I am trying to use functions in C++ dll from C#, but I got an error: "attempt to read or write protected memory. This is often indication that other memory is corrupt"
Anyone know how to fix ?
Here is C++ functions:
typedef void *DGNHandle;
__declspec(dllexport) DGNHandle CPL_DLL DGNOpen( const char *, int );
__declspec(dllexport) DGNElemCore CPL_DLL *DGNReadElement( DGNHandle )
Here is structure in C++:
typedef struct {
int offset;
int size;
int element_id; /*!< Element number (zero based) */
int stype; /*!< Structure type: (DGNST_*) */
int level; /*!< Element Level: 0-63 */
int type; /*!< Element type (DGNT_) */
int complex; /*!< Is element complex? */
int deleted; /*!< Is element deleted? */
int graphic_group; /*!< Graphic group number */
int properties; /*!< Properties: ORing of DGNPF_ flags */
int color; /*!< Color index (0-255) */
int weight; /*!< Line Weight (0-31) */
int style; /*!< Line Style: One of DGNS_* values */
int attr_bytes; /*!< Bytes of attribute data, usually zero. */
unsigned char *attr_data; /*!< Raw attribute data */
int raw_bytes; /*!< Bytes of raw data, usually zero. */
unsigned char *raw_data; /*!< All raw element data including header. */
} DGNElemCore;
And below converted codes are in C#:
[StructLayout(LayoutKind.Sequential )]
public class DGNElemCore
{
public int attr_bytes;
public byte[] attr_data;
public int color;
public int complex;
public int deleted;
public int element_id;
public int graphic_group;
public int level;
public int offset;
public int properties;
public int raw_bytes;
public byte[] raw_data;
public int size;
public int style;
public int stype;
public int type;
public int weight;
}
[DllImport("DgnLib.dll", EntryPoint = "DGNOpen")]
public static extern IntPtr DGNOpen(string fileName, int bUpdate);
[DllImport("DgnLib.dll", EntryPoint = "DGNReadElement")]
public static extern DGNElemCore DGNReadElement(IntPtr DGNHandle)
Codes for testing:
DGNElemCore element = new DGNElemCore();
element = DgnFile.DGNReadElement(dgnFile.oDgnFile) **//Throw error**
Your declaration of DGNElemCore in your C# code is wrong - it needs to exactly match your C structure (especially in size) as otherwise the marshalling code will attempt to marshal memory incorrectly. An example definition which will work (as in not cause problems during marshalling) would be the following
[StructLayout(LayoutKind.Sequential )]
public class DGNElemCore
{
int offset;
int size;
int element_id;
int stype;
int level;
int type;
int complex;
int deleted;
int graphic_group;
int properties;
int color;
int weight;
int style;
int attr_bytes;
IntPtr attr_data;
int raw_bytes;
IntPtr raw_data;
}
Note in particular
The order of members in the C# classes match those in the C struct (although this wont cause an error when calling your function it will give you incorrect values when accessing the members of the marshalled struct)
The char* fields are marshalled as IntPtrs - attempting to marshal pointers to arrays as arrays won't work by default as arrays are larger than pointers, resulting in the marshaller attempting to marshal more memory than is available.
Also I've noticed that your P/Invoke method declarations are wrong. The DGNOpen function returns the structure itself (not a pointer) and so should look more like the following.
public static extern DGNElemCore DGNOpen(string fileName, int bUpdate);
The DGNReadElement function accepts a struct (not a pointer) and returns a pointer to that strucut (not a struct) and so should look more like this
public static extern IntPtr DGNReadElement(DGNHandle handle);
Attributes can be used to change the way that the marshaller works, which can in turn be used to alter the signature of these methods, however if you do this you need to be careful to ensure that the marshalling will still match up to your C++ function declarations.
The problem is that the #include headers might contain declarations that can be misinterpreted by the C++/CLI compilers. C function declarations for example. Best thing to do is to the tell the compiler explicitly about it.
