hey guys.... this would help...
What is C language?
Answers : The C programming language is a standardized programming language developed in the early 1970s by Ken Thompson and Dennis Ritchie for use on the UNIX operating system. It has since spread to many other operating systems, and is one of the most widely used programming languages. C is prized for its efficiency, and is the most popular programming language for writing system software, though it is also used for writing applications. ...
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(...).
What is the difference between "calloc(...)" and "malloc(...)"?
1. calloc(...) allocates a block of memory for an array of elements of a certain size. By default the block is initialized to 0. The total number of memory allocated will be (number_of_elements * size).
malloc(...) takes in only a single argument which is the memory required in bytes. malloc(...) allocated bytes of memory and not blocks of memory like calloc(...).
2. malloc(...) allocates memory blocks and returns a void pointer to the allocated space, or NULL if there is insufficient memory available.
calloc(...) allocates an array in memory with elements initialized to 0 and returns a pointer to the allocated space. calloc(...) calls malloc(...) in order to use the C++ _set_new_mode function to set the new handler mode.
What is the difference between "printf(...)" and "sprintf(...)"?
sprintf(...) writes data to the character array whereas printf(...) writes data to the standard output device.
How to reduce a final size of executable?Size of the final executable can be reduced using dynamic linking for libraries.
Linked Lists -- 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:
What is the output
of the following program? Why?
#include
main() {
typedef union {
int a;
char b[10];
float c;
}
Union;
Union x,y = {100};
x.a = 50;
strcpy(x.b,"hello");
x.c = 21.50;
printf("Union x : %d %s %f n",x.a,x.b,x.c);
printf("Union y : %d %s %f n",y.a,y.b,y.c);
}
String Processing --- Write out a function that prints out all the permutations of a string. For example, abc would give you abc, acb, bac, bca, cab, cba.
void PrintPermu (char *sBegin, char* sRest) {
int iLoop;
char cTmp;
char cFLetter[1];
char *sNewBegin;
char *sCur;
int iLen;
static int iCount;
iLen = strlen(sRest);
if (iLen == 2) {
iCount++;
printf("%d: %s%s\n",iCount,sBegin,sRest);
iCount++;
printf("%d: %s%c%c\n",iCount,sBegin,sRest[1],sRest[0]);
return;
} else if (iLen == 1) {
iCount++;
printf("%d: %s%s\n", iCount, sBegin, sRest);
return;
} else {
// swap the first character of sRest with each of
// the remaining chars recursively call debug print
sCur = (char*)malloc(iLen);
sNewBegin = (char*)malloc(iLen);
for (iLoop = 0; iLoop < iLen; iLoop ++) {
strcpy(sCur, sRest);
strcpy(sNewBegin, sBegin);
cTmp = sCur[iLoop];
sCur[iLoop] = sCur[0];
sCur[0] = cTmp;
sprintf(cFLetter, "%c", sCur[0]);
strcat(sNewBegin, cFLetter);
debugprint(sNewBegin, sCur+1);
}
}
}
void main() {
char s[255];
char sIn[255];
printf("\nEnter a string:");
scanf("%s%*c",sIn);
memset(s,0,255);
PrintPermu(s, sIn);
}
What is C language?
Answers : The C programming language is a standardized programming language developed in the early 1970s by Ken Thompson and Dennis Ritchie for use on the UNIX operating system. It has since spread to many other operating systems, and is one of the most widely used programming languages. C is prized for its efficiency, and is the most popular programming language for writing system software, though it is also used for writing applications. ...
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(...).
What is the difference between "calloc(...)" and "malloc(...)"?
1. calloc(...) allocates a block of memory for an array of elements of a certain size. By default the block is initialized to 0. The total number of memory allocated will be (number_of_elements * size).
malloc(...) takes in only a single argument which is the memory required in bytes. malloc(...) allocated bytes of memory and not blocks of memory like calloc(...).
2. malloc(...) allocates memory blocks and returns a void pointer to the allocated space, or NULL if there is insufficient memory available.
calloc(...) allocates an array in memory with elements initialized to 0 and returns a pointer to the allocated space. calloc(...) calls malloc(...) in order to use the C++ _set_new_mode function to set the new handler mode.
What is the difference between "printf(...)" and "sprintf(...)"?
sprintf(...) writes data to the character array whereas printf(...) writes data to the standard output device.
How to reduce a final size of executable?Size of the final executable can be reduced using dynamic linking for libraries.
Linked Lists -- 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)
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.
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.
