DLL in C++

I need a DLL (in C or C++ for performance): Method 1: convert a string to a byte array Method 2: convert byte array to string DLL will be called from C#. The bytes in the string must be converted to the ***exact*** byte value, not the encoded translation (C# cannot do this, or anyway, I cannot find it). Maxsize: 16K bytearray.? I would like a DLL I can use directly in C#, without Interop and such.