#pragma managed(push, off)
#include "c_include.h"
#pragma managed(pop)
Then you can use C++ libraries from within C++/CLI application like you do with C++ apps. The only thing I always try to do is to wrap 3rd library behind Proxy or Facade design pattern, so that the client would always work with managed classes. This is especially important if your C++/CLI app is a library used by other .NET apps.
Moreover, normally public API classes (or functions) of your DLL should be exposed using following construction:
#ifdef YOUR_DLL_EXPORTS
#define YOUR_API __declspec(dllexport)
#else
#define YOUR_API __declspec(dllimport)
#endif
class YOUR_API ClassToExpose {};
Hope this help
Related
i am desperate to get a complex c datatype correctly marshaled for C#. I already read all the other posts regarding that topic and i am running out of ideas although it seems to me to be quite close to the solution.
The main issue is that the c-struct is having a union of two different struct types. On with only basic types and one including arrays, which causes trouble.
I have created an example to showcase the situation. The struct worring me is called dataStreamConfiguration. The c code looks like this, the struct in question is at the bottom of the example c-code:
#include "stdint.h"
#include "stddef.h"
typedef enum viewCapEnum {
X = 0,
}viewCapEnum;
typedef struct fraction{
uint8_t nominator;
uint8_t denominator;
}fraction;
typedef struct comSize{
fraction A;
fraction B;
}comSize;
typedef enum someEnum{
A = 0,
B,
C,
D
}someEnum;
typedef struct someSize{
fraction X;
fraction Y;
}someSize;
typedef struct featTemplateCap{
someEnum A;
someSize Size;
}featTemplateCap;
typedef struct featTypeCap{
someEnum AB;
someSize CD;
}featTypeCap;
typedef struct viewCap{
uint8_t A;
uint8_t B;
size_t BCount;
viewCapEnum ViewCapEnum[50];
comSize MinComSize;
size_t CapaCount;
featTemplateCap TemplCap[14];
size_t TypeCapaCount;
featTypeCap FeatTypeCapa[14];
uint8_t GCount;
}viewCap;
typedef struct featX{
uint16_t A;
uint16_t B;
int16_t C;
int16_t D;
}featX;
typedef struct pathCap{
uint8_t Count;
uint8_t Size;
featX Feat;
}pathCap;
typedef struct dataStreamConfiguration{
size_t FeatureSelector;
union {
viewCap AsViewCap;
pathCap AsPathCap;
}dataStream;
}dataStreamConfiguration;
The marshalling of datatypes between C and the C# world is working for almoust all but this dataStreamConfiguration struct. So I got the following code, where instead of mapping (somehow) a union to c# both datatypes have been put one after another. So clearly this was not working correctly. It looked like that:
public unsafe struct UInt32Struct {
public UInt32 value;
}
public unsafe struct fraction{
public Byte nominator;
public Byte denominator;
}
public unsafe struct comSize{
public fraction A;
public fraction B;
}
public unsafe struct someSize{
public fraction X;
public fraction Y;
}
public unsafe struct featTemplateCap{
public UInt32 A;
public someSize Size;
}
public unsafe struct featTypeCap{
public UInt32 AB;
public someSize CD;
}
public unsafe struct viewCap{
public Byte A;
public Byte B;
public UInt16 BCount;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 50]
public UInt32Struct[] ViewCapEnum;
public comSize MinComSize;
public UInt16 CapaCount;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 14]
public featTemplateCap[] TemplCap;
public UInt16 TypeCapaCount;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 14]
public featTypeCap FeatTypeCapa[14];
public Byte GCount;
}
public unsafe struct featX{
public UInt16 A;
public UInt16 B;
public Int16 C;
public Int16 D;
}
public unsafe struct pathCap{
public Byte Count;
public Byte Size;
public featX Feat;
}
public unsafe struct dataStreamConfiguration{
public UInt16 FeatureSelector;
public viewCap AsViewCap;
public pathCap AsPathCap;
}
So to get the union to c# I came across the LayoutKind.Explicit and did following:
[StructLayout(LayoutKind.Explicit)]
public unsafe struct dataStreamConfiguration{
[FieldOffset(0)]
public UInt16 FeatureSelector;
[FieldOffset(2)]
public viewCap AsViewCap;
[FieldOffset(2)]
public pathCap AsPathCap;
}
This was not working due to the alignment of the object types, which are incorrectly aligned or overlapped by non-object fields.. I googled a lot. Adjusted the alignment to 4 by [StructLayout(LayoutKind.Explicit, Pack=4)]. However, 4,8,16,32, whatever alignment i have choosen, I got the same error during runtime - incorrectly aligned or overlapped issue.
