2010年7月7日星期三

see all running process in Linux

How do I see all running process in Linux?

You need to use the ps command. It provide information about the currently running processes, including their process identification numbers (PIDs). Both Linux and UNIX support ps command to display information about all running process. ps command gives a snapshot of the current processes. If you want a repetitive update of this status, use top command.

ps command

Type the following ps command to display all running process:
# ps aux | less

Where,

  • -A: select all processes
  • a: select all processes on a terminal, including those of other users
  • x: select processes without controlling ttys

Task: see every process on the system

Abstract Class in Java (reproduced)

Abstract Methods and Classes
An abstract class is a class that is declared abstract—it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed.

An abstract method is a method that is declared without an implementation (without braces, and followed by a semicolon), like this:

abstract void moveTo(double deltaX, double deltaY);
If a class includes abstract methods, the class itself must be declared abstract, as in:
public abstract class GraphicObject {
// declare fields
// declare non-abstract methods
abstract void draw();
}
When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class. However, if it does not, the subclass must also be declared abstract.

Note: All of the methods in an interface (see the Interfaces section) are implicitly abstract, so the abstract modifier is not used with interface methods (it could be—it's just not necessary).

Abstract Classes versus Interfaces

Unlike interfaces, abstract classes can contain fields that are not static and final, and they can contain implemented methods. Such abstract classes are similar to interfaces, except that they provide a partial implementation, leaving it to subclasses to complete the implementation. If an abstract class contains only abstract method declarations, it should be declared as an interface instead.

Multiple interfaces can be implemented by classes anywhere in the class hierarchy, whether or not they are related to one another in any way. Think of Comparable or Cloneable, for example.

By comparison, abstract classes are most commonly subclassed to share pieces of implementation. A single abstract class is subclassed by similar classes that have a lot in common (the implemented parts of the abstract class), but also have some differences (the abstract methods).

An Abstract Class Example

In an object-oriented drawing application, you can draw circles, rectangles, lines, Bezier curves, and many other graphic objects. These objects all have certain states (for example: position, orientation, line color, fill color) and behaviors (for example: moveTo, rotate, resize, draw) in common. Some of these states and behaviors are the same for all graphic objects—for example: position, fill color, and moveTo. Others require different implementations—for example, resize or draw. All GraphicObjects must know how to draw or resize themselves; they just differ in how they do it. This is a perfect situation for an abstract superclass. You can take advantage of the similarities and declare all the graphic objects to inherit from the same abstract parent object—for example, GraphicObject, as shown in the following figure.

Classes Rectangle, Line, Bezier, and Circle inherit from  GraphicObject

Classes Rectangle, Line, Bezier, and Circle inherit from GraphicObject

First, you declare an abstract class, GraphicObject, to provide member variables and methods that are wholly shared by all subclasses, such as the current position and the moveTo method. GraphicObject also declares abstract methods for methods, such as draw or resize, that need to be implemented by all subclasses but must be implemented in different ways. The GraphicObject class can look something like this:

abstract class GraphicObject {
int x, y;
...
void moveTo(int newX, int newY) {
...
}
abstract void draw();
abstract void resize();
}
Each non-abstract subclass of GraphicObject, such as Circle and Rectangle, must provide implementations for the draw and resize methods:
class Circle extends GraphicObject {
void draw() {
...
}
void resize() {
...
}
}
class Rectangle extends GraphicObject {
void draw() {
...
}
void resize() {
...
}
}

When an Abstract Class Implements an Interface

In the section on Interfaces , it was noted that a class that implements an interface must implement all of the interface's methods. It is possible, however, to define a class that does not implement all of the interface methods, provided that the class is declared to be abstract. For example,
abstract class X implements Y {
// implements all but one method of Y
}

class XX extends X {
// implements the remaining method in Y
}
In this case, class X must be abstract because it does not fully implement Y, but class XX does, in fact, implement Y.

Class Members

An abstract class may have static fields and static methods. You can use these static members with a class reference—for example, AbstractClass.staticMethod()—as you would with any other class.

2010年7月6日星期二

Multi-threaded Debugging Techniques By Shameem Akhter and Jason Roberts, April 23, 2007


Shameem Akhter is a platform architect at Intel Corporation, focusing on single socket multi-core architecture and performance analysis. Jason Roberts is a senior software engineer at Intel, and has worked on a number of different multi-threaded software products that span a wide range of applications targeting desktop, handheld, and embedded DSP platforms. This article was excerpted from their book Multi-Core Programming. Copyright (c) 2006 Intel Corporation. All rights reserved.

