C/C++ Questions:
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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
7. 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
8. What is assignment operator?
Default assignment operator handles assigning one object to another of the same class.
Member to member copy (shallow copy)
9. 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
10. 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
11. 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.
12. 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;
13. 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 <>
T min (T i, T j)
{
return i < mystruct =" {" salaray =" 2000" b =" a;" temp =" x;" x =" y;" y =" x;" a="2," b="3;" num =" num" temp =" 2.0;" value =" cuberoot" temp =" 3L;" value =" cuberoot" parent_object_ptr =" new">show() // calls parent->show() i
now we goto virtual world...
class parent
{
virtual void Show()
{
cout << "i'm parent" << parent_object_ptr =" new">show() // calls child->show()
21. What is pure virtual function? or what is abstract class?
When you define only function prototype in a base class without 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
22. 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.
23. 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.
24. What is the use of 'using' declaration?
A using declaration makes it possible to use a name from a namespace without the scope
operator.
25. 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.
26. 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.
27. 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.
28. Name the operators that cannot be overloaded??
sizeof, ., .*, .->, ::, ?:
29. 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.
30. 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.
31. 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.
32. 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.
33. 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.
34. 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.
35. 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
36 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'.
37. 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.
38. 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.
39. 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.
49. 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.
50. 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.
51. 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.
52. 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.
53. 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.
54. 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.
55. 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.
56. How do you access the static member of a class?
::
57. 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.
58. 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.
60. 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.
61. 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.
62. 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.
63. (From Microsoft) Assume I have a linked list contains all of the alphabets from ‘A’ to ‘Z’.
I want to find the letter ‘Q’ in the list, how does you perform the search to find the ‘Q’?
How do you write a function that can reverse a linked-list? (Cisco System)
void reverselist(void)
{
if(head==0)
return;
if(head->next==0)
return;
if(head->next==tail)
{
head->next = 0;
tail->next = head;
}
else
{
node* pre = head;
node* cur = head->next;
node* curnext = cur->next;
head->next = 0;
cur->next = head;
for(; curnext!=0; )
{
cur->next = pre;
pre = cur;
cur = curnext;
curnext = curnext->next;
}
curnext->next = cur;
}
}
64. 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.
65. 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.
66. 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
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.
67. What is a Make file?
Make file is a utility in Unix to help compile large programs. It helps by only compiling
the portion of the program that has been changed
68. 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.
Design and implement a String class that satisfies the following:
Supports embedded nulls
Provide the following methods (at least)
Constructor
Destructor
Copy constructor
Assignment operator
Addition operator (concatenation)
Return character at location
Return substring at location
Find substring
Provide versions of methods for String and for char* arguments
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].
Answer: quicksort ((data + 222), 100);
What is a modifier?
What is an accessor?
Differentiate between a template class and class template.
When does a name clash occur?
Define namespace.
What is the use of ‘using’ declaration.
What is an Iterator class?
List out some of the OODBMS available.
List out some of the object-oriented methodologies.
What is an incomplete type?
What is a dangling pointer?
Differentiate between the message and method.
What is an adaptor class or Wrapper class?
What is a Null object?
What is class invariant?
What do you mean by Stack unwinding?
Define precondition and post-condition to a member function.
What are the conditions that have to be met for a condition to be an invariant of the class?
What are proxy objects?
Name some pure object oriented languages.
Name the operators that cannot be overloaded.
What is a node class?
What is an orthogonal base class?
What is a container class? What are the types of container classes?
What is a protocol class?
What is a mixin class?
What is a concrete class?
What is the handle class?
What is an action class?
When can you tell that a memory leak will occur?
What is a parameterized type?
Differentiate between a deep copy and a shallow copy?
What is an opaque pointer?
What is a smart pointer?
What is reflexive association?
What is slicing?
What is name mangling?
What are proxy objects?
What is cloning?
Describe the main characteristics of static functions.
Will the inline function be compiled as the inline function always? Justify.
Define a way other than using the keyword inline to make a function inline.
How can a '::' operator be used as unary operator?
What is placement new?
What do you mean by analysis and design?
What are the steps involved in designing?
What are the main underlying concepts of object orientation?
What do u meant by "SBI" of an object?
Differentiate persistent & non-persistent objects?
What do you meant by active and passive objects?
What is meant by software development method?
What do you meant by static and dynamic modeling?
How to represent the interaction between the modeling elements?
Why generalization is very strong?
Differentiate Aggregation and containment?
Can link and Association applied interchangeably?
