October 13, 2018

Sreekanth B

Dell Boomi Most Frequently Asked C++ Interview Questions Answers

Refer To A Name Of Class Or Function That Is Defined Within A Namespace?

There are two ways in which we can refer to a name of class or function that is defined within a namespace: Using scope resolution operator through the using keyword. This is shown in following example

namespace name1
{
    class sample1
    {
         // code
    } ;
}
namespace name2
{
     class sample2
     {
         // code
     } ;
}
using namespace name2 ;
void main( )
{
      name1::sample1 s1 ;
      sample2 s2 ;
}
Here, class sample1 is referred using the scope resolution operator. On the other hand we can directly refer to class sample2 because of the statement using namespace name2 ; the using keyword declares all the names in the namespace to be in the current scope. So we can use the names without any qualifiers.

Is It Possible To Provide Default Values While Overloading A Binary Operator?

No!. This is

because even if we provide the default arguments to the parameters of the overloaded operator function we would end up using the binary operator incorrectly. This is explained in the following example

sample operator + ( sample a, sample b = sample (2, 3.5f ) )
{
}

void main( )
{
    sample s1, s2, s3 ;
    s3 = s1 + ; // error
}
Dell Boomi Most Frequently Asked C++ Interview Questions Answers
Dell Boomi Most Frequently Asked C++ Interview Questions Answers

When Should I Use Unitbuf Flag?

The unit buffering (unitbuf) flag should be turned on when we want to ensure that each character is output as soon as it is inserted into an output stream. The same can be done using unbuffered output but unit buffering provides a better performance than the unbuffered output.

What Are Manipulators?

Manipulators are the instructions to the output stream to modify the output in various ways. The manipulators provide a clean and easy way for formatted output in comparison to the formatting flags of the ios class. When manipulators are used, the formatting instructions are inserted directly into the stream. Manipulators are of two types, those that take an argument and those that don't.

Differentiate Between The Manipulator And Setf( ) Function?

The difference between the manipulator and setf( ) function are as follows

The setf( ) function is used to set the flags of the ios but manipulators directly insert the formatting instructions into the stream. We can create user-defined manipulators but setf( ) function uses data members of ios class only. The flags put on through the setf( ) function can be put off through unsetf( ) function. Such flexibility is not available with manipulators.

How To Get The Current Position Of The File Pointer?

We can get the current position of the file pointer by using the tellp( ) member function of ostream class or tellg( ) member function of istream class. These functions return (in bytes) positions of put pointer and get pointer respectively.

What Are Put And Get Pointers?

These are the long integers associated with the streams. The value present in the put pointer specifies the byte number in the file from where next write would take place in the file. The get pointer specifies the byte number in the file from where the next reading should take place.

What Does The Nocreate And Noreplace Flag Ensure When They Are Used For Opening A File?

nocreate and noreplace are file-opening modes. A bit in the ios class defines these modes. The flag nocreate ensures that the file must exist before opening it. On the other hand the flag noreplace ensures that while opening a file for output it does not get overwritten with new one unless ate or app is set. When the app flag is set then whatever we write gets appended to the existing file. When ate flag is set we can start reading or writing at the end of existing file.

What Is The Limitation Of Cin While Taking Input For Character Array?

To understand this consider following statements,

       char str[5] ;
cin >> str ;
While entering the value for str if we enter more than 5 characters then there is no provision in cin to check the array bounds. If the array overflows, it may be dangerous. This can be avoided by using get( ) function. For example, consider following statement,cin.get ( str, 5 ) ; On executing this statement if we enter more than 5 characters, then get( ) takes only first five characters and ignores rest of the characters. Some more variations of get( ) are available, such as shown below

get ( ch ) - Extracts one character only get ( str, n ) - Extracts up to n characters into str get ( str, DELIM ) - Extracts characters into array str until specified delimiter (such as '\n'). Leaves delimiting character in stream.

get ( str, n, DELIM ) - Extracts characters into array str until n characters or DELIM character, leaving delimiting character in stream.

Mention The Purpose Of Istream Class?

The istream class performs activities specific to input. It is derived from the iosclass. The most commonly used member function of this class is the overloaded >> operator which canextract values of all basic types. We can extract even a string using this operator.

Would The Following Code Work?

 
#include<iosteram.>
Void Main( )
 {
 Ostream O ;
 O << "dream. Then Make It Happen!" ;
}

No This is because we cannot create an object of the iostream class since its constructor and copy constructorare declared private.

Assert( ) Macro..?

We can use a macro called assert( ) to test for conditions that should not occur in a code. This macro expands to an if statement. If test evaluates to 0, assert prints an error message and calls abort to abort the program.

#include
#include
void main( )
{
   int i ;
   cout << "\nEnter an integer: " ;
   cin >> i ;
   assert ( i >= 0 ) ;
   cout << i << endl ;
}

Why Is That Unsafe To Deal Locate The Memory Using Free( ) If It Has Been Allocated Using New?

This can be explained with the following example

#include
class sample
{
  int *p ;
  public
     sample( )
     {
       p = new int ;
     }

     ~sample( )
     {
        delete p ;
     }
} ;

void main( )
{
  sample *s1 = new sample ;
  free ( s1 ) ;
  sample *s2 = ( sample * ) malloc ( sizeof ( sample ) ) ;
  delete s2 ;
}
The new operator allocates memory and calls the constructor. In the constructor we have allocated memory on heap, which is pointed to by p. If we release the object using the free( ) function the object would die but the memory allocated in the constructor would leak. This is because free( ) being a C library function does not call the destructor where we have deal located the memory.
As against this, if we allocate memory by calling malloc( ) the constructor would not get called. Hence p holds a garbage address. Now if the memory is deal located using delete, the destructor would get called where we have tried to release the memory pointed to by p. Since p contains garbage this may result in a runtime error.

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