Part 1
C/C++ Interview Questions
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.
What is the difference between realloc() and free()?
The free subroutine frees a block of memory previously allocated by the malloc subroutine. Undefined results occur if the Pointer parameter is not a valid pointer. If the Pointer parameter is a null value, no action will occur. The realloc subroutine changes the size of the block of memory pointed to by the Pointer parameter to the number of bytes specified by the Size parameter and returns a new pointer to the block. The pointer specified by the Pointer parameter must have been created with the malloc, calloc, or realloc subroutines and not been deallocated with the free or realloc subroutines. Undefined results occur if the Pointer parameter is not a valid pointer.
What is function overloading and operator overloading?
Function overloading: C++ enables several functions of the same name to be defined, as long as these functions have different sets of parameters (at least as far as their types are concerned). This capability is called function overloading. When an overloaded function is called, the C++ compiler selects the proper function by examining the number, types and order of the arguments in the call. Function overloading is commonly used to create several functions of the same name that perform similar tasks but on different data types.
Operator overloading allows existing C++ operators to be redefined so that they work on objects of user-defined classes. Overloaded operators are syntactic sugar for equivalent function calls. They form a pleasant facade that doesn’t add anything fundamental to the language (but they can improve understandability and reduce maintenance costs).
What is the difference between declaration and definition?
The declaration tells the compiler that at some later point we plan to present the definition of this declaration.
E.g.: void stars () //function declaration
The definition contains the actual implementation.
E.g.: void stars () // declarator
{
for(int j=10; j > =0; j–) //function body
cout << *;
cout <<>
What are the advantages of inheritance?
It permits code reusability. Reusability saves time in program development. It encourages the reuse of proven and debugged high-quality software, thus reducing problem after a system becomes functional.
How do you write a function that can reverse a linked-list?
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;
}
}
What do you mean by inline function?
The idea behind inline functions is to insert the code of a called function at the point where the function is called. If done carefully, this can improve the application’s performance in exchange for increased compile time and possibly (but not always) an increase in the size of the generated binary executables.
Write a program that ask for user input from 5 to 9 then calculate the average
#include “iostream.h”
int main() {
int MAX = 4;
int total = 0;
int average;
int numb;
for (int i=0; icout << “Please enter your input between 5 and 9: “;
cin >> numb;
while ( numb<5>9) {
cout << “Invalid input, please re-enter: “;
cin >> numb;
}
total = total + numb;
}
average = total/MAX;
cout << “The average number is: ” <<>return 0;
}
What is public, protected, private?
• Public, protected and private are three access specifiers in C++.
• Public data members and member functions are accessible outside the class.
• Protected data members and member functions are only available to derived classes.
• Private data members and member functions can’t be accessed outside the class. However there is an exception can be using friend classes.
Write a function that swaps the values of two integers, using int* as the argument type.
void swap(int* a, int*b) {
int t;
t = *a;
*a = *b;
*b = t;
}
Tell how to check whether a linked list is circular.
Create two pointers, each set to the start of the list. Update each as follows:
while (pointer1) {
pointer1 = pointer1->next;
pointer2 = pointer2->next; if (pointer2) pointer2=pointer2->next;
if (pointer1 == pointer2) {
print (\”circular\n\”);
}
}
OK, why does this work?
If a list is circular, at some point pointer2 will wrap around and be either at the item just before pointer1, or the item before that. Either way, it’s either 1 or 2 jumps until they meet.
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.
What is virtual constructors/destructors?
Answer1
Virtual destructors:
If an object (with a non-virtual destructor) is destroyed explicitly by applying the delete operator to a base-class pointer to the object, the base-class destructor function (matching the pointer type) is called on the object.
There is a simple solution to this problem declare a virtual base-class destructor.
This makes all derived-class destructors virtual even though they don’t have the same name as the base-class destructor. Now, if the object in the hierarchy is destroyed explicitly by applying the delete operator to a base-class pointer to a derived-class object, the destructor for the appropriate class is called. Virtual constructor: Constructors cannot be virtual. Declaring a constructor as a virtual function is a syntax error.
Answer2
Virtual destructors: If an object (with a non-virtual destructor) is destroyed explicitly by applying the delete operator to a base-class pointer to the object, the base-class destructor function (matching the pointer type) is called on the object.
