Quick Tip – How to convert a Java jintArray to a C++ std::vector

Hello ! I’m Xavier Jouvenot and in this small post, I am going to explain how to convert a Java jintArray to a C++ std::vector.

Self promotion: You can find other articles on Android development on my website 😉

Solution

For the people who only want the solution, to quickly copy-paste it in there code, here it is 😉

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_project_class_method(JNIEnv *env, jobject /* this */, jintArray arr) {
jsize size = env->GetArrayLength( arr );
std::vector input( size );
env->GetIntArrayRegion( arr, jsize{0}, size, &input[0] );
}

Explanation

If you read this, it may be that you want to understand how the previous solution achieve the goal of transforming the jintArray into a std::vector<jint>, and this is what I am going to try to explain. 🙂

First of all, we get the jintArray size by using the JNIEnv method GetArrayLength, and store this information in a variable.

Then, with this information, we can create a std::vector with the right size.

And finally, we copy the elements in from the jintArray to the std::vector using the JNIEnv method GetIntArrayRegion, by giving it all the informations that it need : the jintArray, the index where to start the copy, the size of the array, and the location where to copy the array.

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Thank you all for reading this article,And until my next article, have a splendid day 😉

Interesting links

• JNI documentation
• JNI types documentation
• std::vector documentation
• 10xlearner website