Next thing I did - I felt quite lucky about - was to unroll all the arrays in C# datatype for all the arrays in viewCap struct. As I have read that this might cause alignment issues. Well, It didn't work. And I found that the memory has been modified, so I could not find the values I have seen in C appearing now in C#. Most of the values in C# are 0. Ok.
To get rid of this memory modification stuff I put in C# to all other structs [StructLayout(LayoutKind.Sequential)] to keep the order of elements as they are in C. Sadly it didn't help much, I could not find the values of the c-struct in c# either. However, it was finally working, when I got rid of the union and deleted either AsViewCap or AsPathCap (my weak moment of blind rage). Ok, but that was not the solution.
Last help was having a try with IntPtr, so i have created a new struct called dataStreamConfigurationPtr:
public unsafe struct dataStreamConfigurationPtr{
public UInt16 FeatureSelector;
public void* Ptr;
}
[StructLayout(LayoutKind.Sequential)]
public unsafe struct dataStreamConfiguration{
public UInt16 FeatureSelector;
public viewCap AsViewCap;
public pathCap AsPathCap;
}
Instead of having an overlapping memory with StructLayout.Explicit I used an void* to point to the unmanaged memory location. For this I used the old struct definition to get the memory and instead having a union I took the first version where both types are laid out one over another. The idea was to use it like that:
MyFunction(dataStreamConfigurationPtr X, int Status){
//Create obj and appropraite space for data
dataStreamConfiguration DataStream = new dataStreamConfiguration();
DataStream.FeatureSelector = X.FeatureSelector;
unsafe{
IntPtr Ptr = new IntPtr(&X.Ptr);
DataStream.AsViewCap = Marshal.PtrToStructure<viewCap>(Ptr);
DataSteram.AsPathCap = Marshal.PtrToStructure<pathCap>(Ptr);
}
WCFCallback(DataStream, Status);
}
Now the IntPtr is pointing to the right memory, however, this works only for the first item of the structs. So for viewCap the first item A has its correct data whereas item B, BCount,.. all the other item seem to have at least misalligned values or accidental values.. I am quite desperate what to do now, i feel i am so close to a solution but have no idea how to get the other data of the struct from c to c#.
Any suggestions and comments are highly welcome!
Best regards,
Tobias
I would assume you have two use cases and want to interprete the union part based FeatureSelector either as AsViewCap or as AsPathCap on C# side.
That means I assume that you don't intend to do type punning.
One could create two structs then on the managed C# side:
public struct dataStreamConfigurationAsViewCap
{
public UInt64 FeatureSelector;
public viewCap AsViewCap;
}
public struct dataStreamConfigurationAsPathCap
{
public UInt64 FeatureSelector;
public pathCap AsPathCap;
}
You could then only inspect FeatureSelector first and based on the result either interprete it dataStreamConfigurationAsViewCap or as dataStreamConfigurationAsPathCap.
Size
You have several variables with size_t on C side (FeatureSelector, BCount, CapaCount, TypeCapaCount) which you map all to UInt16, which is wrong. UInt16 is the minimum size in the C standard, but the usual implementations especially on platforms running .NET are larger, see also this nice answer. For example on my macOS machine it is 8 bytes.
Maybe it would be a good idea to start with a smaller test case and expand it step by step so that you can identify such problems. And when you encounter a problem, you can more easily create a minimal, complete and testable example.
