I have an unmanaged C++ code and I want to convert it to managed C# code, the unmanaged code is shown below, I've searched but I did not find my answer...I want to know the right way for marshaling the below code, I am not sure how to marshal an enum and then reference it in an structure..the MMTPConxNack structure is a member of a union inside another structure.
the hierarchy is shown below:
typedef enum
{
MMTPCnxNckRsn_NoAnswer=-2,
MMTPCnxNckRsn_SendError=-1,
MMTPCnxNckRsn_Ok=0,
MMTPCnxNckRsn_InvalidMember,
MMTPCnxNckRsn_HubNotReady,
MMTPCnxNckRsn_UnknownMember,
MMTPCnxNckRsn_LastCnxTooRecent,
MMTPCnxNckRsn_InvalidVersion,
MMTPCnxNckRsn_InvalidOptions,
MMTPCnxNckRsn_TooManyCnx
} MMTPCnxNckRsn;
typedef struct
{
MMTPCnxNckRsn Reason;
} MMTPConxNack;
typedef struct
{
long Length;
short Type;
union
{
MMTPConxReq ConxReq;
MMTPConxAck ConxAck;
MMTPConxNack ConxNack; // the structure with an enum inside
MMTPErrInd ErrInd;
} Data;
} MMTPMsg;
actually I want to marshal the MMTPConxNack structure..and I use FieldOffset to define the size. Thanks in advance.
The enum looks like this:
public enum MMTPCnxNckRsn {
MMTPCnxNckRsn_NoAnswer = -2,
MMTPCnxNckRsn_SendError = -1,
MMTPCnxNckRsn_Ok = 0,
MMTPCnxNckRsn_InvalidMember,
MMTPCnxNckRsn_HubNotReady,
MMTPCnxNckRsn_UnknownMember,
MMTPCnxNckRsn_LastCnxTooRecent,
MMTPCnxNckRsn_InvalidVersion,
MMTPCnxNckRsn_InvalidOptions,
MMTPCnxNckRsn_TooManyCnx
}
The containing struct is:
public struct MMTPConxNack {
public MMTPCnxNckRsn Reason;
}
The union is:
[StructLayout(LayoutKind.Explicit)]
public struct MMTPMsgDataUnion
{
[FieldOffset(0)]
public MMTPConxReq ConxReq;
[FieldOffset(0)]
public MMTPConxAck ConxAck;
[FieldOffset(0)]
public MMTPConxNack ConxNack;
[FieldOffset(0)]
public MMTPErrInd ErrInd;
}
This is the tricky part. You use LayoutKind.Explicit and FieldOffset to specify that all the members of the C++ union is overlayed on each other. Obviously you need to have definitions for the other 3 types contained in this union, definitions that we cannot see in the C++ code in the question. I presume you already know how to define those.
Once you have the union declared, the final structure is simple:
public struct MMTPMMsg
{
public int Length;
public short Type;
public MMTPMsgDataUnion Data;
}
You need a C# enum and struct to match the native ones:
public enum MMTPCnxNckRsn
{
MMTPCnxNckRsn_NoAnswer,
MMTPCnxNckRsn_SendError,
MMTPCnxNckRsn_Ok,
MMTPCnxNckRsn_InvalidMember,
MMTPCnxNckRsn_HubNotReady,
MMTPCnxNckRsn_UnknownMember,
MMTPCnxNckRsn_LastCnxTooRecent,
MMTPCnxNckRsn_InvalidVersion,
MMTPCnxNckRsn_InvalidOptions,
MMTPCnxNckRsn_TooManyCnx
}
public struct MMTPConxNack
{
public readonly MMTPCnxNckRsn Reason;
}
And you marshal it like this:
var managedItem = (MMTPConxNack)Marshal.PtrToStructure(pointer,typeof(MMTPConxNack));
Related
Searching failed me, so i just asking it directly
Is there any way in C# to make 16bit WORD with separated access?
Something like AX and another common registers
On c++ it's like
union unsigned short
{
struct
{
char low,high;
} parts;
u16 whole;
} a;
#define ax a.whole
#define al a.parts.low
#define ah a.parts.high
and than i would use it just like
ax=0x3d5f;
ah=0x04;
and such. So the question is - Is there any way to do this without class\structures fro which one i hade to use it like
AX.h=0x04
or like that.
You'll need to use the [StructLayout] attribute, specifying LayoutKind.Explicit so you can directly control the placement of a field. Then for each field, use [FieldOffset] to control its offset from the start of the structure. Like:
using System.Runtime.InteropServices;
...
[StructLayout(LayoutKind.Explicit)]
struct X86Register {
[FieldOffset(0)] public byte reg8; // Like AL
[FieldOffset(1)] public byte reg8h; // Like AH
[FieldOffset(0)] public ushort reg16; // Like AX
[FieldOffset(0)] public uint reg32; // Like EAX
[FieldOffset(0)] public ulong reg64; // Like RAX
}
C# is an object oriented language. There is no way to do ANYTHING without classes or structures in it.