There is a simple solution to this problem – declare a virtual base-class destructor. This makes all derived-class destructors virtual even though they don’t have the same name as the base-class destructor. Now, if the object in the hierarchy is destroyed explicitly by applying the delete operator to a base-class pointer to a derived-class object, the destructor for the appropriate class is called.
Virtual constructor: Constructors cannot be virtual. Declaring a constructor as a virtual function is a syntax error.
Does c++ support multilevel and multiple inheritance?
Yes.
What are the advantages of inheritance?
• It permits code reusability.
• Reusability saves time in program development.
• It encourages the reuse of proven and debugged high-quality software, thus reducing problem after a system becomes functional.
What is the difference between declaration and definition?
The declaration tells the compiler that at some later point we plan to present the definition of this declaration.
E.g.: void stars () //function declaration
The definition contains the actual implementation.
E.g.: void stars () // declarator
{
for(int j=10; j>=0; j–) //function body
cout<<”*”;
cout<
What is the difference between an ARRAY and a LIST?
Answer1
is collection of homogeneous elements.
List is collection of heterogeneous elements.
For memory allocated is static and continuous.
For List memory allocated is dynamic and Random.
: User need not have to keep in track of next memory allocation.
List: User has to keep in Track of next location where memory is allocated.
Answer2
uses direct access of stored members, list uses sequencial access for members.
//With you have direct access to memory position 5
Object x = a[5]; // x takes directly a reference to 5th element of array
//With the list you have to cross all previous nodes in order to get the 5th node:
list mylist;
list::iterator it;
for( it = list.begin() ; it != list.end() ; it++ )
{
if( i==5)
{
x = *it;
break;
}
i++;
}
What is a template?
Templates allow to create generic functions that admit any data type as parameters and return value without having to overload the function with all the possible data types. Until certain point they fulfill the functionality of a macro. Its prototype is any of the two following ones:
template function_declaration; template function_declaration;
The only difference between both prototypes is the use of keyword class or typename, its use is indistinct since both expressions have exactly the same meaning and behave exactly the same way.
You have two pairs: new() and delete() and another pair : alloc() and free(). Explain differences between eg. new() and malloc()
Answer1
1.) “new and delete” are preprocessors while “malloc() and free()” are functions. [we dont use brackets will calling new or delete].
2.) no need of allocate the memory while using “new” but in “malloc()” we have to use “sizeof()”.
3.) “new” will initlize the new memory to 0 but “malloc()” gives random value in the new alloted memory location [better to use calloc()]
Answer2
new() allocates continous space for the object instace
malloc() allocates distributed space.
new() is castless, meaning that allocates memory for this specific type,
malloc(), calloc() allocate space for void * that is cated to the specific class type pointer.
What is the difference between class and structure?
Structure: Initially (in C) a structure was used to bundle different type of data types together to perform a particular functionality. But C++ extended the structure to contain functions also. The major difference is that all declarations inside a structure are by default public.
Class: Class is a successor of Structure. By default all the members inside the class are private.
What is RTTI?
Runtime type identification (RTTI) lets you find the dynamic type of an object when you have only a pointer or a reference to the base type. RTTI is the official way in standard C++ to discover the type of an object and to convert the type of a pointer or reference (that is, dynamic typing). The need came from practical experience with C++. RTTI replaces many homegrown versions with a solid, consistent approach.
What is encapsulation?
Packaging an object’s variables within its methods is called encapsulation.
Explain term POLIMORPHISM and give an example using eg. SHAPE object: If I have a base class SHAPE, how would I define DRAW methods for two objects CIRCLE and SQUARE
Answer1
POLYMORPHISM : A phenomenon which enables an object to react differently to the same function call.
in C++ it is attained by using a keyword virtual
Example
public class SHAPE
{
public virtual void SHAPE::DRAW()=0;
}
Note here the function DRAW() is pure virtual which means the sub classes must implement the DRAW() method and SHAPE cannot be instatiated
public class CIRCLE::public SHAPE
{
public void CIRCLE::DRAW()
{
// TODO drawing circle
}
}
public class SQUARE::public SHAPE
{
public void SQUARE::DRAW()
{
// TODO drawing square
}
}
now from the user class the calls would be like
globally
SHAPE *newShape;
When user action is to draw
public void MENU::OnClickDrawCircle(){
newShape = new CIRCLE();
}
public void MENU::OnClickDrawCircle(){
newShape = new SQUARE();
}
the when user actually draws
public void CANVAS::OnMouseOperations(){
newShape->DRAW();
}
Answer2
class SHAPE{
public virtual Draw() = 0; //abstract class with a pure virtual method
};
class CIRCLE{
public int r;
public virtual Draw() { this->drawCircle(0,0,r); }
};
class SQURE
public int a;
public virtual Draw() { this->drawRectangular(0,0,a,a); }
};
Each object is driven down from SHAPE implementing Draw() function in its own way.
