Re: How can I use a C++ struct from a C# app? - C# Discussion Boards

Re: How can I use a C++ struct from a C# app?

verence33310-Sep-08 1:14

10-Sep-08 1:14

OK, thank you. I'll try to find that. I've already learnt something about marshalling, like for example:

(SOMESTRUCT) aaa = (SOMESTRUCT)Marshal.PtrToStructure(param, typeof(SOMESTRUCT));

And it works if SOMESTRUCT is defined in the C# app. But, what if it isn't, and is a struct that is in a C++ DLL? I just can't cast to a SOMESTRUCT.

I hope I can find that info searching for what you suggest. Anyway, if somebody has more suggestions, I will be glad to read them.

Thank you! Smile | :)

Re: How can I use a C++ struct from a C# app?

leppie10-Sep-08 1:19

leppie

10-Sep-08 1:19

verence333 wrote:
And it works if SOMESTRUCT is defined in the C# app. But, what if it isn't, and is a struct that is in a C++ DLL? I just can't cast to a SOMESTRUCT.

No you cant. You have to define it in C# somewhere so the magic can work Smile | :)

verence333 wrote:
(SOMESTRUCT) aaa = (SOMESTRUCT)Marshal.PtrToStructure(param, typeof(SOMESTRUCT));

You do not need it that explicity most of the time. Eg

extern static void Foo(ref SOMESTRUCT s);

See! All magic Smile | :)

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Re: How can I use a C++ struct from a C# app?

verence33310-Sep-08 1:52

verence333

10-Sep-08 1:52

Interesting, thanks again. Smile | :)

I've come up to this url:

http://msdn.microsoft.com/en-us/library/ms384329(VS.71).aspx[^]

There, they explain how to make it, but the examples don't work. For example, the following line:

MCITY(String* name,int x,int y)

and this other:

String* name;

Throw an error: "Cannot take the address of, get the size of, or declare a pointer to a managed type ('string')". So I still don't know how to marshall a char pointer or char array. :-/

Anyway, it's a start.

Re: How can I use a C++ struct from a C# app?

Gideon Engelberth10-Sep-08 3:28

Gideon Engelberth

10-Sep-08 3:28

There are several attributes in the System.Runtime.InteropServices namespace that will be useful here. You could try something like this:

using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential)]
struct SOMESTRUCT
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst:=100)]
    string Field1;
    int Field2;
    double Field3;
}

I don't know if that should be SizeConst:=100 or just SizeConst=100; I just copied it from the VB editor. At the very least, that should point you in the right direction.

Re: How can I use a C++ struct from a C# app?

verence33310-Sep-08 3:45

verence333

10-Sep-08 3:45

Wow! Thank you so much, Gideon! Yes, it really helped a lot! Big Grin | :-D

(BTW, it's just SizeConst=100)

I could never think that finding this answer was so difficult. I've been searching and asking for several days with no results until now.

Re: How can I use a C++ struct from a C# app?

verence33310-Sep-08 21:05

verence333

10-Sep-08 21:05

Hi!

Gideon, yesterday I used your code to solve the problem, but I needed to add just a little thing (the charset in the StructLayout should be equivalent to the one used in the C++ struct; I just used "Auto" and it works). Just in case somebody has the same question, I'll write it here:

using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
struct SOMESTRUCT
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst=100)]
    string Field1;
    int Field2;
    double Field3;
}

Thank you very much.

Re: How can I use a C++ struct from a C# app?

Alan Balkany10-Sep-08 3:57

Alan Balkany

10-Sep-08 3:57

I had a similar problem, and I was able to avoid the complexities of marshalling by defining the same structure in both C# and C++.

A "char" is C# is NOT the same as a "char" in C++. C# uses unicode chars, which are usually longer than one byte. But a C# "byte" IS the same as a "char" in C++.

After you have what appear to be equivalent structures in both languages, write a test program that sets values in one, and see if you can pass it to the other unchanged. You can also use the sizeof () operator to see if the structure is the same size in both languages. (C# allows sizeof () to be used in unsafe mode.)

Ints and doubles are the same in both languages.

Re: How can I use a C++ struct from a C# app?

verence33310-Sep-08 4:20

verence333

10-Sep-08 4:20

Thank you, Alan. I tried to write the equivalent struct, but my problem was when translating a char[100]. C# does not allow me to make structures with fields that have been initialized to a size. So, if I write this inside a struct in C#:

public byte[] bytes = new byte[100];

I have the following error: "cannot have instance field initializers in structs".

Thanks for the rest of your message, I'll test my program as you suggest. In fact, I tried to do this before, but I couldn't use sizeof() and forgot it; didn't knew I could use it in unsafe mode.

Re: How can I use a C++ struct from a C# app?