What is meant by "method-wars"?
Whether unified method and unified modeling language are same or different?
Who were the three famous amigos and what was their contribution to the object community?
Differentiate the class representation of Booch, Rumbaugh and UML?
What is an USECASE? Why it is needed?
Who is an Actor?
What is guard condition?
Differentiate the following notations?
USECASE is an implementation independent notation. How will the designer give the
implementation details of a particular USECASE to the programmer?
Suppose a class acts an Actor in the problem domain, how to represent it in the static
model?
Why does the function arguments are called as "signatures"?
What is the difference between C and C++? Would you prefer to use one over the other?
C is based on structured programming whereas C++ supports the object-oriented programming paradigm. Due to the advantages inherent in object-oriented programs such as modularity and reuse, C++ is preferred. However almost anything that can be built using C++ can also be built using C.
Explain operator precendence.
Operator precedence is the order in which operators are evaluated in a compound expression. For example, what is the result of the following expression?
6 + 3 * 4 / 2 + 2 Here is a compound expression with an insidious error.
while ( ch = nextChar() != '\0' ) The programmer's intention is to assign ch to the next character then test that character to see whether it is null. Since the inequality operator has higher precendence than the assignment operator, the real result is that the next character is compared to null and ch is assigned the boolean result of the test (i.e. 0 or 1).
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 data encapsulation?
Data Encapsulation is also known as data hiding. The most important advantage of encapsulation is that it lets the programmer create an object and then provide an interface to the object that other objects can use to call the methods provided by the object. The programmer can change the internal workings of an object but this transparent to other interfacing programs as long as the interface remains unchanged.
What is inheritance?
Inheritance is a mechanism through which a subclass inherits the properties and behavior of its superclass; the subclass has a ISA relationship with the superclass. For example Vehicle can be a superclass and Car can be a subclass derived from Vehicle. In this case a Car ISA Vehicle. The superclass 'is not a' subclass as the subclass is more specialized and may contain additional members as compared to the superclass. The greatest advantage of inheritance is that it promotes generic design and code reuse.
What is multiple inheritance? What are its advantages and disadvantages?
Multiple Inheritance is the process whereby a sub-class can be derived from more than one super 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 when two base classes implement a method with the same name.
What is polymorphism?
Polymorphism refers to the ability to have more than one method with the same signature in an inheritance hierarchy. The correct method is invoked at run-time based on the context (object) on which the method is invoked. Polymorphism allows for a generic use of method names while providing specialized implementations for them.
What do the keyword static and const signify?
When a class member is declared to be of a static type, it means that the member is not an instance variable but a class variable. Such a member is accessed using Classname.Membername (as opposed to Object.Membername). Const is a keyword used in C++ to specify that an object's value cannot be changed.
What is a static member of a class?
Static data members exist once for the entire class, as opposed to non-static data members, which exist individually in each instance of a class.
How do you access the static member of a class?<ClassName>::.
What feature of C++ would you use if you wanted to design a member function that guarantees to leave this object unchanged?
It is const as in: int MyFunc? (int test) const;
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 is memory allocated/deallocated in C? How about C++?
Memory is allocated in C using malloc() and freed using free(). In C++ the new() operator is used to allocate memory to an object and the delete() operator is used to free the memory taken up by an object.
What is the difference between public, protected, and private members of a class?
Private members are accessible only by members and friends of the class. Protected members are accessible by members and friends of the class and by members and friends of derived classes. Public members are accessible by everyone.
How do you link a C++ program to C functions?
By using the extern "C" linkage specification around the C function declarations.
The candidate should know about mangled function names and type-safe linkages. They should explain how the extern "C" linkage specification statement turns that feature off during compilation so that the linker properly links function calls to C functions.
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.
Why do C++ compilers need name mangling?
Name mangling is the rule according to which C++ changes function names into function signatures before invoking the linker. Mangled names are used by the linker to differentiate between different functions with the same name.
What is function's signature?
function's signature is its name plus the number and types of the parameters it accepts.
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 is the difference between function overloading and function overriding?
Overloading is a method that allows defining multiple member functions with the same name but different signatures. The compiler will pick the correct function based on the signature. Overriding is a method that allows the derived class to redefine the behavior of member functions which the derived class inherits from a base class. The signatures of both base class member function and derived class member function are the same; however, the implementation and, therefore, the behavior will differ.
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.
Can derived class override some but not all of a set of overloaded virtual member functions inherited from the base class?
