Marshal.StructureToPtr Java 相当于 JNA

Question

我正在做一个项目，我必须与之通信的唯一库是一个 .dll 文件，我拥有的资源是一个带有源代码的 C# 工作项目；我正在使用 JNA 访问本机代码，目前我在调用该方法时运行进入无效内存访问；

c#代码：

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]  
public struct RSSlapInfo
{
    public int fingerType;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    public RSPoint[] fingerPosition;
    public int imageQuality;
    public int rotation;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
    public int[] reserved;
};

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct RSSlapInfoArray
{
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    public RSSlapInfo[] RSSlapInfoA;
};

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct RSPoint
{
    public int x;
    public int y;
};

RSSlapInfoArray slapInfoA = new RSSlapInfoArray();
IntPtr slapInfoArray;

int _size = Marshal.SizeOf(typeof(RSSlapInfoArray));
slapInfoArray = Marshal.AllocHGlobal(_size);
Marshal.StructureToPtr(slapInfoA, slapInfoArray, true);

在调试模式下，我注意到 slapInfoArray 值在上述调用后发生了变化

我的Java代码：

public static class RSSlapInfo extends Structure
{
    public RSSlapInfo(){}
    public int fingerType;
    public RSPoint[] fingerPosition = new RSPoint[4];
    public int imageQuality;
    public int rotation;
    public int[] reserved =new int[3];
}
    
@Structure.FieldOrder({"RSSlapInfoA"})
public static class RSSlapInfoArray extends Structure implements Structure.ByValue
{
    public RSSlapInfoArray() {
    }

    public RSSlapInfo RSSlapInfoA[] = new RSSlapInfo[4];
}

@Structure.FieldOrder({"x","y"})
public static class RSPoint extends Structure
{
    public RSPoint(){
    }

    public int x;
    public int y;
}

在使用 slapInfoArray

进行本机调用之前，目前仍停留在转换此 C# 部分代码的正确方法上

RSSlapInfoArray slapInfoA = new RSSlapInfoArray();
IntPtr slapInfoArray;
    
int _size = Marshal.SizeOf(typeof(RSSlapInfoArray));
slapInfoArray = Marshal.AllocHGlobal(_size);
Marshal.StructureToPtr(slapInfoA, slapInfoArray, true);

Answer 1

Marshal.StructureToPtr() 的文档为您提供了关于您需要做什么的强烈提示：

Marshals data from a managed object to an unmanaged block of memory.

structure A managed object that holds the data to be marshaled. This object must be a structure or an instance of a formatted class.

ptr A pointer to an unmanaged block of memory, which must be allocated before this method is called.

您有结构参数，但您需要分配第二个参数所需的内存块。这可以通过 JNA 的 Memory class.

来完成

更复杂的是，您需要传递的结构实际上包含其他结构的数组，并且必须分配在连续的内存中。您在 RSSlapInfoArray 包装中执行此操作的方式实际上根本没有分配任何内存；它只是声明了一个 java-side 数组，其中包含将传递给本机端的空指针。

您需要做的第一件事是更正您的 RSSlapInfoArray 映射以连续分配结构数组。变化

public RSSlapInfo RSSlapInfoA[] = new RSSlapInfo[4]; // does not allocate anything

至

public RSSlapInfo[] RSSlapInfoA = (RSSlapInfo[]) new RSSlapInfo().toArray(4); // contiguous allocation

您应该对 RSPoint 数组执行类似的操作：

public RSPoint[] fingerPosition = new RSPoint().toArray(4);

关于你的结构映射的另一个注意事项：你已经覆盖了 Structure class 构造函数而没有实现它。您应该删除（不需要的）构造函数或在构造函数中调用 super()。

假设您已经在加载 DLL 的接口中映射了 StructureToPtr，类似于：

void StructureToPtr(Structure structure, Pointer ptr, boolean fDeleteOld);

那么你问题中最后 5 行的 JNA 代码应该是

// Create the managed structure with the array inline
RSSlapInfoArray slapInfoA = new RSSlapInfoArray();
// Allocate a block of memory for it
Memory slapInfoArray = new Memory(slapInfoA.size());
// Call StructureToPtr
YourInterface.INSTANCE.StructureToPtr(slapInfoA, slapInfoArray, true);

Marshal.StructureToPtr Java 相当于 JNA

Marshal.StructureToPtr Java equivalent in JNA

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