如何使用 JNI 将 C 结构转移到 java？
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How to transfer a C structure to java by use of JNI?
提问by Steffen Kuehn
From C I am creating a DLL which is loaded in Java. I call some C functions from java and also call Java functions from C (whith uncomplex data types) - this is working fine.
从 CI 正在创建一个以 Java 加载的 DLL。我从 java 调用了一些 C 函数，也从 C 调用了 Java 函数（带有不复杂的数据类型） - 这工作正常。
I struggle with the transfer of a C structure to Java.
我努力将 C 结构转移到 Java。
Here is a small example descriping what I want to do. It is not complete and maybe not correct because my problem is that I am not sure how to do it.
这是一个描述我想要做的事情的小例子。它不完整，可能不正确，因为我的问题是我不知道该怎么做。
My goal is to pass a structure from the type "StructType" from C to Java in order to use the values in the Java program.
我的目标是将“StructType”类型的结构从 C 传递到 Java，以便在 Java 程序中使用这些值。
In C
在 C
typedef struct {
unsigned char value1;
unsigned char value2;
} StructType;
void passStructToJava(StructType* myStruct)
{
class cls;
jmethodID mid;
/* GlobalEnv, GlobalObj are globlal values which are already set */
cls = (*GlobalEnv)->GetObjectClass(GlobalEnv, GlobalObj);
mid = (*GlobalEnv)->GetMethodID(GlobalEnv, cls, "receiveStructFromC", "(LPackage/StructType;)V");
(*GlobalEnv)->CallVoidMethod(GlobalEnv, GlobalObj, mid, myStruct);
}
In Java
在 Java 中
public class StructType {
public int value1; /* int because there is no uint8 type */
public int value2;
}
public StructType mMyStruct;
public StructType getMyStruct() {
return mMyStruct;
}
public void setMyStruct(StructType myStruct) {
mMyStruct = myStruct;
}
public void receiveStructFromC(StructType myStruct)
{
setMyStruct(myStruct);
}
Thanks in advance for your help.
Steffen
在此先感谢您的帮助。
史蒂芬
回答by dacwe
Check my post in this question: pass data between Java and C
检查我在这个问题中的帖子：在 Java 和 C 之间传递数据
回答by Vladimir Ivanov
I would suggest returning an int array, as far as your structure doesn't consist anything else.
我建议返回一个 int 数组，只要您的结构不包含任何其他内容。
As for returning the object: you can create an object of your StructType class, fill the values with setters and return it.
至于返回对象：您可以创建一个 StructType 类的对象，用 setter 填充值并返回它。
The necessary code samples can be found here.
可以在此处找到必要的代码示例。
Just the example, I haven't check this code.
只是示例，我还没有检查此代码。
returnObj = (*env)->AllocObject(env, objClass);
if (returnObj == 0) printf("NULL RETURNED in AllocObject()\n");
printf("Sizeof returnObj = %d\n", sizeof(returnObj) );
(*env)->SetObjectField (env, returnObj, fid5,
combinedEmployeeNameJava);
(*env)->SetIntField (env, returnObj, fid6, combinedSalary);
