Constructor PPT Updated

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5/26/12 Sourabh Agrawal

Effective CPP

Sourabh Agrawal11-Aug-2011


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AGENDA To suggest a approach to effective way of writing C++

which are more comprehensible, maintainable, portable,extensible, efficient, and likely to behave as you expect .


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Topics Know what functions C++ silently writes and calls

Prefer initialization to assignment in constructors

List members in an initialization list in the order in which they aredeclared

Prevents Constructor from being used to perform implicit typeconversions

Declare a copy constructor and an assignment operator for classeswith dynamically allocated memory

Declare destructors virtual in polymorphic base classes


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Functions C++ silentlywrites and calls in a

Class


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class Empty

{

};

it's essentially the same as if you'dwritten this:

class Empty

{public:

Empty() { }

~Empty() { }


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Prefer initialization toassignment in

constructors


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Class A{

public:A (string initName ){

name = initName;

}

private:string name;};


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Class A{

public:A (string initName ): name

(initName)

{

}

private:string name;};


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Const and Reference class member

variables must be initialized inconstructor.


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List members in the classin its dependency order


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template

class Array

{public:

Array(int low, int high);//Constructor Declaration

size_t size; // No. of elements in array

vector data; // thearray data is stored

int lBound, hBound; // lower

bound, higher bound


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Prevents Constructorfrom being used to

perform implicit typeconversions


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class ABC

{

public:ABC(int x)

{

}

};

void function(ABC Object)

{

cout


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class ABC

{

public:explicit ABC(int x) // Not allowing

implicit casting of integer to ABC

{}

};

void function(ABC Object)

{


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Declare a copyconstructor and an

assignment operator for

classes with dynamicallyallocated memory

l S i


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class String

{

char *data;

public:

String::String(const char *value)

{

if (value)

{

data = new char[strlen(value) + 1];

strcpy(data, value);

}

}

String::~String(){

delete [] data;

}

};int main()

BitwiseCopying

BitwiseCopying


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String a("Hello");String b("World");

b = a; // Both b and a data* are pointing to samememory location

Memory Leak

Leads to MemoryCorru tion

deletea


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Declare destructorsvirtual in polymorphic

base classes


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Acc. to C++ Standard:

When you try to delete a derived

class object through a base classpointer and the base class has a non-virtual the results are undefined.

Polymorphic base classes shoulddeclare virtual destructors. If a classhas any virtual functions, it shouldhave a virtual destructor.


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Handle assignment to

self in operator=


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If you can detect an assignment toself at the top of your assignmentoperator(s), you can return rightaway, possibly saving a lot of workthat you'd otherwise have to gothrough to implement assignment

A more important reason forchecking for assignment to self is toensure correctness.


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Have operator= return areference to *this


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Prevent exceptions fromleaving destructors

Destructors should never emitexceptions. If functions called in adestructor may throw, the destructorshould catch any exceptions, thenswallow them or terminate theprogram.

If class clients need to be able toreact to exceptions thrown during anoperation, the class should provide a


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functions duringconstruction or

destructionDon't call virtual functions during

construction or destruction, becausesuch calls will never go to a morederived class than that of the currentlyexecuting constructor or destructor.


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Thank You !!!

References:Effective C++C++ Standard Draft

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