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In computer science, a composite data type or compound data type is a data type that consists of programming language scalar data types and other composite types that may be heterogeneous and hierarchical in nature.
In the C programming language, struct is the keyword used to define a composite, a.k.a. record, data type – a named set of values that occupy a block of memory. It allows for the different values to be accessed via a single identifier, often a pointer. A struct can contain other data types so is used for mixed-data-type records.
typedef is a reserved keyword in the programming languages C, C++, and Objective-C.It is used to create an additional name (alias) for another data type, but does not create a new type, [1] except in the obscure case of a qualified typedef of an array type where the typedef qualifiers are transferred to the array element type. [2]
C++ has enumeration types that are directly inherited from C's and work mostly like these, except that an enumeration is a real type in C++, giving added compile-time checking. Also (as with structs), the C++ enum keyword is combined with a typedef, so that instead of naming the type enum name, simply name it name.
In C#, a class is a reference type while a struct (concept derived from the struct in C language) is a value type. [5] Hence an instance derived from a class definition is an object while an instance derived from a struct definition is said to be a value object (to be precise a struct can be made immutable to represent a value object declaring attributes as readonly [6]).
Modern C++ compilers are tuned to minimize abstraction penalties arising from heavy use of the STL. The STL was created as the first library of generic algorithms and data structures for C++, with four ideas in mind: generic programming, abstractness without loss of efficiency, the Von Neumann computation model, [2] and value semantics.
The Standard C++ syntax for a non-placement new expression is [2] new new-type-id ( optional-initializer-expression-list) The placement syntax adds an expression list immediately after the new keyword. This expression list is the placement. It can contain any number of expressions. [2] [3] [6]
A class in C++ is a user-defined type or data structure declared with any of the keywords class, struct or union (the first two are collectively referred to as non-union classes) that has data and functions (also called member variables and member functions) as its members whose access is governed by the three access specifiers private, protected or public.