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Save my name, email, and website in this browser for the next time I comment. Therefore, the size of an array should be carefully observed. An array such as char buf[80] however, points to a block of memory allocated by the compiler. If a block of characters ends with NULL i. Because the bytes are constant, you can never amend the content of the string.
Therefore, if you want to amend the content of "Hello world! You have to copy the constant bytes into a character array: char str[]; strcpy str, "Hello world! You can then amend the content of the array later. Because as said before, the array name is a constant pointer which can not be assigned. So it is not a NULL-terminated string and can not be used in string manipulation functions such as strcpy, strlen, strcat, etc.
Average comparison time: half of the array size. Binary search: can only be applied on sorted array. By checking the middle element you will find out which half of the array contains the element. Maximum comparison time: log n arraysize. If an array needs to be searched frequently, then it is worthwhile to spend a great time to sort it first. The first dimension does not need a number, just like single-dimension arrays, but the subsequent dimensions does.
An n x 3 array is located in the memory in such a sequence: 0, 0 0, 1 0, 2 1, 0 1, 1 1, If the compiler knows the number of columns which is 3, it will put the fist element 0, 0 of first row on the first memory location, the first element on second row on the fourth memory location, the first element on third row on the 7th location, Without the number of columns the compiler is not able to organize memory for the array. A pointer with a value of 0 points to nowhere.
If a pointer is a constant pointer, it should be initialized when declared, and it can not be pointed to any other variable. Because of this, a pointer can be used in the called function to receive the array. Then by moving the pointer e.
If the size of the variable to which the pointer is pointing to is 4, then actually the value of the pointer will be increased by 3 x 4. Any type of pointer can be assigned to a pointer to void without casting.
However, it can not be conversed. The result may show which one is pointer to a highernumbered element. Pointer arithmetic including increment and difference is meaningless unless performed on one array, because we are only sure that array elements are located one after another.
We can not assume two separate variables are put together in the memory. The following four expressions is doing the same thing: cout cout cout cout 5. When a pointer is pointed to an array or a string, it is actually pointed to the first element of the array subscription 0. This element can also be represented by ptr[3]. If you point a pointer to the middle of an array, what will happen? The pointer can be used as the name of a new array, whose first element is the element to which the pointer is pointing to.
Notice that the number of bytes for a certain type is different for different systems. Just like an array name is the address of the first array element, a function name is a actually the starting address of the function code. A function pointer holds the address of a function, just like a float pointer holds the address of a float variable. A function pointer can point to either a global function or a class function.
My name is Jessy! My name is John! When you want your program to be applicable to different use cases, you may find that at a certian point in your program, you need to invoke a function which has the same signature but different implementation for different use cases.
Different client who uses your program may have different implementations. In this case, you have to provide a mechanism so that the client may register his own version of that function to your program before the invoking point, so that your program knows which one to call. There are three ways to achieve call-back. The OO approach of callback is to let the client class inherit from and implement an interface.
In your code you simply hold an interface pointer and call the interface methods through that pointer. The client program will create his implementation object, assign its pointer to the interface pointer in your class before the calling pointer in your class is reached.
However, if the client class is already finished and did not implement the interface you want, you have to use a less OO approach. The client programmer or your do it for him should write a separate matching class for the client class, which inherit from the desired interface with the function you will call back, which provides the service you need by manipulating client-class objects.
In your code you have a pointer to the interface and invoke the service provided by the separate class. The least OO approach is to use function pointers like the above example. The user is prompted to select an option from a menu e. Each option is severed by a different function.
Pointers to different functions is stored in an array of function pointers. It is extremely flexible and therefore can generate every kind of errors if misused. For example, you can only cast an object of a sub-class to its super-class.
No other casting between user-defined classes is allowed. However, pointers to different classes can be cast to each other without any restrict. What is passed in the casting is only the address. So you can cast a pointer to an integer to a Employee-class pointer. Then the Employee pointer will just assume that starting from the passed address it can find all attributes of Employee class.
