structures and pointers

• Structure


  A user-defined data type of C++ to represent a collection of logically related data items, which may be of different types, under a common name
• Syntax to define the structure


  1. struct structure_tag

  2. data_type variable1;

  3. data_type variable2;

  4. data_type variableN;

  5. }
• Structure variable


  Variables declared for storing the details, can be initialised
• Memory space for structure variable

  38 Bytes (4 + 20 + 10 + 4)
• Defining a structure without structure tag


  1. struct

  2. int adm_no;

  3. char name[20];

  4. char group[10];

  5. float fee;

  6. st;
• Dot operator (.)


  Connects a structure variable and its element
• Accessing elements of a structure


  • cin >> st.adm_no;
  • cin.getline(st.name,20);
  • st.fee = 2500;
  • cout << st.group;
• If two different structures contain same elements, their variables cannot be assigned
• Nested structure


  An element of a structure is a variable of another structure
• Pointer


  A variable that can hold the address of a memory location
• Syntax to declare pointer variable

  data_type * variable;
• Address of operator (&)

  Used to get the address of a variable
• Indirection or dereference operator (*)

  Used to retrieve the value pointed to by the pointer
• Static memory allocation


  Memory allocation that takes place before the execution of the program, due to variable declaration statements
• Dynamic memory allocation


  Memory allocation during the execution of the program, facilitated by the new operator
• Syntax for dynamic memory allocation

  pointer_variable = new data_type;
• Memory leak


  Orphaned memory blocks that are not freed using the delete operator
• Reasons for memory leak
• Remedy for memory leak
• Operations on pointers


  1. Declaration of integer pointers

  2. Dynamic memory allocation and initialisation

  3. Pointer arithmetic

  4. Displaying pointer value and dereferenced value

  5. Reading value using pointer
• Dynamic array


  Collection of memory locations created during run time using the new operator
• Character pointer


  Used to reference strings
• Accessing elements of a structure using pointer

  structure_pointer->element_name
• Self referential structure


  A structure in which one of the elements is a pointer to the same structure
• Orphaned memory blocks are undesirable and can be avoided by properly de-allocating dynamically allocated memory using delete
• Memory leak can lead to unfavorable effects due to increasing consumption of memory
• Freeing allocated memory


  Using the delete operator
• Nested structure


  A structure within another structure
• Declaring variables of nested structure type


  struct time current_time, next_time;
• Dynamic memory allocation operator

  new
• Representing names of 12 months as an array of strings

  • char *month[12] = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
• A structure can contain another structure as an element
• If 'ptr' is a pointer to the variable 'num', the statement 'num=&ptr;' is invalid
• Swap function using pointers

  Swap the values of two integer variables using pointers
• Accessing array elements using pointers


  Accessing and performing arithmetic operations on array elements using pointers