class Point2D{
int x; int y;
public int color;
protected bool pinned;
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
};
Point2D MyPoint;
You cannot directly access private data members when they are declared (implicitly) private:
MyPoint.x = 5; // Compiler will issue a compile ERROR
//Nor yoy can see them:
int x_dim = MyPoint.x; // Compiler will issue a compile ERROR
On the other hand, you can assign and read the public data members:
MyPoint.color = 255; // no problem
int col = MyPoint.color; // no problem
With protected data members you can read them but not write them: MyPoint.pinned = true; // Compiler will issue a compile ERROR
bool isPinned = MyPoint.pinned; // no problem
What is namespace?
Namespaces allow us to group a set of global classes, objects and/or functions under a name. To say it somehow, they serve to split the global scope in sub-scopes known as namespaces.
The form to use namespaces is:
namespace identifier { namespace-body }
Where identifier is any valid identifier and namespace-body is the set of classes, objects and functions that are included within the namespace. For example:
namespace general { int a, b; } In this case, a and b are normal variables integrated within the general namespace. In order to access to these variables from outside the namespace we have to use the scope operator ::. For example, to access the previous variables we would have to put:
general::a general::b
The functionality of namespaces is specially useful in case that there is a possibility that a global object or function can have the same name than another one, causing a redefinition error.
What is a COPY CONSTRUCTOR and when is it called?
A copy constructor is a method that accepts an object of the same class and copies it’s data members to the object on the left part of assignement:
class Point2D{
int x; int y;
public int color;
protected bool pinned;
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
public Point2D( const Point2D & ) ;
};
Point2D::Point2D( const Point2D & p )
{
this->x = p.x;
this->y = p.y;
this->color = p.color;
this->pinned = p.pinned;
}
main(){
Point2D MyPoint;
MyPoint.color = 345;
Point2D AnotherPoint = Point2D( MyPoint ); // now AnotherPoint has color = 345
What is Boyce Codd Normal form?
A relation schema R is in BCNF with respect to a set F of functional dependencies if for all functional dependencies in F+ of the form a-> , where a and b is a subset of R, at least one of the following holds:
* a- > b is a trivial functional dependency (b is a subset of a)
* a is a superkey for schema R
What is virtual class and friend class?
Friend classes are used when two or more classes are designed to work together and need access to each other's implementation in ways that the rest of the world shouldn't be allowed to have. In other words, they help keep private things private. For instance, it may be desirable for class DatabaseCursor to have more privilege to the internals of class Database than main() has.
What is the word you will use when defining a function in base class to allow this function to be a polimorphic function?
virtual
What do you mean by binding of data and functions?
Encapsulation.
What are 2 ways of exporting a function from a DLL?
1.Taking a reference to the function from the DLL instance.
2. Using the DLL ’s Type Library
What is the difference between an object and a class?
Classes and objects are separate but related concepts. Every object belongs to a class and every class contains one or more related objects.
- A Class is static. All of the attributes of a class are fixed before, during, and after the execution of a program. The attributes of a class don't change.
- The class to which an object belongs is also (usually) static. If a particular object belongs to a certain class at the time that it is created then it almost certainly will still belong to that class right up until the time that it is destroyed.
- An Object on the other hand has a limited lifespan. Objects are created and eventually destroyed. Also during that lifetime, the attributes of the object may undergo significant change.
Suppose that data is an array of 1000 integers. Write a single function call that will sort the 100 elements data [222] through data [321].
quicksort ((data + 222), 100);
What is a class?
Class is a user-defined data type in C++. It can be created to solve a particular kind of problem. After creation the user need not know the specifics of the working of a class.
What is friend function?
As the name suggests, the function acts as a friend to a class. As a friend of a class, it can access its private and protected members. A friend function is not a member of the class. But it must be listed in the class definition.
Which recursive sorting technique always makes recursive calls to sort subarrays that are about half size of the original array?
Mergesort always makes recursive calls to sort subarrays that are about half size of the original array, resulting in O(n log n) time.
What is abstraction?
Abstraction is of the process of hiding unwanted details from the user.
What are virtual functions?
