When the inline function is changed, all functions that call it should be re-compiled. Keyword inline is specially useful for wrapper classes. The copy constructor of the passed object is called to make the copy, requiring extra overhead.
The original values are untouched. This is good for data security, but bad for performance. A reference is not a variable. It is just an alias of a variable. When we talk about a variable, it is actually the address of one memory cell used to hold different values. In machine language we would directly use the address to represent the variable, but in high-level languages identifiers are used to present addresses. Although "b" is created "out of" a, but once created they are equal.
Therefore, when a object is passed by reference, a new alias is created in the called function to refer to the address of that object. With this alias the called object can do anything directly to the object itself.
The calling statement of call-byreference is the same as call-by-value, therefore the programmer may forget that he is calling by reference. When the values of the parameters are the default ones, you can omit the parameters. It is a system-dependent keystroke combination. This calculation has the same priority as manipulation and division. For example, the result of int with float is float.
So do not compare floating-point values for equality. Instead, test whether the absolute value of the difference is less than a specified small value. Using assignment operator can save a bit of compiling and running time. It is useful when the statement is in a loop which will be run many times. As a complete loop, first the condition is checked, if satisfied, the statement is executed, then the control variable is incremented.
Notice that break can only exit one layer of loop. If the number of initializers are less than the number of the array elements, the remaining elements are automatically initialized to zero. But such kind of expression can only be used in declaration. In such way when you need the change the array size you only need to change one place. Only constant variable can be used as array size. Therefore you can not make the array size dynamic by inputting an integer from keyboard in run time and use it as array size.
Therefore by declaring an array of 3 elements then putting a value into the 4th element, you may have overwritten another variables and produced very serious logic errors which is very difficult to find out. 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.
In Java, because all objects are passed by reference and the language even does not support automatic pass-by-value, there is no need for enforcement of copy constructors. For the purpose of cloning objects, Java provides a more robust and automated facility — the clone mechanism.
Factory Method A factory method is a method which uses dynamic memory allocation to clone itself and return a pointer to the new copy. Suppose you have a abstract class Shape and a series of derived concrete classes such as Circle, Square, Rectangle, etc. Suppose you have a method which receives a concrete-class object with a Shape handle and do something on it.
You will lose all information of the derived-class part of data. It can not be modified, and only constant methods can access it. Non-constant methods can not access constant members, even if they do not modify the objects.
Declaring an object to be constant not only can prevent it from being modified, it is also good for performance: today's sophisticated optimizing compilers can perform certain optimizations on constants, but can not do it on variables.
If you return this constant argument back, but did not declare the return type constant, the compiler will complain. Declaring the return by reference constant is to prevent the client from accessing the private data member through the reference. If a method returns one private data member by reference, the client who calls this method can modify reversibly this member.
A constant method can not modify any data member. It still can modify received arguments and local variables. When a constant object is created out of a class, all its nonconstant methods are forbidden to be called by the compiler. In the following example, compiler will prompt error on method call "t1. Member initializers must be used to initialize constant data members. A list of initializers start with a " : " after the constructor header, speparated by ",".
When a parent object is created, the member objects are created first, then they are used to construct the parent object. The order of the creation of member objects is decided by the order they are declared in the class definition, not the order of their member initializers.
Member objects do not have to be initialized explicitly. Not providing a default constructor for the class of a member object when no member initializer is provided for that member object is a syntax error. Member objects still keep their privacy from their owner.
Owner class's methods can not directly access their private data members. Member objects are also called servers, and owners called clients. If a member object is initialized in the constructor with an assignment operator, its default constructor will be called first, then its assignment operator.
If it is initialized with initializer, only its constructor will be called. It is not only the matter of saving one method call, but also the matter of safety. For a class without a properly implemented default constructor or assignment operator, using assignment operator to initialize it may cause unexpected logic errors such as shallow copy.
A function can not declare itself to be a friend of a class. To be able to access a class, this independent function should usually receive an argument of that class, so that it can use the passed handle. When we call an independent function such as "test int i ", we say test1 ; But when we call a method test of object o1, we have to call through this object's handle: o1. When the compiler sees a method call, it implicitly convert it to add one more argument - the object through which the method is called, so that the method knows which object to access.
