C结构到Java JNA结构（指向struct） [英] C struct to Java JNA Structure (pointer to struct)

问题描述

我有一个基于C / C ++结构JNA结构问题。场nScreenIndex，uVendorID，uProductID，uVersionNumber看起来不错，但在他们之后我看到奇怪的字节。我的主要和唯一的目标就是提取P监视器领域。
是的 P监视器的声明和 MONITOR 实施正确的？

C / C ++产地：

  SCREEN * EloGetScreenByIndex（INT nScreenIndex）;typedef结构SCREEN_TAG
{
    INT nScreenIndex;
    USHORT uVendorID;
    USHORT uProductID;
    USHORT uVersionNumber;
    wchar_t的szDevicePath [MAX_PATH];
    HANDLE hCalTouchThread;
    MONITOR * P监视器;
    LPVOID pCWndBeamHandler;
    BOOL bIrBeams;
}屏;typedef结构MONITORS_TAG
{
    INT elo_mon_num;
    INT X;
    诠释Ÿ;
    INT宽度;
    INT高度;
    DWORD方向;
    布尔is_primary;
} MONITOR;
 

和Java / JNA code：

 屏幕EloGetScreenByIndex（INT nScreenIndex）;公共类SCREEN扩展结构{
    公众诠释nScreenIndex;
    公共短uVendorID;
    公共短uProductID;
    公共短uVersionNumber;
    公众的char [] = szDevicePath新的char [WinDef.MAX_PATH]
    公共WinNT.HANDLE hCalTouchThread;
    公共MONITOR P监视器;
    公共PointerByReference pCWndBeamHandler;
    公共布尔bIrBeams;
    ...
}公共班长扩展结构{
    公众诠释elo_mon_num;
    公众诠释X;
    公众诠释Ÿ;
    公众诠释宽度;
    公众诠释高度;
    公众诠释取向;
    公共字节is_primary;    公共MONITOR（）{
        超（）;
    }    @覆盖
    保护名单，LT ;? ＆GT; getFieldOrder（）{
        返回Arrays.asList（elo_mon_num，X，Y，宽度，高度，方向，is_primary）;
    }    公共MONITOR（指针等）{
        超（同行）;
    }    公共静态类ByReference扩展MONITOR实现Structure.ByReference {
    };    公共静态类扩展根据值实现MONITOR {Structure.ByValue
    };
}
 

解决方案

您是如此非常接近正确的。

在Java中的Screen类，您需要定义 P监视器为：

 公共MONITOR.ByReference P监视器;
 

这是<一个href=\"https://github.com/java-native-access/jna/blob/master/www/FrequentlyAskedQuestions.md#when-should-i-use-structurebyreference-structurebyvalue-structure\"相对=nofollow>每页的FAQ 。

  

当我应该使用Structure.ByReference？ Structure.ByValue？结构体[]？

  typedef结构_outerstruct2 {
  simplestruct *按地址; //使用Structure.ByReference
} outerstruct2;
 

作为附录：

  

当我掐灭这件事用编了MinGW的 DLL ，我不得不从 StdCallLibrary ，而不是<$继承C $ C>图书馆 - 这可能不适合你的话，我只是提这个，因为它影响了我的测试

I have problem with JNA Structure based on C/C++ struct. Fields nScreenIndex, uVendorID, uProductID, uVersionNumber looks OK, but after them I see odd bytes. My main and only goal is to "extract" pMonitor fields. Are pMonitor declaration and MONITOR implementation correct?

C/C++ origin:

SCREEN* EloGetScreenByIndex (int nScreenIndex);

typedef struct SCREEN_TAG
{
    int               nScreenIndex;
    USHORT            uVendorID;     
    USHORT            uProductID;    
    USHORT            uVersionNumber;
    wchar_t           szDevicePath [MAX_PATH];
    HANDLE            hCalTouchThread;
    MONITOR*          pMonitor;
    LPVOID            pCWndBeamHandler;
    BOOL              bIrBeams;
} SCREEN;

typedef struct MONITORS_TAG
{
    int     elo_mon_num;
    int     x;
    int     y;
    int     width;
    int     height;
    DWORD   orientation;
    bool    is_primary;
} MONITOR;

and Java/JNA code:

SCREEN EloGetScreenByIndex(int nScreenIndex);

public class SCREEN extends Structure {
    public int nScreenIndex;
    public short uVendorID;
    public short uProductID;
    public short uVersionNumber;
    public char[] szDevicePath = new char[WinDef.MAX_PATH];
    public WinNT.HANDLE hCalTouchThread;
    public MONITOR pMonitor;
    public PointerByReference pCWndBeamHandler;
    public boolean bIrBeams;
    ...
}

public class MONITOR extends Structure {
    public int elo_mon_num;
    public int x;
    public int y;
    public int width;
    public int height;
    public int orientation;
    public byte is_primary;

    public MONITOR() {
        super();
    }

    @Override
    protected List<? > getFieldOrder() {
        return Arrays.asList("elo_mon_num", "x", "y", "width", "height", "orientation", "is_primary");
    }

    public MONITOR(Pointer peer) {
        super(peer);
    }

    public static class ByReference extends MONITOR implements Structure.ByReference {
    };

    public static class ByValue extends MONITOR implements Structure.ByValue {
    };
}

解决方案

You're so very close to right.

in the SCREEN class in java, you need to define pMonitor as:

    public MONITOR.ByReference pMonitor;

This is per the FAQ.

When should I use Structure.ByReference? Structure.ByValue? Structure[]?

typedef struct _outerstruct2 {
  simplestruct *byref; // use Structure.ByReference
} outerstruct2;  

As an addendum:

When I stubbed this up using a mingw compiled dll, I had to inherit from StdCallLibrary and not Library - this may not be the case for you, I'm just mentioning this as it affected my testing.

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