Need to use a 'block' of C++ code in C# app - c#

I was given a block of c++ code that looks like it was from a c++ app that makes use of
Shared Memory for sending messages to other programs.
The c++ code has no #include or anything yet. I was given the code to use in my C# application and I am pretty stuck. I somewhat understand what the code does, but I don't know it well enough to translate it to C# as I am pretty new to coding.
My question is, what is the easiest way to be able to use the functionality of the code in my project? The end result is to send messages to another program, that will in turn do something that I'm not worried about.
I have tried creating different c++ projects and file types in my solution to link them using a reference later on, but I can never get it to compile properly.
Please let me know if you have some advice or a good place to look. I can always provide more information.
Code (I had to remove comments, sorry):
UINT WM_HELO_ZOOM_XYZ = RegisterWindowMessage("WM_HELO_ZOOM_XYZ");
int HELO_Broadcast_Zoom_Message(
double dbX,
double dbY,
double dbZ,
#ifndef HELO_
typedef struct {
UINT uMajVersion;
UINT uMinVersion;
DWORD dwReserved;
double dbX;
double dbY;
double dbZ;
} HELOCoordsStruct;
char *szSharedMemory = "HELO-_Coords";
char szErr[_MAX_PATH*3];
HANDLE hMem = OpenFileMapping(FILE_MAP_WRITE, FALSE, szSharedMemory);
if (NULL == hMem) {
void *pvHead = MapViewOfFile(hMem, FILE_MAP_WRITE, 0,0,0);
if (NULL == pvHead) {
sprintf(szErr, "Unable to view", szSharedMemory);
AfxMessageBox(szErr, MB_OK|MB_ICONSTOP);
HELOCoordsStruct *pHELOCoords = (HELOCoordsStruct *)pvHead;
BOOL bVersionOk=FALSE;
if (1 == pHELOCoords->uMajorVersion) {
if (WM_HELO_ZOOM_XYZ==uMessage) {
pHELOCoords->dbX = dbX;
pHELOCoords->dbY = dbY;
pHELOCoords->dbZ = dbZ;
else {
sprintf(szErr, "Unrecognized HELO- shared memory version: %d.%d", pHELOCoords->uMajVersion, pHELOCoords->uMinVersion);
AfxMessageBox(szErr, MB_OK);
if (NULL != hMem) CloseHandle(hMem);
if (bVersionOk) {
else return(0);
EDIT: The feedback has been completely unreal. I must say that the community sure spoils folks around here.

I think you have three options:
Create a Managed C++ project of type Class Library, put the code in it, make a reference from your main app to this project.
Create an unmanaged C++ DLL project, put the code in a function (or functions), export the function(s) (using .def file), and build the project. Use the functions from that dll using [DllImport] attribute. (See here and here)
Convert the code to C#. This will require some knowledge of unmanaged code, Win32 and P/Invoke (See here and here). And as I see your code, it is takes a little time!
Here is your converted code (option 3):
using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;
namespace UnmanagedBlock
public class ConvertedClass
public uint WM_HELO_ZOOM_XYZ = RegisterWindowMessageA("WM_HELO_ZOOM_XYZ"); // Your code uses the ANSI string
int HELO_Broadcast_Zoom_Message(
double dbX, double dbY, double dbZ, uint uMessage) // Porting the default value for 'uMessage' is not possible
string szSharedMemory = "HELO-_Coords";
IntPtr hMem = OpenFileMapping(FileMapAccessRights.Write, FALSE, szSharedMemory);
if (IntPtr.Zero == hMem)
return 0;
IntPtr pvHead = MapViewOfFile(hMem, FileMapAccessRights.Write, 0, 0, UIntPtr.Zero);
if (IntPtr.Zero == pvHead)
"Unable to view " + szSharedMemory, // Your code does not concat these two strings.
"Error", MessageBoxButtons.OK, MessageBoxIcon.Stop);
return 0;
HELOCoordsStruct pHELOCoords = new HELOCoordsStruct();
Marshal.PtrToStructure(pvHead, pHELOCoords);
int bVersionOk = FALSE;
if (1 == pHELOCoords.uMajVersion) // I think it had a typo (it was uMajorVersion)
if (WM_HELO_ZOOM_XYZ == uMessage)
pHELOCoords.dbX = dbX;
pHELOCoords.dbY = dbY;
pHELOCoords.dbZ = dbZ;
Marshal.StructureToPtr(pHELOCoords, pvHead, false);
bVersionOk = TRUE;
"Unrecognized HELO- shared memory version: " +
pHELOCoords.uMajVersion.ToString() + "." + pHELOCoords.uMinVersion.ToString());
if (IntPtr.Zero != hMem)
if (bVersionOk == TRUE)
PostMessage(HWND_BROADCAST, uMessage, 0, 0);
return 1;
return 0;
private class HELOCoordsStruct
public uint uMajVersion;
public uint uMinVersion;
public uint dwReserved;
public double dbX;
public double dbY;
public double dbZ;
[DllImport("user32", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Unicode)]
public static extern uint RegisterWindowMessageW([In]string lpString);
[DllImport("user32", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi)]
public static extern uint RegisterWindowMessageA([In]string lpString);
[DllImport("kernel32", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Auto)]
public static extern IntPtr OpenFileMapping(FileMapAccessRights dwDesiredAccess, int bInheritHandle, [In]String lpName);
[DllImport("kernel32", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Auto)]
public static extern IntPtr MapViewOfFile(IntPtr hFileMappingObject, FileMapAccessRights dwDesiredAccess, uint dwFileOffsetHigh, uint dwFileOffsetLow, UIntPtr dwNumberOfBytesToMap);
[DllImport("kernel32", CallingConvention = CallingConvention.StdCall)]
public static extern int UnmapViewOfFile(IntPtr lpBaseAddress);
[DllImport("kernel32", CallingConvention = CallingConvention.StdCall)]
public static extern int CloseHandle(IntPtr hObject);
public static extern IntPtr PostMessage(IntPtr hWnd, uint msg, int wParam, int lParam);
public const int FALSE = 0, TRUE = 1;
public enum FileMapAccessRights : uint
Write = 0x2,
Read = 0x4,
Execute = 0x20,
public const IntPtr HWND_BROADCAST = (IntPtr)0xffff;
I've done an exact conversion and I think that it should work fine, however I have not tested it.
Let me know if it works.