#include
main() {
typedef union {
int a;
char b[10];
float c;
}
Union;
Union x,y = {100};
x.a = 50;
strcpy(x.b,"hello");
x.c = 21.50;
printf("Union x : %d %s %f n",x.a,x.b,x.c);
printf("Union y : %d %s %f n",y.a,y.b,y.c);
}
String Processing --- Write out a function that prints out all the permutations of a string. For example, abc would give you abc, acb, bac, bca, cab, cba.
void PrintPermu (char *sBegin, char* sRest) {
int iLoop;
char cTmp;
char cFLetter[1];
char *sNewBegin;
char *sCur;
int iLen;
static int iCount;
iLen = strlen(sRest);
if (iLen == 2) {
iCount++;
printf("%d: %s%s\n",iCount,sBegin,sRest);
iCount++;
printf("%d: %s%c%c\n",iCount,sBegin,sRest[1],sRest[0]);
return;
} else if (iLen == 1) {
iCount++;
printf("%d: %s%s\n", iCount, sBegin, sRest);
return;
} else {
// swap the first character of sRest with each of
// the remaining chars recursively call debug print
sCur = (char*)malloc(iLen);
sNewBegin = (char*)malloc(iLen);
for (iLoop = 0; iLoop < iLen; iLoop ++) {
strcpy(sCur, sRest);
strcpy(sNewBegin, sBegin);
cTmp = sCur[iLoop];
sCur[iLoop] = sCur[0];
sCur[0] = cTmp;
sprintf(cFLetter, "%c", sCur[0]);
strcat(sNewBegin, cFLetter);
debugprint(sNewBegin, sCur+1);
}
}
}
void main() {
char s[255];
char sIn[255];
printf("\nEnter a string:");
scanf("%s%*c",sIn);
memset(s,0,255);
PrintPermu(s, sIn);
}
What will print out?
main()
{
char *p1=“name”;
char *p2;
p2=(char*)malloc(20);
memset (p2, 0, 20);
while(*p2++ = *p1++);
printf(“%s\n”,p2);
}
The pointer p2 value is also increasing with p1 .
*p2++ = *p1++ means copy value of *p1 to *p2 , then increment both addresses (p1,p2) by one , so that they can point to next address . So when the loop exits (ie when address p1 reaches next character to “name” ie null) p2 address also points to next location to “name” . When we try to print string with p2 as starting address , it will try to print string from location after “name” … hence it is null string ….
e.g. :
initially p1 = 2000 (address) , p2 = 3000
*p1 has value “n” ..after 4 increments , loop exits … at that time p1 value will be 2004 , p2 =3004 … the actual result is stored in 3000 - n , 3001 - a , 3002 - m , 3003 -e … we r trying to print from 3004 …. where no data is present … that's why its printing null .
Answer: empty string.
main()
{
char *p1=“name”;
char *p2;
p2=(char*)malloc(20);
memset (p2, 0, 20);
while(*p2++ = *p1++);
printf(“%s\n”,p2);
}
The pointer p2 value is also increasing with p1 .
*p2++ = *p1++ means copy value of *p1 to *p2 , then increment both addresses (p1,p2) by one , so that they can point to next address . So when the loop exits (ie when address p1 reaches next character to “name” ie null) p2 address also points to next location to “name” . When we try to print string with p2 as starting address , it will try to print string from location after “name” … hence it is null string ….
e.g. :
initially p1 = 2000 (address) , p2 = 3000
*p1 has value “n” ..after 4 increments , loop exits … at that time p1 value will be 2004 , p2 =3004 … the actual result is stored in 3000 - n , 3001 - a , 3002 - m , 3003 -e … we r trying to print from 3004 …. where no data is present … that's why its printing null .
Answer: empty string.
What
will be printed as the result of the operation below:
main()
{
int x=20,y=35;
x=y++ + x++;
y= ++y + ++x;
printf(“%d%d\n”,x,y)
;
}
Answer : 5794
main()
{
int x=20,y=35;
x=y++ + x++;
y= ++y + ++x;
printf(“%d%d\n”,x,y)
;
}
Answer : 5794
What will be printed as the result of the operation below:
main()
{
int x=5;
printf(“%d,%d,%d\n”,x,x<<2,>>2)
;
}
Answer: 5,20,1
main()
{
int x=5;
printf(“%d,%d,%d\n”,x,x<<2,>>2)
;
}
Answer: 5,20,1
What
will be printed as the result of the operation below:
#define
swap(a,b) a=a+b;b=a-b;a=a-b;
void main()
{
int x=5, y=10;
swap (x,y);
printf(“%d %d\n”,x,y)
; swap2(x,y);
printf(“%d %d\n”,x,y)
; }
int swap2(int a, int b)
{
int temp;
temp=a;
b=a;
a=temp;
return 0;
}
as x = 5 = 0×0000,0101; so x << 2 -< 0×0001,0100 = 20; x >7gt; 2 -> 0×0000,0001 = 1. Therefore, the answer is 5, 20 , 1
the correct answer is
10, 5
5, 10
Answer: 10, 5
void main()
{
int x=5, y=10;
swap (x,y);
printf(“%d %d\n”,x,y)
; swap2(x,y);
printf(“%d %d\n”,x,y)
; }
int swap2(int a, int b)
{
int temp;
temp=a;
b=a;
a=temp;
return 0;
}
as x = 5 = 0×0000,0101; so x << 2 -< 0×0001,0100 = 20; x >7gt; 2 -> 0×0000,0001 = 1. Therefore, the answer is 5, 20 , 1
the correct answer is
10, 5
5, 10
Answer: 10, 5
What
will be printed as the result of the operation below:
main()
{
char *ptr = ” Tech Preparation”;
*ptr++; printf(“%s\n”,ptr)
; ptr++;
printf(“%s\n”,ptr);
}
1) ptr++ increments the ptr address to point to the next address. In the previous example, ptr was pointing to the space in the string before C, now it will point to C.
2)*ptr++ gets the value at ptr++, the ptr is indirectly forwarded by one in this case.
3)(*ptr)++ actually increments the value in the ptr location. If *ptr contains a space, then (*ptr)++ will now contain an exclamation mark.
Answer: Tech Preparation
main()
{
char *ptr = ” Tech Preparation”;
*ptr++; printf(“%s\n”,ptr)
; ptr++;
printf(“%s\n”,ptr);
}
1) ptr++ increments the ptr address to point to the next address. In the previous example, ptr was pointing to the space in the string before C, now it will point to C.
2)*ptr++ gets the value at ptr++, the ptr is indirectly forwarded by one in this case.
3)(*ptr)++ actually increments the value in the ptr location. If *ptr contains a space, then (*ptr)++ will now contain an exclamation mark.
Answer: Tech Preparation
What
will be printed as the result of the operation below:
main()
{
char s1[]=“Tech”;
char s2[]= “preparation”;
printf(“%s”,s1)
; }
Answer: Tech
main()
{
char s1[]=“Tech”;
char s2[]= “preparation”;
printf(“%s”,s1)
; }
Answer: Tech
What
will be printed as the result of the operation below:
main()
{
char *p1;
char *p2;
p1=(char *)malloc(25);
p2=(char *)malloc(25);
strcpy(p1,”Tech”);
strcpy(p2,“preparation”);
strcat(p1,p2);
printf(“%s”,p1)
;
}
Answer: Techpreparation
main()
{
char *p1;
char *p2;
p1=(char *)malloc(25);
p2=(char *)malloc(25);
strcpy(p1,”Tech”);
strcpy(p2,“preparation”);
strcat(p1,p2);
printf(“%s”,p1)
;
}
Answer: Techpreparation
The
following variable is available in file1.c, who can access it?: static int
average; Answer: all the functions in the file1.c can access the variable.
What
will be the result of the following code?
#define TRUE 0 // some code while(TRUE) { // some code }
This will not go into the loop as TRUE is defined as 0.
#define TRUE 0 // some code while(TRUE) { // some code }
This will not go into the loop as TRUE is defined as 0.
What
will be printed as the result of the operation below:
int x;
int modifyvalue()
{
return(x+=10);
}
int changevalue(int x)
{
return(x+=1);
}
void main()
{
int x=10;
x++;
changevalue(x);
x++;
modifyvalue();
printf("First output:%d\n",x);
x++;
changevalue(x);
printf("Second output:%d\n",x);
modifyvalue();
printf("Third output:%d\n",x);
}
Answer: 12 , 13 , 13
int x;
int modifyvalue()
{
return(x+=10);
}
int changevalue(int x)
{
return(x+=1);
}
void main()
{
int x=10;
x++;
changevalue(x);
x++;
modifyvalue();
printf("First output:%d\n",x);
x++;
changevalue(x);
printf("Second output:%d\n",x);
modifyvalue();
printf("Third output:%d\n",x);
}
Answer: 12 , 13 , 13
What
will be printed as the result of the operation below:
main()
{
int x=10, y=15;
x = x++;
y = ++y;
printf(“%d %d\n”,x,y);
}
Answer: 11, 16
main()
{
int x=10, y=15;
x = x++;
y = ++y;
printf(“%d %d\n”,x,y);
}
Answer: 11, 16
What
will be printed as the result of the operation below:
main()
{
int a=0;
if(a==0)
printf(“Tech Preparation\n”);
printf(“Tech Preparation\n”);
}
Answer: Two lines with “Tech Preparation” will be printed.
main()
{
int a=0;
if(a==0)
printf(“Tech Preparation\n”);
printf(“Tech Preparation\n”);
}
Answer: Two lines with “Tech Preparation” will be printed.
