How to call c++ functions from c# program?

[gilit golit]

I have developed a software in C++.
Now I am trying to add GUI for it .
using windows forms.
I understand that it is not recommended to write it in C++
So I have started to write it in C#.
This is a managed code.
Then I have to call the functions in my software to perform the processing and computing .
I understand that I have to wrap the C++ native code with a CLI managed code.
How do I do it ? and How do I transfer the parameters ? I need clear full instructions with a code sample.

1. How do I define the prototypes of the wrapping functions ? (strings declarations like System::String )
2. How do I convert System::String from the wrapper class functions to the native C++ functions ?

3. What is Invoke ? PInvoke ?

4. Is there any C# method for System::String to convert it to characters array string and via versa


Thanks.

[Jason Mortmer]

If you've built your functionality into a DLL, ensure that you have compiled it as a COM/ActiveX object. That way you can add a reference to it within your C# project and all of the classes will automatically be wrapped in C# code. Alternatively, you can use the System.Runtime. InteropServices namespace within C# to load functions from your DLL using 'DLLImport' and wrapping the functions manually. If you choose to do it this way, you need to look into Marshalling unmanaged types.

[gilit golit]

1. can I get more details and code ?
I still don't know how to do it at all.

I can change my software , or write some new functions,
if you tell me - no problem.

2. In both ways my software becomes the dll ?

3. do I have to declare in the C# extern f (..) for my functions ?
4. Is it true, that c# can call only class methods , and not "normal functions ?
5. How do I pass strings between them ?

[Jason Mortmer]

I cant just paste code, you get nowhere from copying and pasting. Its better if you find out from MSDN about InteropServices .

They are declared as prototypes using the DLLImport attribute:

[DLLImport("Some DLL.DLL")]
public static extern void RandomFunction( int Parameter);

This function doesn't HAVE to be in a class. Your perception of a "normal" function would be a plain 'C' function which is just a static function. If a static function is within a class, the class name just acts like a namespace to contain the function.

[gilit golit]

ok
I have tried compiling the "c" code as dll

Then added it as a reference to the c# program
the c test code is :

#pragma once
///////////#include <stdio.h >
using namespace System;

//extern "C" __declspec( dllexport ) bool __stdcall say_helloHello () {
extern "C"
{ __declspec( dllexport ) void say_helloHello () {
////fprintf(stdout, " SAY HELLOHELLO\n" );
int i = 1;
//return true;
}
}
(in the comments there are other versions that I have tried.).


then in the C#
// C# main
using System.Runtime. InteropServices ;

[DllImport("lib1 test1.dll", EntryPoint = "say_hello" ) ]
//static extern bool say_helloHello () ; another option that I tried
public static extern void say_helloHello () ;

namespace CustomerDetails
{
partial class CustomerForm {
....
}; }


It always complained about "void" marked in Italic . no matter what I wrote there or if I deleted it at all, It said :
Expected class, delagate, enum or struct

help !

[Jason Mortmer]

You are getting that error because you are declaring the prototype OUTSIDE the namespace. C# works in a different way to C/C++, everything needs to be within a namespace in order for the compiler to know where to put the function, and what it has access to.


My working example:

(Inside Visual Studio 2010: Empty Windows DLL Project)
TestDLL.cpp

#include <stdio.h>
 
// Exported DLL function.
__declspec(dllexport) int DLLFunction(int Number1, int Number2)
{
    // Add the 2 numbers and return it.
    return Number1 + Number2;
}

Export.def

LIBRARY TestDLL
EXPORTS
     DLLFunction

(Inside Visual Studio 2010: C# Console Project)

using System;
using System.Runtime.InteropServices;
 
namespace CallTestDLL
{
    class Program
    {
        // ************COMMENT SHOWING A DIFFERENT WAY TO DECLARE THE PROTOTYPE*********************
        //[DllImport("TestDLL.dll", CallingConvention = CallingConvention.Cdecl)]
        //[return: MarshalAs(UnmanagedType.I4)]
        //public static extern int DLLFunction([MarshalAs(UnmanagedType.I4)] int Number1, 
        //                                     [MarshalAs(UnmanagedType.I4)] int Number2);
        // *****************************************************************************************
 
        // Description of DLL import:
        // "TestDLL.dll" is the file being loaded.
        // The calling convention is cdecl as the function was exported in this way.
        // "public static extern" means that this function does not belong to a class (static) and that it is
        // defined elsewhere (in the DLL).
        // The comment above shows what the function would look like if you wanted to Marshal the unmanaged
        // types yourself. However, int is done automatically so there is no need to add the Marshal attributes.
        [DllImport("TestDLL.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern int DLLFunction(int Number1,
                                             int Number2);
 
        static void Main(string[] args)
        {
            // Simple call the function as any other.
            Console.WriteLine(DLLFunction(2, 4));
 
            Console.ReadLine();
        }
    }
}

I hope you understand what you need to do now in order to load your C++ functions.

[gilit golit]

I did copy and paste for your code .