What is an object?
Object is a software bundle of variables and related methods. Objects have state and behavior.
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.
Describe PRIVATE, PROTECTED and PUBLIC – the differences and give examples.
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 do you mean by inheritance?
Inheritance is the process of creating new classes, called derived classes, from existing classes or base classes. The derived class inherits all the capabilities of the base class, but can add embellishments and refinements of its own.
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.
How can you quickly find the number of elements stored in a a) static array b) dynamic array ?
Why is it difficult to store linked list in an array?
How can you find the nodes with repetetive data in a linked list?
Write a prog to accept a given string in any order and flash error if any of the character is different. For example : If abc is the input then abc, bca, cba, cab bac are acceptable but aac or bcd are unacceptable.
Write out a function that prints out all the permutations of a string. For example, abc would give you abc, acb, bac, bca, cab, cba. You can assume that all the characters will be unique.
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?
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.
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’s the best way to declare and define global variables?
The best way to declare global variables is to declare them after including all the files so that it can be used in all the functions.
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 specifiers 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 genericity) 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
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”
}
Assignment Operator - What is the diffrence between a “assignment operator” and a “copy constructor”?
Answer1.
In assignment operator, you are assigning a value to an existing object. But in copy constructor, you are creating a new object and then assigning a value to that object. For example:
complex c1,c2;
c1=c2; //this is assignment
complex c3=c2; //copy constructor
Answer2.
A copy constructor is used to initialize a newly declared variable from an existing variable. This makes a deep copy like assignment, but it is somewhat simpler:
There is no need to test to see if it is being initialized from itself.
There is no need to clean up (eg, delete) an existing value (there is none).
A reference to itself is not returned.
“mutable” Keyword - What is “mutable”?
Answer1.
“mutable” is a C++ keyword. When we declare const, none of its data members can change. When we want one of its members to change, we declare it as mutable.
Answer2.
A “mutable” keyword is useful when we want to force a “logical const” data member to have its value modified. A logical const can happen when we declare a data member as non-const, but we have a const member function attempting to modify that data member. For example:
class Dummy {
public:
bool isValid() const;
private:
mutable int size_ = 0;
mutable bool validStatus_ = FALSE;
// logical const issue resolved
};
bool Dummy::isValid() const
// data members become bitwise const
{
if (size > 10) {
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
}
RTTI - What is RTTI?
Answer1.
RTTI stands for “Run Time Type Identification”. In an inheritance hierarchy, we can find out the exact type of the objet of which it is member. It can be done by using:
1) dynamic id operator
2) typecast operator
Answer2.
RTTI is defined as follows: Run Time Type Information, a facility that allows an object to be queried at runtime to determine its type. One of the fundamental principles of object technology is polymorphism, which is the ability of an object to dynamically change at runtime.
STL Containers - What are the types of STL containers?
There are 3 types of STL containers:
1. Adaptive containers like queue, stack
2. Associative containers like set, map
3. Sequence containers like vector, deque
Virtual Destructor - What is the need for “Virtual Destructor?
Destructors are declared as virtual because if do not declare it as virtual the base class destructor will be called before the derived class destructor and that will lead to memory leak because derived class’s objects will not get freed.Destructors are declared virtual so as to bind objects to the methods at runtime so that appropriate destructor is called.
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);
C QUESTIONS
1. How do you decide which integer type to use?
2. What should the 64-bit type on a machine that can support it?
3. What’s the best way to declare and define global variables
4. and functions?
5. What does extern mean in a function declaration?
6. What’s the auto keyword good for?
7. I can’t seem to define a linked list successfully. I tried
typedef struct {
char *item;
NODEPTR next;
*NODEPTR;
but the compiler gave me error messages. Can’t a structure in C
contain a pointer to itself?
8. How do I declare an array of N pointers to functions returning
pointers to functions returning pointers to characters?