Compiler will allow this, but it is a bad practice since overridden member functions will hide all of the inherited overloads from the base class. You should really override all of them.
What is the difference between assignment and initialization in C++?
Assignment changes the value of the object that has already been constructed. Initialization constructs a new object and gives it a value at the same time.
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.
When are copy constructors called?
Copy constructors are called in three cases: when a function returns an object of that class by value, when the object of that class is passed by value as an argument to a function, and, finally, when you construct an object based on another object of the same class (Circle c1=c2;).
Medior Questions
What is the difference between delete and delete[]?delete deletes one object; delete[] deletes an array of objects.
What is the difference between non-virtual and virtual functions?
The behavior of a non-virtual function is known at compile time while the behavior of a virtual function is not known until the run time.
What is a pure virtual function?
A pure virtual function is a function declared in a base class that has no definition relative to the base.
How do you know that your class needs a virtual destructor?
If your class has at least one virtual function, you should make a destructor for this class virtual. This will allow you to delete a dynamic object through a pointer to a base class object. If the destructor is non-virtual, then the wrong destructor will be invoked during deletion of the dynamic object.
What is an abstract base class?
A class that has one or more pure virtual functions.
What is your reaction to this line of code?
delete this;
It's not a good practice.
A good programmer will insist that the statement is never to be used if the class is to be used by other programmers and instantiated as static, extern, or automatic objects. That much should be obvious.
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. 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.
What is a default constructor?
A constructor that has no arguments or one where all the arguments have default argument values.
The candicate should know that if you don't code a default constructor, the compiler provides one if there are no other constructors. If you are going to instantiate an array of objects of the class, the class must have a default constructor.
Why do you have to provide your own copy constructor and assignment operator for classes with dynamically allocated memory?
If you don't, the compiler will supply and execute the default constructor and the assignment operator, but they will not do the job correctly. The default assignment operator does memberwise assignment and the default copy constructor does memberwise copy. In both cases you will only assign and manipulate pointers to dynamic memory, which will lead to memory leaks and other abnormalities. You should write your own assignment operator and copy constructor, which would copy the pointer to memory so that each object has its own copy.
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.
What is the difference between a shallow copy and a deep copy?
A shallow copy simply creates a new object and inserts in it references to the members of the original object. A deep copy constructs a new object and then creates in it copies of each of the members of the original object.
What is the difference between MyClass p; and MyClass p();?
MyClass p; creates an instance of class MyClass by calling a constructor for MyClass. MyClass p(); declares function p which takes no parameters and returns an object of class MyClass by value.
What issue do auto_ptr objects address?
If you use auto_ptr objects you would not have to be concerned with heap objects not being deleted even if the exception is thrown.
What functions does C++ silently write and call?
Constructors, destructors, copy constructors, assignment operators, and address-of operators.
Does the compiler guarantee that initializers will be executed in the same order as they appear on the initialization list?
No. C++ guarantees that base class subobjects and member objects will be destroyed in the opposite order from which they were constructed. This means that initializers are executed in the order, which supports the above-mentioned guarantee.
Senior Questions
Who is Brad Cox?He authored Object-oriented Programming, An Evolutionary Approach, a book that is generally credited with launching today's industry-wide enthusiasm for object technology.
Who is Grady Booch?Grady Booch has been an object- based/oriented advocate for some time. His latest notations are often referred to as simply the "Booch" method or notation.
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.
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.
Is there any problem with the following:
char *a = NULL;char& p = *a;?
The result is undefined. You should never do this. A reference must always refer to some object.
Advanced Questions
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.
Why were the templates introduced?
Many data structures and algorithms can be defined independently of the type of data they work with. You can increase the amount of shared code by separating data-dependent portions from data-independent portions, and templates were introduced to help you do that.
What is the difference between static_cast(*this) += 5; and static_cast(*this) += 5;?
If you cast *this to be an RWTime object, the copy constructor for RWTime will be called and the new object will be the target of the assignment, *this will remain unchanged. Hardly what you want. The second instance actually increments this by 5.
Traverse the tree:
Preorder traversal
Visit the root
Traverse the left subtree
Traverse the right subtree
Inorder traversal
Traverse the left subtree
Visit the root
Traverse the right subtree
Postorder traversal
Traverse the left subtree
Traverse the right subtree
Visit the root
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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
7. 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
8. What is assignment operator?
Default assignment operator handles assigning one object to another of the same class.
Member to member copy (shallow copy)
9. 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
10. 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
11. 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.
