如何获取java JNA调用DLL以获取参数中返回的数据？ [英] How do I get a java JNA call to a DLL to get data returned in parameters?

问题描述

我有这个java测试

package ftct;

import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Platform;
import com.sun.jna.win32.StdCallLibrary;
import java.util.Date;

public class LibFTCT {


public LibFTCT() {
 }
 public interface LibFTCTLib extends StdCallLibrary {
          LibFTCTLib INSTANCE = (LibFTCTLib) Native.loadLibrary(
             "FTCTLib", LibFTCTLib.class);
      int a(int x);
      int DoCommand(int Command, int Param);
    int GetDataRecord(int RecordNum, int StreamNum, Date ReadingTime,
   double AIN1, double AIN2, double AIN3, double AIN4);

 }
}

它调用Delphi DLL。如果在Delphi中将参数设置为var，则Java会崩溃。否则它们是只读的。

It calls a Delphi DLL. If put the parameters as var in Delphi the Java crashes. Otherwise they are read only.

我希望GetDataRecord在RecordNum中返回数据。我如何在java中执行此操作？

I want GetDataRecord to return data in RecordNum etc. How do I do this in java?

推荐答案

您需要将参数声明为特殊类型，表示通过引用传递的事实。所以如果Delphi参数是这样的：

You need to declare the parameters as special types that convey the fact that they are passed by reference. So if the Delphi parameters are like this:

procedure Foo(var i: Integer; var d: Double);

您将把它映射到这样的Java函数：

you would map that to a Java function like this:

void Foo(IntByReference i, DoubleByReference d);

并调用函数：

IntByReference iref = new IntByReference();
DoubleByReference dref = new DoubleByReference();
INSTANCE.Foo(iref, dref);
int i = iref.getValue();
double d = dref.getValue():

这一切都在文档：

使用ByReference参数

当一个函数接受一个指针型参数时，你可以使用
的ByReference类型中的一个来捕获返回的值，或者将
自己的子类化。例如：

When a function accepts a pointer-to-type argument you can use one of the ByReference types to capture the returned value, or subclass your own. For example:

// Original C declaration
void allocate_buffer(char **bufp, int* lenp);

// Equivalent JNA mapping
void allocate_buffer(PointerByReference bufp, IntByReference lenp);

// Usage
PointerByReference pref = new PointerByReference();
IntByReference iref = new IntByReference();
lib.allocate_buffer(pref, iref);
Pointer p = pref.getValue();
byte[] buffer = p.getByteArray(0, iref.getValue());

或者，您可以使用具有
所需类型的单个元素的Java数组，但是ByReference约定更好地传达了代码的意图
。指针类提供了许多访问器方法
，除了getByteArray（），它有效地作为一个类型转换
在内存上。

Alternatively, you could use a Java array with a single element of the desired type, but the ByReference convention better conveys the intent of the code. The Pointer class provides a number of accessor methods in addition to getByteArray() which effectively function as a typecast onto the memory.

Type-可以通过从PointerType
类派生来声明安全指针。

Type-safe pointers may be declared by deriving from the PointerType class.

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