9. How can I declare a function that can return a pointer to a
function of the same type?
10. What’s the right declaration for main()?
Is void main() correct?
11. What am I allowed to assume about the initial valuesof variables which are not explicitly initialized?
12. If global variables start out as “zero”, is that good enough for null pointers and floating-point zeroes?
13. This code, straight out of a book, isn’t compiling:
int f()
{
char a[] = “Hello, world!”;
14. What’s wrong with this initialization?
char *p = malloc(10);
15. What is the difference between these initializations?
char a[] = “string literal”;
char *p = “string literal”;
16. What’s the difference between these two declarations?
struct x1 { … };
typedef struct { … } x2;
17. Why doesn’t
struct x { … };
x thestruct;
work?
18. Can a structure contain a pointer to itself?
19. What’s the best way of implementing opaque (abstract) data types
in C?
20. I came across some code that declared a structure like this:
struct name {
int namelen;
char namestr[1];
};
and then did some tricky allocation to make the namestr array act like it had several elements. Is this legal or portable?
21. Is there a way to compare structures automatically?
22. How can I pass constant values to functions which accept structure arguments?
23. How can I read/write structures from/to data files?
24. Why does sizeof report a larger size than I expect for a structure type, as if there were padding at the end?
25. How can I determine the byte offset of a field within a structure?
26. How can I access structure fields by name at run time?
27. This program works correctly, but it dumps core after it finishes. Why?
struct list {
char *item;
struct list *next;
}
/* Here is the main program. */
main(argc, argv)
{ … }
28. Can I initialize unions?
29. What is the difference between an enumeration and a set of preprocessor #defines?
30. Is there an easy way to print enumeration values symbolically?
31. Why doesn’t this code:
a[i] = i++;
work?
32. I’ve experimented with the code
int i = 3;
i = i++;
on several compilers. Some gave i the value 3, and some gave 4.Which compiler is correct?
33. Can I use explicit parentheses to force the order of evaluation I want? Even if I don’t, doesn’t precedence dictate it?
34. How can I understand these complex expressions? What’s a “sequence point”?
35. If I’m not using the value of the expression, should I use i++ or ++i to increment a variable?
36. Why doesn’t the code
int a = 1000, b = 1000;
long int c = a * b;
work?
37. I’m trying to declare a pointer and allocate some space for it,
but it’s not working. What’s wrong with this code?
char *p;
*p = malloc(10);
38. Does *p++ increment p, or what it points to?
39. I have a char * pointer that happens to point to some ints, and I want to step it over them. Why doesn’t
((int *)p)++;
work?
40. I have a function which accepts, and is supposed to initialize,
a pointer:
void f(int *ip)
{
static int dummy = 5;
ip = &dummy;
}
But when I call it like this:
int *ip;
f(ip);
the pointer in the caller remains unchanged.Why?
41. Can I use a void ** pointer as a parameter so that a function can accept a generic pointer by reference?
42. I have a function
extern int f(int *);
which accepts a pointer to an int. How can I pass a constant by
reference? A call like
f(&5); doesn’t seem to work.
43. Does C even have “pass by reference”?
44. What is infamous null pointer?
45. How do I get a null pointer in my programs?
46. Is the abbreviated pointer comparison “if(p)” to test for non-null pointers valid? What if the internal representation for null pointers is nonzero?
47. What is NULL and how is it #defined?
48. How should NULL be defined on a machine which uses a nonzero bit pattern as the internal representation of a null pointer?
49. If NULL were defined as follows:
#define NULL ((char *)0)
wouldn’t that make function calls which pass an uncast NULL work?
50. If NULL and 0 are equivalent as null pointer constants, which should I use?
51. What does a run-time “null pointer assignment” error mean? How can I track it down?
52. Why are array and pointer declarations interchangeable as function formal parameters?
53. How can an array be an lvalue, if you can’t assign to it?
54. Practically speaking, what is the difference between arrays and pointers?
55. How do I declare a pointer to an array?
56. How can I set an array’s size at run time? How can I avoid fixed-sized arrays?
57. How can I declare local arrays of a size matching a passed-in array?
58. How can I dynamically allocate a multidimensional array?
59. How do I write functions which accept two-dimensional arrays when the width is not known at compile time?
60. How can I use statically- and dynamically-allocated multidimensional arrays interchangeably when passing them to functions?
