, JNI_ABORT);

}

KroMignon

@Kyeiv said in Way to pass byte[] as char* from Android to C++:

Can anyone prompt me with some ideas?

You function has wrong signature:

static void getData(JNIEnv *env, jobject /*thiz*/, jbyte value)

should be:

static void getData(JNIEnv *env, jobject /*thiz*/, jbyteArray value)

cf. https://doc.qt.io/qt-5/qandroidjniobject.html#object-types

Kyeiv

@KroMignon i corrected it, but can you answer the question? how to cature this jbyteArray as char*?

KroMignon

@Kyeiv said in Way to pass byte[] as char* from Android to C++:

i corrected it, but can you answer the question? how to cature this jbyteArray as char*

Yes I can ;)

void getData(JNIEnv *env, jobject /*thiz*/, jbyteArray value)
{
    // get array pointer and size
    jbyte *bytes = env->GetByteArrayElements(value, false);
    int arrayLength = env->GetArrayLength(value);

    // copy to local variable, for example a QByteArray 
    QByteArray b = QByteArray::fromRawData((const char*)bytes , arrayLength);

    // release memory
    env->ReleaseByteArrayElements(value, bytes, JNI_ABORT);

}