A virtual function allows derived classes to replace the implementation provided by the base class. The compiler makes sure the replacement is always called whenever the object in question is actually of the derived class, even if the object is accessed by a base pointer rather than a derived pointer. This allows algorithms in the base class to be replaced in the derived class, even if users don't know about the derived class.
What is the difference between an external iterator and an internal iterator? Describe an advantage of an external iterator.
An internal iterator is implemented with member functions of the class that has items to step through. .An external iterator is implemented as a separate class that can be "attach" to the object that has items to step through. .An external iterator has the advantage that many difference iterators can be active simultaneously on the same object.
What is a scope resolution operator?
A scope resolution operator (::), can be used to define the member functions of a class outside the class.
What do you mean by pure virtual functions?
A pure virtual member function is a member function that the base class forces derived classes to provide. Normally these member functions have no implementation. Pure virtual functions are equated to zero.
class Shape { public: virtual void draw() = 0; };
What is polymorphism? Explain with an example?
"Poly" means "many" and "morph" means "form". Polymorphism is the ability of an object (or reference) to assume (be replaced by) or become many different forms of object.
Example: function overloading, function overriding, virtual functions. Another example can be a plus ‘+’ sign, used for adding two integers or for using it to concatenate two strings.
What’s the output of the following program? Why?
#include
main()
{
typedef union
{
int a;
char b[10];
float c;
}
Union;
Union x,y = {100};
x.a = 50;
strcpy(x.b,\"hello\");
x.c = 21.50;
printf(\"Union x : %d %s %f \n\",x.a,x.b,x.c );
printf(\"Union y :%d %s%f \n\",y.a,y.b,y.c);
}
Given inputs X, Y, Z and operations | and & (meaning bitwise OR and AND, respectively)
What is output equal to in
output = (X & Y) | (X & Z) | (Y & Z)
Why are arrays usually processed with for loop?
The real power of arrays comes from their facility of using an index variable to traverse the array, accessing each element with the same expression a[i]. All the is needed to make this work is a iterated statement in which the variable i serves as a counter, incrementing from 0 to a.length -1. That is exactly what a loop does.
What is an HTML tag?
Answer: An HTML tag is a syntactical construct in the HTML language that abbreviates specific instructions to be executed when the HTML script is loaded into a Web browser. It is like a method in Java, a function in C++, a procedure in Pascal, or a subroutine in FORTRAN.
Explain which of the following declarations will compile and what will be constant - a pointer or the value pointed at: * const char *
* char const *
* char * const
Note: Ask the candidate whether the first declaration is pointing to a string or a single character. Both explanations are correct, but if he says that it’s a single character pointer, ask why a whole string is initialized as char* in C++. If he says this is a string declaration, ask him to declare a pointer to a single character. Competent candidates should not have problems pointing out why const char* can be both a character and a string declaration, incompetent ones will come up with invalid reasons.
You’re given a simple code for the class Bank Customer. Write the following functions:
* Copy constructor
* = operator overload
* == operator overload
* + operator overload (customers’ balances should be added up, as an example of joint account between husband and wife)
Note:Anyone confusing assignment and equality operators should be dismissed from the interview. The applicant might make a mistake of passing by value, not by reference. The candidate might also want to return a pointer, not a new object, from the addition operator. Slightly hint that you’d like the value to be changed outside the function, too, in the first case. Ask him whether the statement customer3 = customer1 + customer2 would work in the second case.
What problems might the following macro bring to the application?
#define sq(x) x*x
Anything wrong with this code?
T *p = new T[10];
delete p;
Everything is correct, Only the first element of the array will be deleted”, The entire array will be deleted, but only the first element destructor will be called.
Anything wrong with this code?
T *p = 0;
delete p;
Yes, the program will crash in an attempt to delete a null pointer.
How do you decide which integer type to use?
It depends on our requirement. When we are required an integer to be stored in 1 byte (means less than or equal to 255) we use short int, for 2 bytes we use int, for 8 bytes we use long int.
A char is for 1-byte integers, a short is for 2-byte integers, an int is generally a 2-byte or 4-byte integer (though not necessarily), a long is a 4-byte integer, and a long long is a 8-byte integer.
