Question

I am trying to convert a jbyteArray to native c string (char*) in jni? Unfortunately I can’t find any documentation on how to do that. I’m invoking a java function with the following prototype in the c code.

public static byte[] processFile(byte[] p_fileContent)

In the c code I am invoking this function which is returning a byte array. The content of this byte array is a java string. But I need to convert it to a c string.

jbyteArray arr = (jbyteArray) env->CallObjectMethod(clsH, midMain, jb);
printf("%s\n", (char*) arr);

Answer 1

I believe you would use GetByteArrayElements and ReleaseByteArrayElements. Something like:

boolean isCopy;
jbyte* b = GetByteArrayElements(env, arr, &isCopy);

You should be able to cast b to char* at this point in order to access the data in the array. Note that this may create a copy of the data, so you’ll want to make sure to release the memory using ReleaseByteArrayElements:

ReleaseByteArrayElements(env, arr, b, 0);

The last parameter is a mode indicating how changes to b should be handled. 0 indicates that the values are copied back to arr. If you don’t want to copy the data back to arr, use JNI_ABORT instead.

For more details see the JNI Reference.