You can dump the C++ code into a Visual C++ project and build that. When you build it, go into the project settings and select the option that generates tlb files (It's a proxy class for c++/.net interop, I can't remember the name of the option).
Once you have this, you can add a reference to the tlb interop assembly from a C# project.
Also, look here for a Microsoft example

Chances are that if you post the code here, some nice person will port the code from C++ to C# for you. However, for future reference when dealing with using native C++ code from within a .NET application, you can use the InteropServices of the .NET framework to reference native functions in native dlls.
To do this requires a few steps on both the C++ and C# side of things. Firstly you need to build your entry point as an exported function in C++.
For example, say I wanted to write a trivial C++ function to add 2 numbers together and then call it from a C# app, I would have to do the following:
Step 1: Writing the C++ function.
In order for external sources to locate your functions, you need to let the compiler know that the function is to be 'exported'. A point to note is that if you're calling other functions from within your exported function, you do not need to mark them all as exported.
So let's write the "add" function in C++:
#define DLLEXPORT extern "C" declspec(dllexport)
DLLEXPORT int __cdecl add(int x, int y)
return (x + y);
The first line defines a macro we'll use to mark exported methods. The extern "C" part tells the compiler to avoid mangling the exported name of the function (so it will always be 'add', and not something like #YZadd_), next comes the function definition marked as a DLLEXPORT. Before I continue there's one more point on the 'name mangling' in exported functions, and that is for functions declared __stdcall or any of its variations (WINAPI..etc). Functions that are marked for exporting and declared with extern "C" with the calling convention __stdcall will always be appended with #X where X is the number of bytes of the function paramaters (so for the above example if add was declared __stdcall then the exported function name would be add#8. Just keep this in mind if C# ever has trouble locating your functions.
Now, the C++ side of things is done, compile that as a DLL and move over to C#.
In C# it's rather straightforward to import external functions. First you'll need to reference the InteropServices namespace:
using System.Runtime.InteropServices;
And then you will need to make a [DllImport] declaration:
[DllImport(#"path to your C++ dll here")]
public static extern int add(int x, int y) //make sure the function definition matches.
Provided the function names match, that should be all that's required to import the function. Now you can call add just as you would any normal function in C#
int x = 5;
int y = 10;
int z = add(x, y); //z should be 10
That about concludes how to simply export C++ functions and call them from a C# application.

If you can't get the C++ code to work as-is then there's no point trying to graft it into your C# app.
Figure out the C++ code first (read MSDN documentation for the APIs used, ask the person that gave you the code, post specific questions). Once you understand it better and can make it work then you'll have a better chance of figuring out the best way to do what's needed in C#.


