[英]Simplest way to pass float[][] to C++ via JNI
In my Java code I have a 2D float array float[x][4] floatArray
.在我的 Java 代码中,我有一个二维浮点数组
float[x][4] floatArray
。 Here x
can be between 1 and 25. I have to pass this 2D float array to a C++
method via JNI
.这里
x
可以在 1 到 25 之间。我必须通过JNI
将此二维浮点数组传递给C++
方法。 My JNI
method is我的
JNI
方法是
jboolean MyJNIMethod(JNIEnv * env, jobject obj, jobjectArray myArray)
{
//how to convert this myArray to something that can be safely passed to C++ method below
}
Inside MyJNIMethod
I have to call a C++
method and pass 2D float array taken from Java to this method在
MyJNIMethod
中,我必须调用C++
方法并将取自 Java 的二维浮点数组传递给此方法
bool MyCplusPlusMethod(float coordinates[][4])
{
}
I am having a hard time in properly converting jobject to float[][] due to lack of native development knowledge.由于缺乏本地开发知识,我很难将 jobject 正确转换为 float[][]。 Can anyone tell me the simplest and safest possible way?
谁能告诉我最简单和最安全的方法? Thanks
谢谢
Something like this should work:像这样的东西应该工作:
jboolean MyJNIMethod(JNIEnv * env, jobject obj, jobjectArray myArray)
{
int len1 = env -> GetArrayLength(myArray);
jfloatArray dim= (jfloatArray)env->GetObjectArrayElement(myArray, 0);
int len2 = env -> GetArrayLength(dim);
float **localArray;
// allocate localArray using len1
localArray = new float*[len1];
for(int i=0; i<len1; ++i){
jfloatArray oneDim= (jfloatArray)env->GetObjectArrayElement(myArray, i);
jfloat *element=env->GetFloatArrayElements(oneDim, 0);
//allocate localArray[i] using len2
localArray[i] = new float[len2];
for(int j=0; j<len2; ++j) {
localArray[i][j]= element[j];
}
}
//TODO play with localArray, don't forget to release memory ;)
}
Note that this is outline.请注意,这是大纲。 It won't compile;) (I wrote it in this overstacks' editor)
它不会编译;)(我在这个 overstacks 的编辑器中写的)
In your class you should declare native method:在您的 class 中,您应该声明本机方法:
public native void myJNIMethod(float[][] m);
and in your c code corresponding:并在您的 c 代码中对应:
JNIEXPORT jboolean JNICALL Java_ClassName_methodName (JNIEnv *, jobject, jobjectArray);
Here is JNI array operations documentation .这是JNI 数组操作文档。
For releasing the allocated memory you can do something like this:要释放分配的 memory,您可以执行以下操作:
static void releaseMatrixArray(JNIEnv *env, jobjectArray matrix) {
int size = (*env)->GetArrayLength(env, matrix);
for (int i = 0; i < size; i++) {
jfloatArray oneDim = (jfloatArray) (*env)->GetObjectArrayElement(env, matrix, i);
jfloat *elements = (*env)->GetFloatArrayElements(env, oneDim, 0);
(*env)->ReleaseFloatArrayElements(env, oneDim, elements, 0);
(*env)->DeleteLocalRef(env, oneDim);
}
}
release local Array reference:发布本地数组参考:
free(localArray);
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