61. Why doesn’t sizeof properly report the size of an array when the array is a parameter to a function?
62. Why doesn’t this fragment work?
char *answer;
printf(”Type something:\n”);
gets(answer);
printf(”You typed \”%s\”\n”, answer);
63. I just tried the code
char *p;
strcpy(p, “abc”); and it worked. How? Why didn’t it crash?
64. How much memory does a pointer variable allocate?
65. Why am I getting “warning: assignment of pointer from integer lacks a cast” for calls to malloc()?
66. Why does some code carefully cast the values returned by malloc to the pointer type being allocated?
67. Why isn’t a pointer null after calling free()? How unsafe is it to use (assign, compare) a pointer value after it’s been freed?
68. When I call malloc() to allocate memory for a pointer which is local to a function, do I have to explicitly free() it?
69. I’m allocating structures which contain pointers to other dynamically-allocated objects. When I free a structure, do I also have to free each subsidiary pointer?
70. Must I free allocated memory before the program exits?
71. How does free() know how many bytes to free?
72. Can I query the malloc package to find out how big an allocated block is?
73. Is it legal to pass a null pointer as the first argument to realloc()?
74. What’s the difference between calloc() and malloc()? Is it safe to take advantage of calloc’s zero-filling? Does free() work on memory allocated with calloc(), or do you need a cfree()?
75. What is alloca() and why is its use discouraged?
76. Why doesn’t
strcat(string, ‘!’);
work?
77. How can I get the numeric (character set) value corresponding to a character, or vice versa?
78. What is the right type to use for Boolean values in C?
79. Is if(p), where p is a pointer, a valid conditional?
80. How can I write a generic macro to swap two values?What’s the best way to write a multi-statement macro?
81. Is it acceptable for one header file to #include another?
82. What’s the difference between #include and #include “” ?
83. What are the complete rules for header file searching?
84. How can I construct preprocessor #if expressions which compare strings?
85. Does the sizeof operator work in preprocessor #if directives?
86. Can I use an #ifdef in a #define line, to define something two different ways?
87. Is there anything like an #ifdef for typedefs?
88. How can I use a preprocessor #if expression to tell if a machine is big-endian or little-endian?
89. How can I list all of the predefined identifiers?
90. How can I write a macro which takes a variable number of arguments?
91. What is the “ANSI C Standard?”
92. What’s the difference between “const char *p” and “char * const p”?
93. Why can’t I pass a char ** to a function which expects a const char **?
94. What’s the correct declaration of main()?
95. Can I declare main() as void ?
96. What does the message “warning: macro replacement within a string literal” mean?
97. What are #pragmas and what are they good for?
98. What does “#pragma once” mean?
99. Is char a[3] = “abc”; legal? What does it mean?
100. Why can’t I perform arithmetic on a void * pointer?
101. What’s the difference between memcpy() and memmove()?
102. What should malloc(0) do? Return a null pointer or a pointer to 0 bytes?
103. What’s wrong with this code?
char c;
while((c = getchar()) != EOF) …
104. Why does the code
while(!feof(infp)) {
a. fgets(buf, MAXLINE, infp);
b. fputs(buf, outfp);
}
copy the last line twice?
105. How can I read one character at a time, without waiting for the RETURN key?
106. How can I print a ‘%’ character in a printf format string?
107. What printf format should I use for a typedef like size_t when I don’t know whether it’s long or some other type?
108. How can I implement a variable field width with printf?
109. How can I print numbers with commas separating the thousands? What about currency formatted numbers?
110. Why doesn’t the call scanf(”%d”, i) work?
111. How can I specify a variable width in a scanf() format string?
112. Why doesn’t this code:
double d;
scanf(”%f”, &d);
work?
113. How can I tell how much destination buffer space I’ll need for an arbitrary sprintf call? How can I avoid overflowing the destination buffer with sprintf()?
114. What’s the difference between fgetpos/fsetpos and ftell/fseek?
115. What are fgetpos() and fsetpos() good for?
116. How can I redirect stdin or stdout to a file from within a program?
117. How can I read a binary data file properly?
118. How can I convert numbers to strings (the opposite of atoi)? Is there an itoa() function?
119. Why does strncpy() not always place a ” terminator in the destination string?
120. Why do some versions of toupper() act strangely if given an upper-case letter?
121. How can I split up a string into whitespace-separated fields? How can I duplicate the process by which main() is handed argc and argv?