What does extern mean in a function declaration?
Using extern in a function declaration we can make a function such that it can used outside the file in which it is defined.
An extern variable, function definition, or declaration also makes the described variable or function usable by the succeeding part of the current source file. This declaration does not replace the definition. The declaration is used to describe the variable that is externally defined.
If a declaration for an identifier already exists at file scope, any extern declaration of the same identifier found within a block refers to that same object. If no other declaration for the identifier exists at file scope, the identifier has external linkage.
What can I safely assume about the initial values of variables which are not explicitly initialized?
It depends on complier which may assign any garbage value to a variable if it is not initialized.
What is the difference between char a[] = “string”; and char *p = “string”;?
In the first case 6 bytes are allocated to the variable a which is fixed, where as in the second case if *p is assigned to some other value the allocate memory can change.
What’s the auto keyword good for?
Answer1
Not much. It declares an object with automatic storage duration. Which means the object will be destroyed at the end of the objects scope. All variables in functions that are not declared as static and not dynamically allocated have automatic storage duration by default.
For example
int main()
{
int a; //this is the same as writing “auto int a;”
}
Answer2
Local variables occur within a scope; they are “local” to a function. They are often called automatic variables because they automatically come into being when the scope is entered and automatically go away when the scope closes. The keyword auto makes this explicit, but local variables default to auto auto auto auto so it is never necessary to declare something as an auto auto auto auto.
What is the difference between char a[] = “string”; and char *p = “string”; ?
Answer1
a[] = “string”;
char *p = “string”;
The difference is this:
p is pointing to a constant string, you can never safely say
p[3]=’x';
however you can always say a[3]=’x';
char a[]=”string”; - character array initialization.
char *p=”string” ; - non-const pointer to a const-string.( this is permitted only in the case of char pointer in C++ to preserve backward compatibility with C.)
Answer2
a[] = “string”;
char *p = “string”;
a[] will have 7 bytes. However, p is only 4 bytes. P is pointing to an adress is either BSS or the data section (depending on which compiler — GNU for the former and CC for the latter).
Answer3
char a[] = “string”;
char *p = “string”;
for char a[]…….using the array notation 7 bytes of storage in the static memory block are taken up, one for each character and one for the terminating nul character.
But, in the pointer notation char *p………….the same 7 bytes required, plus N bytes to store the pointer variable “p” (where N depends on the system but is usually a minimum of 2 bytes and can be 4 or more)……
How do I declare an array of N pointers to functions returning pointers to functions returning pointers to characters?
Answer1
If you want the code to be even slightly readable, you will use typedefs.
typedef char* (*functiontype_one)(void);
typedef functiontype_one (*functiontype_two)(void);
functiontype_two myarray[N]; //assuming N is a const integral
Answer2
char* (* (*a[N])())()
Here a is that array. And according to question no function will not take any parameter value.
What does extern mean in a function declaration?
It tells the compiler that a variable or a function exists, even if the compiler hasn’t yet seen it in the file currently being compiled. This variable or function may be defined in another file or further down in the current file.
How do I initialize a pointer to a function?
This is the way to initialize a pointer to a function
void fun(int a)
{
}
void main()
{
void (*fp)(int);
fp=fun;
fp(1);
}
How do you link a C++ program to C functions?
By using the extern "C" linkage specification around the C function declarations.
Explain the scope resolution operator.
It permits a program to reference an identifier in the global scope that has been hidden by another identifier with the same name in the local scope.
What are the differences between a C++ struct and C++ class?
The default member and base-class access specifier are different.
How many ways are there to initialize an int with a constant?
Two.
There are two formats for initializers in C++ as shown in the example that follows. The first format uses the traditional C notation. The second format uses constructor notation.
int foo = 123;
int bar (123);
How does throwing and catching exceptions differ from using setjmp and longjmp?
The throw operation calls the destructors for automatic objects instantiated since entry to the try block.
What is a default constructor?
Default constructor WITH arguments class B { public: B (int m = 0) : n (m) {} int n; }; int main(int argc, char *argv[]) { B b; return 0; }
What is a conversion constructor?
