C Interview Questions Part 6

C interview question:The sizeof( ) function doesn’t return the size of the block of memory pointed to by a pointer. Why?

Answer:The sizeof( ) operator does not know that malloc( ) has been used to allocate a pointer. sizeof( ) gives us the size of pointer itself. There is no handy way to find out the size of a block allocated by malloc( ).

C interview qustion: What is FP_SEG And FP_OFF…

Answer:Sometimes while working with far pointers we need to break a far address into its segment and offset. In such situations we can use FP_SEG and FP_OFF macros. Following program illustrates the use of these two macros.

#include

main( )

{

unsigned s, o ;

char far *ptr = "Hello!" ;

s = FP_SEG ( ptr ) ;

o = FP_OFF ( ptr ) ;

printf ( "\n%u %u", s, o ) ;

}

C interview question:How do I write a program to convert a string containing number in a hexadecimal form to its equivalent decimal?

Answer: The following program demonstrates this:

main( )

{

char str[] = "0AB" ;

int h, hex, i, n ;

n = 0 ; h = 1 ;

for ( i = 0 ; h == 1 ; i++ )

{

if ( str[i] >= '0' && str[i] <= '9' )

hex = str[i] - '0' ;

else

{

if ( str[i] >= 'a' && str[i] <= 'f' )

hex = str[i] - 'a' + 10 ;

else

if ( str[i] >= 'A' && str[i] <= 'F' )

hex = str[i] - 'A' + 10 ;

else

h = 0 ;

}

if ( h == 1 )

n = 16 * n + hex ;

}

printf ( "\nThe decimal equivalent of %s is %d",

str, n ) ;

}

The output of this program would be the decimal equivalent of 0AB is 171.

C interview question:How do I write code that reads the segment register settings?

Answer: We can use segread( ) function to read segment register settings. There are four segment registers—code segment, data segment, stack segment and extra segment. Sometimes when we use DOS and BIOS services in a program we need to know the segment register's value. In such a situation we can use segread( ) function. The following program illustrates the use of this function.

#include

main( )

{

struct SREGS s ;

segread ( &s ) ;

printf ( "\nCS: %X DS: %X SS: %X ES: %X",s.cs,

s.ds, s.ss, s.es ) ;

}

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C Interview Questions Part 5

C interview question:Explain the functions memcmp( ) and memicmp( )

Answer:The functions memcmp( ) and memicmp( ) compares first n bytes of given two blocks of memory or strings.However, memcmp( ) performs comparison as unsigned chars whereas memicmp( ) performs comparison as chars but ignores case (i.e. upper or lower case). Both the functions return an integer value where 0 indicates that two memory buffers compared are identical. If the value returned is greater than 0 then it indicates that the first buffer is bigger than the second one. The value less than 0 indicate that the first buffer is less than the second buffer. The following code snippet demonstrates use of both

#include

main( )

{

char str1[] = "This string contains some

characters" ;

char str2[] = "this string contains" ;

int result ;

result = memcmp ( str1, str2, strlen ( str2 ) ) ;

printf ( "\nResult after comapring buffer using

memcmp( )" ) ;

show ( result ) ;

result = memicmp ( str1, str2, strlen ( str2 ) ) ;

printf ( "\nResult after comapring buffer using

memicmp( )" ) ;

show ( result ) ;

}

show ( int r )

{

if ( r == 0 )

printf ( "\nThe buffer str1 and str2 hold

identical data" ) ;

if ( r > 0 )

printf ( "\nThe buffer str1 is bigger than buffer

str2" ) ;

if ( r < 0 )

printf ( "\nThe buffer str1 is less than buffer

str2" ) ;

C interview question:How do I write code to find an amount of free disk space available on current drive?

Anwer: Use getdfree( ) function as shown in follow code.

#include

main( )

{

int dr ; struct dfree disk ;

long freesp ;

dr = getdisk( ) ;

getdfree ( dr + 1 , &disk ) ;

if ( disk.df_sclus == 0xFFFF )

{

printf ( "\ngetdfree( ) function failed\n");

exit ( 1 ) ;

}

freesp = ( long ) disk.df_avail

* ( long ) disk.df_bsec

* ( long ) disk.df_sclus ;

printf ( "\nThe current drive %c: has %ld bytes

available as free space\n", 'A' + dr, freesp ) ;

}

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