Still working on a problem that started from here Calling C++ dll function from C#: Of structs, strings and wchar_t arrays. , but with a different approach.
Following the example Calling Managed Code from Unmanaged Code and vice-versa I wrote a managed wrapper in C++ to access the unmanages class in the unmanaged C++ dll.
It looks like this:
//in header file
public __gc class TSSLDllWrapper
{
public:
TSSLDllWrapper();
//this is the unmanaged class
CcnOCRsdk * _sdk;
bool convertHKID_Name(char *code, RECO_DATA *o_data);
};
//in .cpp file
TSSLDllWrapper::TSSLDllWrapper(void)
{
_sdk = new CcnOCRsdk();
}
bool TSSLDllWrapper::convertHKID_Name(char *code, RECO_DATA *o_data)
{
return _sdk->convertHKID_Name(code, o_data);
}
//C++ RECO_DATA structure definition:
struct RECO_DATA{
wchar_t FirstName[200];
wchar_t Surname[200];
};
Now I have a dll that I can import into my C# project.
Here is the problem however: When I want to call the method from the dll file, like this:
TSSLDllWrapper wrapper = new TSSLDllWrapper();
bool res = wrapper.convertHKID_NameSimple( //need to pass parameters here );
It expects the C++ parameters - pointers to char and RECO_DATA.
How can I fix this and pass C++ types from C# code?
One way to convert most C data types is to use the PInvoke Interop Assitant . It will create proper C# / VB.Net types for most C structures. Here is the output for RECO_DATA
[System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential, CharSet=System.Runtime.InteropServices.CharSet.Unicode)]
public struct RECO_DATA {
/// wchar_t[200]
[System.Runtime.InteropServices.MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.ByValTStr, SizeConst=200)]
public string FirstName;
/// wchar_t[200]
[System.Runtime.InteropServices.MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.ByValTStr, SizeConst=200)]
public string Surname;
}
For the char* parameter, you can pass IntPtr.Zero or use Marshal.StringToCoTaskMemAnsi to get the job done.
A couple of points I stumbled on while creating a dll wrapper:
Therefore, my wrapper looks like this (as suggested in using a class defined in a c++ dll in c# code ):
public class __declspec(dllexport) Wrapper
{
public:
CcnOCRsdk* SDKCreate()
{
return new CcnOCRsdk();
}
bool CcnOCRsdk_HKID(CcnOCRsdk* pSDK, char *code, RECO_DATA *o_data)
{
return pSDK->convertHKID_Name(code, o_data);
}
void SDKDelete(CcnOCRsdk* pSDK)
{
delete pSDK;
}
};
__declspec(dllexport) on the class level exports all public members of the class. SDKCreate() returns a pointer to that CcnOCRsdk class from the unmanaged dll which member function I have to call. CcnOCRsdk_HKID calls that member function. Note that the pointer to the CcnOCRsdk is passed.
After the code builds into the dll, I have to use the DUMPBIN to find out what are the 'mangled' entry points for the wrapper dll I wrote.
For my wrapper, the results look like this
1 0 00001240 ??4Wrapper@TSSL@@QAEAAV01@ABV01@@Z = __t2m@??4Wrapper@TSSL@@QAEAAV01@ABV01@@Z ([T2M] public: class TSSL::Wrapper & __thiscall TSSL::Wrapper::operator=(class TSSL::Wrapper const &)) 2 1 00001220 ?CcnOCRsdk_HKID@Wrapper@TSSL@@QAE_NPAVCcnOCRsdk@@PADPAURECO_DATA@@@Z = __t2m@?CcnOCRsdk_HKID@Wrapper@TSSL@@QAE_NPAVCcnOCRsdk@@PADPAURECO_DATA@@@Z ([T2M] public: bool __thiscall TSSL::Wrapper::CcnOCRsdk_HKID(class CcnOCRsdk *,char *,struct RECO_DATA *)) 3 2 00001200 ?SDKCreate@Wrapper@TSSL@@QAEPAVCcnOCRsdk@@XZ = ?SDKCreate@Wrapper@TSSL@@QAEPAVCcnOCRsdk@@XZ (public: class CcnOCRsdk * __thiscall TSSL::Wrapper::SDKCreate(void)) 4 3 00001410 ?SDKDelete@Wrapper@TSSL@@QAEXPAVCcnOCRsdk@@@Z = ?SDKDelete@Wrapper@TSSL@@QAEXPAVCcnOCRsdk@@@Z (public: void __thiscall TSSL::Wrapper::SDKDelete(class CcnOCRsdk *))
Now I'm finally ready to use my wrapper in the C#. When I did this without specifying the entry point exactly as in my output from dumpbin, I got 'unable to find entry point' error.
[DllImport(@"TSSLWrapper.dll", EntryPoint = "?SDKCreate@Wrapper@TSSL@@QAEPAVCcnOCRsdk@@XZ")]
public static extern IntPtr SDKCreate();
[DllImport(@"TSSLWrapper.dll", EntryPoint = "?CcnOCRsdk_HKID@Wrapper@TSSL@@QAE_NPAVCcnOCRsdk@@PADPAURECO_DATA@@@Z")]
public static extern bool CcnOCRsdk_HKID(IntPtr ptr, string num, out RECO_DATA o_data);
The RECO_DATA is defined as JaredPar suggested.
And the last step is to enjoy the results. First I have to call the class constructor, and then pass the pointer to the actual call to the function
RECO_DATA recoData = new cnOCRsdk.RECO_DATA();
string num = "262125355174";
IntPtr ptr = cnOCRsdk.SDKCreate();
bool res = cnOCRsdk.CcnOCRsdk_HKID(ptr, num, out recoData);
My res returns true, and I get the results I expected in recoData.
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