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Using structures

Structures are extremely powerful data types. Not only can you pass a whole structure as a parameter to a function, or return one as a value from a function. You can even assign one structure to another.

You can get and set the values of the members of a structure with the . dot character. This is called the member operator. The general form of a member reference is:

structure_name.member_name

In the following example, the year 1852 is assigned to the year_of_birth member of the structure variable person1, of type struct personal_data. Similarly, month 5 is assigned to the month_of_birth member, and day 4 is assigned to the day_of_birth member.

struct personal_data person1;

person1.year_of_birth = 1852;
person1.month_of_birth = 5;
person1.day_of_birth = 4;

Besides the dot operator, C also provides a special -> member operator for use in conjunction with pointers, because pointers and structures are used together so often. (See Pointers to structures.)

Structures are easy to use For example, you can assign one structure to another structure of the same type (unlike strings, for example, which must use the string library routine strcpy). Here is an example of assigning one structure to another:

struct personal_data person1, person2;

person2 = person1;

The members of the person2 variable now contain all the data of the members of the person1 variable.

Structures are passed as parameters in the usual way:

my_structure_fn (person2);

You would declare such a function thus:

void my_structure_fn (struct personal_data some_struct)
{
}

Note that in order to declare this function, the struct personal_data type must be declared globally.

Finally, a function that returns a structure variable would be declared thusly:

struct personal_data structure_returning_fn ()
{
  struct personal_data random_person;
  return random_person;
}

Of course, random_person is a good name for the variable returned by this bare-bones function, because without unless one writes code to initialize it, it can only be filled with garbage values.