What is far pointer?when will you use far pointer?
Sometimes you can get away with using a small memory model in
most of a given program. There might be just a few things that don’t fit
in your small data and code segments. When that happens, you can
use explicit far pointers and function declarations to get at the rest of
memory. A far function can be outside the 64KB segment most
functions are shoehorned into for a small-code model. (Often, libraries
are declared explicitly far, so they’ll work no matter what code model
the program uses.) A far pointer can refer to information outside the
64KB data segment. Typically, such pointers are used with farmalloc()
and such, to manage a heap separate from where all the rest of the
data lives. If you use a small-data, large-code model, you should
explicitly make your function pointers far.
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printf() Function What is the output of printf("%d")? 1. When we write printf("%d",x); this means compiler will print the value of x. But as here, there is nothing after %d so compiler will show in output window garbage value. 2. When we use %d the compiler internally uses it to access the argument in the stack (argument stack). Ideally compiler determines the offset of the data variable depending on the format specification string. Now when we write printf("%d",a) then compiler first accesses the top most element in the argument stack of the printf which is %d and depending on the format string it calculated to offset to the actual data variable in the memory which is to be printed. Now when only %d will be present in the printf then compiler will calculate the correct offset (which will be the offset to access the integer variable) but as the actual data object is to be printed is not present at that memory location so it will print what ever will be the contents of that memory location. 3. Some compilers check the format string and will generate an error without the proper number and type of arguments for things like printf(...) and scanf(...).
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C interview question1: What is a stack ? Answer: The stack is a region of memory within which our programs temporarily store data as they execute. For example, when a program passes parameters to functions, C places the parameters on the stack. When the function completes, C removes the items from the stack. Similarly, when a function declares local variables, C stores the variable's values on the stack during the function's execution. Depending on the program's use of functions and parameters, the amount of stack space that a program requires will differ.
C interview question2:Allocating memory for a 3-D array
Answer: #include "alloc.h"
#define MAXX 3
#define MAXY 4
#define MAXZ 5
main( )
{
int ***p, i, j, k ;
p = ( int *** ) malloc ( MAXX * sizeof ( int ** ) ) ;
for ( i = 0 ; i < MAXX ; i++ )
{
p[i] = ( int ** ) malloc ( MAXY * sizeof ( int * ) ) ;
for ( j = 0 ; j < MAXY ; j++ )
p[i][j] = ( int * ) malloc ( MAXZ * sizeof ( int ) ) ;
}
for ( k = 0 ; k < MAXZ ; k++ )
{
for ( i = 0 ; i < MAXX ; i++ )
{
for ( j = 0 ; j < MAXY ; j++ )
{
p[i][j][k] = i + j + k ;
printf ( "%d ", p[i][j][k] ) ;
}
printf ( "\n" ) ;
}
printf ( "\n\n" ) ;
}
}
C interview question3:How to distinguish between a binary tree and a tree? Answer: A node in a tree can have any number of branches. While a binary tree is a tree structure in which any node can have at most two branches. For binary trees we distinguish between the subtree on the left and subtree on the right, whereas for trees the order of the subtrees is irrelevant.
Consider two binary trees, but these binary trees are different. The first has an empty right subtree while the second has an empty left subtree. If the above are regarded as trees (not the binary trees), then they are same despite the fact that they are drawn differently. Also, an empty binary tree can exist, but there is no tree having zero nodes.
C interview question4:How do I use the function ldexp( ) in a program? Answer: The math function ldexp( ) is used while solving the complex mathematical equations. This function takes two arguments, a double value and an int respectively. The order in which ldexp( ) function performs calculations is ( n * pow ( 2, exp ) ) where n is the double value and exp is the integer. The following program demonstrates the use of this function.
#include
void main( )
{
double ans ;
double n = 4 ;
ans = ldexp ( n, 2 ) ;
printf ( "\nThe ldexp value is : %lf\n", ans ) ;
}
Here, ldexp( ) function would get expanded as ( 4 * 2 * 2 ), and the output would be the ldexp value is : 16.000000
C interview question5:Can we get the mantissa and exponent form of a given number? Answer:The function frexp( ) splits the given number into a mantissa and exponent form. The function takes two arguments, the number to be converted as a double value and an int to store the exponent form. The function returns the mantissa part as a double value. Following example demonstrates the use of this function.
#include
void main( )
{
double mantissa, number ;
int exponent ;
number = 8.0 ;
mantissa = frexp ( number, &exponent ) ;
printf ( "The number %lf is ", number ) ;
printf ( "%lf times two to the ", mantissa ) ;
printf ( "power of %d\n", exponent ) ;
return 0 ;
}
C interview question1:If we have declared an array as global in one file and we are using it in another file then why doesn't the sizeof operator works on an extern array?
Answer: An extern array is of incomplete type as it does not contain the size. Hence we cannot use sizeof operator, as it cannot get the size of the array declared in another file. To resolve this use any of one the following two solutions:
1. In the same file declare one more variable that holds the size of array. For example,
array.c
int arr[5] ;
int arrsz = sizeof ( arr ) ;
myprog.c
extern int arr[] ;
extern int arrsz ;
2. Define a macro which can be used in an array
declaration. For example,
myheader.h
#define SZ 5
array.c
#include "myheader.h"
int arr[SZ] ;
myprog.c
#include "myheader.h"
extern int arr[SZ] ;
C interview question2:How do I write printf( ) so that the width of a field can be specified at runtime?
