我的C声明如下：
int myData(uint myHandle,tchar *dataname,long *Time,uint *maxData,DATASTRUCT **data); typedef struct { byte Rel; __int64 Time; char Validated; unsigned char Data[1]; } DATASTRUCT ;
我的C#声明如下：
[DllImport("myData.dll",EntryPoint = "myData")]
public static extern int myData(uint myHandle,[MarshalAs(UnmanagedType.LPTStr)] string dataname,out long Time,out uint maxData,ref DATASTRUCT[] data);
[StructLayout(LayoutKind.Sequential,Pack = 1)]
public struct DATASTRUCT
{
public sbyte Rel;
public long Time;
public byte Validated;
public double Data;
}
string dataToShow = "description"; long Time; uint maxData; // How many structs will be returned,i.e. how much data is available uint myHandle = 1; DATASTRUCT[] dataInformation = new DATASTRUCT[3]; // doesn't matter what I specify as the array size? myData(myHandle,dataToShow,out Time,out maxData,ref dataInformation);
在执行时,即使有3个返回,上述函数也将成功返回只有一个结构.为什么会这样？
附加信息;我试过通过以下方式将指针传递给结构数组的指针：
- ref DATASTRUCT[] data; // Works but only returns one struct - [Out,MarshalAs(UnmanagedType.LPArray)] DATASTRUCT[] data; // returns the number of defined structs with garbage
据我了解,我可能需要使用IntPtr进行一些手动编组,但我不知道如何实现这一点,所以任何建议都将受到赞赏.
解决方法
好吧,好像你的本地库做了分配,所以你需要做的就是提供一个指针,你可以通过它来访问分配的数据.
将您的API定义更改为(注意,我将maxData参数更改为uint,.NET中为64位,本机为32位).
[DllImportAttribute("myData.dll",out uint Time,out IntPtr pData);
我不记得你是否需要最后一个参数的out关键字,但我想是的.
然后,调用myData：
uint nAllocs = 0,time = 0; IntPtr pAllocs = IntPtr.Zero; myData(1,"description",out time,out nAllocs,out pAllocs);
现在,pAllocs应该指向非托管内存,将这些内容编组到托管内存中并不太难：
[StructLayoutAttribute(LayoutKind.Sequential,Pack = 1)]
public struct DATASTRUCT
{
public byte Rel;
public long Time;
public byte Validated;
public IntPtr Data; //pointer to unmanaged string.
}
int szStruct = Marshal.SizeOf(typeof(DATASTRUCT));
DATASTRUCT[] localStructs = new DATASTRUCT[nAllocs];
for(uint i = 0; i < nallocs; i++)
localStructs[i] = (DATASTRUCT)Marshal.PtrToStructure(new IntPtr(pAllocs.ToInt32() + (szStruct * i)),typeof(DATASTRUCT));
现在你应该有一系列本地结构.
需要注意的一点您可能需要将项目设置为编译为x86,以将IntPtr的大小标准化为4字节(DWORD)而不是Anycpu的默认值8.
