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AdvancedAdvanced C++C++

ProgrammingProgramming

Guillaume Caumon, September 2007Guillaume Caumon, September 2007

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Introduction

C++ supports a variety of programming styles:

procedural (as FORTRAN, pascal, C, )procedural (as FORTRAN, pascal, C, )

object-oriented (as Eifel, JAVA, )object-oriented (as Eifel, JAVA, )

genericgeneric

Features interact with each other.Features interact with each other.

C++ is very flexible,C++ is very flexible, but also very confusing...but also very confusing...

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Software development

Energy = CostEnergy = Cost

TimeTimeReleaseRelease

Maintenance:Maintenance:- Bug fixesBug fixes- User requestsUser requests- Backward compatibilityBackward compatibility

ConceptionConception

DevelopmentDevelopment

TestingTesting

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Introduction

The goal of this course is to provide some keys toThe goal of this course is to provide some keys to

choose the design which:choose the design which:

eases the maintenance process;eases the maintenance process;

optimizes performance;optimizes performance;

optimizes memory requirements.optimizes memory requirements.

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Prerequisites

A working knowledge of C++ and of the basicA working knowledge of C++ and of the basic

object-oriented concepts.object-oriented concepts.

What is a pointer ?What is a pointer ?

What is a class ?What is a class ?

What is inheritance ?What is inheritance ?

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Outline

Some Programming Rules

Optimizing C++ programs

Generic Programming A short STL overview

Some Design Patterns

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I- SomeI- Some C++ features andC++ features and

programming rulesprogramming rules

MiscellaneousMiscellaneous

Object designObject design

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Resolving ambiguities: namespace

ANSI featureANSI featurenamespace Gocad1 {namespace Gocad1 {class MainWindow{ };class MainWindow{ };

}}namespace Gocad2 {namespace Gocad2 {

class MainWindow{ };class MainWindow{ };}}

using namespace Gocad1;using namespace Gocad1;

Gocad1::MainWindow window();Gocad1::MainWindow window();

using Gocad2::MainWindow;using Gocad2::MainWindow;

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References or pointers ?

References are as cheap as pointers,References are as cheap as pointers,

and more convenientand more convenient

Rules:Rules: In function parameters, useIn function parameters, use

const T& varconst T& varinstead ofinstead ofT varT varA nil reference does not exist, so use pointersA nil reference does not exist, so use pointers

whenever you would need nil references.whenever you would need nil references. pointers can be reassigned, references cant.pointers can be reassigned, references cant.

Goal: refer to objectsGoal: refer to objects

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Exercise#include #include

class Traced {class Traced {public:public:

Traced();Traced();Traced( int parameter );Traced( int parameter );Traced( const Traced& rhs );Traced( const Traced& rhs );~Traced();~Traced();Traced& operator=( const Traced& rhs );Traced& operator=( const Traced& rhs );

private:private:int impl_;int impl_;

};};Using std::vector;Using std::vector;

Class Dummy {Class Dummy {execute_val( vector flags );execute_val( vector flags );execute_p( vector* flags );execute_p( vector* flags );execute_ref( vector& flags );execute_ref( vector& flags );execute_cref( const vector& flags );execute_cref( const vector& flags );

};};

traced.h

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Exerciseint main( int argc, char** argv ) {int main( int argc, char** argv ) {

cout

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Exceptions

Goals : improve program safetyGoals : improve program safety

try {try {// some code that might cause pbs// some code that might cause pbs

}}

throw messagethrow message

catch ( message ) {catch ( message ) {// special processing Doctor Watson// special processing Doctor Watson

}}

How ? Framework to bypass the function call stackHow ? Framework to bypass the function call stack

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Constructor and assignment

int main() {int main() {String s1 = tutu;String s1 = tutu;String s2( toto );String s2( toto );s2 = s1;s2 = s1;

};};

class String {class String {public:public:

String( const char* value );String( const char* value );String( const String& rhs );String( const String& rhs );~String();~String();

String& operator=( const String& rhs);String& operator=( const String& rhs);private:private:

char* data_;char* data_;};};

file.h

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Implicit type conversions

class Rational {class Rational {

Rational( int num, int denom = 1 );Rational( int num, int denom = 1 );double operator double() const;double operator double() const;

};};void print_rational(void print_rational(

ostream& out, const Rational& fractionostream& out, const Rational& fraction) {) {out num()

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Avoiding implicit conversions

class Rational {class Rational {explicit Rational(explicit Rational(

int num,int num,int denom = 1int denom = 1

););operator double() const;operator double() const;

};};

