Structure and Pointers

Pointers cannot hold the address of primitive types but also can hold the address of user-defined types such as structures. The address of the structure can be accessed in the same manner as that of other address, using (&) ampersand operator. In order to understand this, let us consider the following structure.

struct date

{

            int dd;

            int mm;

            int yy;

}day, *p;

…………..

p= &date;

In the above example, a variable day is declared as a date type variable which contains dd, mm and yy as its members. We have also declared a pointer variable p which points to a structure date. In other words, p is a pointer variable which will contains the address of some date type variable.

The statement,

p = &day;

assign the address of variable day which of type date to pointer variable p.

Since all the members of structure are stored in contiguous memory locations, so using p we can access each of its member. Thus to access a single member of a structure, we use *p followed by a dot operator which is then followed by member name. So it is Syntax would be:

*p.member /* wrong */

but as dot operator has precedence over indirection operator so we should parenthesize the above expression to give precedence to the above expression to give precedence to indirection operator. It will now look like

(*p).member

For example : To access mm member of the variable day of date we shall write

(*p).mm

Similarly we can access other member as

(*p).dd

(*p).yy

An alternative to this operator is - >. The - > is a special operator used to access a structure member through a pointer variable.

An individual structure member can be accessed by writing

ptr - > member

Here ptr is structure type pointer variable. In our example, the mm member can be accessed by writing.

p - >mm

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