AccessViolationException when accessing function with char * argument in c++ dll with C#

Problem Trying to use a function in a c++ dll with the following prototype...
int connectDfuBootloader(char * usbIndex)
...from C#, using any of these P/Invoke signatures, causes an AccessViolationException:
[DllImport(#"CubeProgrammer_API.dll", CallingConvention = CallingConvention.Cdecl)]
private static extern int connectDfuBootloader(IntPtr usbIndex);
public static int connectDfuBootloader(string usbIndex)
IntPtr value = Marshal.StringToHGlobalAuto(usbIndex);
return connectDfuBootloader(value);
[DllImport(#"CubeProgrammer_API.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int connectDfuBootloader(string usbIndex);
[DllImport(#"CubeProgrammer_API.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int connectDfuBootloader(StringBuilder usbIndex);
Variations on the theme of MarshalAs, tried LPStr, LPTStr etc...
[DllImport(#"CubeProgrammer_API.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int connectDfuBootloader([MarshalAs(UnmanagedType.LPStr)]string usbIndex);
Variations on the theme of specifying the character set, ANSI, Unicode, etc
[DllImport(#"CubeProgrammer_API.dll", CallingConvention = CallingConvention.Cdecl, CharSet =CharSet.Ansi)]
public static extern int connectDfuBootloader(string usbIndex);
Can anyone offer any suggestions?
Other things I've tried
Various StackOverflow posts, such as
AccessViolationException when accessing unmanaged C++ DLL with C#
Also, I tried making my own small C++ dll for test purposes, which contained a function with the same signature as the problem one above:
int functionAlpha(char * a)
if (a[0] == 'a')
return 10;
return 20;
This function I was able to access from C# without issue, using any of the methods above, e.g.
[DllImport(#"test.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int functionAlpha(string a);
Which makes me think there is something special about the 'int connectDfuBootloader(char * usbIndex)' function. But they have the same signature, why would one work and the other not? I do not have the source code for the dll, so can't look in there to see if there are any other differences.
Update - Tried C++/CLI wrapper as suggested by #Taekahn below, same thing!
So, I have this in a header in the C++/CLI wrapper project:
#include "include/CubeProgrammer_API.h"
using namespace System;
namespace CLI
public ref class CubeWrapper
int wrappedConnectDfuBootloader(String^ a);
Then in a cpp file in the wrapper project, I have:
namespace CLI
static char* string_to_ncchar_array(String^ string)
char* str = (char*)(Marshal::StringToHGlobalAnsi(string)).ToPointer();
return str;
int CubeWrapper::wrappedConnectDfuBootloader(String^ a)
a = "USB0";
// Calls the function from the linked c++ dll I'm trying to wrap
return connectDfuBootloader(string_to_ncchar_array(a));
And it gives the same result, System.AccessViolationException! What could be going on here?
Also tried using the dll from c++
Tried the same sequence of operations with the dll from a c++ application, and it worked fine.
Turns out that dxiv was on the right track; looked through some of the c++ example code supplied with the API and saw that several callbacks had to be setup first. Once I sorted those, problem fixed.

PInvoking AddSecurityPackageA

I am working on a project where I need to PInvoke the secur32!AddSecurityPackageA function, but I am still learning the ins and outs of how to do this by hand and could use some help.
Here are a the references I am working with:
And here's a sample of my code where I am trying to define the struct and call the function:
[DllImport("secur32.dll", EntryPoint = "AddSecurityPackageA")]
public static extern void AddSecurityPackageA(
ref string pszPackageName,
[StructLayout(LayoutKind.Sequential, CharSet =CharSet.Ansi)]
public ulong Size;
public ulong Type;
public ulong Flags;
public ulong SignatureSize;
public IntPtr Signature;
string dll = #"c:\temp\test.dll";
AddSecurityPackageA(ref dll, ref pkgOpts);
My questions are:
At lines 3 and 4, is this an appropriate use of ref and is this generally correct according to the MSDN docs?
At line 14, the C++ struct on MSDN has this as a void pointer, but while researching I found that the C# equivalent is an IntPtr. Is that correct or do I need to use unsafe?
In general, has anyone found any really good PInvoke tutorials outside of reading other people's code? I'm moving over from Python so it is quite a bit different and much of what I've found is either "draw a circle, draw the rest of the owl" or insanely lengthy MSDN documentation that makes a lot of assumptions.
Thank you!
Some comments:
Use the W function rather than the A function. You don't want to limit yourself to ANSI. This is a Unicode world.
The function has a return value. You must declare the function with a matching return value type. Presumably it is uint or int but you should check in the C++ header file.
ref string is wrong. It should be string.
ref SECURITY_PACKAGE_OPTIONS[] is wrong. It is not an array. It is a pointer to a struct. Since you declared SECURITY_PACKAGE_OPTIONS as a class, a reference type, you can replace ref SECURITY_PACKAGE_OPTIONS[] with SECURITY_PACKAGE_OPTIONS.
C++ unsigned long is 32 bits, so it should be uint in C#.
IntPtr is correct, but that leaves unresolved the question of how to declare the digital signature and obtain a pointer to it. I think it's outside the remit of this question for us to track down an example of how to do that.
This one works for me:
[DllImport("secur32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern uint AddSecurityPackage(
string pszPackageName,
[DllImport("secur32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern uint DeleteSecurityPackage(
string pszPackageName