122. How can I sort a linked list?
123. How can I sort more data than will fit in memory?
124. How can I get the current date or time of day in a C program?
125. How can I add N days to a date? How can I find the difference between two dates?
126. How can I get random integers in a certain range?
127. How can I generate random numbers with a normal or Gaussian distribution?
128. What does it mean when the linker says that _end is undefined?
129. When I set a float variable to, say, 3.1, why is printf printing it as 3.0999999?
130. What’s a good way to check for “close enough” floating-point equality?
131. How do I round numbers?
132. Why doesn’t C have an exponentiation operator?
133. How do I test for IEEE NaN and other special values?
134. What’s a good way to implement complex numbers in C?
135. How can %f be used for both float and double arguments in printf()? Aren’t they different types?
136. How can I write a function that takes a variable number of arguments?
137. How can I write a function that takes a format string and a variable number of arguments, like printf(), and passes them to printf() to do most of the work?
138. How can I write a function analogous to scanf(), that calls scanf() to do most of the work?
139. How can I discover how many arguments a function was actually called with?
140. How can I write a function which takes a variable number of arguments and passes them to some other function (which takes a variable number of arguments)?
141. How can I call a function with an argument list built up at run time?
C QUESTIONS
1. What does static variable mean?
2. What is a pointer?
3. What is a structure?
4. What are the differences between structures and arrays?
5. In header files whether functions are declared or defined?
6. What are the differences between malloc() and calloc()?
7. What are macros? what are its advantages and disadvantages?
8. Difference between pass by reference and pass by value?
9. What is static identifier?
10. Where are the auto variables stored?
11. Where does global, static, local, register variables, free memory and C Program instructions get stored?
12. Difference between arrays and linked list?
13. What are enumerations?
14. Describe about storage allocation and scope of global, extern, static, local and register variables?
15. What are register variables? What are the advantage of using register variables?
16. What is the use of typedef?
17. Can we specify variable field width in a scanf() format string? If possible how?
18. Out of fgets() and gets() which function is safe to use and why?
19. Difference between strdup and strcpy?
20. What is recursion?
21. Differentiate between a for loop and a while loop? What are it uses?
22. What are the different storage classes in C?
23. Write down the equivalent pointer expression for referring the same element a[i][j][k][l]?
24. What is difference between Structure and Unions?
25. What the advantages of using Unions?
26. What are the advantages of using pointers in a program?
27. What is the difference between Strings and s?
28. In a header file whether functions are declared or defined?
29. What is a far pointer? where we use it?
30. How will you declare an array of three function pointers where each function receives two ints and returns a float?
31. what is a NULL Pointer? Whether it is same as an uninitialized pointer?
32. What is a NULL Macro? What is the difference between a NULL Pointer and a NULL Macro?
33. What does the error ‘Null Pointer Assignment’ mean and what causes this error?
34. What is near, far and huge pointers? How many bytes are occupied by them?
35. How would you obtain segment and offset addresses from a far address of a memory location?
36. Are the expressions arr and &arr same for an array of integers?
37. Does mentioning the array name gives the base address in all the contexts?
38. Explain one method to process an entire string as one unit?
39. What is the similarity between a Structure, Union and enumeration?
40. Can a Structure contain a Pointer to itself?
41. How can we check whether the contents of two structure variables are same or not?
42. How are Structure passing and returning implemented by the complier?
43. How can we read/write Structures from/to data files?
44. What is the difference between an enumeration and a set of pre-processor # defines?
45. what do the ‘c’ and ‘v’ in argc and argv stand for?
46. Are the variables argc and argv are local to main?
47. What is the maximum combined length of command line arguments including the space between adjacent arguments?
48. If we want that any wildcard characters in the command line arguments should be appropriately expanded, are we required to make any special provision? If yes, which?
49. Does there exist any way to make the command line arguments available to other functions without passing them as arguments to the function?
50. What are bit fields? What is the use of bit fields in a Structure declaration?
51. To which numbering system can the binary number 1101100100111100 be easily converted to?
52. Which bit wise operator is suitable for checking whether a particular bit is on or off?
53. Which bit wise operator is suitable for turning off a particular bit in a number?
54. Which bit wise operator is suitable for putting on a particular bit in a number?
55. Which bit wise operator is suitable for checking whether a particular bit is on or off?
56. which one is equivalent to multiplying by 2:Left shifting a number by 1 or Left shifting an unsigned int or char by 1?