One approach in this direction could be the following:
Small Test Case
some.h
#ifndef some_h
#define some_h
#include <stdio.h>
typedef struct viewCap {
uint8_t A;
uint8_t B;
} viewCap;
typedef struct pathCap {
uint16_t X;
uint16_t Y;
size_t Num;
} pathCap;
typedef struct dataStreamConfiguration {
size_t FeatureSelector;
union {
viewCap AsViewCap;
pathCap AsPathCap;
} dataStream;
} dataStreamConfiguration;
dataStreamConfiguration *dscViewCap(void);
dataStreamConfiguration *dscPathCap(void);
extern void free_struct(dataStreamConfiguration *ptr);
#endif /* some_h */
some.c
#include "some.h"
#include <stdlib.h>
#include <stdint.h>
#include <stddef.h>
dataStreamConfiguration *dscViewCap(void) {
dataStreamConfiguration *dsc = calloc(1, sizeof(dataStreamConfiguration));
dsc->FeatureSelector = 0;
dsc->dataStream.AsViewCap.A = 42;
dsc->dataStream.AsViewCap.B = 84;
return dsc;
}
dataStreamConfiguration *dscPathCap(void) {
dataStreamConfiguration *dsc = calloc(1, sizeof(dataStreamConfiguration));
dsc->FeatureSelector = 1;
dsc->dataStream.AsPathCap.X = 0xAAAA;
dsc->dataStream.AsPathCap.Y = 0x5555;
dsc->dataStream.AsPathCap.Num = 0x3333333333333333;
return dsc;
}
void free_dsc(dataStreamConfiguration *ptr) {
free(ptr);
}
int main(void) {
return 0;
}
UnionFromC.cs
using System.Runtime.InteropServices;
namespace UnionFromC
{
public static class Program
{
public struct viewCap
{
public Byte A;
public Byte B;
}
public struct pathCap
{
public UInt16 X;
public UInt16 Y;
public UInt64 Num;
}
public struct dataStreamConfigurationAsViewCap
{
public UInt64 FeatureSelector;
public viewCap AsViewCap;
}
public struct dataStreamConfigurationAsPathCap
{
public UInt64 FeatureSelector;
public pathCap AsPathCap;
}
[DllImport("StructLib", EntryPoint = "dscViewCap")]
private static extern IntPtr NativeDSCViewCap();
[DllImport("StructLib", EntryPoint = "dscPathCap")]
private static extern IntPtr NativeDSCPathCap();
[DllImport("StructLib", EntryPoint = "free_dsc")]
private static extern void NativeFreeDSC(IntPtr ptr);
static void Main()
{
IntPtr _intPtrViewCap = NativeDSCViewCap();
var viewDSC = Marshal.PtrToStructure<dataStreamConfigurationAsViewCap>(_intPtrViewCap);
Console.WriteLine("\nInterpretation as view cap:");
Console.WriteLine($" FeatureSelector: {viewDSC.FeatureSelector}");
Console.WriteLine($" A: {viewDSC.AsViewCap.A}");
Console.WriteLine($" B: {viewDSC.AsViewCap.B}");
NativeFreeDSC(_intPtrViewCap);
IntPtr _intPtrPathCap = NativeDSCPathCap();
var pathDSC = Marshal.PtrToStructure<dataStreamConfigurationAsPathCap>(_intPtrPathCap);
Console.WriteLine("\nInterpretation as path cap:");
Console.WriteLine($" FeatureSelector: {pathDSC.FeatureSelector}");
Console.WriteLine($" A: {pathDSC.AsPathCap.X:X4}");
Console.WriteLine($" B: {pathDSC.AsPathCap.Y:X4}");
Console.WriteLine($" Num: {pathDSC.AsPathCap.Num:X8}");
NativeFreeDSC(_intPtrPathCap);
}
}
}
Output of the Test
Interpretation as view cap:
FeatureSelector: 0
A: 42
B: 84
Interpretation as path cap:
FeatureSelector: 1
A: AAAA
B: 5555
Num: 3333333333333333
This is one solution how to get data from C/C++ to C#. Here I will describe what I did wrong and what one has to take care of.