Debugging multi-threaded applications can be a challenging task. The increased complexity of multi-threaded programs results in a large number of possible states that the program may be in at any given time. Determining the state of the program at the time of failure can be difficult; understanding why a particular state is troublesome can be even more difficult. Multi-threaded programs often fail in unexpected ways, and often in a nondeterministic fashion. Bugs may manifest themselves in a sporadic fashion, frustrating developers who are accustomed to troubleshooting issues that are consistently reproducible and predictable. Finally, multi-threaded applications can fail in a drastic fashion-deadlocks cause an application or worse yet, the entire system, to hang. Users tend to find these types of failures to be unacceptable.

General Debug Techniques

Regardless of which library or platform that you are developing on, several general principles can be applied to debugging multi-threaded software applications.

The first technique for eliminating bugs in multi-threaded code is to avoid introducing the bug in the first place. Many software defects can be prevented by using proper software development practices. The later a problem is found in the product development lifecycle, the more expensive it is to fix. Given the complexity of multi-threaded programs, it is critical that multi-threaded applications are properly designed up front.

How often have you, as a software developer, experienced the following situation? Someone on the team that you're working on gets a great idea for a new product or feature. A quick prototype that illustrates the idea is implemented and a quick demo, using a trivial use-case, is presented to management. Management loves the idea and immediately informs sales and marketing of the new product or feature. Marketing then informs the customer of the feature, and in order to make a sale, promises the customer the feature in the next release. Meanwhile, the engineering team, whose original intent of presenting the idea was to get resources to properly implement the product or feature sometime in the future, is now faced with the task of delivering on a customer commitment immediately. As a result of time constraints, it is often the case that the only option is to take the prototype, and try to turn it into production code.

While this example illustrates a case where marketing and management may be to blame for the lack of following an appropriate process, software developers are often at fault in this regard as well. For many developers, writing software is the most interesting part of the job. There's a sense of instant gratification when you finish writing your application and press the run button. The results of all the effort and hard work appear instantly. In addition, modern debuggers provide a wide range of tools that allow developers to quickly identify and fix simple bugs. As a result, many programmers fall into the trap of coding now, deferring design and testing work to a later time. Taking this approach on a multi-threaded application is a recipe for disaster for several reasons:

  • Multi-threaded applications are inherently more complicated than single-threaded applications. Hacking out a reliable, scalable implementation of a multi-threaded application is hard; even for experienced parallel programmers. The primary reason for this is the large number of corner cases that can occur and the wide range of possible paths of the application. Another consideration is the type of run-time environment the application is running on. The access patterns may vary wildly depending on whether or not the application is running on a single-core or multi-core platform, and whether or not the platform supports simultaneous multithreading hardware. These different run-time scenarios need to be thoroughly thought out and handled to guarantee reliability in a wide range of environments and use cases.

  • Multi-threaded bugs may not surface when running under the debugger. Multi-threading bugs are very sensitive to the timing of events in an application. Running the application under the debugger changes the timing, and as a result, may mask problems. When your application fails in a test or worse, the customer environment, but runs reliably under the debugger, it is almost certainly a timing issue in the code. While following a software process can feel like a nuisance at times, taking the wrong approach and not following any process at all is a perilous path when writing all but the most trivial applications. This holds true for parallel programs. While designing your multi-threaded applications, you should keep these points in mind.

  • Design the application so that it can run sequentially. An application should always have a valid means of sequential execution. The application should be validated in this run mode first. This allows developers to eliminate bugs in the code that are not related to threading. If a problem is still present in this mode of execution, then the task of debugging reduces to single-threaded debugging. In many circumstances, it is very easy to generate a sequential version of an application. For example, an OpenMP application compiled with one of the Intel compilers can use the openmp-stubs option to tell the compiler to generate sequential OpenMP code.

  • Use established parallel programming patterns. The best defense against defects is to use parallel patterns that are known to be safe. Established patterns solve many of the common parallel programming problems in a robust manner. Reinventing the wheel is not necessary in many cases.

  • Include built-in debug support in the application. When trying to root cause an application fault, it is often useful for programmers to be able to examine the state of the system at any arbitrary point in time. Consider adding functions that display the state of a thread-or all active threads. Trace buffers, described in the next section, may be used to record the sequence of accesses to a shared resource. Many modern debuggers support the capability of calling a function while stopped at a breakpoint. This mechanism allows developers to extend the capabilities of the debugger to suit their particular application's needs.

