Structure and Union Members

 

The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.

The latest version of this topic can be found at Structure and Union Members.

A "member-selection expression" refers to members of structures and unions. Such an expression has the value and type of the selected member.

  
postfix-expression  
.  
identifier  
postfix-expression  
–>  
identifier  
  

This list describes the two forms of the member-selection expressions:

  1. In the first form, postfix-expression represents a value of struct or union type, and identifier names a member of the specified structure or union. The value of the operation is that of identifier and is an l-value if postfix-expression is an l-value. See L-Value and R-Value Expressions for more information.

  2. In the second form, postfix-expression represents a pointer to a structure or union, and identifier names a member of the specified structure or union. The value is that of identifier and is an l-value.

The two forms of member-selection expressions have similar effects.

In fact, an expression involving the member-selection operator (–>) is a shorthand version of an expression using the period (.) if the expression before the period consists of the indirection operator (*) applied to a pointer value. Therefore,

  
expression  
–>  
identifier  
  

is equivalent to

  
(*  
expression  
) .  
identifier  
  

when expression is a pointer value.

The following examples refer to this structure declaration. For information about the indirection operator (*) used in these examples, see Indirection and Address-of Operators.

struct pair   
{  
    int a;  
    int b;  
    struct pair *sp;  
} item, list[10];  

A member-selection expression for the item structure looks like this:

item.sp = &item;  

In the example above, the address of the item structure is assigned to the sp member of the structure. This means that item contains a pointer to itself.

(item.sp)–>a = 24;  

In this example, the pointer expression item.sp is used with the member-selection operator (–>) to assign a value to the member a.

list[8].b = 12;  

This statement shows how to select an individual structure member from an array of structures.

Member Access Operators: . and ->

Show: