Class VS Struct for Data Only

Class vs Struct for data only?

There is no real advantage of using one over the other, in c++, the only difference between a struct and a class is the default visibility of it's members (structs default to public, classes default to private).

Personally, I tend to prefer structs for POD types and use classes for everything else.

EDIT: litb made a good point in the comment so I'm going to quote him here:

one important other difference is that
structs derive from other
classes/struct public by default,
while classes derive privately by
default.

When should you use a class vs a struct in C++?

The differences between a class and a struct in C++ are:

struct members and base classes/structs are public by default.
class members and base classes/structs 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.

C/C++ Struct vs Class

In C++, structs and classes are pretty much the same; the only difference is that where access modifiers (for member variables, methods, and base classes) in classes default to private, access modifiers in structs default to public.

However, in C, a struct is just an aggregate collection of (public) data, and has no other class-like features: no methods, no constructor, no base classes, etc. Although C++ inherited the keyword, it extended the semantics. (This, however, is why things default to public in structs—a struct written like a C struct behaves like one.)

While it's possible to fake some OOP in C—for instance, defining functions which all take a pointer to a struct as their first parameter, or occasionally coercing structs with the same first few fields to be "sub/superclasses"—it's always sort of bolted on, and isn't really part of the language.

What's the difference between struct and class in .NET?

In .NET, there are two categories of types, reference types and value types.

Structs are value types and classes are reference types.

The general difference is that a reference type lives on the heap, and a value type lives inline, that is, wherever it is your variable or field is defined.

A variable containing a value type contains the entire value type value. For a struct, that means that the variable contains the entire struct, with all its fields.

A variable containing a reference type contains a pointer, or a reference to somewhere else in memory where the actual value resides.

This has one benefit, to begin with:

value types always contains a value
reference types can contain a null-reference, meaning that they don't refer to anything at all at the moment

Internally, reference types are implemented as pointers, and knowing that, and knowing how variable assignment works, there are other behavioral patterns:

copying the contents of a value type variable into another variable, copies the entire contents into the new variable, making the two distinct. In other words, after the copy, changes to one won't affect the other
copying the contents of a reference type variable into another variable, copies the reference, which means you now have two references to the same somewhere else storage of the actual data. In other words, after the copy, changing the data in one reference will appear to affect the other as well, but only because you're really just looking at the same data both places

When you declare variables or fields, here's how the two types differ:

variable: value type lives on the stack, reference type lives on the stack as a pointer to somewhere in heap memory where the actual memory lives (though note Eric Lipperts article series: The Stack Is An Implementation Detail.)
class/struct-field: value type lives completely inside the type, reference type lives inside the type as a pointer to somewhere in heap memory where the actual memory lives.

What are the differences between struct and class in C++?

You forget the tricky 2nd difference between classes and structs.

Quoth the standard (§11.2.2 in C++98 through C++11):

In absence of an access-specifier
for a base class, public is assumed
when the derived class is declared
struct and private is assumed when the class is declared class.

And just for completeness' sake, the more widely known difference between class and struct is defined in (11.2):

Member of a class defined with the
keyword class are private by
default. Members of a class defined
with the keywords struct or union
are public by default.

Additional difference: the keyword class can be used to declare template parameters, while the struct keyword cannot be so used.

When to use struct over class in c++

The only difference between the two is that by default struct are public while class members are private.

My rule is to use struct when I mean a clump of related data without any special semantics on reading/writing them. Use class when I intend to wrap the data in richer semantics (read methods) that are more meaningful, provide any needed protection, or implement something more abstract.

Should I use a structure instead of a class to hold string only data in C#?

I can't see any value in making the customer a struct. The string fields will all be reference types, so you might as well make the whole thing a reference type (ie. class).

I'd be inclined to use one of the built-in collection types rather than create my on type for Customers. Something like:

List<Customer> Customers = new List<Customer>();

Class VS Struct for Data Only