Structure and Union Members (., ->)

Description

Use the period to reference members of structures and unions directly. Use the arrow operator to reference members of structures and unions pointed to by pointers. The arrow operator combines the functions of indirection through a pointer and member selection. If P is a pointer to a structure with a member M, the expression P->M is identical to (*P).M.

The postfix-expression in the first alternative must be a structure or a union. The expression is followed by a period (.) and an identifier. The identifier must name a member defined as part of the structure or union referenced in the postfix-expression. The value of the expression is the value of the named member. It is an lvalue if the postfix-expression is an lvalue.

If the postfix-expression is a pointer to a structure or a pointer to a union, follow it with an arrow (composed of the - character followed by the |) and an identifier. The identifier must name a member of the structure or union which the pointer references. The value of the primary expression is the value of the named member. The resulting expression is an lvalue.

The . operator and the -> operator are closely related. If S is a structure, M is a member of structure S, and &S is a valid pointer expression, S.M is the same as (&S)->M.