12. 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;
13. 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 <>
T min (T i, T j)
{
return i < mystruct =" {" salaray =" 2000" b =" a;" temp =" x;" x =" y;" y =" x;" a="2," b="3;" num =" num" temp =" 2.0;" value =" cuberoot" temp =" 3L;" value =" cuberoot" parent_object_ptr =" new">show() // calls parent->show() i
now we goto virtual world...
class parent
{
virtual void Show()
{
cout << "i'm parent" << parent_object_ptr =" new">show() // calls child->show()
21. What is pure virtual function? or what is abstract class?
When you define only function prototype in a base class without 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
22. 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.
23. 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.
24. What is the use of 'using' declaration?
A using declaration makes it possible to use a name from a namespace without the scope
operator.
25. 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.
26. 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.
27. 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.
28. Name the operators that cannot be overloaded??
sizeof, ., .*, .->, ::, ?:
29. 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.
30. 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.
31. 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.
32. 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.
33. 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.
34. 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.
35. 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
36 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'.
37. 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.
38. 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.
39. 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.
49. 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.
50. 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.
51. 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.
52. 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.
53. 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.
54. 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.
55. 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.
56. How do you access the static member of a class?
57. 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.
58. 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.
60. 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.
61. 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.
62. 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.
63. (From Microsoft) Assume I have a linked list contains all of the alphabets from ‘A’ to ‘Z’.
I want to find the letter ‘Q’ in the list, how does you perform the search to find the ‘Q’?
How do you write a function that can reverse a linked-list? (Cisco System)
void reverselist(void)
{
if(head==0)
return;
if(head->next==0)
return;
if(head->next==tail)
{
head->next = 0;
tail->next = head;
}
else
{
node* pre = head;
node* cur = head->next;
node* curnext = cur->next;
head->next = 0;
cur->next = head;
for(; curnext!=0; )
{
cur->next = pre;
pre = cur;
cur = curnext;
curnext = curnext->next;
}
curnext->next = cur;
}
}
64. 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.
65. 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.
66. 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
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.
67. What is a Make file?
Make file is a utility in Unix to help compile large programs. It helps by only compiling
the portion of the program that has been changed
68. 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.
Design and implement a String class that satisfies the following:
Supports embedded nulls
Provide the following methods (at least)
Constructor
Destructor
Copy constructor
Assignment operator
Addition operator (concatenation)
Return character at location
Return substring at location
Find substring
Provide versions of methods for String and for char* arguments
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].
Answer: quicksort ((data + 222), 100);
What is a modifier?
What is an accessor?
Differentiate between a template class and class template.
When does a name clash occur?
Define namespace.
What is the use of ‘using’ declaration.
What is an Iterator class?
List out some of the OODBMS available.
List out some of the object-oriented methodologies.
What is an incomplete type?
What is a dangling pointer?
Differentiate between the message and method.
What is an adaptor class or Wrapper class?
What is a Null object?
What is class invariant?
What do you mean by Stack unwinding?
Define precondition and post-condition to a member function.
What are the conditions that have to be met for a condition to be an invariant of the class?
What are proxy objects?
Name some pure object oriented languages.
Name the operators that cannot be overloaded.
What is a node class?
What is an orthogonal base class?
What is a container class? What are the types of container classes?
What is a protocol class?
What is a mixin class?
What is a concrete class?
What is the handle class?
What is an action class?
When can you tell that a memory leak will occur?
What is a parameterized type?
Differentiate between a deep copy and a shallow copy?
What is an opaque pointer?
What is a smart pointer?
What is reflexive association?
What is slicing?
What is name mangling?
What are proxy objects?
What is cloning?
Describe the main characteristics of static functions.
Will the inline function be compiled as the inline function always? Justify.
Define a way other than using the keyword inline to make a function inline.
How can a '::' operator be used as unary operator?
What is placement new?
What do you mean by analysis and design?
What are the steps involved in designing?
What are the main underlying concepts of object orientation?
What do u meant by "SBI" of an object?
Differentiate persistent & non-persistent objects?
What do you meant by active and passive objects?
What is meant by software development method?
What do you meant by static and dynamic modeling?
How to represent the interaction between the modeling elements?
Why generalization is very strong?
Differentiate Aggregation and containment?
Can link and Association applied interchangeably?
What is meant by "method-wars"?
Whether unified method and unified modeling language are same or different?
Who were the three famous amigos and what was their contribution to the object community?
Differentiate the class representation of Booch, Rumbaugh and UML?
What is an USECASE? Why it is needed?
