Class and Struct

In C, there is no such special thing called class, and class is just an ordinary identifier. For example,

int class=2012;

The struct in C contains data members only, and all of them are visible in the same scope as struct itself.

In Java, there is no such thing called struct, but we can use class to implement struct. The class may contain member functions besides data fields, and programmer is able to declare the visibility for each member.

Interesting while kind of confusing, C++ has them both: class and struct. In many ways, C++ compilers treat them the same. Below are some short notes about class and struct in C++.

1. Both class and struct can have member data and member functions, and are able to specify their visibilities.
2. Both class and struct can inherit from and be inherited by another class or struct. To state more clearly, class can inherit from either class or a struct, and similarly, struct can inherit from either class or struct.
3. Both class and struct may contain pointers to the same class/struct type, but can't contain objects or references of the same class/struct type.
4. Both keywords class and struct can be omitted when declaring objects. While in C, the keywords struct, as well as union and enum, can not be omitted when declaring unless a typedef was used or anonymous variable is being declared.
5. C++ compilers don't distinguish the keywords class and struct in terms of type name. In other words, you may not define a class with name A and then define a struct with name A. The compilers will report "redefinition error". This is also true for struct, union and enum in C, although the keywords must be included for declaration.
6. The members of a class are private by default, and the members of a struct are public by default.
7. The inheritance for a class is also private by default, and the inheritance for a struct is public by default.
8. In C and C++, all definitions for class, struct, union and enum must end with a semicolon ;, while in Java, no such ; outside the closing brace for class and enum definitions. (There is no struct or union in Java.)