Attempted to read or write protected memory while importing function from c++ dll

[bltfr]

hi,
I have a native c++ dll and i am trying to import a function of the class in the dll to use it in c# so i wrote a wrapper :

public struct myclassUnman{
	
	public:
		[DllImport("mydll.dll", 
				  EntryPoint="??0myclass@@QAE@XZ", 
				  CallingConvention=CallingConvention::ThisCall)]
		static void ctor(myclassUnman*);

		[DllImport("mydll.dll", 
				  EntryPoint="??1myclass@@QAE@XZ", 
				  CallingConvention=CallingConvention::ThisCall)]
		static void dtor(myclassUnman*);	

		[DllImport("mydll.dll", 
				  EntryPoint="?getboolvalue@myclass@@QAE_NPAEH@Z", 
				  CallingConvention=CallingConvention::ThisCall)]
		static bool getboolvalue(myclassUnman*,unsigned char*,int);

	};
	public ref class myclassWrap
	{
	public: 
		myclassWrap(){
			tv = new myclassUnman();
			myclassUnman::ctor(mu);
		}
		~myclassWrap(){
			myclassUnman::dtor(mu);
		}
		bool getboolvalue(unsigned char* a,int b){
			return myclassUnman::getboolvalue(mu,a,b);
		}
		
	private:
		myclassUnman *mu;
	};

the prototype of function in the dll :

public: bool __thiscall myclass::getboolvalue(unsigned char *,int)

and finally in my c# code i call the wrapper but it gives an exception in the following line:

return myclassUnman::getboolvalue(tv,a,b);

Exception is:

Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

my c# code:

 unsafe
            {
                myclassWrap mw = new myclassWrap();
                Console.WriteLine(mw.getboolvalue((byte*)11, 2));

             }

please help me.