What
will the following piece of code do
int f(unsigned int x)
{
int i;
for (i=0; x!0; x>>=1){
if (x & 0X1)
i++;
}
return i;
}
Answer: returns the number of ones in the input parameter X
int f(unsigned int x)
{
int i;
for (i=0; x!0; x>>=1){
if (x & 0X1)
i++;
}
return i;
}
Answer: returns the number of ones in the input parameter X
What will happen in these three cases?
if(a=0){
//somecode
}
if (a==0){
//do something
}
if (a===0){
//do something
}
if(a=0){
//somecode
}
if (a==0){
//do something
}
if (a===0){
//do something
}
What
are x, y, y, u
#define Atype int*
typedef int *p;
p x, z;
Atype y, u;
Answer: x and z are pointers to int. y is a pointer to int but u is just an integer variable
#define Atype int*
typedef int *p;
p x, z;
Atype y, u;
Answer: x and z are pointers to int. y is a pointer to int but u is just an integer variable
What does static variable mean?
there are 3 main uses for the static.
1. If you declare within a function:
It retains the value between function calls
2.If it is declared for a function name:
By default function is extern..so it will be visible from other files if the function declaration is as static..it is invisible for the outer files
3. Static for global variables:
By default we can use the global variables from outside files If it is static global..that variable is limited to with in the file
there are 3 main uses for the static.
1. If you declare within a function:
It retains the value between function calls
2.If it is declared for a function name:
By default function is extern..so it will be visible from other files if the function declaration is as static..it is invisible for the outer files
3. Static for global variables:
By default we can use the global variables from outside files If it is static global..that variable is limited to with in the file
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))
Macros are a necessary evils of life. The purists don’t like them, but without it no real work gets done.
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))
Macros are a necessary evils of life. The purists don’t like them, but without it no real work gets done.
What are the differences between malloc() and calloc()?
There are 2 differences.
First, is in the number of arguments. malloc() takes a single argument(memory required in bytes), while calloc() needs 2 arguments(number of variables to allocate memory, size in bytes of a single variable).
Secondly, malloc() does not initialize the memory allocated, while calloc() initializes the allocated memory to ZERO.
There are 2 differences.
First, is in the number of arguments. malloc() takes a single argument(memory required in bytes), while calloc() needs 2 arguments(number of variables to allocate memory, size in bytes of a single variable).
Secondly, malloc() does not initialize the memory allocated, while calloc() initializes the allocated memory to ZERO.
What are the different storage classes in C?
C has three types of storage: automatic, static and allocated.
Variable having block scope and without static specifier have automatic storage duration.
Variables with block scope, and with static specifier have static scope. Global variables (i.e, file scope) with or without the the static specifier also have static scope.
Memory obtained from calls to malloc(), alloc() or realloc() belongs to allocated storage class.
C has three types of storage: automatic, static and allocated.
Variable having block scope and without static specifier have automatic storage duration.
Variables with block scope, and with static specifier have static scope. Global variables (i.e, file scope) with or without the the static specifier also have static scope.
Memory obtained from calls to malloc(), alloc() or realloc() belongs to allocated storage class.
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. For example, in the following declarations:
char *s1 = “Calvin and Hobbes”;
char *s2 = “Calvin and Hobbes”;
the strings pointed by s1 and s2 may reside in the same memory location. But, it is not true for the following:
char ca1[] = “Calvin and Hobbes”;
char ca2[] = “Calvin and Hobbes”;
[1] The value of a string is the sequence of the values of the contained characters, in order.
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. For example, in the following declarations:
char *s1 = “Calvin and Hobbes”;
char *s2 = “Calvin and Hobbes”;
the strings pointed by s1 and s2 may reside in the same memory location. But, it is not true for the following:
char ca1[] = “Calvin and Hobbes”;
char ca2[] = “Calvin and Hobbes”;
[1] The value of a string is the sequence of the values of the contained characters, in order.
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)
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)
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” );
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” );
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;
The bitwise AND operator, again. In the following code snippet, the bit number 24 is reset to zero.
some_int = some_int & ~KBit24;
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;
The bitwise OR operator. In the following code snippet, the bit number 24 is turned ON:
some_int = some_int | KBit24;
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 );
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 );
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.
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.
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’.
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’.
How
can method defined in multiple base classes with same name can be invoked from
derived class simultaneously
ex:
class x
{
public:
m1();
};
class y
{
public:
m1();
};
class z :public x, public y
{
public:
m1()
{
x::m1();
y::m1();
}
};
ex:
class x
{
public:
m1();
};
class y
{
public:
m1();
};
class z :public x, public y
{
public:
m1()
{
x::m1();
y::m1();
}
};
Write a program to interchange 2 variables without using the
third one.
a=7;
b=2;
a = a + b;
b = a - b;
a = a - b;
a=7;
b=2;
a = a + b;
b = a - b;
a = a - b;
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.