ANSI featureANSI feature

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Overloading operators (I)

class Rational {class Rational {

Rational& operator =( const Rational& rhs );Rational& operator =( const Rational& rhs );

bool operator ==( const Rational& rhs );bool operator ==( const Rational& rhs );

Rational operator +( const Rational& rhs );Rational operator +( const Rational& rhs );

Rational& operator +=( const Rational& lhs );Rational& operator +=( const Rational& lhs );

Rational& operator++(); // ++a (prefix)Rational& operator++(); // ++a (prefix)Rational operator++(int); // a++ (postfix)Rational operator++(int); // a++ (postfix)

};};

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Overloading operators (II)

class Rational {class Rational {// // Rational operator+( int rhs );Rational operator+( int rhs );

friend Rational operator+(friend Rational operator+(

int lhs, const Rational& rhsint lhs, const Rational& rhs););

};};

Rational operator+(Rational operator+(int lhs, const Rational& rhsint lhs, const Rational& rhs

) { // }) { // }

If the left-hand side of the expression is of a differentIf the left-hand side of the expression is of a different

type, the operator MUST be a non-membertype, the operator MUST be a non-member

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Modifying non const member in const

member

ANSI: use theANSI: use themutablemutable keywordkeyword

Non ANSI: use const castNon ANSI: use const cast

Downgrade the const memberDowngrade the const member

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I-I- C++ main programmingC++ main programmingrulesrules

MiscellaneousMiscellaneous

Object designObject design

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What is OOP?

Object-Oriented Programming is a philosophyObject-Oriented Programming is a philosophy

where the source code of a program is split intowhere the source code of a program is split into

reusable objects.reusable objects.

What is an object, then?What is an object, then?

An object is made of two parts:An object is made of two parts:

- The interfaceThe interface = catalog of the object features= catalog of the object features

-The implementationThe implementation = internal machinery= internal machinery

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The interface in C++

Usually defined in a header (.h) file:Usually defined in a header (.h) file:

class Car {class Car {public:public:

//// MembersMembers can be accessed from any objectcan be accessed from any object

protectedprotected:://// Can only be accessed by Car and its derived objectsCan only be accessed by Car and its derived objects

privateprivate:://// Can only be accessed by Car for its own use.Can only be accessed by Car for its own use.

};};

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Aggregation or Composition?

Aggregation is a relationship

in which one object is a partof another.

A aggregates BA aggregates B

==B is part of A, but theirB is part of A, but their

lifetimes may be differentlifetimes may be different

Ex: cEx: cars and wheels, engine,

etc.

Composition is a relationship

in which one object is anintegral part of another

A composes BA composes B

==

B is part of A, and theirB is part of A, and their

lifetimes are the samelifetimes are the same

Ex: person and brain, lung,Ex: person and brain, lung,

etc.etc.

CarCar WheelWheel PersonPerson BrainBrain44

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Classes: Basic Design Rules

Minimize the number of public member functionsMinimize the number of public member functions

Avoid default constructorsAvoid default constructors

Hide implementation functions and dataHide implementation functions and data

Hide all member variablesHide all member variables

Avoid overloading (can be ambiguous)Avoid overloading (can be ambiguous)

UseUse constconst members whenever possible / neededmembers whenever possible / needed

Be aware of compiler generated functionsBe aware of compiler generated functions

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Inheritance: quick review

A circleA circle is ais a shapeshape

CircleCircle

GeomShapeGeomShape

class GeomShape {class GeomShape {////

};};

class Circle : public GeomShape {class Circle : public GeomShape {////

};};

file.h

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Public Inheritance Philosophy

Public inheritancePublic inheritance is ais a

In other words:In other words:

What is applies to a base classWhat is applies to a base classapplies to its derived classesapplies to its derived classes

Three aspects to consider:Three aspects to consider:class public interfaceclass public interface

class relationship with derived classesclass relationship with derived classes

class internal cookwareclass internal cookware

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Polymorphism

class Employee {class Employee {public :public :

virtualvirtual float income();float income(); // 1000// 1000};};

class Boss : public Employee {class Boss : public Employee {public :public :

virtualvirtual float income();float income(); // 10000// 10000};};

BossBoss

EmployeeEmployee

Mechanism that allows a derived class to modify theMechanism that allows a derived class to modify thebehavior of a member declared in a base classbehavior of a member declared in a base class

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Polymorphism

BossBoss

EmployeeEmployee

A pure virtual function just defines the interface, andA pure virtual function just defines the interface, andleaves the implementation to derived classesleaves the implementation to derived classes

class Employee {class Employee {public :public :

virtualvirtual float income() = 0;float income() = 0;// not implemented// not implemented

