11. What is the
difference between printf() and sprintf() ?
sprintf() writes data to the character array
whereas printf(...) writes data to the standard output device.
12. How to reduce a
final size of executable?
Size of the final executable can be reduced
using dynamic linking for libraries.
13. Can you tell me
how to check whether a linked list is circular?
Create two pointers, and set both 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");
}
}
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, its either 1 or 2 jumps until they meet.
14. Advantages of
a macro over a function?
Macro gets to see the Compilation
environment, so it can expand __ __TIME__ __FILE__ #defines. It is expanded by
the preprocessor.
For example, you can’t do this without macros
#define PRINT(EXPR) printf( #EXPR “=%d\n”, EXPR)
PRINT( 5+6*7 ) // expands into printf(”5+6*7=%d”, 5+6*7 );
You can define your mini language with macros:
#define strequal(A,B) (!strcmp(A,B))
15. What is the
difference between strings and character arrays?
A major difference is: string will have static
storage duration, whereas as a character array will not, unless it is explicity
specified by using the static keyword.
Actually, a string is a character array with
following properties:
* the multibyte character sequence, to which we generally call string, is used
to initialize an array of static storage duration. The size of this array is
just sufficient to contain these characters plus the terminating NUL
character.
* it not specified what happens if this array, i.e., string, is modified.
* Two strings of same value[1] may share same memory area.
16. Write down the
equivalent pointer expression for referring the same
element a[i][j][k][l] ?
a[i] == *(a+i)
a[i][j] == *(*(a+i)+j)
a[i][j][k] == *(*(*(a+i)+j)+k)
a[i][j][k][l] == *(*(*(*(a+i)+j)+k)+l)
17. Which bit
wise operator is suitable for checking whether a particular bit is on or
off?
The bitwise AND operator. Here is an example:
enum {
KBit0 = 1,
KBit1,
…
KBit31,
};
if ( some_int & KBit24 )
printf ( “Bit number 24 is ON\n” );
else
printf ( “Bit number 24 is OFF\n” );
18. Which bit wise
operator is suitable for turning off a particular bit in a number?
The bitwise AND operator, again. In the
following code snippet, the bit number 24 is reset to zero.
some_int = some_int & ~KBit24;
19. Which bit wise
operator is suitable for putting on a particular bit in a number?
The bitwise OR operator. In the following
code snippet, the bit number 24 is turned ON:
some_int = some_int | KBit24;
20. Does there exist any
other function which can be used to convert an integer or a float to a
string?
Some implementations provide a nonstandard
function called itoa(), which converts an integer to string.
#include
char *itoa(int value, char *string, int radix);
DESCRIPTION
The itoa() function constructs a string representation of an integer.
PARAMETERS
value: Is the integer to be converted to string representation.
string: Points to the buffer that is to hold resulting string.
The resulting string may be as long as seventeen bytes.
radix: Is the base of the number; must be in the range 2 - 36.
A portable solution exists. One can use sprintf():
char s[SOME_CONST];
int i = 10;
float f = 10.20;
sprintf ( s, “%d %f\n”, i, f );
21. Why
does malloc(0) return valid memory address ? What's the use?
malloc(0) does not return a non-NULL under
every implementation. An implementation is free to behave in a manner it finds
suitable, if the allocation size requested is zero. The implmentation may
choose any of the following actions:
* A null pointer is returned.
* The behavior is same as if a space of non-zero size was requested. In this
case, the usage of return value yields to undefined-behavior.
Notice, however, that if the implementation
returns a non-NULL value for a request of a zero-length space, a pointer
to object of ZERO length is returned! Think, how an object of zero
size should be represented
For implementations that return non-NULL
values, a typical usage is as follows:
void
func ( void )
{
int *p; /* p is a one-dimensional array, whose size will vary during
the the lifetime of the program */
size_t c;
p = malloc(0); /* initial allocation */
if (!p)
{
perror (”FAILURE” );
return;
}
/* … */
while (1)
{
c = (size_t) … ; /* Calculate allocation size */
p = realloc ( p, c * sizeof *p );
/* use p, or break from the loop */
/* … */
}
return;
}
Notice that this program is not portable, since an implementation is free
to return NULL for a malloc(0) request, as the C Standard does not support
zero-sized objects.
22. Difference
between const char* p and char const* p
In const char* p, the character pointed by
‘p’ is constant, so u cant change the value of character pointed by p but u can
make ‘p’ refer to some other location.
In char const* p, the ptr ‘p’ is constant not
the character referenced by it, so u cant make ‘p’ to reference to any other
location but u can change the value of the char pointed by ‘p’.
23. What is the
result of using Option Explicit?
When writing your C program, you can include
files in two ways. The first way is to surround the file you want to
include with the angled brackets < and >. This method of inclusion
tells the preprocessor to look for the file in the predefined default
location. This predefined default location is often an INCLUDE environment
variable that denotes the path to your include files.
For instance, given the INCLUDE
variable
INCLUDE=C:\COMPILER\INCLUDE;S:\SOURCE\HEADERS; using the #include version
of file inclusion, the compiler first checks
the C:\COMPILER\INCLUDE directory for the specified file. If the file
is not found there, the compiler then checks the S:\SOURCE\HEADERS
directory. If the file is still not found, the preprocessor checks the current
directory.
The second way to include files is to
surround the file you want to include with double quotation marks. This method
of inclusion tells the preprocessor to look for the file in the current
directory first, then look for it in the predefined locations you have set up.
Using the #include file version of file inclusion and applying it to the
preceding example, the preprocessor first checks the current directory for the
specified file. If the file is not found in the current directory, the
C:COMPILERINCLUDE directory is searched. If the file is still not found, the
preprocessor checks the S:SOURCEHEADERS directory.
The #include method of file inclusion is
often used to include standard headers such as stdio.h or stdlib.h.
The #include file include nonstandard header
files that you have created for use in your program. This is because these
headers are often modified in the current directory, and you will want the
preprocessor to use your newly modified version of the header rather than the
older, unmodified version.
24. What is the
benefit of using an enum rather than a #define constant?
The use of an enumeration constant (enum) has
many advantages over using the traditional symbolic constant style of #define.
These advantages include a lower maintenance requirement, improved program
readability, and better debugging capability.
1) The first advantage is that enumerated constants are generated automatically
by the compiler. Conversely, symbolic constants must be manually assigned
values by the programmer.
2) Another advantage of using the enumeration constant method is that your
programs are more readable and thus can be understood better by others who
might have to update your program later.
3) A third advantage to using enumeration
constants is that some symbolic debuggers can print the value of an enumeration
constant. Conversely, most symbolic debuggers cannot print the value of a
symbolic constant. This can be an enormous help in debugging your program,
because if your program is stopped at a line that uses an enum, you can simply
inspect that constant and instantly know its value. On the other hand, because
most debuggers cannot print #define values, you would most likely have to
search for that value by manually looking it up in a header file.
25. What is
the quickest sorting method to use?
The answer depends on what you mean by
quickest. For most sorting problems, it just doesn’t matter how quick the sort
is because it is done infrequently or other operations take significantly more
time anyway. There are three sorting methods in this author’s toolbox that are
all very fast and that are useful in different situations. Those methods are
quick sort, merge sort, and radix sort.
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