A structure is a user-defined data type containing a collection of logically related data which may be of different types such as int, double, char, and so on. All of them are encapsulated (packed) in a single unit with a single name. The classes of C++ are in fact generalization of C-structures. A class in C++ with only public members is similar to a C-structure. All members of a structure in C are by default public. However, in a class declaration in C++, if there is no access specifier, the members are private by default. We know that arrays can be used to represent a group of data items that belong to the same type, such as int or float. This restriction is not there in structures.

The C language permits structures to be nested, in which a structure can contain structure members. A structure may be declared inside another structure. Also, a structure may be a data member of another structure. The important thing to note is how to initialize the data members of inner structures and how to access the data members of inner structures. The use of such nested structures facilitates representation and processing of complex data.

The C language allows an array to be used as a structure member. This enables us to group related structure members and is also useful for declaring character strings as structure members. This section explains how we can effectively use such structures. This includes

Union is a collection of data items of different data types. It can hold data of only one member at a time though it has members of different data types. If a union has two members of different data types, they are allocated the same memory.

The program given below reads the information about a person and prints it on the screen. It uses a structure containing a pointer member name to represent the information about a person. Note that the program uses the dstr_read function.