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I have load an unmanaged dll from c# dot net. ITs signature is like below
This method returns the printer initialization string.
HRESULT WINAPI EndInit(
LPWSTR lpRbdFilename, LPSTR lpBuffer,
UINT uSize
) ;
Parameters
LpRbdFilename The file name of the RBD file. The string is Null-terminated. lpBuffer                
   A pointer to the buffer to receive the printer init string.
uSize               The maximum size of the buffer in TCHARs. The buffer length must include room 
for a terminating null character.

Return value
If the function succeeds, the return value is zero.
If the function fails, the return value is the error code.


What I have tried:

I have written the code like
[DllImport("tjp.dll", EntryPoint = "EndInit")]
public static extern string EndInit([MarshalAsAttribute(UnmanagedType.LPWStr)] string Rbd, char[] str, uint i);


and calling by sending by the following value by below code
var res = StartInit();
              
                if (res == 0)
            {

               
                    FileLogger.Info("Printer is connected.");
            }
               
                
                string path = "C:\\Users\\Iftekher Alam\\Desktop\\KBZ\\Emptly_Cheque_Printer\\noname.rbd";
               

            
                char[] buffer = new char[200000000];
            buffer[0] = 'H';
            buffer[1] = 'r';




            var loadEnd = EndInit(path, buffer, Convert.ToUInt32(buffer.Length));
                if (loadEnd == 0)
                {
                    FileLogger.Info("Document is printing...");
                }


EndInit
should return zero(0) int value if the method succeeded. But I got null value from the call.
Posted
Updated 23-Mar-21 7:38am

1 solution

C#
public static extern string EndInit([MarshalAsAttribute(UnmanagedType.LPWStr)] string Rbd, char[] str, uint i)

You have declared the function to return a string, but it returns an int according to your description. So what you saw as null, was actually zero, which is the success code.
 
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Comments
Amir Hamza Kayes 23-Mar-21 13:48pm    
sorry to paste previous method here. later I made that return type as int. But after that it has also the same result
Richard MacCutchan 23-Mar-21 14:01pm    
Return valueIf the function succeeds, the return value is zero.If the function fails, the return value is the error code.

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