Answer: This is shown in following code snippet.
main( )
{
int w, no ;
printf ( "Enter number and the width for the
number field:" ) ;
scanf ( "%d%d", &no, &w ) ;
printf ( "%*d", w, no ) ;
}
Here, an '*' in the format specifier in printf( ) indicates that an int value from the argument list should be used for the field width.
C interview question3:How to find the row and column dimension of a given 2-D array?
Answer: Whenever we initialize a 2-D array at the same place where it has been declared, it is not necessary to mention the row dimension of an array. The row and column dimensions of such an array can be determined programmatically as shown in following program.
void main( )
{
int a[][3] = { 0, 1, 2,9,-6, 8,7, 5, 44,23, 11,15 } ;
int c = sizeof ( a[0] ) / sizeof ( int ) ;
int r = ( sizeof ( a ) / sizeof ( int ) ) / c ;
int i, j ;
printf ( "\nRow: %d\nCol: %d\n", r, c ) ;
for ( i = 0 ; i < r ; i++ )
{
for ( j = 0 ; j < c ; j++ )
printf ( "%d ", a[i][j] ) ;
printf ( "\n" ) ;
}
}
C interview quesion4:What is access( ) function...
Answer:The access( ) function checks for the existence of a file and also determines whether it can be read,written to or executed. This function takes two arguments the filename and an integer indicating the access mode. The values 6, 4, 2, and 1 checks for read/write, read, write and execute permission of a given file, whereas value 0 checks whether the file exists or not. Following program demonstrates how we can use access( ) function to check if a given file exists.
#include
main( )
{
char fname[67] ;
printf ( "\nEnter name of file to open" ) ;
gets ( fname ) ;
if ( access ( fname, 0 ) != 0 )
{
printf ( "\nFile does not exist." ) ;
return ;
}
} C interview question5:How do I convert a floating-point number to a string?
Answer: Use function gcvt( ) to convert a floating-point number to a string. Following program demonstrates the use of this function.
#include
main( )
{
char str[25] ;
float no ;
int dg = 5 ; /* significant digits */
no = 14.3216 ;
gcvt ( no, dg, str ) ;
printf ( "String: %s\n", str ) ;
}
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Answer:Function atexit( ) recevies parameter as the address of function of the type void fun ( void ). The function whose address is passed to atexit( ) gets called before the termination of program. If atexit( ) is called for more than one function then the functions are called in "first in last out" order. You can verify that from the output.
#include
void fun1( )
{
printf("Inside fun1\n");
}
void fun2( )
{
printf("Inside fun2\n");
}
main( )
{
atexit ( fun1 ) ;
/* some code */
atexit ( fun2 ) ;
printf ( "This is the last statement of
program?\n" );
}
C interview question2
: How do I write a user-defined function, which deletes each character in a string str1, which matches any character in string str2?
Answer: The function is as shown below:
Compress ( char str1[], char str2[] )
{
int i, j, k ;
for ( i = k = 0 ; str1[i] != ‘\0’ ; i++ )
{
for ( j = 0 ; str2[j] != ‘\0’ && str2[j] !=
str1[i] ; j++ );
if ( str2[j] == ‘\0’ )
str1[k++] = str1[I] ;
}
str1[k] = ‘\0’
}
C interview question3:How does free( ) know how many bytes to free?
Answer: The malloc( ) / free( ) implementation remembers the size of each block allocated and returned, so it is not necessary to remind it of the size when freeing.
C interview question4:What is the use of randomize( ) and srand( ) function?
Answer: While generating random numbers in a program, sometimes we require to control the series of numbers that random number generator creates. The process of assigning the random number generators starting number is called seeding the generator. The randomize( ) and srand( ) functions are used to seed the random number generators. The randomize( ) function uses PC's clock to produce a random seed, whereas the srand( ) function allows us to specify the random number generator's starting value.
C interview question5:How do I determine amount of memory currently available for allocating?
Answer: We can use function coreleft( ) to get the amount of memory available for allocation. However, this function does not give an exact amount of unused memory. If, we are using a small memory model, coreleft( ) returns the amount of unused memory between the top of the heap and stack. If we are using a larger model, this function returns the amount of memory between the highest allocated memory and the end of conventional memory. The function returns amount of memory in terms of bytes.
C interview question6:How does a C program come to know about command line arguments?
Answer: When we execute our C program, operating system loads the program into memory. In case of DOS, it first loads 256 bytes into memory, called program segment prefix. This contains file tables,environment segment, and command line information. When we compile the C program the compiler inserts additional code that parses the command, assigning it to the argv array, making the arguments easily accessible within our C program.
C interview question7:When we open a file, how does functions like fread( )/fwrite( ), etc. get to know from where to read or to write the data?
Answer: When we open a file for read/write operation using function like fopen( ), it returns a pointer to the structure of type FILE. This structure stores the file pointer called position pointer, which keeps track of current location within the file. On opening file for read/write operation, the file pointer is set to the start of the file. Each time we read/write a character, the position pointer advances one character. If we read one line of text at a step from the file, then file pointer advances to the start of the next line. If the file is opened in append mode, the file pointer is placed at the very end of the file. Using fseek( ) function we can set the file pointer to some other place within the file. Keywords: c interview questions c++ faq faq on pointers in c faq on arrays in c faq videos c tutorial faqs on strings in c steve summit faq on pointers in c faq on arrays in c c++ faq programming in c textbook c tutorial c programming resources c language reference