A constructor that accepts one argument of a different type.
What is the difference between a copy constructor and an overloaded assignment operator?
A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.
When should you use multiple inheritance?
There are three acceptable answers: "Never," "Rarely," and "When the problem domain cannot be accurately modeled any other way."
Explain the ISA and HASA class relationships. How would you implement each in a class design?
A specialized class "is" a specialization of another class and, therefore, has the ISA relationship with the other class. An Employee ISA Person. This relationship is best implemented with inheritance. Employee is derived from Person. A class may have an instance of another class. For example, an employee "has" a salary, therefore the Employee class has the HASA relationship with the Salary class. This relationship is best implemented by embedding an object of the Salary class in the Employee class.
When is a template a better solution than a base class?
When you are designing a generic class to contain or otherwise manage objects of other types, when the format and behavior of those other types are unimportant to their containment or management, and particularly when those other types are unknown (thus, the generosity) to the designer of the container or manager class.
What is a mutable member?
One that can be modified by the class even when the object of the class or the member function doing the modification is const.
What is an explicit constructor?
A conversion constructor declared with the explicit keyword. The compiler does not use an explicit constructor to implement an implied conversion of types. It’s purpose is reserved explicitly for construction.
What is the Standard Template Library (STL)?
A library of container templates approved by the ANSI committee for inclusion in the standard C++ specification.
A programmer who then launches into a discussion of the generic programming model, iterators, allocators, algorithms, and such, has a higher than average understanding of the new technology that STL brings to C++ programming.
Describe run-time type identification.
The ability to determine at run time the type of an object by using the typeid operator or the dynamic_cast operator.
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.
This solution assumes that two library vendors don’t use the same namespace identifier, of course.
Are there any new intrinsic (built-in) data types?
Yes. The ANSI committee added the bool intrinsic type and its true and false value keywords.
Will the following program execute?
void main()
{
void *vptr = (void *) malloc(sizeof(void));
vptr++;
}
Answer1
It will throw an error, as arithmetic operations cannot be performed on void pointers.
Answer2
It will not build as sizeof cannot be applied to void* ( error “Unknown size” )
Answer3
How can it execute if it won’t even compile? It needs to be int main, not void main. Also, cannot increment a void *.
Answer4
According to gcc compiler it won’t show any error, simply it executes. but in general we can’t do arthematic operation on void, and gives size of void as 1
Answer5
The program compiles in GNU C while giving a warning for “void main”. The program runs without a crash. sizeof(void) is “1? hence when vptr++, the address is incremented by 1.
Answer6
Regarding arguments about GCC, be aware that this is a C++ question, not C. So gcc will compile and execute, g++ cannot. g++ complains that the return type cannot be void and the argument of sizeof() cannot be void. It also reports that ISO C++ forbids incrementing a pointer of type ‘void*’.
Answer7
in C++
voidp.c: In function `int main()’:
voidp.c:4: error: invalid application of `sizeof’ to a void type
voidp.c:4: error: `malloc’ undeclared (first use this function)
voidp.c:4: error: (Each undeclared identifier is reported only once for each function it appears in.)
voidp.c:6: error: ISO C++ forbids incrementing a pointer of type `void*’
But in c, it work without problems
void main()
{
char *cptr = 0?2000;
long *lptr = 0?2000;
cptr++;
lptr++;
printf(” %x %x”, cptr, lptr);
}
Will it execute or not?
Answer1
For Q2: As above, won’t compile because main must return int. Also, 0×2000 cannot be implicitly converted to a pointer (I assume you meant 0×2000 and not 0?2000.)
Answer2
Not Excute.
Compile with VC7 results following errors:
error C2440: ‘initializing’ : cannot convert from ‘int’ to ‘char *’
error C2440: ‘initializing’ : cannot convert from ‘int’ to ‘long *’
Not Excute if it is C++, but Excute in C.