};};class Boss : public Employee {class Boss : public Employee {

public :public :virtualvirtual float income();float income(); // implemented// implemented

};};

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Public Inheritance PhilosophyInheritance of theinterface

Inheritance of theimplementation

Non virtualfunction

Mandatory Mandatory

Virtual function Mandatory By default,

Possible to

redefine

Pure virtualfunction

Mandatory Re-definition ismandatory

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Private Inheritance Philosophy

Private inheritancePrivate inheritance is implemented in term ofis implemented in term ofThis is an equivalent variant of agregation:This is an equivalent variant of agregation:

class Car : private engine {class Car : private engine {////};};

class Car {class Car {private:private:

Engine engine_;Engine engine_;};};

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Inheritance and fonctionsvirtual

function

pure virtual

function

Constructor

is

Destructor

is

Isolatedclass

base class

pureabstract

class

Derived(concrete)class

publicpublic

publicpublic

virtualvirtual

publicpublic

virtualvirtual

publicpublic

virtualvirtual

publicpublic

publicpublic

protectedprotected

publicpublic

NoNo

NoNo

Yes / noYes / no

Yes/noYes/no

YesYes

(must)(must)

YesYes

(must)(must)

YesYes

(must)(must)

NoNo

cancanhave...have...

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Polymorphism Mechanism

Derived::vf1Derived::vf1

Derived::vf3Derived::vf3

DerivedDerived

BaseBasevtbl_vtbl_

Base::vf1Base::vf1

Base::vf2Base::vf2

Base::vf3Base::vf3

BaseBasevtbl_vtbl_

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Consequences

Never call a virtual function in a constructorNever call a virtual function in a constructor

Be aware of the increased size of classesBe aware of the increased size of classes

with virtual functionswith virtual functions

Calling a virtual function is more expensiveCalling a virtual function is more expensive

than calling a non-virtual functionthan calling a non-virtual function

Never declare a virtual function inlineNever declare a virtual function inline

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Cast operators

Avoid c-style casting operators.Avoid c-style casting operators.ANSI C++ provides 4 cast operators :ANSI C++ provides 4 cast operators :

Type* reinterpret_cast(expression)Type* reinterpret_cast(expression)

Type* static_cast(expression)Type* static_cast(expression)Type* const_cast(expression)Type* const_cast(expression)

Type* dynamic_cast(expression)Type* dynamic_cast(expression)

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Additional guidelines...

Avoid multiple inheritance: use compositionAvoid multiple inheritance: use composition

Forbid default parameters in virtual functionsForbid default parameters in virtual functions

Dont redefine (overload) a non virtual functionDont redefine (overload) a non virtual function

Differentiate between layering and inheritanceDifferentiate between layering and inheritance

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II-II- Optimization in C++Optimization in C++

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Optimization

Main issue: algorithm complexity and memoryMain issue: algorithm complexity and memoryrequirementsrequirements

Main question: which part of the code should beMain question: which part of the code should be

optimized ?optimized ?

20% of the code is used 80% of the time20% of the code is used 80% of the time

Code maintenance and debug vs. optimization.Code maintenance and debug vs. optimization.

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Lazy evaluation

Compute only when neededCompute only when needed

Examples:Examples:

Matrix operator +Matrix operator +

Gocad association mechanismGocad association mechanism

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Anticipated evaluation

Compute once, and cache information.Compute once, and cache information.

Examples:Examples:

Statistics managerStatistics manager

Dynamic arraysDynamic arrays

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Return value optimization

class Complex {class Complex {////

};};const Complex operator*(const Complex operator*(

const Complex& a, const Complex bconst Complex& a, const Complex b) {) {

Complex c;Complex c;

c.set_real( a.real() * b.real() );c.set_real( a.real() * b.real() );c.set_im( a.im() + b.im() );c.set_im( a.im() + b.im() );return c;return c;

}}

A first try...A first try...

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};};const Complex& operator*(const Complex& operator*(


Complex c;Complex c;

c.set_real( a.real() * b.real() );c.set_real( a.real() * b.real() );c.set_im( a.im() + b.im() );c.set_im( a.im() + b.im() );return c;return c;

}}

A second try...A second try...

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};};const Complex operator*(const Complex operator*(


return Complex(return Complex(

a.real() * b.real(),a.real() * b.real(),a.im() + b.im()a.im() + b.im()

););}}

A last try...A last try...

...But dont alter your code quality for that !!...But dont alter your code quality for that !!

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Some rules...