2010年7月5日星期一

大数阶乘

大数的操作问题,用基本的数据类型都有溢出的风险。在此,介绍一种比较好的思路,来计算大数的阶乘,比如。100!

首先,定义两个整型的数组:
int fac[1000];//暂且先设定是1000位,我称之为“结果数组”
int add[1000];//我称之为“进位数组”

现在具体说明两个数组的作用:

1.fac[1000]
比如说,一个数5的阶乘是120,那么我就用这个数组存储它:
fac[0]=0
fac[1]=2
fac[2]=1
现在明白了数组 fac的作用了吧。用这样的数组我们可以放阶乘后结果是1000位的数。

2.在介绍add[1000]之前,我介绍一下算法的思想,就以 6!为例:
从上面我们知道了5!是怎样存储的。
就在5!的基础上来计算6!,演示如下:

fac[0]=fac[0]*6=0
fac[1]=fac[1]*6=12
fac[2]=fac[2]*6=6

3. 现在就用到了我们的:“进位数组”add[1000].
先得说明一下:add[i]就是在第2步中用算出的结果中,第i位向第i+1位的进位数值。还是接上例:
add[0]=0;
add[1]=1; // 计算过程:就是 (fac[1]+add[0]) / 10=1
add[2]=0; // 计算过程:就是 (fac[2]+add[1]) /10=0
.......
.......
.......

add[i+1] =( fac[i+1] + add[i] ) / 10

现在就知道了我们的数组add[]是干什么的了吧,并且明白了add[i]是如何求得的了吧。



4.知道了add[1000]的值,现在就在 1. 和 3 . 两步的基础上来计算最终的结果。(第2步仅作为我们理解的步骤,我们下面的计算已经包含了它)

fac[0] = ( fac[0]*6 ) mod 10 =0
fac[1] = ( fac[1]*6 + add[0] ) mod 10 =2
fac[2] = ( fac[2]*6 + add[1] ) mod 10=7

到这里我们已经计算完了6!。然后就可以将数组fac[1000]中的数,以字符的形式按位输出到屏幕上了。

5.还有一点需要说明,就是我们需要一个变量来记录fac[1000]中实际用到了几位,比如5!用了前 3位;
我们在这里定义为 top
为了计算top,我们有用到了add[1000],还是以上面的为例:

5!时,top=3,在此基础上我们来看6!时top=?
由于 add[2]=0
所以 top=3(没有变)
也就是说,如果最高位有进位时,我们的top=top+1,否则,top值不变。

6.总结一下,可以发现,我们把阶乘转化为 两个10以内的数的乘法,还有两个10以内的数的家法了。
因此,不管再大的数,基本上都能算出了,只要你的数组够大就行了。

程序实现:

#include "stdafx.h"
#include

using namespace std;

#define MAX 1000

int fac[MAX]={1,};
int add[MAX]={0,};

int top=1;//计算结果位数

void calculate(int n);

void print();

int main(int argc, char * argv[])
{
cout<<"please input the number:"; int n; cin>>n;
calculate(n);
cout<<<"!="; print(); cout<<" 总共"<<<"位"<<=0) { exit(1); } for (int i=1;i<=n;i++) { int m=top; for (int j=0;j0){
top++;
int tmp=fac[top-1];
fac[top-1]=(tmp+add[top-2])%10;
add[top-1]=(tmp+add[top-2])/10;
}
}
}
}

// 打印输出结果
void print(){
int j=0;
for(int i=top-1;i>=0;i--)
{
if ((j++)%20==0)
{
cout<
}
cout<
}
cout<
}

2010年6月27日星期日

C++ interview questions

C/C++ Programming interview questions and answers

By Satish Shetty, July 14th, 2004

What is encapsulation??

Containing and hiding information about an object, such as internal data structures and code. Encapsulation isolates the internal complexity of an object's operation from the rest of the application. For example, a client component asking for net revenue from a business object need not know the data's origin.

What is inheritance?

Inheritance allows one class to reuse the state and behavior of another class. The derived class inherits the properties and method implementations of the base class and extends it by overriding methods and adding additional properties and methods.

What is Polymorphism??

Polymorphism allows a client to treat different objects in the same way even if they were created from different classes and exhibit different behaviors.