Who is an Actor?
What is guard condition?
Differentiate the following notations?
USECASE is an implementation independent notation. How will the designer give the
implementation details of a particular USECASE to the programmer?
Suppose a class acts an Actor in the problem domain, how to represent it in the static
model?
Why does the function arguments are called as "signatures"?
What is the difference between C and C++? Would you prefer to use one over the other?
C is based on structured programming whereas C++ supports the object-oriented programming paradigm. Due to the advantages inherent in object-oriented programs such as modularity and reuse, C++ is preferred. However almost anything that can be built using C++ can also be built using C.
Explain operator precendence.
Operator precedence is the order in which operators are evaluated in a compound expression. For example, what is the result of the following expression?
6 + 3 * 4 / 2 + 2 Here is a compound expression with an insidious error.
while ( ch = nextChar() != '\0' ) The programmer's intention is to assign ch to the next character then test that character to see whether it is null. Since the inequality operator has higher precendence than the assignment operator, the real result is that the next character is compared to null and ch is assigned the boolean result of the test (i.e. 0 or 1).
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 data encapsulation?
Data Encapsulation is also known as data hiding. The most important advantage of encapsulation is that it lets the programmer create an object and then provide an interface to the object that other objects can use to call the methods provided by the object. The programmer can change the internal workings of an object but this transparent to other interfacing programs as long as the interface remains unchanged.
What is inheritance?
Inheritance is a mechanism through which a subclass inherits the properties and behavior of its superclass; the subclass has a ISA relationship with the superclass. For example Vehicle can be a superclass and Car can be a subclass derived from Vehicle. In this case a Car ISA Vehicle. The superclass 'is not a' subclass as the subclass is more specialized and may contain additional members as compared to the superclass. The greatest advantage of inheritance is that it promotes generic design and code reuse.
What is multiple inheritance? What are its advantages and disadvantages?
Multiple Inheritance is the process whereby a sub-class can be derived from more than one super 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 when two base classes implement a method with the same name.
What is polymorphism?
Polymorphism refers to the ability to have more than one method with the same signature in an inheritance hierarchy. The correct method is invoked at run-time based on the context (object) on which the method is invoked. Polymorphism allows for a generic use of method names while providing specialized implementations for them.
What do the keyword static and const signify?
When a class member is declared to be of a static type, it means that the member is not an instance variable but a class variable. Such a member is accessed using Classname.Membername (as opposed to Object.Membername). Const is a keyword used in C++ to specify that an object's value cannot be changed.
What is a static member of a class?
Static data members exist once for the entire class, as opposed to non-static data members, which exist individually in each instance of a class.
How do you access the static member of a class?<ClassName>::
What feature of C++ would you use if you wanted to design a member function that guarantees to leave this object unchanged?
It is const as in: int MyFunc? (int test) const;
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 is memory allocated/deallocated in C? How about C++?
Memory is allocated in C using malloc() and freed using free(). In C++ the new() operator is used to allocate memory to an object and the delete() operator is used to free the memory taken up by an object.
What is the difference between public, protected, and private members of a class?
Private members are accessible only by members and friends of the class. Protected members are accessible by members and friends of the class and by members and friends of derived classes. Public members are accessible by everyone.
How do you link a C++ program to C functions?
By using the extern "C" linkage specification around the C function declarations.
The candidate should know about mangled function names and type-safe linkages. They should explain how the extern "C" linkage specification statement turns that feature off during compilation so that the linker properly links function calls to C functions.
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.
Why do C++ compilers need name mangling?
Name mangling is the rule according to which C++ changes function names into function signatures before invoking the linker. Mangled names are used by the linker to differentiate between different functions with the same name.
What is function's signature?
function's signature is its name plus the number and types of the parameters it accepts.
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 is the difference between function overloading and function overriding?
Overloading is a method that allows defining multiple member functions with the same name but different signatures. The compiler will pick the correct function based on the signature. Overriding is a method that allows the derived class to redefine the behavior of member functions which the derived class inherits from a base class. The signatures of both base class member function and derived class member function are the same; however, the implementation and, therefore, the behavior will differ.
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.
Can derived class override some but not all of a set of overloaded virtual member functions inherited from the base class?
Compiler will allow this, but it is a bad practice since overridden member functions will hide all of the inherited overloads from the base class. You should really override all of them.
What is the difference between assignment and initialization in C++?
Assignment changes the value of the object that has already been constructed. Initialization constructs a new object and gives it a value at the same time.