The printout:
2001 2004
Answer3
In C++
[$]> g++ point.c
point.c: In function `int main()’:
point.c:4: error: invalid conversion from `int’ to `char*’
point.c:5: error: invalid conversion from `int’ to `long int*’
in C
———————————–
[$] etc > gcc point.c
point.c: In function `main’:
point.c:4: warning: initialization makes pointer from integer without a cast
point.c:5: warning: initialization makes pointer from integer without a cast
[$] etc > ./a.exe
2001 2004
What is the difference between Mutex and Binary semaphore?
semaphore is used to synchronize processes. where as mutex is used to provide synchronization between threads running in the same process.
In C++, what is the difference between method overloading and method overriding?
Overloading a method (or function) in C++ is the ability for functions of the same name to be defined as long as these methods have different signatures (different set of parameters). Method overriding is the ability of the inherited class rewriting the virtual method of the base class.
What methods can be overridden in Java?
In C++ terminology, all public methods in Java are virtual. Therefore, all Java methods can be overwritten in subclasses except those that are declared final, static, and private.
What are the defining traits of an object-oriented language?
The defining traits of an object-oriented langauge are:
* encapsulation
* inheritance
* polymorphism
Write a program that ask for user input from 5 to 9 then calculate the average
int main()
{
int MAX=4;
int total =0;
int average=0;
int numb;
cout<<"Please enter your input from 5 to 9"; cin>>numb;
if((numb <5)&&(numb>9))
cout<<"please re type your input"; else for(i=0;i<=MAX; i++) { total = total + numb; average= total /MAX; } cout<<"The average number is"<
validStatus_ = TRUE; // fine to assign
size = 0; // fine to assign
}
}
Answer2.
"mutable" keyword in C++ is used to specify that the member may be updated or modified even if it is member of constant object. Example:
class Animal {
private:
string name;
string food;
mutable int age;
public:
void set_age(int a);
};
void main() {
const Animal Tiger(’Fulffy’,'antelope’,1);
Tiger.set_age(2);
// the age can be changed since its mutable
}
Differences of C and C++
Could you write a small program that will compile in C but not in C++ ?
In C, if you can a const variable e.g.
const int i = 2;
you can use this variable in other module as follows
extern const int i;
C compiler will not complain.
But for C++ compiler u must write
extern const int i = 2;
else error would be generated.
Bitwise Operations - Given inputs X, Y, Z and operations | and & (meaning bitwise OR and AND, respectively), what is output equal to in?
output = (X & Y) | (X & Z) | (Y & Z);
What is a modifier?
A modifier, also called a modifying function is a member function that changes the value of at least one data member. In other words, an operation that modifies the state of an object. Modifiers are also known as ‘mutators’. Example: The function mod is a modifier in the following code snippet:
class test
{
int x,y;
public:
test()
{
x=0; y=0;
}
void mod()
{
x=10;
y=15;
}
};
What is an accessor?
An accessor is a class operation that does not modify the state of an object. The accessor functions need to be declared as const operations
Differentiate between a template class and class template.
Template class: A generic definition or a parameterized class not instantiated until the client provides the needed information. It’s jargon for plain templates. Class template: A class template specifies how individual classes can be constructed much like the way a class specifies how individual objects can be constructed. It’s jargon for plain classes.
When does a name clash occur?
A name clash occurs when a name is defined in more than one place. For example., two different class libraries could give two different classes the same name. If you try to use many class libraries at the same time, there is a fair chance that you will be unable to compile or link the program because of name clashes.
Define namespace.
It is a feature in C++ to minimize name collisions in the global name space. This namespace keyword assigns a distinct name to a library that allows other libraries to use the same identifier names without creating any name collisions. Furthermore, the compiler uses the namespace signature for differentiating the definitions.
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.
The simplest and safest iterators are those that permit read-only access to the contents of a container class.
What is an incomplete type?
Incomplete types refers to pointers in which there is non availability of the implementation of the referenced location or it points to some location whose value is not available for modification.
int *i=0x400 // i points to address 400
*i=0; //set the value of memory location pointed by i.
Incomplete types are otherwise called uninitialized pointers.
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. 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 " << s1 =" 10;" 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
cout<
//if head->next ==0 should return head instead of 0;
return 0;
{
node* prev = head;
node* curr = head->next;
node* next = curr->next;
for(; next!=0; )
{
curr->next = prev;
prev = curr;
curr = next;
next = next->next;
}
curr->next = prev;
head->next = 0;
head = curr;
}
return head;
}
What is polymorphism?