From now on we will talk more about OO issues. As a class, it combined the data attributes and the behavior attributes of an object together, and formed an object which can simulate both aspects of a real-world object. To distinguish independent functions such as those string handling functions in "string. The "public:" and "private:" labels are called "member access specifiers". All data members and methods declared by the "public" specifier are accessible from outside, and all declared by "private" are only accessible for methods.
Actually an object contains only the data members. Methods do not belong to any specific object. The belong to the class. All objects share one copy of methods. It may improve the performance, but it is not good for information hiding, because the client of the object is able to "see" the implementation of its methods.
If a method is defined outside the class body, you have to use keyword "inline" if you want it to be inlined. Only the simplest methods can be defined inside the class body. To define the method outside the class body, you have to use scope resolution operator "::", which we have used before to access global variables, when a local variable with the same name had been declared.
Use "class name::" in front of the method definition to make it unique, because other classes may have methods of the same name. Methods which changes the data members are sometimes called "commands", and methods which do not change are called "queries".
Separating the commands and queries leads to simpler, more flexible and easy-understanding interfaces. There is no return type even not void for this special method. Default arguments are recommended for constructors so that even if no arguments are passed to the object the data members can still be initialized to a consistent state. STL containers requires the objects to have default constructors.
Constructor can be overloaded. Normally three kinds of constructors are needed: 1. Default constructor: no arguments; 2. Constructor: object; has all arguments to construct an unique 3. Copy constructor: has an argument its own type, to copy a new object out of it. The default constructor and normal constructor can be merged into one if the normal constructor uses default arguments. If no constructor is provided, the compiler automatically insert a default constructor. This default constructor does not perform any operation.
So the data members of the object may not be consistent. Built-in types are not initialized when created. When you call this method, if you pass a "Parent" object instead of "Child", the compiler will implicitly call the one-argument constructor and convert the "Parent" object to "Child".
If you want to have an array of objects that do not have a default constructor, the work-around is to have an array of pointers and initialize them using operator new.
If copy constructor is not provided, compiler will provide a default copy constructor, which makes default memberwise copy, which can not deal with objects with pointer members. There are two rules for the parameter of copy constructor: 1. Otherwise the copy constructor call results in infinite recursion, because for call-by-value, a copy of the object passed to the copy constructor must be made, which results in the copy constructor being called recursively. The object argument passed to the copy constructor must be constant.
Otherwise it can not be applied on constant object. Independent functions have file scope. Data members and methods are directly accessible by other methods of the same class. So two kinds of variables may appear in a method: local variables with block scope which is destroyed after the call, and data members. Public members of a class is designed to be an interface for its clients.
This helps to hide implementation details from the clients, reducing bugs and improving program modifiability. Because of this, the use of "friends" is deemed by some people to be a violation of information hiding.
Both structures and classes have private, public and protected access. Default of classes is private, default for structure is public.
They can also translate the data format used internally during implementation into the format for clients. Stack memory resources held by the object such as its compilercreated members are released automatically when the object leaves scope or explicitly deleted.
A destructor is only needed to release resources which can not be automatically released, such as dynamically allocated memory using "new" or network or database connection.
Although writing the same statements again can avoid a method call and thus good for performance, it is bad for maintenance, because once the program need to be changed both places should be changed meantime. Extra attention should be paid to always keep them identical. So always use a method call to avoid repeating code. For automatic local objects, constructors are called when execution reaches the point where the objects are declared.
Destructors are called when the objects leave scope i. For static local objects, constructors are called only first time when the execution reaches the point where the objects are declared. It is the same in Java. For objects without dynamic members i. But for objects containing pointers to other objects, a default memberwise copy will only point the pointers of the two objects to the same other object.
This is called shallow copy. It is the same as default memberwise copy. Therefore, copy constructor is a must for any class which needs deep copy that default memberwise copy can not achieve. Copy constructor is therefore given big importance and becomes one of the four elements of the OCF: all classes should provide their properly implemented copy constructors.
If you are preparing for any competitive examination, this book is an excellent resource. This edition includes a new chapter on C Language, which will help the students understand these concepts better. Post Comment. Download PDF. Note :. If you likes to read the soft copy of this book, and you wants to buy hard copy of this book officially from the Publisher. Buy links to this book are given. To buy this book from the official publisher click on the Buy this book button.
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