You can use it to access the object. When you say int a; int b[]; float b; Employee c; The compiler reads the type definition of the object for object c it is the class definition of class Employee and knows the size of the object. Therefore it will complain. It is also not responsible for initializing the allocated memory. So usually there is a memset function call after malloc to initialize it explicitly.
It reads the type definition and allocate exactly the amout of memory needed to hold the object of the given type, then it calls the constructor of that type to initialize the object. Therefore, malloc is the most flexible way to allocate memory, for it does the least thing for you and leave you with all freedom. But it is also error-prone. Besides, C-style function memset may breach the encapsulation law. It can directly access private data members of an object.
It calls the destructor of the type before freeing the memory. So for the sake of performance, if you can decide the size of the memory, always allocate memory at compile time using declarations. Local objects created by declaration is discarded after leaving scope, but objects created by dynamic memory allocation is not destroyed after leaving scope. If not deleted it exists until the end of run. It is still pointing to the same memory location which has now been reclaimed by the OS.
Therefore, if you delete it again the OS will shut down your program, because you are trying to delete something in the OS's territory. Therefore, to prevent somebody or even yourself from accidentally deleting a pointer after it has already been deleted, assign 0 to a pointer after deleting it.
Then the object itself including all its data members are destroyed and memory released to the OS. It is the one who created an instance of this class on the heap who is responsible for deleting this object, not the object itself, because the object can only be deleted when it is created on the heap, and the code in the class implementation has no way to know whether each instance of itself is created on the heap or stack.
It has the same effect as when a client deletes this object. Consider the following example. Delete ; but there will be a run-time error, because inside Delete function we are still deleting a statically-created object.
This proves one thing: after an object is deleted from the heap, the memory space it used to occupy is retrieved by the OS, and you can not access it anymore. But sometimes all the objects share one data member. Both public and private members can be accessed this way. A static method can not access any non-static data members. As said before in the discussion about "this" pointer, a normal method receives implicitly the handle of the object so that it knows which objec to access.
But a static method is not attached to any object of the class and thus does not receive any object handle. So it has no way to access any object data member. It can only access static data members. Static data members are also called "class data", and static methods are also called "class methods". In file "Employee. Because no object is created yet, this statement tells the compiler to allocate a memory space for "total" of the size of an integer.
It is a very useful debugging tool. It helps you to filter out bugs at a early stage before it causes complex confusions. For example, the original class is: In "origin. You can simply declare that class as a data type with a forward class declaration. This is the key factor that makes it possible to hide the private data members of the original class from clients.
They can also be overloaded for any user-defined type, to perform the same or similar operation. For built-in type e. However, you can not put this function in class CMyOwnClass, because a and b are not left-hand operand.
But it is preferable to make it a method. The use of friend here violates the encapsulation of a class. Also, subscripts no longer have to be integers; characters or strings could be used, for example. Normally it will do the job, but for objects with pointers, it will create a new pointer pointing to the same memory location instead of new memory location.
Programs containing these four components are said to be in Orthodox Canonical Form. So we have to create a temporary local object to hold the value of the original object, then increment the original object, and return the temporary one.
The base-class version of method is only overridden from external point of view — they are still accessible from the derived class internally. The derived-class method often needs to call its overridden base-class method to perform part of the job related to the base-class data members.
In this case, if you forget to use the scope resolution operator in front of the invoked overridden base-class method, it will actually call itself and thus create a infinite recursion until the memory is run out. This rule looks a bit wierd. In Java, a base-class method can be overloaded in the derived-class and both methods can be accessed by clients if they are both public.
If a base-class constructor is not explicitly invoked, the compiler will implicitly call the base-class default constructor. If no baseclass default constructor is provided, the compiler will issue a syntax error. When it is to be deleted, the derived-class destructor is called first, then the base-class destructor. In a multi-level inheritance, the constructor of a certain level is only responsible to call the constructor of the next-level class.
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