Polymorphism is the idea that a base class can be inherited by several classes. A base class pointer can point to its child class and a base class array can store different child class objects.
How do you find out if a linked-list has an end? (i.e. the list is not a cycle)
You can find out by using 2 pointers. One of them goes 2 nodes each time. The second one goes at 1 nodes each time. If there is a cycle, the one that goes 2 nodes each time will eventually meet the one that goes slower. If that is the case, then you will know the linked-list is a cycle.
How can you tell what shell you are running on UNIX system?
You can do the Echo $RANDOM. It will return a undefined variable if you are from the C-Shell, just a return prompt if you are from the Bourne shell, and a 5 digit random numbers if you are from the Korn shell. You could also do a ps -l and look for the shell with the highest PID.
What is Boyce Codd Normal form?
A relation schema R is in BCNF with respect to a set F of functional dependencies if for all functional dependencies in F+ of the form a->b, where a and b is a subset of R, at least one of the following holds:
* a->b is a trivial functional dependency (b is a subset of a)
* a is a superkey for schema R
What is pure virtual function?
A class is made abstract by declaring one or more of its virtual functions to be pure. A pure virtual function is one with an initializer of = 0 in its declaration
Write a Struct Time where integer m, h, s are its members
struct Time
{
int m;
int h;
int s;
};
How do you traverse a Btree in Backward in-order?
Process the node in the right subtree
Process the root
Process the node in the left subtree
What is the two main roles of Operating System?
As a resource manager
As a virtual machine
In the derived class, which data member of the base class are visible?
In the public and protected sections.
C++ programming on UNIX
Could you tell something about the Unix System Kernel?
The kernel is the heart of the UNIX openrating system, it’s reponsible for controlling the computer’s resouces and scheduling user jobs so that each one gets its fair share of resources.
What are each of the standard files and what are they normally associated with?
They are the standard input file, the standard output file and the standard error file. The first is usually associated with the keyboard, the second and third are usually associated with the terminal screen.
Detemine the code below, tell me exectly how many times is the operation sum++ performed ?
for ( i = 0; i < j =" 100;"> 100 - i; j–)
sum++;
(99 * 100)/2 = 4950
The sum++ is performed 4950 times.
Give 4 examples which belongs application layer in TCP/IP architecture?
FTP, TELNET, HTTP and TFTP
What’s the meaning of ARP in TCP/IP?
The "ARP" stands for Address Resolution Protocol. The ARP standard defines two basic message types: a request and a response. a request message contains an IP address and requests the corresponding hardware address; a replay contains both the IP address, sent in the request, and the hardware address.
What is a Makefile?
Makefile is a utility in Unix to help compile large programs. It helps by only compiling the portion of the program that has been changed.
A Makefile is the file and make uses to determine what rules to apply. make is useful for far more than compiling programs.
What is deadlock?
Deadlock is a situation when two or more processes prevent each other from running. Example: if T1 is holding x and waiting for y to be free and T2 holding y and waiting for x to be free deadlock happens.
What is semaphore?
Semaphore is a special variable, it has two methods: up and down. Semaphore performs atomic operations, which means ones a semaphore is called it can not be inturrupted.
The internal counter (= #ups - #downs) can never be negative. If you execute the “down” method when the internal counter is zero, it will block until some other thread calls the “up” method. Semaphores are use for thread synchronization.
Is C an object-oriented language?
C is not an object-oriented language, but limited object-oriented programming can be done in C.
Name some major differences between C++ and Java.
C++ has pointers; Java does not. Java is platform-independent; C++ is not. Java has garbage collection; C++ does not. Java does have pointers. In fact all variables in Java are pointers. The difference is that Java does not allow you to manipulate the addresses of the pointer
C++ Networking Interview Questions and Answers
What is the difference between Stack and Queue?
Stack is a Last In First Out (LIFO) data structure.