This is because these headers are rarely (if ever) modified, and they should always be read from your compiler’s standard include file directory.
The #include file method of file inclusion is often used to 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.
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.
This is because these headers are rarely (if ever) modified, and they should always be read from your compiler’s standard include file directory.
The #include file method of file inclusion is often used to 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.
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.
For instance, if you had an enumerated constant type for error codes that could occur in your program, your enum definition could look something like this:
enum Error_Code
{
OUT_OF_MEMORY,
INSUFFICIENT_DISK_SPACE,
LOGIC_ERROR,
FILE_NOT_FOUND
};
In the preceding example, OUT_OF_MEMORY is automatically assigned the value of 0 (zero) by the compiler because it appears first in the definition. The compiler then continues to automatically assign numbers to the enumerated constants, making INSUFFICIENT_DISK_SPACE equal to 1, LOGIC_ERROR equal to 2, and FILE_NOT_FOUND equal to 3, so on.
If you were to approach the same example by using symbolic constants, your code would look something like this:
#define OUT_OF_MEMORY 0
#define INSUFFICIENT_DISK_SPACE 1
#define LOGIC_ERROR 2
#define FILE_NOT_FOUND 3
values by the programmer. Each of the two methods arrives at the same result: four constants assigned numeric values to represent error codes. Consider the maintenance required, however, if you were to add two constants to represent the error codes DRIVE_NOT_READY and CORRUPT_FILE. Using the enumeration constant method, you simply would put these two constants anywhere in the enum definition. The compiler would generate two unique values for these constants. Using the symbolic constant method, you would have to manually assign two new numbers to these constants. Additionally, you would want to ensure that the numbers you assign to these constants are unique.
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.
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.
For instance, if you had an enumerated constant type for error codes that could occur in your program, your enum definition could look something like this:
enum Error_Code
{
OUT_OF_MEMORY,
INSUFFICIENT_DISK_SPACE,
LOGIC_ERROR,
FILE_NOT_FOUND
};
In the preceding example, OUT_OF_MEMORY is automatically assigned the value of 0 (zero) by the compiler because it appears first in the definition. The compiler then continues to automatically assign numbers to the enumerated constants, making INSUFFICIENT_DISK_SPACE equal to 1, LOGIC_ERROR equal to 2, and FILE_NOT_FOUND equal to 3, so on.
If you were to approach the same example by using symbolic constants, your code would look something like this:
#define OUT_OF_MEMORY 0
#define INSUFFICIENT_DISK_SPACE 1
#define LOGIC_ERROR 2
#define FILE_NOT_FOUND 3
values by the programmer. Each of the two methods arrives at the same result: four constants assigned numeric values to represent error codes. Consider the maintenance required, however, if you were to add two constants to represent the error codes DRIVE_NOT_READY and CORRUPT_FILE. Using the enumeration constant method, you simply would put these two constants anywhere in the enum definition. The compiler would generate two unique values for these constants. Using the symbolic constant method, you would have to manually assign two new numbers to these constants. Additionally, you would want to ensure that the numbers you assign to these constants are unique.
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.
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. Even in cases in which
sorting speed is of the essence, there is no one answer. It depends on not only
the size and nature of the data, but also the likely order. No algorithm is
best in all cases.
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.
The Quick Sort
The quick sort algorithm is of the divide and conquer type. That means it works by reducing a sorting problem into several easier sorting problems and solving each of them. A dividing value is chosen from the input data, and the data is partitioned into three sets: elements that belong before the dividing value, the value itself, and elements that come after the dividing value. The partitioning is performed by exchanging elements that are in the first set but belong in the third with elements that are in the third set but belong in the first Elements that are equal to the dividing element can be put in any of the three setsthe algorithm will still work properly.
The Merge Sort
The merge sort is a divide and conquer sort as well. It works by considering the data to be sorted as a sequence of already-sorted lists (in the worst case, each list is one element long). Adjacent sorted lists are merged into larger sorted lists until there is a single sorted list containing all the elements. The merge sort is good at sorting lists and other data structures that are not in arrays, and it can be used to sort things that don’t fit into memory. It also can be implemented as a stable sort.
The Radix Sort
The radix sort takes a list of integers and puts each element on a smaller list, depending on the value of its least significant byte. Then the small lists are concatenated, and the process is repeated for each more significant byte until the list is sorted. The radix sort is simpler to implement on fixed-length data such as ints.
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.
