Question

I have a dll which comes from a third party, which was written in C++. Here is some information that comes from the dll documentation:

//start documentation  RECO_DATA{ wchar_t Surname[200]; wchar_t Firstname[200]; } 

Description: Data structure for receiving the function result. All function result will be stored as Unicode (UTF-8).

Method:

bool recoCHN_P_Name(char *imgPath,RECO_DATA *o_data); 

Input:

char * imgPath 

the full path of the image location for this function to recognize

RECO_DATA * o_data 

data object for receiving the function result. Function return: True if Success, otherwise false will return.

//end documentation 

I am trying to call the recoCHN_P_Name from my C# application. To this end, I came up with this code:

The code to import the dll:

    public class cnOCRsdk {     [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]     public struct RECO_DATA{         [MarshalAs(UnmanagedType.ByValTStr, SizeConst=200)]         public string FirstName;         [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 200)]         public string Surname;         }      [DllImport(@'cnOCRsdk.dll', EntryPoint='recoCHN_P_Name')]     public static extern bool recoCHN_P_Name(byte[] imgPath, RECO_DATA o_data); } 

The code to call the function:

            cnOCRsdk.RECO_DATA recoData = new cnOCRsdk.RECO_DATA();          string path = @'C:\WINDOWS\twain_32\twainrgb.bmp';          System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();         byte[] bytes = encoding.GetBytes(path);          bool res = cnOCRsdk.recoCHN_P_Name(bytes, recoData); 

And the error I’m getting is ”Unable to find an entry point named ‘recoCHN_P_Name’ in DLL ‘cnOCRsdk.dll’.’ I’m suspecting that I’m having an error in converting a type from C++ to C#. But where exactly … ?

Answer 1

First make sure the function is actually exported:

In the Visual Studio Command Prompt, use dumpbin /exports whatever.dll