Queue is a First In First Out (FIFO) data structure
Write a fucntion that will reverse a string.
char *strrev(char *s)
{
int i = 0, len = strlen(s);
char *str;
if ((str = (char *)malloc(len+1)) == NULL)
/*cannot allocate memory */
err_num = 2;
return (str);
}
while(len)
str[i++]=s[–len];
str[i] = NULL;
return (str);
}
What is the software Life-Cycle?
The software Life-Cycle are
1) Analysis and specification of the task
2) Design of the algorithms and data structures
3) Implementation (coding)
4) Testing
5) Maintenance and evolution of the system
6) Obsolescence
What is the difference between a Java application and a Java applet?
The difference between a Java application and a Java applet is that a Java application is a program that can be executed using the Java interpeter, and a JAVA applet can be transfered to different networks and executed by using a web browser (transferable to the WWW).
Name 7 layers of the OSI Reference Model?
-Application layer
-Presentation layer
-Session layer
-Transport layer
-Network layer
-Data Link layer
-Physical layer
C++ Algorithm Interview Questions and Answers
What are the advantages and disadvantages of B-star trees over Binary trees?
Answer1
B-star trees have better data structure and are faster in search than Binary trees, but it’s harder to write codes for B-start trees.
Answer2
The major difference between B-tree and binary tres is that B-tree is a external data structure and binary tree is a main memory data structure. The computational complexity of binary tree is counted by the number of comparison operations at each node, while the computational complexity of B-tree is determined by the disk I/O, that is, the number of node that will be loaded from disk to main memory. The comparision of the different values in one node is not counted.
Write the psuedo code for the Depth first Search.
dfs(G, v) //OUTLINE
Mark v as "discovered"
For each vertex w such that edge vw is in G:
If w is undiscovered:
dfs(G, w); that is, explore vw, visit w, explore from there as much as possible, and backtrack from w to v. Otherwise:
"Check" vw without visiting w. Mark v as "finished".
Describe one simple rehashing policy.
The simplest rehashing policy is linear probing. Suppose a key K hashes to location i. Suppose other key occupies H[i]. The following function is used to generate alternative locations:
rehash(j) = (j + 1) mod h
where j is the location most recently probed. Initially j = i, the hash code for K. Notice that this version of rehash does not depend on K.
Describe Stacks and name a couple of places where stacks are useful.
A Stack is a linear structure in which insertions and deletions are always made at one end, called the top. This updating policy is called last in, first out (LIFO). It is useful when we need to check some syntex errors, such as missing parentheses.
Suppose a 3-bit sequence number is used in the selective-reject ARQ, what is the maximum number of frames that could be transmitted at a time?
If a 3-bit sequence number is used, then it could distinguish 8 different frames. Since the number of frames that could be transmitted at a time is no greater half the numner of frames that could be distinguished by the sequence number, so at most 4 frames can be transmitted at a time.
Multithreading programming in Win32
Here is the simple application that creates 100 threads and each thread executes the StartThraed() function
DWORD WINAPI StartThread(LPVOID threadID)
{
int tid = atoi((char *)threadID);
cout<<
return 0;
}
int main()
{
HANDLE hThread1;
DWORD dwGenericThread;
char threadID[10];
for (int x = 0; x < 10; ++x)
{
for (int y = 0; y < 10; ++y)
{
sprintf(threadID, "%d", y*10+x);
hThread1 = CreateThread(NULL,0,StartThread,&threadID,0,&dwGenericThread);
if(hThread1 == NULL)
{
DWORD dwError = GetLastError();
cout<<"SCM:Error in Creating thread"<<
return 0;
}
WaitForSingleObject(hThread1,INFINITE);
CloseHandle(hThread1);
}
}
}
DWORD WINAPI StartThread(LPVOID threadID)
{
int tid = atoi((char *)threadID);
cout<
return 0;
}
int main()
{
HANDLE hThread1;
DWORD dwGenericThread;
char threadID[10];
for (int x = 0; x < 10; ++x)
{
for (int y = 0; y < 10; ++y)
{
sprintf(threadID, "%d", y*10+x);
hThread1 = CreateThread(NULL,0,StartThread,&threadID,0,&dwGenericThread);
if(hThread1 == NULL)
{
DWORD dwError = GetLastError();
cout<<"SCM:Error in Creating thread"<
return 0;
}
WaitForSingleObject(hThread1,INFINITE);
CloseHandle(hThread1);
}
}
}
Singleton class, a different way
We all knew that, the below class will give us only one instance of the class.
