标签：
在项目开发时，要调用C++封装的DLL，普通的类型C#上一般都对应，只要用DllImport传入从DLL中引入函数就可以了。但是当传递的是结构体、结构体数组或者结构体指针的时候，就会发现C#上没有类型可以对应。这时怎么办，第一反应是C#也定义结构体，然后当成参数传弟。然而，当我们定义完一个结构体后想传递参数进去时，会抛异常，或者是传入了结构体，但是返回值却不是我们想要的，经过调试跟踪后发现，那些值压根没有改变过，代码如下。
[DllImport("workStation.dll")]
private static extern bool fetchInfos(Info[] infos);
public struct Info
{
public int OrderNO;
public byte[] UniqueCode;
public float CpuPercent;
};
private void buttonTest_Click(object sender, EventArgs e)
{
try
{
Info[] infos=new Info[128];
if (fetchInfos(infos))
{
MessageBox.Show("Fail");
}
else
{
string message = "";
foreach (Info info in infos)
{
message += string.Format("OrderNO={0}\r\nUniqueCode={1}\r\nCpu={2}",
info.OrderNO,
Encoding.UTF8.GetString(info.UniqueCode),
info.CpuPercent
);
}
MessageBox.Show(message);
}
}
catch (System.Exception ex)
{
MessageBox.Show(ex.Message);
}
}
[StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
public struct Info
{
public int OrderNO;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
public byte[] UniqueCode;
public float CpuPercent;
};
[DllImport("workStation.dll")]
private static extern bool fetchInfos(IntPtr infosIntPtr);
[StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
public struct Info
{
public int OrderNO;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
public byte[] UniqueCode;
public float CpuPercent;
};
private void buttonTest_Click(object sender, EventArgs e)
{
try
{
int workStationCount = 128;
int size = Marshal.SizeOf(typeof(Info));
IntPtr infosIntptr = Marshal.AllocHGlobal(size * workStationCount);
Info[] infos = new Info[workStationCount];
if (fetchInfos(infosIntptr))
{
MessageBox.Show("Fail");
return;
}
for (int inkIndex = 0; inkIndex < workStationCount; inkIndex++)
{
IntPtr ptr = (IntPtr)((UInt32)infosIntptr + inkIndex * size);
infos[inkIndex] = (Info)Marshal.PtrToStructure(ptr, typeof(Info));
}
Marshal.FreeHGlobal(infosIntptr);
string message = "";
foreach (Info info in infos)
{
message += string.Format("OrderNO={0}\r\nUniqueCode={1}\r\nCpu={2}",
info.OrderNO,
Encoding.UTF8.GetString(info.UniqueCode),
info.CpuPercent
);
}
MessageBox.Show(message);
}
catch (System.Exception ex)
{
MessageBox.Show(ex.Message);
}
}
要注意的是，这时接口已经改成IntPtr了。通过以上方式，终于把结构体数组给传进去了。不过，这里要注意一点，不同的编译器对结构体的大小会不一定，比如上面的结构体
在BCB中如果没有字节对齐的话，有时会比一般的结构体大小多出2两个字节。因为BCB默认的是2字节排序，而VC是默认1 个字节排序。要解决该问题，要么在BCB的结构体中增加字节对齐，要么在C#中多开两个字节（如果有多的话）。字节对齐代码如下。
#pragma pack(push,1)
struct Info
{
int OrderNO;
public char UniqueCode[32];
float CpuPercent;
};
#pragma pack(pop)
用Marsh.AllocHGlobal为结构体指针开辟内存空间，目的就是转变化非托管内存，那么如果不用Marsh.AllocHGlobal，还有没有其他的方式呢？
其实，不论C++中的是指针还是数组，最终在内存中还是一个一个字节存储的，也就是说，最终是以一维的字节数组形式展现的，所以我们如果开一个等大小的一维数组，那是否就可以了呢？答案是可以的，下面给出了实现。
[DllImport("workStation.dll")]
private static extern bool fetchInfos(IntPtr infosIntPtr);
[DllImport("workStation.dll")]
private static extern bool fetchInfos(byte[] infos);
[StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
public struct Info
{
public int OrderNO;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
public byte[] UniqueCode;
public float CpuPercent;
};
private void buttonTest_Click(object sender, EventArgs e)
{
try
{
int count = 128;
int size = Marshal.SizeOf(typeof(Info));
byte[] inkInfosBytes = new byte[count * size];
if (fetchInfos(inkInfosBytes))
{
MessageBox.Show("Fail");
return;
}
Info[] infos = new Info[count];
for (int inkIndex = 0; inkIndex < count; inkIndex++)
{
byte[] inkInfoBytes = new byte[size];
Array.Copy(inkInfosBytes, inkIndex * size, inkInfoBytes, 0, size);
infos[inkIndex] = (Info)bytesToStruct(inkInfoBytes, typeof(Info));
}
string message = "";
foreach (Info info in infos)
{
message += string.Format("OrderNO={0}\r\nUniqueCode={1}\r\nCpu={2}",
info.OrderNO,
Encoding.UTF8.GetString(info.UniqueCode),
info.CpuPercent
);
}
MessageBox.Show(message);
}
catch (System.Exception ex)
{
MessageBox.Show(ex.Message);
}
}
#region bytesToStruct
/// <summary>
/// Byte array to struct or classs.
/// </summary>
/// <param name=”bytes”>Byte array</param>
/// <param name=”type”>Struct type or class type.
/// Egg:class Human{...};
/// Human human=new Human();
/// Type type=human.GetType();</param>
/// <returns>Destination struct or class.</returns>
public static object bytesToStruct(byte[] bytes, Type type)
{
int size = Marshal.SizeOf(type);//Get size of the struct or class.
if (bytes.Length < size)
{
return null;
}
IntPtr structPtr = Marshal.AllocHGlobal(size);//Allocate memory space of the struct or class.
Marshal.Copy(bytes, 0, structPtr, size);//Copy byte array to the memory space.
object obj = Marshal.PtrToStructure(structPtr, type);//Convert memory space to destination struct or class.
Marshal.FreeHGlobal(structPtr);//Release memory space.
return obj;
}
#endregion
标签：
原文地址：http://www.cnblogs.com/JUSTSOSOBLOG/p/4264377.html
