copy a class, C#

You are probably talking about a deep copy (deep copy vs shallow copy)?

You either have to:

1. implement (hard code) a method of your own,
2. try to implement (or find) an implementation that uses Reflection or Emit to do it dynamically (explained here),
3. use serialization and deserialization to create a deep copy, if the object is marked with a [Serializable] attribute.

public static T DeepCopy<T>(T other)
{
    using (MemoryStream ms = new MemoryStream())
    {
        BinaryFormatter formatter = new BinaryFormatter();
        formatter.Serialize(ms, other);
        ms.Position = 0;
        return (T)formatter.Deserialize(ms);
    }
}

To get a shallow copy, you can use the Object.MemberwiseClone() method, but it is a protected method, which means you can only use it from inside the class.

With all the deep copy methods, it is important to consider any references to other objects, or circular references which may result in creating a deeper copy than what you wanted.

EDIT:

⚠️ Security warning: Please read about the danger of using BinaryFormatter which may include remote code execution… You can instead use the preferred alternatives listed in the provided link.