You can use implementation inheritance to achieve polymorphism in languages such as C++ and Java.

Base class object's pointer can invoke methods in derived class objects.

You can also achieve polymorphism in C++ by function overloading and operator overloading.

What is constructor or ctor?

Constructor creates an object and initializes it. It also creates vtable for virtual functions. It is different from other methods in a class.

What is destructor?

Destructor usually deletes any extra resources allocated by the object.

What is default constructor?

Constructor with no arguments or all the arguments has default values.

What is copy constructor?

Constructor which initializes the it's object member variables ( by shallow copying) with another object of the same class. If you don't implement one in your class then compiler implements one for you.

for example:
Boo Obj1(10); // calling Boo constructor

Boo Obj2(Obj1); // calling boo copy constructor
Boo Obj2 = Obj1;// calling boo copy constructor

When are copy constructors called?

Copy constructors are called in following cases:
a) when a function returns an object of that class by value
b) when the object of that class is passed by value as an argument to a function
c) when you construct an object based on another object of the same class
d) When compiler generates a temporary object

What is assignment operator?

Default assignment operator handles assigning one object to another of the same class. Member to member copy (shallow copy)

What are all the implicit member functions of the class? Or what are all the functions which compiler implements for us if we don't define one.??

default ctor
copy ctor
assignment operator
default destructor
address operator

What is conversion constructor?

constructor with a single argument makes that constructor as conversion ctor and it can be used for type conversion.

for example:

class Boo
{
public:
Boo( int i );
};

Boo BooObject = 10 ; // assigning int 10 Boo object

What is conversion operator??

class can have a public method for specific data type conversions.

for example:
class Boo
{
double value;
public:
Boo(int i )
operator double()
{
return value;
}
};

Boo BooObject;

double i = BooObject; // assigning object to variable i of type double. now conversion operator gets called to assign the value.

What is diff between malloc()/free() and new/delete?

malloc allocates memory for object in heap but doesn't invoke object's constructor to initiallize the object.

new allocates memory and also invokes constructor to initialize the object.

malloc() and free() do not support object semantics
Does not construct and destruct objects
string * ptr = (string *)(malloc (sizeof(string)))
Are not safe
Does not calculate the size of the objects that it construct
Returns a pointer to void
int *p = (int *) (malloc(sizeof(int)));
int *p = new int;
Are not extensible
new and delete can be overloaded in a class

"delete" first calls the object's termination routine (i.e. its destructor) and then releases the space the object occupied on the heap memory. If an array of objects was created using new, then delete must be told that it is dealing with an array by preceding the name with an empty []:-

Int_t *my_ints = new Int_t[10];

...

delete []my_ints;

what is the diff between "new" and "operator new" ?


"operator new" works like malloc.

What is difference between template and macro??

There is no way for the compiler to verify that the macro parameters are of compatible types. The macro is expanded without any special type checking.

If macro parameter has a postincremented variable ( like c++ ), the increment is performed two times.

Because macros are expanded by the preprocessor, compiler error messages will refer to the expanded macro, rather than the macro definition itself. Also, the macro will show up in expanded form during debugging.

for example:

Macro:

#define min(i, j) (i < j ? i : j)

template:
template
T min (T i, T j)
{
return i < j ? i : j;
}



What are C++ storage classes?

auto
register
static
extern

auto: the default. Variables are automatically created and initialized when they are defined and are destroyed at the end of the block containing their definition. They are not visible outside that block

register: a type of auto variable. a suggestion to the compiler to use a CPU register for performance

static: a variable that is known only in the function that contains its definition but is never destroyed and retains its value between calls to that function. It exists from the time the program begins execution

extern: a static variable whose definition and placement is determined when all object and library modules are combined (linked) to form the executable code file. It can be visible outside the file where it is defined.

What are storage qualifiers in C++ ?

They are..

const
volatile
mutable

Const keyword indicates that memory once initialized, should not be altered by a program.

volatile keyword indicates that the value in the memory location can be altered even though nothing in the program
code modifies the contents. for example if you have a pointer to hardware location that contains the time, where hardware changes the value of this pointer variable and not the program. The intent of this keyword to improve the optimization ability of the compiler.

mutable keyword indicates that particular member of a structure or class can be altered even if a particular structure variable, class, or class member function is constant.

struct data
{
char name[80];
mutable double salary;
}

const data MyStruct = { "Satish Shetty", 1000 }; //initlized by complier

strcpy ( MyStruct.name, "Shilpa Shetty"); // compiler error
MyStruct.salaray = 2000 ; // complier is happy allowed

What is reference ??

reference is a name that acts as an alias, or alternative name, for a previously defined variable or an object.

prepending variable with "&" symbol makes it as reference.

for example:

int a;
int &b = a;


What is passing by reference?