Alan Balkany10-Sep-08 4:43

Alan Balkany

10-Sep-08 4:43

Here's how you do it:

public unsafe struct test
{
int num;
fixed byte bytes[10];
double num2;
};

It's explained here: http://blogs.msdn.com/ericgu/archive/2004/08/12/213676.aspx[^]

Re: How can I use a C++ struct from a C# app?

verence33310-Sep-08 5:27

verence333

10-Sep-08 5:27

Awesome! Thank you very much, Alan! Big Grin | :-D

This makes my job MUCH easier.

What's difference between a DLL file & an assembly file ?

Mohammad Dayyan10-Sep-08 0:14

Mohammad Dayyan

10-Sep-08 0:14

Hi.
Can anyone describe that clearly ?

Thank you.

Re: What's difference between a DLL file & an assembly file ?

blackjack215010-Sep-08 0:25

blackjack2150

10-Sep-08 0:25

An assembly is either an EXE or a DLL.

Re: What's difference between a DLL file & an assembly file ?

Mohammad Dayyan10-Sep-08 0:30

Mohammad Dayyan

10-Sep-08 0:30

blackjack2150 wrote:
An assembly is either an EXE or a DLL.

Means for example MyApplication.exe is an assembly file ?

Re: What's difference between a DLL file & an assembly file ?

leppie10-Sep-08 0:32

leppie

10-Sep-08 0:32

IF it is written in a .NET language, yes, it is an assembly.

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Re: What's difference between a DLL file & an assembly file ?

Mohammad Dayyan10-Sep-08 0:35

Mohammad Dayyan

10-Sep-08 0:35

Thank you leppie.
Then What's difference between them (DLL files & assembly files) Confused | :confused:

Re: What's difference between a DLL file & an assembly file ?

leppie10-Sep-08 0:41

leppie

10-Sep-08 0:41

A dll can be either a native dll or a .NET assembly. The subject is very broad and I suggest you read up in MSDN on how the CLR works.

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Re: What's difference between a DLL file & an assembly file ?

Giorgi Dalakishvili10-Sep-08 0:42

Giorgi Dalakishvili

10-Sep-08 0:42

.NET assembly[^]

Dynamic-link library[^]

Giorgi Dalakishvili

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Re: What's difference between a DLL file & an assembly file ?

Mohammad Dayyan10-Sep-08 0:46

Mohammad Dayyan

10-Sep-08 0:46

Thank you my friend.

Re: What's difference between a DLL file & an assembly file ?

Giorgi Dalakishvili10-Sep-08 0:49

Giorgi Dalakishvili

10-Sep-08 0:49

Glad to help you Smile | :)

Giorgi Dalakishvili

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Re: What's difference between a DLL file & an assembly file ?

leppie10-Sep-08 0:58

leppie

10-Sep-08 0:58

Lol, I think we should just point everyone to Wikipedia Smile | :)

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Re: What's difference between a DLL file & an assembly file ?

g_amol10-Sep-08 0:58

g_amol

10-Sep-08 0:58

A dynamic-link library (DLL) is an executable file that acts as a shared library of functions

Assemblies though may at times be equated to dlls its actuall nothing but “Actual Dlls”.

When it comes to dlls it gives way to a problem called “DLL hell”. That is when some appln is using a dll. A new version of the dll is now installed. Then the application will start using the new dll. If this dll is not backward compatible then it will result in a erro. This is called dll hell however new concept of assemblies in .Net avoid this. Here each dll is going to be used by particular application only this avoids the dll hell problem

In the past Dynamic Link Libraries (DLL) were located by the system environment's PATH setting and the Windows Registry. Globally and shared DLLs were stored in the Windows system folder. The identification was specified by the DLL's file name. These mechanisms do have certain drawbacks. One is that we can't move applications in our file system because the Windows Registry does have paths stored

With Microsoft.NET the Windows Registry is not used anymore and the libraries are stored either together with an application as Private Assemblies or in a Global Assembly Cache (GAC) as Global Assemblies to be shared among applications. Assemblies are signed and verified to recognise content modifications. They are identified by name and version to resolve incompatibility issues.

A Windows DLL contains library code to be used by any program running on Windows. A DLL may contain either structured or object oriented libraries.

COM (Component Object Model) is the component model based on the object oriented design, which means that the components represented by the COM component exists in the form of classes and objects implementing a standard specification defined by COM. COM components can be used by any program running on Windows Operating System; be it is written with VB, C++, Java or even some .NET compliant language like C# and VB.NET.

Dot NET assembly is the component standard specified by the .NET. Hence, dot net assemblies are understandable to only Microsoft.NET and can be used only in .NET managed applications.

Re: What's difference between a DLL file & an assembly file ?

Mark Salsbery10-Sep-08 6:15

Mark Salsbery

10-Sep-08 6:15