Structures, Union, and Memory Allocation

Structure Definition :

• Structure is a data type to store group of data with various of data type

• Structure component called member/field/element.

• Heterogeneous (various element data type)

• Structure in other programming language also called record

• Nested Structure is a structure with one of its element is another structure.

Structure Declaration :

Syntax

struct name_structure {

    dataType1 name_field1;

    dataType2 name_field2;

    …

};

Variable can be defined at declaration time

struct name_structure {

  dataType1 name_field1;

  dataType2 name_field2;

…

} name_variable_structure ;

Structure variable declaration

struct name_structure  name_variable_structure; 

Union Definition :

• Union is used for memory join. By using union, a memory location can be assigned for two or more variable with different data types

• Memory capacity used by union is the largest capacity used by any element of the union

Union Declaration :

Union Data Declaration

union name_union{

         typedata1   name_var1;

         typedata2   name_var2;

         ....

}   name_var_union;

Union Variable Declaration

union   name_union       name_var_union;

Memory Allocation Definition :

• Memory allocation:

  acquiring some memory space (RAM) managed by the OS to be used by a program.

• Memory de-allocation:

  releasing memory space (RAM) back to the OS.