Method of passing arguments to a function which takes parameter of type reference.

for example:

void swap( int & x, int & y )
{
int temp = x;
x = y;
y = temp;
}

int a=2, b=3;

swap( a, b );

Basically, inside the function there won't be any copy of the arguments "x" and "y" instead they refer to original variables a and b. so no extra memory needed to pass arguments and it is more efficient.


When do use "const" reference arguments in function?

a) Using const protects you against programming errors that inadvertently alter data.
b) Using const allows function to process both const and non-const actual arguments, while a function without const in the prototype can only accept non constant arguments.
c) Using a const reference allows the function to generate and use a temporary variable appropriately.


When are temporary variables created by C++ compiler?

Provided that function parameter is a "const reference", compiler generates temporary variable in following 2 ways.

a) The actual argument is the correct type, but it isn't Lvalue

double Cube(const double & num)
{
num = num * num * num;
return num;

}

double temp = 2.0;
double value = cube(3.0 + temp); // argument is a expression and not a Lvalue;

b) The actual argument is of the wrong type, but of a type that can be converted to the correct type

long temp = 3L;
double value = cuberoot ( temp); // long to double conversion


What is virtual function?

When derived class overrides the base class method by redefining the same function, then if client wants to access redefined the method from derived class through a pointer from base class object, then you must define this function in base class as virtual function.

class parent
{
void Show()
{
cout << "i'm parent" << endl;
}
};

class child: public parent
{
void Show()
{
cout << "i'm child" << endl;
}

};

parent * parent_object_ptr = new child;

parent_object_ptr->show() // calls parent->show() i

now we goto virtual world...

class parent
{
virtual void Show()
{
cout << "i'm parent" << endl;
}
};

class child: public parent
{
void Show()
{
cout << "i'm child" << endl;
}

};

parent * parent_object_ptr = new child;

parent_object_ptr->show() // calls child->show()


What is pure virtual function? or what is abstract class?

When you define only function prototype in a base class without implementation and do the complete implementation in derived class. This base class is called abstract class and client won't able to instantiate an object using this base class.

You can make a pure virtual function or abstract class this way..

class Boo
{
void foo() = 0;
}

Boo MyBoo; // compilation error


What is Memory alignment??

The term alignment primarily means the tendency of an address pointer value to be a multiple of some power of two. So a pointer with two byte alignment has a zero in the least significant bit. And a pointer with four byte alignment has a zero in both the two least significant bits. And so on. More alignment means a longer sequence of zero bits in the lowest bits of a pointer.

What problem does the namespace feature solve?

Multiple providers of libraries might use common global identifiers causing a name collision when an application tries to link with two or more such libraries. The namespace feature surrounds a library's external declarations with a unique namespace that eliminates the potential for those collisions.

namespace [identifier] { namespace-body }

A namespace declaration identifies and assigns a name to a declarative region.
The identifier in a namespace declaration must be unique in the declarative region in which it is used. The identifier is the name of the namespace and is used to reference its members.

What is the use of 'using' declaration?

A using declaration makes it possible to use a name from a namespace without the scope operator.

What is an Iterator class?

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. Something like a pointer.

What is a dangling pointer?

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.

What do you mean by Stack unwinding?

It is a process during exception handling when the destructor is called for all local objects in the stack between the place where the exception was thrown and where it is caught.

Name the operators that cannot be overloaded??

sizeof, ., .*, .->, ::, ?:

What is a container class? What are the types of container classes?

A container class is a class that is used to hold objects in memory or external storage. A container class acts as a generic holder. A container class has a predefined behavior and a well-known interface. A container class is a supporting class whose purpose is to hide the topology used for maintaining the list of objects in memory. When a container class contains a group of mixed objects, the container is called a heterogeneous container; when the container is holding a group of objects that are all the same, the container is called a homogeneous container.

What is inline function??

The __inline keyword tells the compiler to substitute the code within the function definition for every instance of a function call. However, substitution occurs only at the compiler's discretion. For example, the compiler does not inline a function if its address is taken or if it is too large to inline.


What is overloading??

