i) Variables & Control Flow
1.What
is the difference between declaring a variable and defining a variable?
Declaration
of a variable in C hints the compiler about the type and size of the variable
in compile time. Similarly,
declaration of a function hints about type and size of function parameters. No space is reserved in memory for
any variable in case of declaration.
declaration of a function hints about type and size of function parameters. No space is reserved in memory for
any variable in case of declaration.
Example:
int
a;
Here variable 'a' is declared of data type 'int'
Defining a variable means declaring it and also allocating space to hold it.
We can say "Definition = Declaration + Space reservation".
Example:
int
a = 10;
Here variable "a" is described as an int to the compiler and memory is allocated to hold value 10.
2.What
is a static variable?
Static
variable is a special variable that is stored in the data segment unlike the
default automatic variable that
is
stored in stack. A static variable can be initialized by using keyword static
before variable name.
Example:
static
int a = 5;
A static variable behaves in a different manner depending upon whether it is a global variable or a local variable.
A static global variable is same as an ordinary global variable except that it cannot be accessed by other files in the same program / project even with the use of keyword extern. A static local variable is different from local variable. It is initialized only once no matter how many times that function in which it resides is called. It may be used as a count variable.
Example:
#include <stdio.h>
//program in file f1.c
void count(void) {
static int count1 = 0;
int count2 = 0;
count1++;
count2++;
printf("\nValue of count1 is %d, Value of count2 is %d", count1, count2);
}/
*Main function*/
int main(){
count();
count();
count();
return 0;
}
Output:
Value of count1 is 1, Value of count2 is 1
Value of count1 is 2, Value of count2 is 1
Value of count1 is 3, Value of count2 is 1
Value of count1 is 2, Value of count2 is 1
Value of count1 is 3, Value of count2 is 1
3.What
is a register variable?
Register
variables
are stored in the CPU registers. Its default value is a garbage value. Scope of
a register variable is local to the block in which it is defined. Lifetime is
till control remains within the block in which the register variable is
defined. Variable stored in a CPU register can always be accessed faster than
the one that is stored in memory. Therefore, if a variable is used at many
places in a program, it is better to declare its storage class as register
Example:
register int x=5;
Variables for loop counters can be declared as register. Note that register keyword may be ignored by some compilers.
4.Where
is an auto variables stored?
Main
memory and CPU registers are the two memory locations where auto variables are
stored. Auto variables are defined under automatic storage class. They are
stored in main memory. Memory is allocated to an automatic variable when the
block which contains it is called and it is de-allocated at the completion of
its block execution.
Auto
variables:
Storage
:
main memory.
Default
value :
garbage value.
Scope
:
local to the block in which the variable is defined.
Lifetime
:
till the control remains within the block in which the variable is defined.
5.What
is scope & storage allocation of extern and global variables?
Extern
variables:
Extern
variables belong to the External storage class and are stored in the
main memory. extern is used when we have to refer a function or variable that
is implemented in other file in the same project. The scope of the extern
variables is Global.
Example:
/***************
Index: f1.c
****************/
#include <stdio.h>
extern int x;
int main() {
printf("value of x %d", x);
return 0;
}
extern int x;
int main() {
printf("value of x %d", x);
return 0;
}
/***************
Index: f2.c
****************/
Index: f2.c
****************/
int x = 3;
Here, the program written in file f1.c has the main function and reference to variable x. The file f2.c has the declaration of variable x. The compiler should know the datatype of x and this is done by extern definition.
Global
variables:
Global
variables are variables which are
declared above the main( ) function. These variables are accessible throughout
the program. They can be accessed by all the functions in the program. Their
default value is zero.
Example:
#include <stdio.h>
int x = 0;
/* Variable x is a global variable.
It can be accessed throughout the program */
void increment(void) {
x = x + 1;
printf("\n value of x: %d", x);
}
int main()
{
printf("\n value of x: %d", x);
increment();
return 0;
}
printf("\n value of x: %d", x);
increment();
return 0;
}
6.What
is scope & storage allocation of register, static and local variables?
Register
variables:
Register variables belong to the
register storage class and are stored in the CPU registers. The scope of the
register variables is local to the block in which the variables are defined.
The variables which are used for more number of times in a program are declared
as register variables for faster access.
Example:
loop
counter variables.
register int y=6;
Static
variables:
Memory
is allocated at the beginning of the program execution and it is reallocated
only after the program terminates. The scope of the static variables is local
to the block in which the variables are defined.
Example:
#include <stdio.h>
void decrement()
void decrement()
{
static int a=5;
a--;
printf("Value of a:%d\n", a);
}
static int a=5;
a--;
printf("Value of a:%d\n", a);
}
int main()
{
decrement();
return 0;
}
decrement();
return 0;
}
Here 'a' is initialized only once. Every time this function is called, 'a' does not get initialized. so output would be 4 3 2 etc.,
Local variables:
Local
variables are variables which are
declared within any function or a block. They can be accessed only by function
or block in which they are declared. Their default value is a garbage value.
7.What
are storage memory, default value, scope and life of Automatic and Register
storage class?
1.
Automatic storage class :
Storage : main memory.
Default value : garbage value.
Scope : local to the block in which the variable is defined.
Lifetime : till control remains within the block.
Default value : garbage value.
Scope : local to the block in which the variable is defined.
Lifetime : till control remains within the block.
2.
Register storage class:
Storage : CPU
registers.
Default value : garbage value.
Scope : local to the block in which the variable is defined.
Lifetime : till control remains within the block.
Default value : garbage value.
Scope : local to the block in which the variable is defined.
Lifetime : till control remains within the block.
8.What
are storage memory, default value, scope and life of Static and External
storage class?
1.
Static storage class :
Storage : main
memory.
Default value : zero
Scope : local to the block in which the variable is defined.
