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Ebook The C programming language (2/E): Part 2

Part 2 book “The C programming language” has contents: Structures, input and output, the unix system interface, example-an implementation of fopen and getc, standard input and output, character pointers and functions, initialization of pointer arrays, pointers to structures. | CHAPTER 6 Structures A structure is a collection of one or more variables possibly of different types grouped together under a single name for convenient handling. Structures are called records in some languages notably Pascal. Structures help to organize complicated data particularly in large programs because they permit a group of related variables to be treated as a unit instead of as separate entities. One traditional example of a structure is the payroll record an employee is described by a set of attributes such as name address social security number salary etc. Some of these in turn could be structures a name has several components as does an address and even a salary. Another example more typical for c comes from graphics a point is a pair of coordinates a rectangle is a pair of points and so on. The main change made by the ANSI standard is to define structure assignment structures may be copied and assigned to passed to functions and returned by functions. This has been supported by most compilers for many years but the properties are now precisely defined. Automatic structures and arrays may now also be initialized. 6.1 Basics of Structures Let us create a few structures suitable for graphics. The basic object is a point which we will assume has an X coordinate and a y coordinate both integers. y . 4 3 0 0 127 128 STRUCTURES CHAPTER 6 The two components can be placed in a structure declared like this struct point int x int y The keyword struct introduces a structure declaration which is a list of declarations enclosed in braces. An optional name called a structure tag may follow the word struct as with point here . The tag names this kind of structure and can be used subsequently as a shorthand for the part of the declaration in braces. The variables named in a structure are called members. A structure member or tag and an ordinary i.e. non-member variable can have the same name without conflict since they can always be distinguished by context. .