Structures

I A structure is a collection of one or more variables, possibly of different types, grouped together under a single name for convenient handling. The variables contained in a structure are knows as its members. I Use the struct keyword followed by an optional tag to declare a structure. For example, in the following declaration, point is the tag and x, y are members of the structure. struct point { int x; int y; struct point pt; I A structure can be initialized by following its definition with a list of initializers, each a constant expression, for the members: struct point pt = { 100, 200}; The Dot Operator I A member of a particular structure is referred to in an expression by a construction of the form structure-name.member The structure member operator. (dot) connects the structure name and the member name. For example: printf("%d,%d", pt.x, pt.y); I Structures can be nested. For example: struct rect { struct point bottomLeft; struct point topRight; struct rect screen; Then screen.topRight.x refers to the x coordinate of the topRight member of screen. Operations on Structures I The only legal operations on a structure are I copying it or assigning to it as a unit, I taking its address with &, I and accessing its members using the dot. operator. I Copy and assignment include passing arguments to functions and returning values from functions as well. I Structures may not be compared. I A structure may be initialized by a list of constant member values. Pointers to Structures I Structure pointers are just like pointers to ordinary variables. For example: struct point *pp; says that pp is a pointer to a structure of type struct point. If pp points to a point structure, *pp is the structure, and (*pp).x and (*pp).y are the members. To use pp, we might write, for example, struct point origin, *pp; pp = &origin; printf("origin is (%d,%d)\n", (*pp).x, (*pp).y); I Pointers to structures are so frequently used that an alternative notation is provided as a shorthand. If p is a pointer to a structure, then p->member-of-structure refers to the particular member. So we could write instead printf("origin is (%d,%d)\n", pp->x, pp->y); Precedence of. and-> operators I Both. and-> associate from left to right, so if we have struct rect r, *rp = &r; //then these four expressions are equivalent: r.pt1.x rp->pt1.