To recall in our minds my requirement has been (still is) that any data represented as union in C/C++, needs to be represented as such in C#. This means for following structure:
typedef struct dataStreamConfiguration{
size_t FeatureSelector;
union {
viewCap AsViewCap;
pathCap AsPathCap;
}dataStream;
}dataStreamConfiguration;
Any data inside AsViewCap must have its kind of representation in AsPathCap, because its simple the same memory. If one of these two are modified, the other is also. To handle C/C++ unions in C# you need to provide a memory layout. As Stephan Schlecht already meantioned it is vital to know the alignment! My project is compiled for 32bit the alignment is at the 4 Byte boarder. Thus my initial layout in my question was simply wrong. You need to check the layout in your C/C++ project and adjust it in the C# struct definion properly: Here is my corrected code, both union members start at 4th Byte:
[StructLayout(LayoutKind.Explicit)]
public unsafe struct dataStreamConfiguration{
[FieldOffset(0)]
public UInt16 FeatureSelector;
[FieldOffset(4)]
public viewCap AsViewCap;
[FieldOffset(4)]
public pathCap AsPathCap;
}
Doing this you are half way there! Yes! But there is one more thing. With this change the Code will compile but, you will get an exception at runtime. Yes, at runtime. Quite quick but it is so. The error message something like: "object-field at offset 4 is incorrectly aligned or overlapped by a non-object field"
C# is bugging is because in C# there are basic types like Integer etc. and reference types.
These reference types can give us errors if we do not handel them correctly. C# has a very nice working marshalling, but in case of unions, its up to you to make it as nice as it can get.
Explenation:
What went wrong in my code is that the struct viewCap is having arrays, marshalled by the C# marshaller. The marshaller is doing his duty and creating an array. However, an array is a reference type and created on the heap. What you will get on the stack (data transfer C++ <-> C#) is the reference address to the array on the heap. Hmpf! Thus the second structure in the union with its basic types would overlapping the address and thus invalidating the reference. Gladly the runtime environment stops us from doing that :-) Moreover, C# is defragmenting the memory. If the struct layout is not efficient regarding memory usage C# will reoder the content. You can avoid this by annotating the struct which the layout kind: Sequential.
Remember:
If you got an array inside a type which is part of a union (C/C++), you cannot use the C# marshaller! Use Layoutkind Explicit for unions and Sequential for structs!
Solution:
There might be several other solutions I am not aware of, but what is 100% working is to unroll the arrays. Yes, it's a lot of work. But it works!
So the final struct looks like this:
[StructLayout(LayoutKind.Sequential)]
public unsafe struct viewCap{
public Byte A;
public Byte B;
public UInt16 BCount;
public UInt32Struct ViewCapEnum_0;
public UInt32Struct ViewCapEnum_1;
public UInt32Struct ViewCapEnum_2;
public UInt32Struct ViewCapEnum_3;
[...]
public comSize MinComSize;
public UInt16 CapaCount;
public featTemplateCap TemplCap_0;
public featTemplateCap TemplCap_1;
public featTemplateCap TemplCap_2;
public featTemplateCap TemplCap_3;
[...]
public UInt16 TypeCapaCount;
public featTypeCap FeatTypeCapa_0;
public featTypeCap FeatTypeCapa_1;
public featTypeCap FeatTypeCapa_2;
public featTypeCap FeatTypeCapa_3;
[...]
public Byte GCount;
}
Happy runtime environment, happy life!
Yes, for this specific solution you would need to adjust the code which is using the arrays. However, its bulletproof and understandable how this works under the hood which makes it easy for maintenance. As my code is generated, an unrolled array is no big deal.
I found several questions on this topic but nothing, which fits my exact problem. I'm having structs in a C DLL, for example like this one here:
extern "C"
{
struct CStruct
{
int alpha;
double beta;
};
}
CSharpStruct has the same structure as its C friend, like this:
public struct CSharpStruct
{
public int alpha;
public double beta;
}
and want to deliver the data by reference to a c# program.