The Quick Sort
The quick sort algorithm is of the divide and conquer type. That means it works by reducing a sorting problem into several easier sorting problems and solving each of them. A dividing value is chosen from the input data, and the data is partitioned into three sets: elements that belong before the dividing value, the value itself, and elements that come after the dividing value. The partitioning is performed by exchanging elements that are in the first set but belong in the third with elements that are in the third set but belong in the first Elements that are equal to the dividing element can be put in any of the three setsthe algorithm will still work properly.
The Merge Sort
The merge sort is a divide and conquer sort as well. It works by considering the data to be sorted as a sequence of already-sorted lists (in the worst case, each list is one element long). Adjacent sorted lists are merged into larger sorted lists until there is a single sorted list containing all the elements. The merge sort is good at sorting lists and other data structures that are not in arrays, and it can be used to sort things that don’t fit into memory. It also can be implemented as a stable sort.
The Radix Sort
The radix sort takes a list of integers and puts each element on a smaller list, depending on the value of its least significant byte. Then the small lists are concatenated, and the process is repeated for each more significant byte until the list is sorted. The radix sort is simpler to implement on fixed-length data such as ints.
when should the volatile modifier be used?
The volatile modifier is a directive to the compiler’s optimizer that operations involving this variable should not be optimized in certain ways. There are two special cases in which use of the volatile modifier is desirable. The first case involves memory-mapped hardware (a device such as a graphics adaptor that appears to the computer’s hardware as if it were part of the computer’s memory), and the second involves shared memory (memory used by two or more programs running simultaneously).
Most computers have a set of registers that can be accessed faster than the computer’s main memory. A good compiler will perform a kind of optimization called redundant load and store removal. The compiler looks for places in the code where it can either remove an instruction to load data from memory because the value is already in a register, or remove an instruction to store data to memory because the value can stay in a register until it is changed again anyway.
If a variable is a pointer to something other than normal memory, such as memory-mapped ports on a peripheral, redundant load and store optimizations might be detrimental. For instance, here’s a piece of code that might be used to time some operation:
time_t time_addition(volatile const struct timer *t, int a)
{
int n;
int x;
time_t then;
x = 0;
then = t->value;
for (n = 0; n < 1000; n++)
{
x = x + a;
}
return t->value - then;
}
In this code, the variable t-> value is actually a hardware counter that is being incremented as time passes. The function adds the value of a to x 1000 times, and it returns the amount the timer was incremented by while the 1000 additions were being performed. Without the volatile modifier, a clever optimizer might assume that the value of t does not change during the execution of the function, because there is no statement that explicitly changes it. In that case, there’s no need to read it from memory a second time and subtract it, because the answer will always be 0. The compiler might therefore optimize the function by making it always return 0.
If a variable points to data in shared memory, you also don’t want the compiler to perform redundant load and store optimizations. Shared memory is normally used to enable two programs to communicate with each other by having one program store data in the shared portion of memory and the other program read the same portion of memory. If the compiler optimizes away a load or store of shared memory, communication between the two programs will be affected.
The volatile modifier is a directive to the compiler’s optimizer that operations involving this variable should not be optimized in certain ways. There are two special cases in which use of the volatile modifier is desirable. The first case involves memory-mapped hardware (a device such as a graphics adaptor that appears to the computer’s hardware as if it were part of the computer’s memory), and the second involves shared memory (memory used by two or more programs running simultaneously).
Most computers have a set of registers that can be accessed faster than the computer’s main memory. A good compiler will perform a kind of optimization called redundant load and store removal. The compiler looks for places in the code where it can either remove an instruction to load data from memory because the value is already in a register, or remove an instruction to store data to memory because the value can stay in a register until it is changed again anyway.
If a variable is a pointer to something other than normal memory, such as memory-mapped ports on a peripheral, redundant load and store optimizations might be detrimental. For instance, here’s a piece of code that might be used to time some operation:
time_t time_addition(volatile const struct timer *t, int a)
{
int n;
int x;
time_t then;
x = 0;
then = t->value;
for (n = 0; n < 1000; n++)
{
x = x + a;
}
return t->value - then;
}
In this code, the variable t-> value is actually a hardware counter that is being incremented as time passes. The function adds the value of a to x 1000 times, and it returns the amount the timer was incremented by while the 1000 additions were being performed. Without the volatile modifier, a clever optimizer might assume that the value of t does not change during the execution of the function, because there is no statement that explicitly changes it. In that case, there’s no need to read it from memory a second time and subtract it, because the answer will always be 0. The compiler might therefore optimize the function by making it always return 0.
If a variable points to data in shared memory, you also don’t want the compiler to perform redundant load and store optimizations. Shared memory is normally used to enable two programs to communicate with each other by having one program store data in the shared portion of memory and the other program read the same portion of memory. If the compiler optimizes away a load or store of shared memory, communication between the two programs will be affected.
How can you determine the size of an allocated portion of
memory?