Overload to avoid implicit type conversions (fineOverload to avoid implicit type conversions (finetuning only)tuning only)

Prefer operatorPrefer operator+=+= to operatorto operator++

Prefer generic programming to virtual functionsPrefer generic programming to virtual functions

Use inline functions, but not too much...Use inline functions, but not too much...

Postpone variable declarationPostpone variable declaration

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Example: dynamic arraysGoal: add items dynamically to a set.Goal: add items dynamically to a set.

Problem:Problem:

- dynamic memory allocation is time-consuming- dynamic memory allocation is time-consuming

- the number of elements is not known from the start- the number of elements is not known from the start

Proposal:Proposal:

Allocate N elements, then add itemsAllocate N elements, then add items

Allocate 2N elements, then copy existing items, then add itemsAllocate 2N elements, then copy existing items, then add items

Allocate 4N elements, then copy existing items, then add itemsAllocate 4N elements, then copy existing items, then add items

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III-III- Generic Programming in C++Generic Programming in C++

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Parameterize classes

Case of most container classes: store dataCase of most container classes: store dataof arbitrary types.of arbitrary types.

template class List {template class List {public :public :List( int nb_items );List( int nb_items );~List();~List();

void append_item( const T& item );void append_item( const T& item );void remove_item( const T& item );void remove_item( const T& item );void remove_all();void remove_all();////

};};

list.h

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or fonctions

/**/**

* Swaps two objects of type T.* Swaps two objects of type T.* T should provide copy constructor* T should provide copy constructor* and operator=* and operator=*/*/

template void swap(template void swap(

T& t1, T& t2T& t1, T& t2););

swap.h

template void swap(template void swap(T& t1, T& t2T& t1, T& t2

) {) {T tmp(t1);T tmp(t1);t1 = t2;t1 = t2;t2 = tmp;t2 = tmp;

}}

swap.h

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Templates

Template code is compiled only when it isTemplate code is compiled only when it is

used (used (template instanciationtemplate instanciation))

Keyword class (or typename) or int canKeyword class (or typename) or int can

be used to qualify template arguments.be used to qualify template arguments.

Members can be required from templateMembers can be required from template

argumentsarguments

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Example

template class List {template class List {////};};

/**/**

* Sorts a List of objects of type T.* Sorts a List of objects of type T.* T must provide order operators

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Functors

Goal: replace pointers to functionsGoal: replace pointers to functionsHow ?How ?

[return type][return type]operator()(operator()( [type param][type param] ););

Supports inline functionsSupports inline functionsType checkingType checking

Example:Example:

GeneratorGeneratorUnary FunctionUnary Function

Binary functionBinary function

PredicatesPredicates

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Generic Programming

Idea:Idea:

Replace virtual functions by mandatoryReplace virtual functions by mandatory

functions of template argumentsfunctions of template arguments

Example: theExample: the GSTLGSTL[N. Rmy A. Shtuka B. Lvy [N. Rmy A. Shtuka B. Lvy J. Caers]J. Caers]
http://var/www/apps/conversion/tmp/scratch_1/GsTL_gocad.ppthttp://var/www/apps/conversion/tmp/scratch_1/GsTL_gocad.ppthttp://var/www/apps/conversion/tmp/scratch_1/GsTL_gocad.ppt

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Example: Matrix objects (1)class Matrix {class Matrix {

public:public:virtual double operator()( int i, int j ) = 0;virtual double operator()( int i, int j ) = 0;

};};

class SymmetricMatrix : public Matrix {class SymmetricMatrix : public Matrix {

Public:Public:virtual double operator()( int i, int j );virtual double operator()( int i, int j );

};};

class UpperTriangularMatrix : public Matrix {class UpperTriangularMatrix : public Matrix {public:public:virtual double operator()( int i, int j );virtual double operator()( int i, int j );

};};

Any problem?Any problem?

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Static Polymorphism

Replace virtual function by a template

parameter

Delegate the function to the template argument

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Example: Matrix objects (2)class SymmetricStorage {class SymmetricStorage {

public:public:double operator()( int i, int j );double operator()( int i, int j );

};};class UpperTriangularMatrix {class UpperTriangularMatrix {////};};

template class Matrix {template class Matrix {public:public:

double operator()( int i, int j ) {double operator()( int i, int j ) {return storage_(i, j);return storage_(i, j);}}

private:private:STORAGE storage_;STORAGE storage_;

};};

( )

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Example: Matrix objects (2)

template class Matrix {template class Matrix {public:public:////bool is_invertible();bool is_invertible();

bool is_sparse();bool is_sparse();bool is_symmetric_positive_definite();bool is_symmetric_positive_definite();

