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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.
C also provides a special type of member known as a bit field, which is an integer with an explicitly specified number of bits. A bit field is declared as a structure (or union) member of type int, signed int, unsigned int, or _Bool, [note 4] following the member name by a colon (:) and the number of bits it should occupy. The total number of ...
In addition, a (non-static) member-function can be declared as const. In this case, the this pointer inside such a function is of type object_type const * rather than merely of type object_type *. [2] This means that non-const functions for this object cannot be called from inside such a function, nor can member variables be modified.
The contents of whole structs cannot be compared using a single built-in operator (the elements must be compared individually). Union is a structure with overlapping members; it allows multiple data types to share the same memory location. Array indexing is a secondary notation, defined in terms of pointer arithmetic. Whole arrays cannot be ...
static is a reserved word in many programming languages to modify a declaration. The effect of the keyword varies depending on the details of the specific programming language, most commonly used to modify the lifetime (as a static variable) and visibility (depending on linkage), or to specify a class member instead of an instance member in classes.
Object-oriented languages such as C++ extend constantness even further. Individual members of a struct or class may be made const even if the class is not. Conversely, the mutable keyword allows a class member to be changed even if an object was instantiated as const. Even functions can be const in C++.
[26] [27] In C++, an abstract class is a class having at least one abstract method given by the appropriate syntax in that language (a pure virtual function in C++ parlance). [25] A class consisting of only pure virtual methods is called a pure abstract base class (or pure ABC) in C++ and is also known as an interface by users of the language. [13]
An object that applies this pattern can provide the equivalent of a namespace, providing the initialization and finalization process of a static class or a class with static members with cleaner, more concise syntax and semantics. It supports specific cases where a class or object can be considered structured, procedural data.