You can’t, really. free() can , but there’s no way for your program to
know the trick free() uses. Even if you disassemble the library and discover
the trick, there’s no guarantee the trick won’t change with the next release of
the compiler.
Can static variables be declared in a header file?
You can’t declare a static variable without defining it as well (this is because the storage class modifiers static and extern are mutually exclusive). A static variable can be defined in a header file, but this would cause each source file that included the header file to have its own private copy of the variable, which is probably not what was intended.
You can’t declare a static variable without defining it as well (this is because the storage class modifiers static and extern are mutually exclusive). A static variable can be defined in a header file, but this would cause each source file that included the header file to have its own private copy of the variable, which is probably not what was intended.
How do you override a defined macro?
You can use the #undef preprocessor directive to undefine (override) a
previously defined macro.
How can you check to see whether a symbol is defined?
You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef).
Can you define which header file to include at compile time? Yes. This can be done by using the #if, #else, and #endif preprocessor directives. For example, certain compilers use different names for header files. One such case is between Borland C++, which uses the header file alloc.h, and Microsoft C++, which uses the header file malloc.h. Both of these headers serve the same purpose, and each contains roughly the same definitions. If, however, you are writing a program that is to support Borland C++ and Microsoft C++, you must define which header to include at compile time. The following example shows how this can be done:
#ifdef _ _BORLANDC_ _
#include
#else
#include
#endif
You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef).
Can you define which header file to include at compile time? Yes. This can be done by using the #if, #else, and #endif preprocessor directives. For example, certain compilers use different names for header files. One such case is between Borland C++, which uses the header file alloc.h, and Microsoft C++, which uses the header file malloc.h. Both of these headers serve the same purpose, and each contains roughly the same definitions. If, however, you are writing a program that is to support Borland C++ and Microsoft C++, you must define which header to include at compile time. The following example shows how this can be done:
#ifdef _ _BORLANDC_ _
#include
#else
#include
#endif
Can a variable be both const and volatile?
Yes. The const modifier means that this code cannot change the value of the variable, but that does not mean that the value cannot be changed by means outside this code. For instance, in the example in FAQ 8, the timer structure was accessed through a volatile const pointer. The function itself did not change the value of the timer, so it was declared const. However, the value was changed by hardware on the computer, so it was declared volatile. If a variable is both const and volatile, the two modifiers can appear in either order.
Yes. The const modifier means that this code cannot change the value of the variable, but that does not mean that the value cannot be changed by means outside this code. For instance, in the example in FAQ 8, the timer structure was accessed through a volatile const pointer. The function itself did not change the value of the timer, so it was declared const. However, the value was changed by hardware on the computer, so it was declared volatile. If a variable is both const and volatile, the two modifiers can appear in either order.
Can include files be nested?
Answer Yes. Include files can be nested any number of times. As long as you use precautionary measures , you can avoid including the same file twice. In the past, nesting header files was seen as bad programming practice, because it complicates the dependency tracking function of the MAKE program and thus slows down compilation. Many of today’s popular compilers make up for this difficulty by implementing a concept called precompiled headers, in which all headers and associated dependencies are stored in a precompiled state.
Many programmers like to create a custom header file that has #include statements for every header needed for each module. This is perfectly acceptable and can help avoid potential problems relating to #include files, such as accidentally omitting an #include file in a module.
Answer Yes. Include files can be nested any number of times. As long as you use precautionary measures , you can avoid including the same file twice. In the past, nesting header files was seen as bad programming practice, because it complicates the dependency tracking function of the MAKE program and thus slows down compilation. Many of today’s popular compilers make up for this difficulty by implementing a concept called precompiled headers, in which all headers and associated dependencies are stored in a precompiled state.
Many programmers like to create a custom header file that has #include statements for every header needed for each module. This is perfectly acceptable and can help avoid potential problems relating to #include files, such as accidentally omitting an #include file in a module.
Write the equivalent expression for x%8?
x&7
x&7
When does the compiler not implicitly generate the address
of the first element of an array?
Whenever an array name appears in an expression such as
- array as an operand of the sizeof operator
- array as an operand of & operator
- array as a string literal initializer for a character array
Then the compiler does not implicitly generate the address of the address of the first element of an array.
Whenever an array name appears in an expression such as
- array as an operand of the sizeof operator
- array as an operand of & operator
- array as a string literal initializer for a character array
Then the compiler does not implicitly generate the address of the address of the first element of an array.
What is the benefit of using #define to declare a constant?
Using the #define method of declaring a constant enables you to declare a constant in one place and use it throughout your program. This helps make your programs more maintainable, because you need to maintain only the #define statement and not several instances of individual constants throughout your program.