I created a method in the C DLL which is able to return
a pointer to the struct like this one here: (test data)
const EXPORT_API CStruct* GetStruct()
{
CStruct1.alpha = 21;
CStruct1.beta = 23.141;
return &CStruct1;
}
and I am able to access the data in c# in this way:
[DllImport("ASimplePlugin")]
private static extern IntPtr GetStruct();
//...
IntPtr cStruct = GetStruct();
CSharpStruct test = (CSharpStruct) Marshal.PtrToStructure(cStruct, typeof(CSharpStruct));
After that I can access the data from C, but Marshal.PtrToStructure
copies them from the IntPtr reference into the C# struct by Value.
What I want to achieve is to have a direct reference to the c values
in the c# struct so that changing it in c# changes the values in c.
How is this possible?
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 am trying to call a function from C# to a .DLL written in Borland C++ whose signature is:
extern "C" __declspec(dllexport) ls50errortype __stdcall Ls50P2Open(ls50p2apiconfiginfostruct &configinfo);
The corresponding call in C#:
[DllImport("C:\\Lumistar\\LDPS_8x\\Ls50P2_Dll.dll", EntryPoint = "Ls50P2Open", CallingConvention = System.Runtime.InteropServices.CallingConvention.StdCall, CharSet = CharSet.Ansi, SetLastError = true)]
public static extern void Ls50P2Open(ref ls50p2apiconfiginfostruct configinfo);
The structure of interest (ls50p2apiconfiginfostruct) is composed of nested structures and enums (copied from the C++ header):
typedef enum
{
MFMODEL_LS50P1,
MFMODEL_4422PCI,
MFMODEL_LS50P2,
MFMODEL_LS70P2,
MFMODEL_LS5070,
MFMODEL_LAST
}ecardmodel;
typedef enum
{
CHANNELDEVICE_NONE,
CHANNELDEVICE_50,
CHANNELDEVICE_70,
CHANNELDEVICE_LAST
}ls50p2channeldevicetype;
typedef enum
{
LS50V2DCARD_NONE,
LS50V2DCARD_40V1_10,
LS50V2DCARD_40V1_20,
LS50V2DCARD_40V2_10,
LS50V2DCARD_40V2_20,
LS50V2DCARD_38,
LS50V2DCARD_LAST
}ls50p2daughtercardtype;
typedef struct
{
bool HasDaughterCard;
ls50p2daughtercardtype DCardType;
bool SpecialStatusCapable;
int MaxBitsyncInputs;
bool HasBitsyncConfidenceLevel;
bool HasBitsync2ndCh;
bool SpecialStatusCapable2ndCh;
bool HasBitsyncConfidenceLevel2ndCh;
ls50p2daughtercardtype DCardType2ndCh;
int MaxBitsyncInputs2ndCh;
}ls50p2daughtercardinfostruct;
typedef struct
{
ecardmodel DeviceModel;
ls50p2channeldevicetype ChannelDataTypeAry[2];
ls50p2daughtercardinfostruct DaughterCardInfo;
bool HasExtendedBertPatterns;
int FirmwareVersionAry[2];
int NumPremodFiltersAry[2];
double Ls50SimPreModFilterKhzAry[2][LS50V2_MAX50SIMPREMODFILTERS];
double Ls50SimMinFmDeviationKhzAry[2];
double Ls50SimMaxFmDeviationKhzAry[2];
}ls50p2cardconfigstruct;
typedef struct
{
unsigned char *DataBuf;
HANDLE hNewDataRdy;
DWORD MaxBufLength;
DWORD CurrentBufLength;
int NumHeaderBytes;
}ls50p2carddatastruct;
typedef struct
{
ls50p2cardconfigstruct CardConfigInfo[MAXMFCARDS];
int Ls50P2CardCount;
ls50p2carddatastruct DataInfo[MAXMFCARDS][2];
}ls50p2apiconfiginfostruct;
Here's the corresponding struct in C#:
public enum ecardmodel
{
MFMODEL_LS50P1,
MFMODEL_4422PCI,
MFMODEL_LS50P2,
MFMODEL_LS70P2,
MFMODEL_LS5070,
MFMODEL_LAST
}
public enum ls50p2channeldevicetype
{
CHANNELDEVICE_NONE,
CHANNELDEVICE_50,
CHANNELDEVICE_70,
CHANNELDEVICE_LAST
};
public enum ls50p2daughtercardtype