class Singleton
{
private:
static Singleton* singleton;
private:
Singleton();
public:
static Singleton* getIntsance();
};
Just think that is there any other way to do the same. Yes, we have onother solution for it. See below
class Singleton
{
private:
static Singleton* singleton;
private:
~Singleton();
public:
static Singleton* getIntsance();
};
Destructor is in private scope now.
class Singleton
{
private:
static Singleton* singleton;
private:
Singleton();
public:
static Singleton* getIntsance();
};
Just think that is there any other way to do the same. Yes, we have onother solution for it. See below
class Singleton
{
private:
static Singleton* singleton;
private:
~Singleton();
public:
static Singleton* getIntsance();
};
Destructor is in private scope now.
how to find out middle element of a linked list in a single traversal
program:
Node* findMidNode(Node* start)
{
Node* midNode = start;
while(start != NULL || start->next != NULL)
{
midNode = midNode->next;
start = start->next->next;
}
return midNode;
}
Algorithm:
midNode is pointing to next of the midNode in every iteration and
start is pointing to next to next (i.e., increment 2) of start in every iteration.
so, when start is at the end, then midNode is pointing to middle element of the List.
Node* findMidNode(Node* start)
{
Node* midNode = start;
while(start != NULL || start->next != NULL)
{
midNode = midNode->next;
start = start->next->next;
}
return midNode;
}
Algorithm:
midNode is pointing to next of the midNode in every iteration and
start is pointing to next to next (i.e., increment 2) of start in every iteration.
so, when start is at the end, then midNode is pointing to middle element of the List.
reverse the linked list using recursive method
Algorithm:
Here the algorithm is, pointing p and q to the next elements in every iteration. Once we reached the end, then start pointing to back, i.e.., q->next = p;
//structure
struct Node
{
int data;
struct Node* next;
};
//global variables...
struct node* start = NULL;
struct node* p = NULL;
struct node* q = NULL;
//assusme that we have added some elements into the List, and start
//is pointing to first element in the list
reverseList(start);
void reverseList(struct Node* node)
{
if (node->next == NULL)
break;
p = node->next;
q = p->next;
if (q->next != NULL)
{
reverseList(q);
}
else
{
start->next = NULL;
start = q;
}
q->next = p;
}
how to print the bits in a reverse order (without using any variable)
Suppose, 123 is represented as 01111011. But we have to print it in reverse order, i.e.., 11011110
program
int main()
{
int i = 123;
while(i!=0)
{
if (i & 1)
printf("1");
else
printf("0");
i >>= 1;
}
}
program
int main()
{
int i = 123;
while(i!=0)
{
if (i & 1)
printf("1");
else
printf("0");
i >>= 1;
}
}
virtual destructor purpose
Ans: Destructor
purpose of virtual destructor:
We know that, virtual destructor will help to call correct Version of destructor in dynamic binding.
class Base
{
private:
int x;
public:
virtual int getValue() {return x;}
};
class Derived : public Base
{
private:
int y;
public:
int getValue() {return y;}
};
int main()
{
Base* b = new Der();
delete b;
}
In the above program, do we need a virtual destructor?
No, we don't need a virtual destructor in the above program.
Here, there is no problem in deleting delete b;
suppose the Derived class is some thing like this
class Derived : public Base
{
private:
int y;
int* p;
public:
int getValue() {return y;}
};
then the problem will occur. What is this problem.
The problem is ....
Assume that you have allotted memory for "int *p" and the destructor is not virutal
in the case Base* pb = new Derived( );. The destructor of base class gets called
and there is no way we can free the memory allotted for p inside derived.
So, a memory leak.
Yes, to avoid memory leaks we have to use virtual destructor.
Not only for memory leaks, but also used to releasing Filehandles/resources and unlocking mutexes.
No comments:
Post a Comment