Second value not getting passed to C++ function during pinvoke

I have a c++ function which I am calling from c# using pinInvoke. Following is my cpp method-
int test(DWORD verb,DWORD verb2 )
return verb2 *100;
My function is exposed as -
extern "C" {
__declspec(dllexport) int test(DWORD verb, DWORD verb2);
Following is my c# code where I am calling the above method:
public class API
[DllImport("mydll.dll", EntryPoint = "test", SetLastError = true, CallingConvention = CallingConvention.Cdecl)]
[return: MarshalAs(UnmanagedType.U4)]
public static extern uint test(
[MarshalAs(UnmanagedType.U8)]ulong verb,
[MarshalAs(UnmanagedType.U8)]ulong verb2);
static void Main(string[] args)
uint x = DPAPI.test(26,10);
Console.Write("result is-"+x);
Here the second value is getting passed as 0,so wrong result is coming. Am I doing something wrong while passing the value?
What I have tried:
I am relatively new to Pinvoke. So I tried debugging to see whether the value is not getting passed to c++ code or whether the c++ code is not returning proper values.I found that the value getting passed itself was wrong.
DWORD is a 32 but unsigned integer. You are mapping that to a 64 bit type. That is the problem. Your p/invoke should be:
[DllImport("mydll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int test(uint verb, uint verb2);
Note that I removed the needless EntryPoint and the erroneous SetLastError from the DllImport attribute.
I also wonder why you have selected DWORD. Unless you are passing those values onto Win32 functions it would likely make more sense to use intrinsic types. Why not use int or unsigned int in your C++ code?

Buffer overrun detected

I have an one question when I use C# DllImport C++ dll, I use the visual studio 2010 & checked the "Enable unmanaged code debugging", when it's running, always show the message "Buffer overrun detected! ... A buffer overrun has been detected which has corrupted the program's internal state. The program cannot safely continue execution and must now be terminated."
This dll is Third-party vendors to provide, and they says it's no error to run this dll, how can i fixed it?
My M++ dll function is,
int avc_to_avi_convert(char* chPath_avc, char* chPath_avi, int pPrivate, PROGRESS_CALLBACK progress_callback);
void avc_to_avi_close(int* pFd_avi);
typedef void (*PROGRESS_CALLBACK)(int iPercent, int pPrivate);
And i am use it in my C# dllimport like this :
public delegate void PROGRESS_CALLBACK(int _iPercent, int _pPrivate);
[DllImportAttribute(#"..\xxx.dll", EntryPoint = "avc_to_avi_convert", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
public static extern unsafe int avc_to_avi_convert([MarshalAs(UnmanagedType.LPStr)] StringBuilder _inputAVC, [MarshalAs(UnmanagedType.LPStr)] StringBuilder _ouputAVI, int pPrivate, PROGRESS_CALLBACK _pg);
[DllImportAttribute(#"..\xxx.dll", EntryPoint = "avc_to_avi_close", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
public static extern unsafe void avc_to_avi_close(int pFd_avi);
private void button1_Click(object sender, EventArgs e)
int i = 0;
StringBuilder inputFile = new StringBuilder(Application.StartupPath + #"\avc\abc.avc");//(#"C:\avc\abc.avc");
StringBuilder outputFile = new StringBuilder(Application.StartupPath + #"\avi\abc.avi");//(#"C:\avi\abc.avi");
if (avc_to_avi_convert(
progress_func) > 0) {
public void progress_func(int iProgress, int pPrivate)
if (iProgress == 100)
else if (iProgress == -1)
//convert error
else if (iProgress == -2)
//Not enough disk space
//update progress
I changed my code to,
[DllImportAttribute(#"..\xxx.dll", EntryPoint = "avc_to_avi_convert", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Unicode)]
public static extern unsafe int avc_to_avi_convert([MarshalAs(UnmanagedType.BStr)] String _inputAVC, [MarshalAs(UnmanagedType.BStr)] String _ouputAVI, int pPrivate, PROGRESS_CALLBACK _pg);
[DllImportAttribute(#"..\xxx.dll", EntryPoint = "avc_to_avi_close", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Unicode)]
public static extern void avc_to_avi_close(ref int avi);
And ran it, and I still get the same error.
1.) Are you sure about the calling convention? Try CallingConvention.StdCall. Read this:
2.) Try a different values for the CharSet attribute and use String instead of StringBuilder for the path arguments. This is a good reference:
3.) Also, the avc_to_avi_close method should look like this:
[DllImportAttribute("xxx.dll", EntryPoint="avc_to_avi_close")]
public static extern void avc_to_avi_close(ref int avi);
4.) Other things you my want to try:
Use unusual combinations of CharSet and MarshalAs. For example you know from the link above that Unicode should be used with LPWStr and Ansi with LPStr but you can of course try other combinations.
Your extern methods need not to be marked unsafe.
If you have exhausted all other options, why don't you try to write a C++ program that is analogous to your C# code:
If it crashes you proved that the error is in the library.
If it doesn't crash you know the error is in your use of PInovke, and you can go through all the 12+ combinations from my answer one by one.
You are passing a delegate to p/invoke and then letting the garbage collector free it. This causes the crash, because when the delegate object is finalized, the trampoline set up to allow calls from native code is deallocated. Then the native code invokes a dangling function pointer.
The garbage collector is totally unaware of any objects being used from inside native code. You MUST keep a reference to the delegate alive for the duration of the call. Try adding a delegate variable (don't use implicit conversion which creates a temporary) and then use GCHandle to keep the delegate alive for as long as the native code is using it.

