Sending a C# string as an argument to a unmanaged C++ DLL function

Question

I want to send my C# string to a C++ DLL function. I have succeeded, both with StringBuilder:

[C#]
public static extern int installHook(StringBuilder directory);
StringBuilder myText = new StringBuilder(512);
myfunc(myText);

[C++]
int OPENGLHOOK_API myfunc(char* directory)
{
    ::MessageBoxA(NULL,directory,"test123",0);
}

and with a simple string & wchar:

[C#]
public static extern int installHook(string directory);
myfunc("myText");

[C++]
int OPENGLHOOK_API installHook(wchar* directory)
{
    wstring s = directory;
    const wchar_t* wstr = s.c_str();
    size_t wlen = wcslen(wstr) + 1;
    char newchar[100];
    size_t convertedChars = 0;
    wcstombs_s(&convertedChars, newchar, wlen, wstr, _TRUNCATE);

    ::MessageBoxA(NULL,newchar,"test123",0);
}

as it was mentioned in other thread on StackOverflow. The problem is that everytime I do this, I get an error because the function signatures are not the same:

Managed Debugging Assistant 'PInvokeStackImbalance' has detected a problem in 'C:\Users\Dave\Documents\Visual Studio 2010\Projects\OpenGLInjector\Loader\bin\Release\Loader.vshost.exe'. Additional Information: A call to PInvoke function 'Loader!Loader.Form1::myfunc' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature.

Any idea how I can fix my problem/what to do from here?

possible duplicate of [pinvokestackimbalance -- how can I fix this or turn it off?](http://stackoverflow.com/questions/3506796/pinvokestackimbalance-how-can-i-fix-this-or-turn-it-off) — ChrisWue, Jun 07 '11 at 19:33
i'd like it to be.. I could turn off the MDA, but that doesn't rly fix my problem does it? — David Menard, Jun 07 '11 at 19:34
@David : Then that implies that your functions are being exported as `__cdecl`, but .NET P/Invoke expects `__stdcall` by default. You'll need to reconcile these. — ildjarn, Jun 07 '11 at 19:38

Brandon Moretz · Accepted Answer · 2011-06-07T19:50:31.417

3

I believe the problem is the default calling convention between the two languages. C# is __stdcall and c++ is __cdecl, I believe. Try explicitly stating __stdcall on your C++ method signatures and see if that doesn't resolve the error.

C++:

int OPENGLHOOK_API __stdcall installHook(wchar* directory)

C#:

[DllImport( "yourdll.dll", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Unicode )]
static extern int installHook(string directory);

edited Jun 07 '11 at 19:50

answered Jun 07 '11 at 19:40

Brandon Moretz

7,512
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thanks, where exactly do I do this? do i replace the __declspec(dllexport)? - NVM got it, that works great, thanks – David Menard Jun 07 '11 at 19:46
Shouldn't the C++ be int __stdcall installHook(wchar* directory), i.e. without the OPENGLHOOK_API because OPENGLHOOK_API expands to __declspec(dllexport) ? – user1725145 Jun 28 '14 at 10:22

score -1 · Answer 2 · answered Jun 07 '11 at 19:43

-1

You need to explicitly describe the unmanaged calling convention for 32bit, and in addition, you will need to explicitly describe the unmanaged string type- ASCII, UTF16, etc.

answered Jun 07 '11 at 19:43

Puppy

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Isn't the default calling convention for C# __stdcall independent of of the platform? – Brandon Moretz Jun 07 '11 at 19:47
@Brandon Moretz: x64 doesn't have different calling conventions. – Puppy Jun 07 '11 at 20:40
@Downvoter : Doing what this answer suggests would have completely solved the OP's problem; why the downvote? – ildjarn Jun 08 '11 at 00:53
Sorry to be so thick, but where do you explicitly describe the unmanaged string type? – user1725145 Jun 28 '14 at 09:03

Sending a C# string as an argument to a unmanaged C++ DLL function

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