9.4 STRUCTURES AND POINTERS

The address(&) operator can be used to access the beginning address of a structure, in the same manner as any other address.Thus, if variable represents a structure type variable, then &variable represents the starting address of that variable.We can declare a pointer variable for a structure by writing

type *ptvar;

where type is a data type that identifies the composition of the structure, and ptvar represents the name of the pointer variable.The beginning address of a structure can be assigned to this pointer by writing

ptvar = &variable;

The variable declaration and pointer declaration can be combined with the structure declaration by writing

struct   {
member 1;
member 2;
...............
member n;
} variable, *ptvar;

An individual member of a structure can be accessed in terms of its corresponding pointer variable by writing

ptvar->member;


which is equivalent to writing


variable.member;


The operator -> is comparable to the period operator (.).


Consider the simple C program shown below,


#include < stdio.h >


main()
{
int n=5120;
char t = 'R';
float b = 100.35;


typedef  struct   {
int month;
int day;
int year;
} date;



struct  {
int *acct_no;
char *acct_type;
char *name;
float *balance;
date lastpayment;
} customer, *pc = &customer;


customer.acct_no = &n;
customer.acct_type = &t;
customer.name = "Smith";
customer.balance = &b;


printf("%d  %c  %s  %.2f\n", *customer.acct_no, *customer.acct_type, customer.name, *customer.balance); 

printf("%d  %c  %s  %.2f\n", *pc->acct_no, *pc->acct_type, pc->name, pc->balance); 

}


The members acct_no, acct_type, name, balance are written as pointers within the second structure.Thus, the value to which acct_no points can be accessed by writing either
*customer.acct_no or *pc->acct_no.The same way other members can also be accessed.

Execution of the program results in the following two lines of output.

5120  R  Smith  100.35
5120  R  Smith  100.35

These two lines of output are identical, as expected.