The differences between a class and a struct in C++ is:
struct members and base classes/structs are public by default.class members and base classes/struts are private by default.
Both classes and structs can have a mixture of public, protected and private members, can use inheritance and can have member functions.
I would recommend you:
- use
struct for plain-old-data structures without any class-like features;
- use
class when you make use of features such as private or protected members, non-default constructors and operators, etc.
There is actually a (subtle) difference between the two. Imagine you have the following code in File1.cs:
// File1.cs
using System;
namespace Outer.Inner
{
class Foo
{
static void Bar()
{
double d = Math.PI;
}
}
}
Now imagine that someone adds another file (File2.cs) to the project that looks like this:
// File2.cs
namespace Outer
{
class Math
{
}
}
The compiler searches Outer before looking at those using directives outside the namespace, so it finds Outer.Math instead of System.Math. Unfortunately (or perhaps fortunately?), Outer.Math has no PI member, so File1 is now broken.
This changes if you put the using inside your namespace declaration, as follows:
// File1b.cs
namespace Outer.Inner
{
using System;
class Foo
{
static void Bar()
{
double d = Math.PI;
}
}
}
Now the compiler searches System before searching Outer, finds System.Math, and all is well.
Some would argue that Math might be a bad name for a user-defined class, since there's already one in System; the point here is just that there is a difference, and it affects the maintainability of your code.
It's also interesting to note what happens if Foo is in namespace Outer, rather than Outer.Inner. In that case, adding Outer.Math in File2 breaks File1 regardless of where the using goes. This implies that the compiler searches the innermost enclosing namespace before it looks at any using directive.
Best Solution
The internal layout of a managed struct is undocumented and undiscoverable. Implementation details like member order and packing are intentionally hidden. With the [StructLayout] attribute, you force the P/Invoke marshaller to impose a specific layout and packing.
That the default just happens to match what you need to get your code to work is merely an accident. Although not an uncommon one. Note the Type.StructLayoutAttribute property.