Classes Friends

1
Classes Friends
Department of Computer and Information
Science,School of Science, IUPUI
CSCI 240
Dale Roberts, Lecturer Computer Science,
IUPUI E-mail droberts_at_cs.iupui.edu
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Friend Function -- Example 

• define size 50
• class student char name public
  student(char ip) name new charsize
  strcpy(name, ip) print() cout ltlt "Name " ltlt
  name ltlt endl
• //friend function friend void
  dangerous_fn(student)

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Friend Function -- Example 

• void dangerous_fn(student s) strcpy(s.name,
  "DANGER")
• main() student s1("John") s1.print()
  dangerous_fn(s1) s1.print()
• OUTPUT WILL BE Name JohnName DANGER

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Friend Classes -- Danger!?

• Not Directly Associated with the Class
• All the Member Functions of the Friend Class Can
  Access Non-Public Data Members of the Original
  Class
• Can be Friend of More than One Classes
• Violation of Encapsulation
• SHOULD BE USED ONLY WHEN REQUIRED

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Friend Class -- Example

• define size 50
• class student char name public
  student(char ip) name new charsize
  strcpy(name, ip) print() cout ltlt "Name " ltlt
  name ltlt endl
• //friend class friend class dummy

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Friend Class -- Example

• class dummy //Friend Class public void
  danger_member_fn(student s) strcpy(s.name,
  "FRIEND or FOE?")
• main() student s("John") s.print()
  dummy risk risk.danger_member_fn(s) s.print()
  
• OUTPUT WILL BE Name John Name FRIEND or FOE?

7
Acknowledgements

• These slides were originally prepared by Rajeev
  Raje, modified by Dale Roberts.