Composite type

In computer science, a composite data type or compound data type is any data type which can be constructed in a program using the programming language's primitive data types and other composite types. It is sometimes called a structure or aggregate data type, although the latter term may also refer to arrays, lists, etc. The act of constructing a composite type is known as composition.

A struct is C's and C++'s notion of a composite type, a datatype that composes a fixed set of labeled fields or members. It is so called because of the struct keyword used in declaring them, which is short for structure or, more precisely, user-defined data structure.

In C++, the only difference between a struct and a class is the default access level, which is private for classes and public for structs.

Note that while classes and the class keyword were completely new in C++, the C programming language already had a crude type of structs. For all intents and purposes, C++ structs form a superset of C structs: virtually all valid C structs are valid C++ structs with the same semantics.

A struct declaration consists of a list of fields, each of which can have any type. The total storage required for a struct object is the sum of the storage requirements of all the fields, plus any internal padding.

For example:

defines a type, referred to as struct Account. To create a new variable of this type, we can write struct Account myAccount; which has an integer component, accessed by myAccount.account_number, and a floating-point component, accessed by myAccount.balance, as well as the first_name and last_name components. The structure myAccount contains all four values, and all four fields may be changed independently.

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