With the C++ language, you can overload functions and operators. Overloading is the practice of supplying more than one definition for a given function name in the same scope.

- Any two functions in a set of overloaded functions must have different argument lists.
- Overloading functions with argument lists of the same types, based on return type alone, is an error.

What is Overriding?

To override a method, a subclass of the class that originally declared the method must declare a method with the same name, return type (or a subclass of that return type), and same parameter list.
The definition of the method overriding is:
· Must have same method name.
· Must have same data type.
· Must have same argument list.
Overriding a method means that replacing a method functionality in child class. To imply overriding functionality we need parent and child classes. In the child class you define the same method signature as one defined in the parent class.

What is "this" pointer?

The this pointer is a pointer accessible only within the member functions of a class, struct, or union type. It points to the object for which the member function is called. Static member functions do not have a this pointer.

When a nonstatic member function is called for an object, the address of the object is passed as a hidden argument to the function. For example, the following function call

myDate.setMonth( 3 );

can be interpreted this way:

setMonth( &myDate, 3 );

The object's address is available from within the member function as the this pointer. It is legal, though unnecessary, to use the this pointer when referring to members of the class.

What happens when you make call "delete this;" ??

The code has two built-in pitfalls. First, if it executes in a member function for an extern, static, or automatic object, the program will probably crash as soon as the delete statement executes. There is no portable way for an object to tell that it was instantiated on the heap, so the class cannot assert that its object is properly instantiated. Second, when an object commits suicide this way, the using program might not know about its demise. As far as the instantiating program is concerned, the object remains in scope and continues to exist even though the object did itself in. Subsequent dereferencing of the pointer can and usually does lead to disaster.

You should never do this. Since compiler does not know whether the object was allocated on the stack or on the heap, "delete this" could cause a disaster.

How virtual functions are implemented C++?

Virtual functions are implemented using a table of function pointers, called the vtable. There is one entry in the table per virtual function in the class. This table is created by the constructor of the class. When a derived class is constructed, its base class is constructed first which creates the vtable. If the derived class overrides any of the base classes virtual functions, those entries in the vtable are overwritten by the derived class constructor. This is why you should never call virtual functions from a constructor: because the vtable entries for the object may not have been set up by the derived class constructor yet, so you might end up calling base class implementations of those virtual functions

What is name mangling in C++??

The process of encoding the parameter types with the function/method name into a unique name is called name mangling. The inverse process is called demangling.

For example Foo::bar(int, long) const is mangled as `bar__C3Fooil'.
For a constructor, the method name is left out. That is Foo::Foo(int, long) const is mangled as `__C3Fooil'.

What is the difference between a pointer and a reference?

A reference must always refer to some object and, therefore, must always be initialized; pointers do not have such restrictions. A pointer can be reassigned to point to different objects while a reference always refers to an object with which it was initialized.

How are prefix and postfix versions of operator++() differentiated?

The postfix version of operator++() has a dummy parameter of type int. The prefix version does not have dummy parameter.

What is the difference between const char *myPointer and char *const myPointer?

Const char *myPointer is a non constant pointer to constant data; while char *const myPointer is a constant pointer to non constant data.

How can I handle a constructor that fails?

throw an exception. Constructors don't have a return type, so it's not possible to use return codes. The best way to signal constructor failure is therefore to throw an exception.

How can I handle a destructor that fails?

Write a message to a log-file. But do not throw an exception.
The C++ rule is that you must never throw an exception from a destructor that is being called during the "stack unwinding" process of another exception. For example, if someone says throw Foo(), the stack will be unwound so all the stack frames between the throw Foo() and the } catch (Foo e) { will get popped. This is called stack unwinding.
During stack unwinding, all the local objects in all those stack frames are destructed. If one of those destructors throws an exception (say it throws a Bar object), the C++ runtime system is in a no-win situation: should it ignore the Bar and end up in the } catch (Foo e) { where it was originally headed? Should it ignore the Foo and look for a } catch (Bar e) { handler? There is no good answer -- either choice loses information.
So the C++ language guarantees that it will call terminate() at this point, and terminate() kills the process. Bang you're dead.

What is Virtual Destructor?

Using virtual destructors, you can destroy objects without knowing their type - the correct destructor for the object is invoked using the virtual function mechanism. Note that destructors can also be declared as pure virtual functions for abstract classes.

if someone will derive from your class, and if someone will say "new Derived", where "Derived" is derived from your class, and if someone will say delete p, where the actual object's type is "Derived" but the pointer p's type is your class.


