C＃如何能够复制结构的mem而不能测试相等性？

Question

I can assign one struct's value to another and the memory gets copied automatically. But if I want to test whether two structs contain the same data (as if I had just done an assignment), I have to explicitly code it. Why is that? It seems like the framework should have a default implementation of operator == for structs.

Answer 1

The default implementation of ValueType.Equals does exactly what you want. So if you do:

s1 = ...;
s2 = ...;
s1.Equals(s2);

The call to "Equals" will do the automatic deep comparison you are looking for.

In general, C# tends to favor not using overloaded operators, which is probably why it doesn't implement the operator.

Also, philosophically, C# tends to shy away from implicit behavior, including things like implicit generation of methods.

Answer 2

The framework has a default Equals implementation. The == operator is a C# feature that you must implement yourself, using Equals if you wish.

Answer 3

If you have the execute native code permission, just call memcmp :

static class memcmpsig<T> where T : struct
{
    [DllImport("msvcrt.dll", CallingConvention=CallingConvention.Cdecl)]
    static extern int memcmp(ref T left, ref T right, UIntPtr count);
}

static class CompareExtension
{
    int CompareTo<T>(this T left, T right) { return memcmpsig<T>::memcmp(left, right, Marshal::SizeOf(typeof(T));
}