Using a class, it would for instance be implemented like this:
public class A
{
private byte[] raw;
public A()
{
raw = new byte[2];
}
public byte Low
{
get
{
return raw[0];
}
set
{
raw[0] = value;
}
}
public byte High
{
get
{
return raw[1];
}
set
{
raw[1] = value;
}
}
}
The first one in my c++ namespace is
public struct channel_vars {
int fetch_data; /* Boolean flag */
void * data; /* (malloc'd) address of data */
unsigned int lines; /* Number of lines returned */
}
I don't know what the void* is supposed to turn into when managed
The second one is
public struct hdf_call_vars_t {
struct channel_vars p_vars;
struct channel_vars s_vars;
enum FILE_VERSION file_vers; /* Set in top level sub. used in lower */
int fetch_n; /* Boolean flag */
s_line_header_t * n_addr; /* malloc'd address of ndata */
unsigned int n_lines;
csdt_file_header_t hdr;
};
In the one above, s_line_header_t is itself a struct which is made up of doubles and ints and another structure that is also made up of basic types like ints etc.
Since managed code doesn't allow pointers, how do I convert these structures to managed types? All this code is in my c++ -cli project.
thanks,
sb
You can use IntPtr class in managed code to map your field that uses pointer on unmaged code
If you are moving to c# All classes are functionally identical to pointers. They operate almost in the same way in that they can either point to a class or be null.
void* is a bit more tricky. This can point to anything. In c# all objects inherit from the base object class. So replace all void* with object and you should be fine, since you will need a cast to get back out of a both a void* and an object.
public struct ChannelVars {
public bool FetchData;
public object Data;
public uint Lines;
}
public struct HDFCallVarsT {
public ChannelVars PVars;
public ChannelVars SVars;
//enum FILE_VERSION file_vers; //you will need to get the enum set here correctly
public bool FetchN;
public SLineHeaderT NAddr; //SLineHeaderT must be a class somewhere
public uint NLines;
public CSDTFileHeaderT HDR; //CSDTFileHeaderT must be a class somewhere
};
I try to Marshal a unmanaged c++ dll in c#, but the marshaller fails when creating my union.
Why does this code fail?
[StructLayout(LayoutKind.Sequential)]
public struct StructWithArray
{
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
public int[] MySimpleArray;
//More Stuff
}
[StructLayout(LayoutKind.Explicit)]
public struct Union
{
[FieldOffset(0)]
public int Int; //Or anything else
[FieldOffset(0), MarshalAs(UnmanagedType.Struct)]
public StructWithArray MyStructWithArray;
//More Structs
}
And then constructing the Union:
Union MyUnion = new Union();
It fails if I run the code with the following Message: (Translated)
{"The Type "Union" of the Assembly [...] could not be loaded because it contained an Objectfield at Offset 0, which is not aligned correctly or got overlapped by a field which isnt a ObjectField":"Union"}
Any Suggestions?
Ps: The original code is heavily simplified to show only the Problem. There are much more Structs, and the Union is also contained by another Struct.
Declare MySimpleArray as a fixed unsafe array:
[StructLayout(LayoutKind.Sequential)]
public unsafe struct StructWithArray
{
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
public fixed int MySimpleArray[2];
//More Stuff
}
[StructLayout(LayoutKind.Explicit)]
public struct Union
{
[FieldOffset(0)]
public int Int; //Or anything else
[FieldOffset(0), MarshalAs(UnmanagedType.Struct)]
public StructWithArray MyStructWithArray;
//More Structs
}
I am calling into a native dll from C#. For the specific function in question, one of the parameters I need is a structure which contains a doubly-indirect field (pointer to a pointer).
For example, take the following C prototype and structs:
int someFunc(SomeStruct* result);
struct SomeStruct
{
DWORD foo;
AnotherStruct** ppResultStruct;
}
struct AnotherStruct
{
DWORD bar;
}
The following C# code provides only a single level of indirection for the field AnotherStruct, which is incorrect:
[DllImport("my.dll")]
public static extern int someFunc(SomeClass result);
[StructLayout(LayoutKind.Sequential)
public class SomeClass
{
int foo;
AnotherClass resultClass;
}
[StructLayout(LayoutKind.Sequential)]
public class AnotherClass
{
int bar;
}
How can I achieve the double-indirection that's required here? I know how to do it in the case of a doubly-indirect parameter to a function, but I'm confused by the fact that it's embedded in a struct.
Maybe I should declare the AnotherClass field as an IntPtr, and then resort to unsafe code to assign it an appropriate value. Is that a valid approach, and are there any other/better options?
Without a custom marashaler you cannot build a class that both contains a standard inline struct definition and double indirection. This type of marshaling requires a bit of magic to achieve.