{
LS50V2DCARD_NONE,
LS50V2DCARD_40V1_10,
LS50V2DCARD_40V1_20,
LS50V2DCARD_40V2_10,
LS50V2DCARD_40V2_20,
LS50V2DCARD_38,
LS50V2DCARD_LAST
}
[StructLayout(LayoutKind.Sequential)]
public struct ls50p2daughtercardinfostruct
{
public bool HasDaughterCard;
public ls50p2daughtercardtype DCardType;
public bool SpecialStatusCapable;
public int MaxBitsyncInputs;
public bool HasBitsyncConfidenceLevel;
public bool HasBitsync2ndCh;
public bool SpecialStatusCapable2ndCh;
public bool HasBitsyncConfidenceLevel2ndCh;
public ls50p2daughtercardtype DCardType2ndCh;
public int MaxBitsyncInputs2ndCh;
}
[StructLayout(LayoutKind.Sequential)]
public struct ls50p2cardconfigstruct
{
public ecardmodel DeviceModel;
public ls50p2daughtercardtype[] ChannelDataTypeAry;
public ls50p2daughtercardinfostruct DaughterCardInfo;
public bool HasExtendedBertPatterns;
public int[] FirmwareVersionAry;
public int[] NumPremodFiltersAry;
public double[] Ls50SimPreModFilterKhzAry;
public double[] Ls50SimMinFmDeviationKhzAry;
public double[] Ls50SimMaxFmDeviationKhzAry;
}
[StructLayout(LayoutKind.Sequential)]
public struct ls50p2carddatastruct
{
public StringBuilder DataBuf;
public IntPtr hNewDataRdy;
public uint MaxBufLength;
public uint CurrentBufLength;
public int NumHeaderBytes;
}
[StructLayout(LayoutKind.Sequential)]
public struct ls50p2apiconfiginfostruct
{
public ls50p2cardconfigstruct[] CardConfigInfo;
public int Ls50P2CardCount;
public ls50p2carddatastruct[,] DataInfo;
}
Here's the code in C# that I use to call the function:
ls50p2apiconfiginfostruct lscfg = new ls50p2apiconfiginfostruct();
lscfg.CardConfigInfo = new ls50p2cardconfigstruct[8];
for (int i = 0; i < 8; i++)
{
lscfg.CardConfigInfo[i].ChannelDataTypeAry = new ls50p2daughtercardtype[2];
}
lscfg.DataInfo = new ls50p2carddatastruct[8, 2];
Ls50P2Open(ref lscfg);
I have tried making this struct in C# but I haven't had much success (problems with enums, 2D arrays, fixed sized buffers). What is the correct way to create this structure in C#? Would this need to be done in an unsafe context?
Now for some reason I get the following error when running the code:
An unhandled exception of type 'System.Runtime.InteropServices.COMException' occurred in Library.dll
Additional information: Old format or invalid type library. (Exception from HRESULT: 0x80028019 (TYPE_E_UNSUPFORMAT))
What does your C# structure looks like. Are you using the StructLayoutAttribute?
http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.structlayoutattribute.aspx
You can use it with the option sequential so you just would have to fill your c# structure with fields in the right order.
I believe the array problem is more or less answered here; Improper marshaling: C# array to a C++ unmanaged array
The accepted answer shows how to safely marshal a dynamically allocated array.
As for the enums, they shouldn't pose any problems, there is a clean 1:1 mapping. In fact, I would do it as described in this msdn post; http://blogs.msdn.com/b/abhinaba/archive/2007/08/27/sharing-enums-across-c-and-c.aspx
You can simply define all your enums in a .cs file then include it in both projects and everything will work fine.
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;
}