I opened new project -> c++ -> CLR -> empty project

In the configuration it is set to clr
Common Language Runtime Support (/clr)
I copied the command line to here, so you can see the
project properties setting :


/Zi /clr /nologo /W3 /WX- /Od /Oy- /D "WIN32" /D "_DEBUG" /D "_UNICODE" /D "UNICODE" /EHa /GS /fp:precise /Zc:wchar_t /Zc:forScope /Fp"Debug\TestDL L.pch" /Fa"Debug\" /Fo"Debug\" /Fd"Debug\vc100. pdb" /analyze- /errorReport:que ue


But it did not generate any dll file.
It generated TestDLL.exp and TestDLL.exe
The compilation succeeded , but it gave the following warning :
1>------ Build started: Project: TestDLL, Configuration: Debug Win32 ------
1>Build started 08/02/2011 9:52:12 AM.
1>InitializeBui ldStatus:
1> Creating "Debug\TestDLL. unsuccessfulbui ld" because "AlwaysCrea te" was specified.
1>GenerateTarge tFrameworkMonik erAttribute:
1>Skipping target "GenerateTarget FrameworkMonike rAttribute" because all output files are up-to-date with respect to the input files.
1>ClCompile:
1> All outputs are up-to-date.
1> TestDLL.cpp
1> All outputs are up-to-date.
1>Link:
1> Creating library c:\documents and settings\ilana\ my documents\visua l studio 2010\Projects\T estDLL\Debug\Te stDLL.lib and object c:\documents and settings\ilana\ my documents\visua l studio 2010\Projects\T estDLL\Debug\Te stDLL.exp
1>TestDLL.exp : warning LNK4070: /OUT:TestDLL.dll directive in .EXP differs from output filename 'c:\documents and settings\ilana\ my documents\visua l studio 2010\Projects\T estDLL\Debug\Te stDLL.exe'; ignoring directive
1> TestDLL.vcxproj -> c:\documents and settings\ilana\ my documents\visua l studio 2010\Projects\T estDLL\Debug\Te stDLL.exe
1>FinalizeBuild Status:
1> Deleting file "Debug\TestDLL. unsuccessfulbui ld".
1> Touching "Debug\TestDLL. lastbuildstate" .
1>
1>Build succeeded.
1>
1>Time Elapsed 00:00:01.37
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped =========

what did I do wrong ?



I have also tried :
No Common Language Runtime Support
and got
1>------ Build started: Project: TestDLL, Configuration: Debug Win32 ------
1>Build started 08/02/2011 10:09:41 AM.
1>InitializeBui ldStatus:
1> Creating "Debug\TestDLL. unsuccessfulbui ld" because "AlwaysCrea te" was specified.
1>ClCompile:
1> All outputs are up-to-date.
1> TestDLL.cpp
1>ManifestResou rceCompile:
1> All outputs are up-to-date.
1>Link:
1> Creating library c:\documents and settings\ilana\ my documents\visua l studio 2010\Projects\T estDLL\Debug\Te stDLL.lib and object c:\documents and settings\ilana\ my documents\visua l studio 2010\Projects\T estDLL\Debug\Te stDLL.exp
1>TestDLL.exp : warning LNK4070: /OUT:TestDLL.dll directive in .EXP differs from output filename 'c:\documents and settings\ilana\ my documents\visua l studio 2010\Projects\T estDLL\Debug\TestDLL.exe'; ignoring directive
1>Manifest:
1> All outputs are up-to-date.
1>LinkEmbedMani fest:
1> All outputs are up-to-date.
1> TestDLL.vcxproj -> c:\documents and settings\ilana\ my documents\visua l studio 2010\Projects\T estDLL\Debug\Te stDLL.exe
1>FinalizeBuild Status:
1> Deleting file "Debug\TestDLL. unsuccessfulbui ld".
1> Touching "Debug\TestDLL. lastbuildstate" .
1>
1>Build succeeded.
1>
1>Time Elapsed 00:00:01.20
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ========

[gilit golit]

Hi
Now, I have found out that I can set the Configuration Type:

Project properties -> Configuration properties -> General ->
Project Defaults: -> Configuration Type :
and I have set it to : Dynamic Library (.dll)


It did work !

Thanks ! ! !
You gave me a full detailed answer !


(next I will have to use the C# project as windows form appliaction .
I hope it will work ...... )
P.s. Why did I have to open th C++ project as an empty project,
and not class library project ?

[gilit golit]

Now, I have tried the same with two functions : it did not work !
I just added another function, and declared it in the Exp.def file
as follows :
TestDLL.cpp
__declspec(dlle xport) int DLLFunction(int Number1, int Number2)
{
return Number1 + Number2;
}

__declspec(dlle xport) int DLLFunction2(in t Number1, int Number2)
{
// just return a constant number.
return 200 ;
}

TestDLL.cpp
LIBRARY TestDLL
EXPORTS
DLLFunction
DLLFunction2
;

Everything was compiled ,
but failed immideatly at runtime ,
saying Unhandled exception : could not load CallTestDLL.pro gram because the method DLLFunction2 has no implementation <No RVA>


help !

[gilit golit]

ok

1. I have found out , that for every function in the c# calling project , I have to do the DllImport . as follows:



[DllImport("Test DLL.dll", CallingConventi on = CallingConventi on.Cdecl)]
public static extern int DLLFunction(int Number1,
int Number2);
[DllImport("Test DLL.dll", CallingConventi on = CallingConventi on.Cdecl)]
public static extern int DLLFunction2(in t Number1,
int Number2);
[DllImport("Test DLL.dll", CallingConventi on = CallingConventi on.StdCall)]
public static extern int say_hello(strin g name1);
static void Main(string[] args)


right ?


2.
Also , If I am not wrong , To define the function in the Exp.def file or to define it as "extern "C" { ... } is equivalent.

Right ?


3.
Still I want to know how to pass a string or a character array in both directions , and to be able to parse it in the c dll and the conversions .


4. when should we use "CallingConvent ion.StdCall" and when "CallingConvent ion.Cdecl" ?


Regards