57. Write a program to compare two strings without using the strcmp() function.
58. Write a program to concatenate two strings.
59. Write a program to interchange 2 variables without using the third one.
60. Write programs for String Reversal & Palindrome check
61. Write a program to find the Factorial of a number
62. Write a program to generate the Fibinocci Series
63. Write a program which employs Recursion
64. Write a program which uses Command Line Arguments
65. Write a program which uses functions like strcmp(), strcpy()? etc
66. What are the advantages of using typedef in a program?
67. How would you dynamically allocate a one-dimensional and two-dimensional array of integers?
68. How can you increase the size of a dynamically allocated array?
69. How can you increase the size of a statically allocated array?
70. When reallocating memory if any other pointers point into the same piece of memory do you have to readjust these other pointers or do they get readjusted automatically?
71. Which function should be used to free the memory allocated by calloc()?
72. How much maximum can you allocate in a single call to malloc()?
73. Can you dynamically allocate arrays in expanded memory?
74. What is object file? How can you access object file?
75. Which header file should you include if you are to develop a function which can accept variable number of arguments?
76. Can you write a function similar to printf()?
77. How can a called function determine the number of arguments that have been passed to it?
78. Can there be at least some solution to determine the number of arguments passed to a variable argument list function?
79. How do you declare the following:
80. An array of three pointers to chars
81. An array of three char pointers
82. A pointer to array of three chars
83. A pointer to function which receives an int pointer and returns a float pointer
84. A pointer to a function which receives nothing and returns nothing
85. What do the functions atoi(), itoa() and gcvt() do?
86. Does there exist any other function which can be used to convert an integer or a float to a string?
87. How would you use qsort() function to sort an array of structures?
88. How would you use qsort() function to sort the name stored in an array of pointers to string?
89. How would you use bsearch() function to search a name stored in array of pointers to string?
90. How would you use the functions sin(), pow(), sqrt()?
91. How would you use the functions memcpy(), memset(), memmove()?
92. How would you use the functions fseek(), freed(), fwrite() and ftell()?
93. How would you obtain the current time and difference between two times?
94. How would you use the functions randomize() and random()?
95. How would you implement a substr() function that extracts a sub string from a given string?
96. What is the difference between the functions rand(), random(), srand() and randomize()?
97. What is the difference between the functions memmove() and memcpy()?
98. How do you print a string on the printer?
99. Can you use the function fprintf() to display the output on the screen?
C++ QUESTIONS
1. What is a class?
2. What is an object?
3. What is the difference between an object and a class?
4. What is the difference between class and structure?
5. What is public, protected, private?
6. What are virtual functions?
7. What is friend function?
8. What is a scope resolution operator?
9. What do you mean by inheritance?
10. What is abstraction?
11. What is polymorphism? Explain with an example.
12. What is encapsulation?
13. What do you mean by binding of data and functions?
14. What is function overloading and operator overloading?
15. What is virtual class and friend class?
16. What do you mean by inline function?
17. What do you mean by public, private, protected and friendly?
18. When is an object created and what is its lifetime?
19. What do you mean by multiple inheritance and multilevel inheritance? Differentiate between them.
20. Difference between realloc() and free?
21. What is a template?
22. What are the main differences between procedure oriented languages and object oriented languages?
23. What is R T T I ?
24. What are generic functions and generic classes?
25. What is namespace?
26. What is the difference between pass by reference and pass by value?
27. Why do we use virtual functions?
28. What do you mean by pure virtual functions?
29. What are virtual classes?
30. Does c++ support multilevel and multiple inheritance?
31. What are the advantages of inheritance?
32. When is a memory allocated to a class?
33. What is the difference between declaration and definition?
34. What is virtual constructors/destructors?
35. In c++ there is only virtual destructors, no constructors. Why?
36. What is late bound function call and early bound function call? Differentiate.
37. How is exception handling carried out in c++?
38. When will a constructor executed?
39. What is Dynamic Polymorphism?
40. Write a macro for swapping integers.
本文来源：https://www.2haoxitong.net/k/doc/34ea3b7bfab069dc51220100.html
文档为doc格式