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.
When are copy constructors called?
Copy constructors are called in three cases: when a function returns an object of that class by value, when the object of that class is passed by value as an argument to a function, and, finally, when you construct an object based on another object of the same class (Circle c1=c2;).
Medior Questions
What is the difference between delete and delete[]?delete deletes one object; delete[] deletes an array of objects.
What is the difference between non-virtual and virtual functions?
The behavior of a non-virtual function is known at compile time while the behavior of a virtual function is not known until the run time.
What is a pure virtual function?
A pure virtual function is a function declared in a base class that has no definition relative to the base.
How do you know that your class needs a virtual destructor?
If your class has at least one virtual function, you should make a destructor for this class virtual. This will allow you to delete a dynamic object through a pointer to a base class object. If the destructor is non-virtual, then the wrong destructor will be invoked during deletion of the dynamic object.
What is an abstract base class?
A class that has one or more pure virtual functions.
What is your reaction to this line of code?
delete this;
It's not a good practice.
A good programmer will insist that the statement is never to be used if the class is to be used by other programmers and instantiated as static, extern, or automatic objects. That much should be obvious.
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. 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.
What is a default constructor?
A constructor that has no arguments or one where all the arguments have default argument values.
The candicate should know that if you don't code a default constructor, the compiler provides one if there are no other constructors. If you are going to instantiate an array of objects of the class, the class must have a default constructor.
Why do you have to provide your own copy constructor and assignment operator for classes with dynamically allocated memory?
If you don't, the compiler will supply and execute the default constructor and the assignment operator, but they will not do the job correctly. The default assignment operator does memberwise assignment and the default copy constructor does memberwise copy. In both cases you will only assign and manipulate pointers to dynamic memory, which will lead to memory leaks and other abnormalities. You should write your own assignment operator and copy constructor, which would copy the pointer to memory so that each object has its own copy.
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.
What is the difference between a shallow copy and a deep copy?
A shallow copy simply creates a new object and inserts in it references to the members of the original object. A deep copy constructs a new object and then creates in it copies of each of the members of the original object.
What is the difference between MyClass p; and MyClass p();?
MyClass p; creates an instance of class MyClass by calling a constructor for MyClass. MyClass p(); declares function p which takes no parameters and returns an object of class MyClass by value.
What issue do auto_ptr objects address?
If you use auto_ptr objects you would not have to be concerned with heap objects not being deleted even if the exception is thrown.
What functions does C++ silently write and call?
Constructors, destructors, copy constructors, assignment operators, and address-of operators.
Does the compiler guarantee that initializers will be executed in the same order as they appear on the initialization list?
No. C++ guarantees that base class subobjects and member objects will be destroyed in the opposite order from which they were constructed. This means that initializers are executed in the order, which supports the above-mentioned guarantee.
Senior Questions
Who is Brad Cox?He authored Object-oriented Programming, An Evolutionary Approach, a book that is generally credited with launching today's industry-wide enthusiasm for object technology.
Who is Grady Booch?Grady Booch has been an object- based/oriented advocate for some time. His latest notations are often referred to as simply the "Booch" method or notation.
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.
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.
Is there any problem with the following:
char *a = NULL;char& p = *a;?
The result is undefined. You should never do this. A reference must always refer to some object.
Advanced Questions
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.
Why were the templates introduced?
Many data structures and algorithms can be defined independently of the type of data they work with. You can increase the amount of shared code by separating data-dependent portions from data-independent portions, and templates were introduced to help you do that.
What is the difference between static_cast
If you cast *this to be an RWTime object, the copy constructor for RWTime will be called and the new object will be the target of the assignment, *this will remain unchanged. Hardly what you want. The second instance actually increments this by 5.
Traverse the tree:
Preorder traversal
Visit the root
Traverse the left subtree
Traverse the right subtree
Inorder traversal
Traverse the left subtree
Visit the root
Traverse the right subtree
Postorder traversal
Traverse the left subtree
Traverse the right subtree
Visit the root
What's the difference between "const Fred* p", "Fred* const p" and "const Fred* const p"?
You have to read pointer declarations right-to-left.
- const Fred* p means "p points to a Fred that is const" — that is, the Fred object can't be changed via p.
- Fred* const p means "p is a const pointer to a Fred" — that is, you can change the Fred object via p, but you can't change the pointer p itself.
- const Fred* const p means "p is a const pointer to a const Fred" — that is, you can't change the pointer p itself, nor can you change the Fred object via p.
posted by Naskars at
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