////};};

Delegation toDelegation to STORAGESTORAGE::- Burdens theBurdens the STORAGESTORAGE conceptconcept- May end up with inconsistenciesMay end up with inconsistencies

E l M i bj (3)

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Example: Matrix objects (3)

template class Matrix {template class Matrix {public:public:LEAF& leaf() {LEAF& leaf() {return static_cast( *this );return static_cast( *this );

}}};};class SymmetricMatrix:class SymmetricMatrix:public Matrix {public Matrix {////

};};

Derived type is known at compile-timeDerived type is known at compile-time

Derived classes can define their own functionsDerived classes can define their own functions

T l t S i li ti

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Template Specialization

Redefine the implementation for some

template arguments

A li ti t

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Application: metaprograms

template class Factorial {template class Factorial {public:public:enum { value = N * Factorial::value };enum { value = N * Factorial::value };

};};

template class Factorial {template class Factorial {public:public:enum { value = 1 };enum { value = 1 };

};};

Void f() {Void f() {const int fact4 = Factorial::value;const int fact4 = Factorial::value;

}}

A li ti t

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Application: metaprograms

Practical interest:Practical interest:

Specialization for optimizing behavior for small objectsSpecialization for optimizing behavior for small objects

Example :Example :

Expand loops in vector / tensor /matrix calculusExpand loops in vector / tensor /matrix calculus

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IV-IV- Overview of the STLOverview of the STL

I l d fil

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Include files

#include #include

#include #include

#include #include

#include #include

#include #include

#include #include

..

STL t i

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STL containers

std::vector vect(30);std::vector vect(30);

vect[2] = 3;vect[2] = 3;

////

for(for(

std::vector::iterator it(vect.begin());std::vector::iterator it(vect.begin());

it != vect.end(); it++it != vect.end(); it++) {) {

int& cur_value = *it;int& cur_value = *it;

}}

STL l ith

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STL algorithms

OrderingOrdering

PermutationsPermutations

Search and replaceSearch and replace

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V- Some design patternsV- Some design patterns

Fi it t t hi

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Finite state machine

Class TransactionBased {Class TransactionBased {public:public:

start_task1();start_task1();

do_action1();do_action1();end_task1();end_task1();

start_task2();start_task2(); // can be started only if task1 was completed// can be started only if task1 was completeddo_action2();do_action2();

end_task2();end_task2();

private:private:enum State{ UNDEF=0, TASK1=2, TASK2 = 4};enum State{ UNDEF=0, TASK1=2, TASK2 = 4};

};};

To solve a linear system of equationsTo solve a linear system of equations

add equation coefficients one by one, then invert the matrixadd equation coefficients one by one, then invert the matrix

C it

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Composite

GraphicGraphic

TextText PicturePictureLineLine

Treat a collection of objects as an objectTreat a collection of objects as an objectitselfitself

Si l t

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Singleton

Ensure that an object is instantiated onlyEnsure that an object is instantiated onlyonceonce

SingletonSingleton

static Singleton* instance()static Singleton* instance()

Obser er

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Observer

Define a dependency between objectsDefine a dependency between objects

ConcreteObserverConcreteObserver

SubjectSubjectnotify()notify()

ObserverObserverupdate()update()

Factory method

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Factory method

Create the right type of elements in anCreate the right type of elements in anabstract frameworkabstract framework

CreatorCreatorcreate_product()create_product() ProductProduct

ConcreteCreatorConcreteCreator ConcreteProductConcreteProduct

Conclusions

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Conclusions

Concrete Applications...Concrete Applications...

Programming projectProgramming project

Oral presentation of the use of oneOral presentation of the use of one

particular design pattern in Gocad (Dec 2,particular design pattern in Gocad (Dec 2,

2005)2005)

In your masters projectsIn your masters projects

References

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References

Brokken et Kubat, C++ Annotations,http://www.icce.rug.nl/docs/cpp.shtml

Stroustrup, Le langage C++ (3e ed.), AddissonWesley, 1996.

Gamma et al., Design Patterns,Addisson Wesley,1995.

Meyers, Effective C++,Addisson Wesley. Meyers, MoreEffective C++,Addisson Wesley. Meyers, Effective STL,Addisson Wesley. http://www.oonumerics.org/blitz/papers/ Gautieret al., Cours de Programmation par objets,

Masson.
http://www.icce.rug.nl/docs/cpp.shtmlhttp://www.oonumerics.org/blitz/papers/http://www.oonumerics.org/blitz/papers/http://www.icce.rug.nl/docs/cpp.shtml

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