Introduction to Effective C Programming

1
Introduction to Effective C Programming

• Kwanghee Ko
• Design Laboratory
• Department of Ocean Engineering
• Massachusetts Institute of Technology
• Day 3

2
General Guidelines

• Avoid returning handles to internal data.
• Avoid member functions that return non-const
  pointers or references to members less accessible
  than themselves.
• Never return a reference to a local object or to
  a dereferenced pointer initialized by new with in
  the function (memory leakage).
• Postpone variable definitions as long as
  possible.

3
General Guidelines

• Public inheritance models isa relation?
• Ex. A bus is a vehicle?
• Never redefine an inherited non-virtual function.
• Never redefine an inherited default parameter
  value.
• Avoid cast down the inheritance hierarchy.
• Model has-a or is-implemented-in-terms-of
  through layering.

4
General Guidelines

• Use multiple inheritance judiciously.

5
Ambiguities under Multiple Inheritance

• Case 1

Derived d d.g() // OK d.h() // OK d.f()
// Ambiguous!!! d.Base1f() // OK d.Base2f()
// OK
Base 1 f() g()
Base 2 f() h()
Derived j() k()
6
Ambiguities under Multiple Inheritance

• Case 2

Top int x
Left int y
Right int z
Bottom int a
7
Ambiguities under Multiple Inheritance

• Case 2

Default inheritance mechanism -gt maintains
separate copies of the data members inherited
from all base classes.
Top int x
Left int y
Right int z
Bottom int a
8
Ambiguities under Multiple Inheritance

• Case 2 (Non-virtual Base class)

Top int x
Top int x
Top int x
Top int x
Left int y
Right int z
Left int y
Right int z
Bottom int a
Bottom int a
9
Ambiguities under Multiple Inheritance

• Case 2 Virtual Base Class

class Leftpublic virtual Top class
Rightpublic virtual Top
Top int x
virtual
virtual
Top int x
Left int y
Right int z
Left int y
Right int z
Bottom int a
Bottom int a
10
Ambiguities under Multiple Inheritance

• Case 2 Virtual Base Class

Top int x
Inherently ambiguous!!! Ex) Bottom b b.x
-gt b.Leftx? b.Rightx?
b.Topx?
virtual
virtual
Left int y
Right int z
Bottom int a
11
Ambiguities under Multiple Inheritance

• Case 2 Virtual Base Class

Top int x

• Assignment for Topx happens twice.
• Bottom-gtLeft-gtTop
• Bottom-gtRight-gtTop

virtual
virtual
Left int y
Right int z
Bottom int a
12
Ambiguities under Multiple Inheritance

• Case 2 Virtual Base Class

Top int x

• Assignment for Topx happens twice.
• Bottom-gtLeft-gtTop
• Bottom-gtRight-gtTop

virtual
virtual
Left int y
Right int z
Solution???
Bottom int a
13
General Guidelines

• Use multiple inheritance judiciously.
• Before using virtual base classes, understand
  them thoroughly.
• Use an experimental program to understand its
  behavior.
• If a public base class does not have a virtual
  destructor, no derived class should have a
  destructor.
• If a multiple inheritance hierarchy has any
  destructors, every base class should have a
  virtual destructor.

14
General Guidelines

• Declare a copy constructor and an assignment
  operator for classes with dynamically allocated
  memory.
• Prefer initialization to assignment in
  constructors.
• List members in an initialization list in the
  order in which they are declared.
• Make sure base classes have virtual destructors.
• Have operator return a reference to this.
• Assign to all data members in operator.
• Check for assignment to self in operator.
• Overloading vs. default argument.