Return contents of a std::wstring from C++ into C#

I have an unmanaged C++ DLL that I have wrapped with a simple C interface so I can call PInvoke on it from C#. Here is an example method in the C wrapper:
const wchar_t* getMyString()
// Assume that someWideString is a std::wstring that will remain
// in memory for the life of the incoming calls.
return someWideString.c_str();
Here is my C# DLLImport setup.
[DllImport( "my.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl )]
private static extern string GetMyString();
However the string is not correctly marshalled, often screwing up the first character or sometimes way off showing a bunch of chinese characters instead. I have logged output from the implementation on the C side to confirm that the std::wstring is correctly formed.
I have also tried changing the DLLImport to return an IntPtr and convert with a wrapped method using Marshal.PtrToStringUni and it has the same result.
[DllImport( "my.dll", CallingConvention = CallingConvention.Cdecl )]
private static extern IntPtr GetMyString();
public string GetMyStringMarshal()
return Marshal.PtrToStringUni( GetMyString() );
Any ideas?
Update with Answer
So as mentioned below, this is not really an issue with my bindings but the lifetime of my wchar_t*. My written assumption was wrong, someWideString was in fact being copied during my calls to the rest of the application. Therefore it existed only on the stack and was being let go before my C# code could finish marshalling it.
The correct solution is to either pass a pointer in to my method as described by shf301, or make sure my wchar_t* reference does not get moved / reallocated / destroyed before my C# interface has time to copy it.
Returning the std::wstring down to my C layer as a "const &std::wstring" means my call to c_str() will return a reference that won't be immediately dealloc'd outside the scope of my C method.
The calling C# code then needs to use Marshal.PtrToStringUni() to copy data from the reference into a managed string.
You are going to have to rewrite your getMyString function for the reasons mentioned in Hans Passant's answer.
You need to have the C# code pass a buffer in to your C++ code. That way the your code (ok, the CLR Marshaller) controls the lifetime of the buffer and you don't get into any undefined behavior.
Below is an implementation:
void getMyString(wchar_t *str, int len)
wcscpy_s(str, len, someWideString.c_str());
[DllImport( "my.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode )]
private static extern void GetMyString(StringBuffer str, int len);
public string GetMyStringMarshal()
StringBuffer buffer = new StringBuffer(255);
GetMyString(buffer, buffer.Capacity);
return buffer.ToString();
You need to specify MarshalAs attribute for the return value:
[DllImport( "my.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
[return : MarshalAs(UnmanagedType.LPWStr)]
private static extern string GetMyString();
Make sure the function is indeed cdecl and that the wstring object is not destroyed when the function returns.