Structure and Union

Structure: -

          It is a user defined data type which provides a unit or block in which more than one variable of different data type can be kept together.

All the element of structure is loaded in memory only when the structure type variable is created.

There are two way of creating structural variable:-

     1.     At the time of structure creation.

2.  Within any function

Since the structure name is used as data type and since this name is given by user therefore structure is called as user defined data type.

The structural variable is necessary to create the memory space is always allocated by structural variable name, not by the structure name. After that all the element of the structure are loaded within structural variable area.

The entire structural variable occupies separate memory area but shares the same properties and they can be used for separate purpose.

          Array and Structure: -

The relation between array and structure can be used in two ways.

     1.     Array with structure :-     In this case each element of structure is created as array, rather than creating structural variable as array type.

     2.     Array of structure :-     In this case we have to create structural variable as array type, rather than creating each element as array type.

Structure and function: -

There are two types of relation can be establish between structure and function.

     

     1.     Structure as a function argument :-     Like simple variable and array, a function can be accept structure type data also, in this case we need to declare the structure type variable as function argument and simply specify the structure variable name as actual argument at the time of calling.

     2.     Function returning structure :-     A function can return structure type variable also. In this case we have to specify the structure name as returning type in function prototype.

Structure and pointer: -

Like simple variables and array, a complete structure can also be managed by pointer. 

In this case we need to create structural variable as pointer type and assigned an address of simple structural variable into structural pointer.

Union: -

        It is also a user define data type which provides a unit or block in which heterogeneous types of data can be kept together.

Like structure, the element of union are also loaded within union type variable area so we need to create union type variable.

There are two ways of creating union type variable first one is at the time of union creation and the other one is within any function.

The basic difference between structure and union is that the element of structure occupies separate memory space within structural variable area whereas the elements of union share the same space within union type variable area.

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