Language in C Interview Questions and Answers
Ques 71. How to set the system date through a C program ?
We can set the system date using the setdate( ) function as shown in the following program. The function assigns the current time to a
structure date.
#include "stdio.h"
#include "dos.h"
main( )
{
struct date new_date ;
new_date.da_mon = 10 ;
new_date.da_day = 14 ;
new_date.da_year = 1993 ;
setdate ( &new_date ) ;
}
Ques 72. How can I write a general-purpose swap without using templates?
Given below is the program which uses the stringizing preprocessor directive ## for building a general purpose swap macro which can swap two integers, two floats, two chars, etc.
#define swap( a, b, t ) ( g ## t = ( a ), ( a ) = ( b ), ( b ) = g ## t )
int gint;
char gchar;
float gfloat ;
main( )
{
int a = 10, b = 20 ;
char ch1 = 'a' , ch2 = 'b' ;
float f1 = 1.12, f2 = 3.14 ;
swap ( a, b, int ) ;
printf ( "na = %d b = %d", a, b ) ;
swap ( ch1, ch2, char ) ;
printf ( "nch1 = %c ch2 = %c", ch1, ch2 ) ;
swap ( f1, f2, float ) ;
printf ( "nf1 = %4.2f f2 = %4.2f", f1, f2 ) ;
}
swap ( a, b, int ) would expand to,
( gint = ( a ), ( a ) = ( b ), ( b ) = gint )
Ques 73. What is a heap ?
Heap is a chunk of memory. When in a program memory is allocated dynamically, the C run-time library gets the memory from a collection of unused memory called the heap. The heap resides in a program's data segment. Therefore, the amount of heap space available to the program is fixed, and can vary from one program to another.
Ques 74. How to obtain a path of the given file?
The function searchpath( ) searches for the specified file in the subdirectories of the current path. Following program shows how to make use of the searchpath( ) function.
#include "dir.h"
void main ( int argc, char *argv[] )
{
char *path ;
if ( path = searchpath ( argv[ 1 ] ) )
printf ( "Pathname : %sn", path ) ;
else
printf ( "File not foundn" ) ;
}
Ques 75. Can we get the process identification number of the current program?
Yes! The macro getpid( ) gives us the process identification number of the program currently running. The process id. uniquely identifies a program. Under DOS, the getpid( ) returns the Program Segment Prefix as the process id. Following program illustrates the use of this macro.
#include <stdio.h>
#include <process.h>
void main( )
{
printf ( "The process identification number of this program is %Xn",
getpid( ) ) ;
}
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