Can you think of a situation where your program would crash without reaching the breakpoint which you set at the beginning of main()?

C++ allows for dynamic initialization of global variables before main() is invoked. It is possible that initialization of global will invoke some function. If this function crashes the crash will occur before main() is entered.

Name two cases where you MUST use initialization list as opposed to assignment in constructors.

Both non-static const data members and reference data members cannot be assigned values; instead, you should use initialization list to initialize them.

Can you overload a function based only on whether a parameter is a value or a reference?

No. Passing by value and by reference looks identical to the caller.

What are the differences between a C++ struct and C++ class?

The default member and base class access specifiers are different.

The C++ struct has all the features of the class. The only differences are that a struct defaults to public member access and public base class inheritance, and a class defaults to the private access specifier and private base class inheritance.

What does extern "C" int func(int *, Foo) accomplish?

It will turn off "name mangling" for func so that one can link to code compiled by a C compiler.

How do you access the static member of a class?

::

What is multiple inheritance(virtual inheritance)? What are its advantages and disadvantages?

Multiple Inheritance is the process whereby a child can be derived from more than one parent class. The advantage of multiple inheritance is that it allows a class to inherit the functionality of more than one base class thus allowing for modeling of complex relationships. The disadvantage of multiple inheritance is that it can lead to a lot of confusion(ambiguity) when two base classes implement a method with the same name.

What are the access privileges in C++? What is the default access level?

The access privileges in C++ are private, public and protected. The default access level assigned to members of a class is private. Private members of a class are accessible only within the class and by friends of the class. Protected members are accessible by the class itself and it's sub-classes. Public members of a class can be accessed by anyone.

What is a nested class? Why can it be useful?

A nested class is a class enclosed within the scope of another class. For example:

// Example 1: Nested class
//
class OuterClass
{
class NestedClass
{
// ...
};
// ...
};
Nested classes are useful for organizing code and controlling access and dependencies. Nested classes obey access rules just like other parts of a class do; so, in Example 1, if NestedClass is public then any code can name it as OuterClass::NestedClass. Often nested classes contain private implementation details, and are therefore made private; in Example 1, if NestedClass is private, then only OuterClass's members and friends can use NestedClass.

When you instantiate as outer class, it won't instantiate inside class.

What is a local class? Why can it be useful?

local class is a class defined within the scope of a function -- any function, whether a member function or a free function. For example:

// Example 2: Local class
//
int f()
{
class LocalClass
{
// ...
};
// ...
};
Like nested classes, local classes can be a useful tool for managing code dependencies.


Can a copy constructor accept an object of the same class as parameter, instead of reference of the object?


No. It is specified in the definition of the copy constructor itself. It should generate an error if a programmer specifies a copy constructor with a first argument that is an object and not a reference.

if you have any comments/questions please email me at

copyright (c) 2004, Satish Shetty, All rights reserved,

visit my homepage at http://www.shettysoft.com

2010年1月19日星期二

some good sentences for paper writing

1 precision and recall experiment should be conducted to see whether this method can actually improve the quality of the final ranking list
2 about the similarity threshold, the threshold is relied on the user to set it. However, how such threshold should be set is not clearly illustrated.
3 The authors of this paper tried to address a new problem, of developing a new distance measure for subtrees, which has not been proposed / solved before

4 and avoided the drawbacks of total mapping

5 there is just one sentence mentioning a very important information, and no further illustration is presented later

6 the authors claimed that

7 However, such claim is not convincing, and more details and illustration are needed to convince the reader that the efficiency of the PPI is really OK, and this should also be demonstrated in the later experiment section

8 This paper identified two critical problems/drawbacks of previous works

9 decreasing the page rank of spam sites could be directly achieved by using previous work

10 We three reviewers agree with some weak points of the paper, such as unavailability of category tags for most of the pages, the to-be-improved presentation and in-comprehensive experiment.

the which is not significant.



////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
some points in writing the
1 Do NOT start a sentence with “AND”. I have said this many times, and hope this is the last time.also not add the First
2 A paper must be consistent, so does a review.Not enough pages should not count as a weak point to reject paper
3 author+"proposed to"
4 "presents" should be "represent"
5 be concise
6 explain that why
7 method->technique

////////////////////////////////////////////////
major problem:
1

2 's and in the begining

////////////////////////////////////////////
question: to merge them?