CSCI 1110 - C++ LectureNotes
Chapter 14 - Records (C++ Structs)

Records

Arrays of Records

Hierarchial Records

Records

• A Record is a structured data type with a fixed number of components that are accessed by name rather than by index. The components may be heterogeneous (of different types).
  
  
• A Field is a component or member of a record.
  
  
• In C++ records are declared using the struct statement.




  enum GradeType {A, B, C, D, F};
  typedef char NameString[20];

  struct StudentRec
  {
    NameString firstName;
    NameString lastName;
    long       studentId;
    float      gpa;
    float      programAvg;
    float      examAvg;
    float      labAvg;
    int        finalExam;
    GradeType  coursegrade;
  }

  StudentRec aStudent;
  StudentRec aPupil; 



• Each member of the struct is accessed by using the member selector operator (.).




  aStudent.courseGrade =
        aStudent.examAvg * 0.30 +
        aStudent.programAvg * 0.25 +
        aStudent.labAvg * 0.30 +
        aStudent.finalExam * 0.15; 


• Members of a struct can be intitalizes when the declaration is made:




  StudentRec aStudent =
  {
    "Ophelia",
    "Payne",
    12345678,
    0.725,
    54.3,
    62.0,
    25.4,
    76.0,
    D
  }; 


• The members firstName and lastName are arrays. To access their individual components, specify the entire name of the field followed by the index of the array member enclosed in square brackets.




  aStudent.firstName[2] = 'i'; 


• The following table compares aggregate operations for arrays and structs.
  
  

Aggregate Operation	Arrays	Structs
I/O	Strings only	No
Assignment operation =	No	Yes
Arithmetic	No	No
Comparison	No	No
Parameter passage	By reference only	By value or by reference
Function return value	No	Yes

 

• Unlike arrays, the contents of a struct can be assigned to another variable of the same type.




  aPupil = aStudent;

• Alternate forms of the struct statement:




  struct StudentRec
  {
    NameString firstName;
    NameString lastName;
    long       studentId;
    float      gpa;
    float      programAvg;
    float      examAvg;
    float      labAvg;
    int        finalExam;
    GradeType  coursegrade;
   } aStudent, aPupil;

The form above combines the definition of the struct with the declaration of two variables of that type.

  struct
  {
    int firstMember;
    float secondMember;
  }  someVar;

This form results in what is known as an anonymous type - no other variables of the same type are possible since the type does not have a name.

Arrays of Records

• Structs can be used as the members of arrays. For example:




  const int MAX_STUDENTS = 200;
  enum GradeType {A, B, C, D, F};
  typedef char NameString[20];

  struct StudentRec
  {
    NameString firstName;
    NameString lastName;
    long       studentId;
    float      gpa;
    float      programAvg;
    float      examAvg;
    float      labAvg;
    int        finalExam;
    GradeType  coursegrade;
  }

  StudentRec gradeBook[MAX_STUDENTS];
 



• To access individual members of the array, you must specify both the array index and the field of the struct.




  gradeBook[2].finalExam = 96.0;

Hierarchical Records

• Components of structs can be any other data type - including another struct. Such records are called Hierarchical Records.



Example:

  struct PhoneNumber
  {
    char areaCode[4];
    char exchange[4];
    char number[5];
  };

  typedef char String20[21];

  struct AddressRec
  {
    String20 Street;
    String20 Line2;
    String20 City;
    char     State[3];
    char     Zip[10];
   };

   struct NameRec
   {
     String20 Last;
     char     Initial;
     String20 First;
    };

   struct StudentRec
   {
     NameRec     name;
     AddressRec  localAddress;
     AddressRec  permAddress;
     PhoneRec    homePhone;
     PhoneRec    workPhone;
    };

• To reference a member of a hierarchical record, you must fully specify which member you mean.
  
  
  
    StudentRec aStudent;
  
    cout << aStudent.homePhone.areaCode;