For instance, if your program used the value of pi (approximately 3.14159) several times, you might want to declare a constant for pi as follows:
#define PI 3.14159
Using the #define method of declaring a constant is probably the most familiar way of declaring constants to traditional C programmers. Besides being the most common method of declaring constants, it also takes up the least memory. Constants defined in this manner are simply placed directly into your source code, with no variable space allocated in memory. Unfortunately, this is one reason why most debuggers cannot inspect constants created using the #define method.
Using the #define method of declaring a constant enables you to declare a constant in one place and use it throughout your program. This helps make your programs more maintainable, because you need to maintain only the #define statement and not several instances of individual constants throughout your program.
For instance, if your program used the value of pi (approximately 3.14159) several times, you might want to declare a constant for pi as follows:
#define PI 3.14159
Using the #define method of declaring a constant is probably the most familiar way of declaring constants to traditional C programmers. Besides being the most common method of declaring constants, it also takes up the least memory. Constants defined in this manner are simply placed directly into your source code, with no variable space allocated in memory. Unfortunately, this is one reason why most debuggers cannot inspect constants created using the #define method.
How can I search for data in a linked list?
Unfortunately, the only way to search a linked list is with a linear search, because the only way a linked list’s members can be accessed is sequentially. Sometimes it is quicker to take the data from a linked list and store it in a different data structure so that searches can be more efficient.
Unfortunately, the only way to search a linked list is with a linear search, because the only way a linked list’s members can be accessed is sequentially. Sometimes it is quicker to take the data from a linked list and store it in a different data structure so that searches can be more efficient.
Why should we assign NULL to the elements (pointer) after
freeing them?
This is paranoia based on long experience. After a pointer has been freed, you can no longer use the pointed-to data. The pointer is said to dangle; it doesn’t point at anything useful. If you NULL out or zero out a pointer immediately after freeing it, your program can no longer get in trouble by using that pointer. True, you might go indirect on the null pointer instead, but that’s something your debugger might be able to help you with immediately. Also, there still might be copies of the pointer that refer to the memory that has been deallocated; that’s the nature of C. Zeroing out pointers after freeing them won’t solve all problems;
This is paranoia based on long experience. After a pointer has been freed, you can no longer use the pointed-to data. The pointer is said to dangle; it doesn’t point at anything useful. If you NULL out or zero out a pointer immediately after freeing it, your program can no longer get in trouble by using that pointer. True, you might go indirect on the null pointer instead, but that’s something your debugger might be able to help you with immediately. Also, there still might be copies of the pointer that refer to the memory that has been deallocated; that’s the nature of C. Zeroing out pointers after freeing them won’t solve all problems;
When should a type cast be used?
There are two situations in which to use a type cast. The first use
is to change the type of an operand to an arithmetic operation so that the
operation will be performed properly.
The second case is to cast pointer types to and from void * in order to interface with functions that expect or return void pointers. For example, the following line type casts the return value of the call to malloc() to be a pointer to a foo structure.
struct foo *p = (struct foo *) malloc(sizeof(struct foo));
The second case is to cast pointer types to and from void * in order to interface with functions that expect or return void pointers. For example, the following line type casts the return value of the call to malloc() to be a pointer to a foo structure.
struct foo *p = (struct foo *) malloc(sizeof(struct foo));
What is a null pointer?
There are times when it’s necessary to have a pointer that doesn’t point to anything. The macro NULL, defined in , has a value that’s guaranteed to be different from any valid pointer. NULL is a literal zero, possibly cast to void* or char*. Some people, notably C++ programmers, prefer to use 0 rather than NULL.
The null pointer is used in three ways:
1) To stop indirection in a recursive data structure
2) As an error value
3) As a sentinel value
There are times when it’s necessary to have a pointer that doesn’t point to anything. The macro NULL, defined in , has a value that’s guaranteed to be different from any valid pointer. NULL is a literal zero, possibly cast to void* or char*. Some people, notably C++ programmers, prefer to use 0 rather than NULL.
The null pointer is used in three ways:
1) To stop indirection in a recursive data structure
2) As an error value
3) As a sentinel value
What is the difference between a string copy (strcpy) and a
memory copy (memcpy)? When should each be used?
The strcpy() function is designed to work exclusively with strings. It copies each byte of the source string to the destination string and stops when the terminating null character () has been moved. On the other hand, the memcpy() function is designed to work with any type of data. Because not all data ends with a null character, you must provide the memcpy() function with the number of bytes you want to copy from the source to the destination.
The strcpy() function is designed to work exclusively with strings. It copies each byte of the source string to the destination string and stops when the terminating null character () has been moved. On the other hand, the memcpy() function is designed to work with any type of data. Because not all data ends with a null character, you must provide the memcpy() function with the number of bytes you want to copy from the source to the destination.
No comments:
Post a Comment