C++ Programming

A dangling pointer arises when you use

the address of an object after

its lifetime is over. This may occur

in situations like returning

addresses of the automatic variables

from a function or using the

address of the memory block after

it is freed. The following

code snippet shows this:

class Sample

{

public:

int *ptr;

Sample(int i)

{

ptr = new int(i);

}

~Sample()

{

delete ptr;

}

void PrintVal()

{

cout << "The value is " << *ptr;

}

};

void SomeFunc(Sample x)

{

cout << "Say i am in someFunc " << endl;

}

int main()

{

Sample s1 = 10;

SomeFunc(s1);

s1.PrintVal();

}

In the above example when PrintVal() function is

called it is called by the pointer that has been

freed by the destructor in SomeFunc.

A class that is used to traverse through the objects maintained by a container class. There are five categories of iterators: input iterators, output iterators, forward iterators, bidirectional iterators, random access. An iterator is an entity that gives access to the contents of a container object without violating encapsulation constraints. Access to the contents is granted on a one-at-a-time basis in order. The order can be storage order (as in lists and queues) or some arbitrary order (as in array indices) or according to some ordering relation (as in an ordered binary tree). The iterator is a construct, which provides an interface that, when called, yields either the next element in the container, or some value denoting the fact that there are no more elements to examine. Iterators hide the details of access to and update of the elements of a container class.

The simplest and safest iterators are those that permit read-only access to the contents of a container class.

Precondition: A precondition is a condition that must be true on entry to a member function. A class is used correctly if preconditions are never false. An operation is not responsible for doing anything sensible if its precondition fails to hold. For example, the interface invariants of stack class say nothing about pushing yet another element on a stack that is already full. We say that isful() is a precondition of the push operation. Post-condition: A post-condition is a condition that must be true on exit from a member function if the precondition was valid on entry to that function. A class is implemented correctly if post-conditions are never false. For example, after pushing an element on the stack, we know that isempty() must necessarily hold. This is a post-condition of the push operation.

Released in 1985, C++ is an object-oriented programming language created by Bjarne Stroustrup. C++ maintains almost all aspects of the C language, while simplifying memory management and adding several features - including a new datatype known as a class (you will learn more about these later) - to allow object-oriented programming. C++ maintains the features of C which allowed for low-level memory access but also gives the programmer new tools to simplify memory management.

C++ used for:

C++ is a powerful general-purpose programming language. It can be used to create small programs or large applications. It can be used to make CGI scripts or console-only DOS programs. C++ allows you to create programs to do almost anything you need to do. The creator of C++, Bjarne Stroustrup, has put together a partial list of applications written in C++.

Objects that stand for other objects are called proxy objects or surrogates.

template <class t="">

class Array2D

{

public:

class Array1D

{

public:

T& operator[] (int index);

const T& operator[] (int index)const;

};

Array1D operator[] (int index);

const Array1D operator[] (int index) const;

};

The following then becomes legal:

Array2D<float>data(10,20);

cout<<data[3][6]; // fine

Here data[3] yields an Array1D object and the operator [] invocation on that object yields the float in position(3,6) of the original two dimensional array. Clients of the Array2D class need not be aware of the presence of the Array1D class. Objects of this latter class stand for one-dimensional array objects that, conceptually, do not exist for clients of Array2D. Such clients program as if they were using real, live, two-dimensional arrays. Each Array1D object stands for a one-dimensional array that is absent from a conceptual model used by the clients of Array2D. In the above example, Array1D is a proxy class. Its instances stand for one-dimensional arrays that, conceptually, do not exist.