125 COMPLEX STRUCTURES

1
12-5 COMPLEX STRUCTURES

• Structures can contain
• Strings
• Arrays
• Other structures

These slides are intended for students at IUPUI
who are users of the book B.A. Forouzan, R.F.
Gilberg, Computer Science A Structured Approach
Using C, Brooks/Cole, second edition, 2001, ISBN
0-534-37482-4. Additions have been made to
existing slides from Brooks/Cole and some new
slides have been added by Kris A. Dines, Ph.D.,
Indiana University-Purdue University (IUPUI)
(kdines_at_iupui.edu) for a C course in Electrical
Engineering. Please see Brooks/Cole website
(www.brookscole.com) to download original slides.
2
Structures with Arrays Inside

• typedef struct
• char name32
• int idNum
• double gpa
• Student
• //.
• Student s1
• s1.name0J
• s1.name1i
• s1.name2m
• s1.name3\0
• //..

• typedef struct
• char name
• //etc
• Student
• //
• Student s1
• // dynamically allocated string (array)
• s1.name(char)malloc(32sizeof(char))
• s1.name0J
• s1.name1i // s1.((name1))i
• s1.name2m
• s1.name3\0

3
Shallow Copy vs. Deep Copy

• Student s1
• Student s2
• s2s1 // shallow copy
• typedef struct
• char name32
• int idNum
• double gpa
• Student

• typedef struct
• char name32
• int idNum
• double gpa
• Student

the pointer, name, is copied, but not contents of
array.
Shared
name is copied?same address in both
Assignment of structures results in a shallow
copy Pointers in the structure? memory they point
to is same
4
Shallow Copy vs. Deep Copy

• // Using a function to copy
• void StudentCopy(Point s1, Point s2)
• int i
• s2-gtidNums1.idNum
• s2-gtgpas1.gpa
• i0
• while(s1.namei!\0)
• s2-gtnameis1.namei
• i

Need pointer to struct to affect where its data
lives
Passed by value means a copy is passed including
copy of pointer name
5
Object-Oriented Philosophy

• C struct or typdef is a like a Class
• Class contains data and functions that operate
  upon it (using it). In C, we just haved the data
• Declaration gives an instance of the class
  object
• Student s1 // classStudent
• // instance s1 (an object)

6
Object-Oriented Conventions C

• Student.h contains typedef prototypes of
  functions in Student.c
• Student.c contains functions that operate upon
  student objects
• ? an instance of Student is the first argument
• Student.c includes Student.h
• Main Programs using Student functions and/or data
  types include Student.h

7
File Layout
Every function in Student.c has Student as prefix
of name. ( or Student_ )

• // Student.c
• include Student.c
• void StudentCopy(Point s1,
• Point s2)
• int i
• s2-gtidNums1.idNum
• s2-gtgpas1.gpa
• i0
• while(s1.namei!\0)
• s2-gtnameis1.namei
• i

• // Student.h
• ifndef STUDENT_H
• define STUDENT_H
• typedef struct
• char name32
• int idNum
• double gpa
• Student
• void StudentCopy(Student s1,
• Student s2)
• endif
• // main
• include Student.h

8
Data EncapsulationHiding the implementation

• Data members of Student are accessed only via
  functions (get/set) Never directly except within
  Student.c
• void Student_SetGPA(Student s, double gpa)
• s-gtgpagpa
• double Student_GetGPA(Student s)
• return s-gtgpa
• void Student_SetName(Student s, char name)
• s-gtnamename
• char Student_GetName(Student s)
• return s-gtname

9
Constructor/Destructor

• // constructor (in file, Student.c)
• Student Student_New(int idNum, double gpa, char
  name)
• Student result
• result(Student )malloc(sizeof(Student)) //
  create a Student
• result-gtidNumidNum
• result-gtgpagpa
• result-gtnamename
• return result

10
Constructor/Destructor

• void Student_Delete(Student s)
• free(s)

11
Structures and Functions

• Pass the structure type if you just need a copy
  of its data members
• Pass a pointer to the structure type if you want
  to permanently change its data members as seen by
  the calling function.

12
Figure 12-18 Arrays Inside of Structures
13
Array of Structures

• int numStudents1024
• Student eceStudentsnumStudents // all ece
  students
• eceStudents37.idNum44
• eceStudents37.gpa4.0
• eceStudents37.name0J
• //etc....

14
Figure 12-20
15
Figure 12-23
16
Some Tips on Structures

• Adhere to object-oriented design style
• Usually best to pass pointers to structures as
  fucntion args avoids copying the data
• Usually best to return pointer to structure if
  created inside a function
• e.g., result of multiplying 2 Fractions

17
Union

• Memory overlay
• Same memory used for different data types at
  different times.
• Only one type at a time

18
Union Example

• typedef union
• int ivalue // 4-bytes
• double dvalue // 8-bytes
• IntDouble
• // enough room will be allocated to hold longest
  data type
• IntDouble a
• a.ivalue3 // store as an int
• int ba.ivalue // OK
• a.dvalue3.14
• int ca.dvalue // NOT OK data is a double

19
Figure 12-24
20
Figure 12-25