The best way to approach this is to treat the double indirection as a pointer which it actual is. Then use a pretty property to take care of the evilness
[StructLayout(LayoutKind.Sequential)
public class SomeClass
{
int foo;
IntPtr resultPtr;
AnotherStruct resultStruct {
get {
var temp = (IntPtr)Marshal.PtrToStructure(resultPtr, typeof(IntPtr));
return (AnotherStruct)Marshal.PtrToStructure(temp, typeof(AnotherStruct));
}
}
}
[StructLayout(LayoutKind.Sequential)]
public class AnotherStruct
{
int bar;
}
I have a function in unmanaged C/C++ code (dll) that returns a structure containing a char array. I created C# struct to receive this return value uppon calling the function. And uppon calling this function i get 'System.Runtime.InteropServices.MarshalDirectiveException'
This is C declaration:
typedef struct T_SAMPLE_STRUCT {
int num;
char text[20];
} SAMPLE_STRUCT;
SAMPLE_STRUCT sampleFunction( SAMPLE_STRUCT ss );
This is C# declaration:
struct SAMPLE_STRUCT
{
public int num;
public string text;
}
class Dllwrapper
{
[DllImport("samplecdll.dll")]
public static extern SAMPLE_STRUCT sampleFunction(SAMPLE_STRUCT ss);
}
I am using 1-byte ASCII.
Does anyone has a hint or a solution on how to do this?
The trick to converting a C array member is to use the MarshalAs(UnmanagedType.ByValTStr). This can be used to tell the CLR to marshal the array as an inlined member vs. a normal non-inlined array. Try the following signature.
[System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential, CharSet=System.Runtime.InteropServices.CharSet.Ansi)]
public struct T_SAMPLE_STRUCT {
/// int
public int num;
/// char[20]
[System.Runtime.InteropServices.MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.ByValTStr, SizeConst=20)]
public string text;
}
public partial class NativeMethods {
/// Return Type: SAMPLE_STRUCT->T_SAMPLE_STRUCT
///ss: SAMPLE_STRUCT->T_SAMPLE_STRUCT
[System.Runtime.InteropServices.DllImportAttribute("<Unknown>", EntryPoint="sampleFunction")]
public static extern T_SAMPLE_STRUCT sampleFunction(T_SAMPLE_STRUCT ss) ;
}
This signature is brought to you by the PInovke Interop Assistant (link) available on CodePlex. It can automatically translate most PInvoke signatures from native code to C# or VB.Net.
This is not an easy structure for P/Invoke to marshal: it's easier to marshal structures that contain char* instead of char[] (although you're then left with the problem of allocating the char* from unmanaged code and later freeing it from managed code).
Assuming you're sticking with the current design, one option is to declare the string array as:
public fixed char text[20];
Unfortunately you must then add the unsafe keyword to any code that accesses this array.
Struct definition in C:
#pragma pack(push, 1)
typedef struct T_SAMPLE_STRUCT {
int num;
char text[20];
};
#pragma pack(pop)
Definition in C#:
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
public struct T_SAMPLE_STRUCT
{
[MarshalAs(UnmanagedType.I4)]
public int num;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 20)]
public string text;
}
I have managed to do this by separating function to:
void receiveStruct( SAMPLE_STRUCT ss )
void returnStruct(SAMPLE_STRUCT &ss)
I have changed struct definition as JaredPar told me:
[StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct T_SAMPLE_STRUCT
{
/// int
public int num;
/// char[20]
[MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst = 20)]
public string text;
}
And now it works.
Thanks!
As an interesting aside, since you already have the answer, the basic issue here is that the struct just needs to be the right size. Since managed types don't have inline arrays, you just have to make up the space that it would otherwise need. When you write in C++/CLI, you'll often see the StructLayoutAttribute with an explicit Size parameter. This makes the runtime allocate the right amount of memory for the type, which allows it to be blittable to the native side. It follows that these should work, as well:
[StructLayout(LayoutKind.Sequential, Size=24)]
public struct T_SAMPLE_STRUCT
{
public int num;
// to get the string here, you'd need to get a pointer
public char firstChar;
}
// or
[StructLayout(LayoutKind.Sequential)]
public struct T_SAMPLE_STRUCT
{
public int num;
public byte c0;
public byte c1;
public byte c2;
public byte c3;
public byte c4;
public byte c5;
public byte c6;
public byte c7;
public byte c8;
public byte c9;
public byte c10;
public byte c11;
public byte c12;
public byte c13;
public byte c14;
public byte c15;
public byte c16;
public byte c17;
public byte c18;
public byte c19;
}
Of course, these are much harder to use from managed code (you'd need to copy memory or use pointers), but they illustrate the concept of a blittable type, which is primarily how types are passed between native and managed code.
First you have to put
StructLayout[Sequential] attribute on your struct and I think it will work
[ StructLayout( LayoutKind.Sequential, CharSet=CharSet.Ansi )]
struct SAMPLE_STRUCT
{
public int num;
[ MarshalAs( UnmanagedType.ByValArray, SizeConst=20 )]
public char[] text;
}