Lifetime : till the value of the variable persists between different function calls.
Default value : zero
Scope : local to the block in which the variable is defined.
Lifetime : till the value of the variable persists between different function calls.
2.
External storage class :
Storage : main memory
Default value: zero
Scope : global
Lifetime : as long as the program execution doesn't come to an end.
Default value: zero
Scope : global
Lifetime : as long as the program execution doesn't come to an end.
9.What
is the difference between 'for' and 'while' loops?
For loop:
When
it is desired to do initialization, condition check and increment/decrement in
a single statement of an iterative loop, it is recommended to use 'for'
loop.
Syntax:
for(initialization;condition;increment/decrement)
{
/
/block of statements increment or decrement
}
Program: Program to illustrate for loop
#include<stdio.h>
int main()
{
int i;
for (i = 1; i <= 5; i++)
{
//print the number
printf("\n %d", i);
}
return 0;
}
Output: 12345
Explanation:
The loop repeats for 5 times and prints value of 'i' each time. 'i' increases by 1 for every cycle of loop.
While
loop:
When
it is not necessary to do initialization, condition check and
increment/decrement in a single statement of an iterative loop, while loop
could be used. In while loop statement, only condition statement
is present.
Syntax:
#include<stdio.h>
int main()
{
int i = 0, flag = 0;
int a[10] = { 0, 1, 4, 6, 89, 54, 78, 25, 635, 500 };
//This loop is repeated until the condition is false.
while (flag == 0)
{
if (a[i] == 54)
{
//as element is found, flag = 1, the loop terminates
flag = 1;
}
else
{
i++;
}
printf("Element found at %d th location", i);
return 0;
}
Output: Element found at 5th location
Explanation:
Here flag is initialized to zero. 'while' loop repeats until the value of flag is zero, increments i by 1. 'if' condition checks whether number 54 is found. If found, value of flag is set to 1 and 'while' loop terminates.
ii) Operators, Constants & Structures
1.Which
bitwise operator is suitable for checking whether a particular bit is ON or
OFF?
Bitwise AND operator:
Example:
Suppose
in byte that has a value 10101101 . We wish to check whether bit number 3 is ON
(1) or OFF (0) . Since we want to check the bit number 3, the second
operand for AND operation we choose is binary
00001000,
which is equal to 8 in decimal.
Explanation:
ANDing operation:
10101101 original bit pattern
00001000
AND mask
-----------
00001000
resulting bit pattern
-----------
The
resulting value we get in this case is 8, i.e. the value of the second operand.
The result turned out to be a 8 since the third bit of operand was ON. Had it
been OFF, the bit number 3 in the resulting bit pattern would have evaluated to
0 and complete bit pattern would have been 00000000. Thus depending upon the
bit number to be checked in the first operand we decide the second operand, and
on ANDing these two operands the result decides whether the bit was ON or
OFF.
2.Which
bitwise operator is suitable for turning OFF a particular bit in a
number?
Bitwise
AND operator (&), one's complement operator(~)
Example:
To
unset the 4th bit of byte_data or to turn off a particular bit in a number.
Explanation:
Consider,
char
byte_data= 0b00010111;
byte_data=
(byte_data)&(~(1<<4));
1
can be represented in binary as 0b00000001 = (1<<4)
<<
is a left bit shift operator,
it
shifts the bit 1 by 4 places towards left.
(1<<4)
becomes 0b00010000
And
~ is the one's complement operator in C language.
So
~(1<<4) = complement of 0b00010000
=
0b11101111
Replacing
value of byte_data and ~(1<<4) in
(byte_data)&(~(1<<4));
we
get (0b00010111) & (0b11101111)
Perform
AND operation to below bytes.
00010111
11101111
-----------
00000111
-----------
Thus
the 4th bit is unset.
3.What
is equivalent of multiplying an unsigned int by 2: left shift of number by 1 or
right shift of number by 1?
Left
shifting of an unsigned integer is equivalent to multiplying an unsigned int by
2.
Eg1: 14<<1;
Consider a number 14-----00001110 (8+4+2)is its binary equivalent
left
shift it by 1--------------00011100(16+8+4) which is 28.
Eg2: 1<<1;
consider the number as 1---00000001(0+0+1).
left
shift that by 1------------00000010(0+2+0) which is 2.
left
shift by 1 bit of a number=2*number
left
shift by 1 bit of 2*number=2*2*number
left
shift by n bits of number=(2^n)*number
Program: Program to illustrate left shift and right shift operations.
#include<stdio.h>
int main(void)
{
int x=10,y=10;
printf("left shift of 10 is %d \n",x<<1);
printf("right shift of 10 is %d \n",y>>1);
return 0;
}
Output:
left shift of 10 is 20
right shift of 10 is 5
Explanation:
Left
shift (by 1 position) multiplies a number by two. Right shift divides a number
by 2.
4.What
is an Enumeration Constant?
Enumeration
is a data type. We can create our own data type and define values that
the variable can take. This can help in making program more readable. enum
definition is similar to that of a structure.
Example:
consider
light_status as a data type. It can have two possible values - on or off.
enum light_status
{
on, off
};
enum light_status bulb1, bulb2;
/* bulb1, bulb2 are the variables */
Declaration of enum has two parts:
a) First part declares the data type and specifies the possible
values, called 'enumerators'.
b) Second part declares the variables of this data type.
We can give values to these variables:
bulb1 = on;
bulb2 = off;
A
structure is a collection of pre-defined data types to create a user-defined
data type. Let us say we need to create records of students. Each student has
three fields:
int roll_number;
char name[30];
int total_marks;
This concept would be particularly useful in grouping data types. You could declare a structure student as:
struct student
{
int roll_number;
char name[30];
int total_marks;
}
student1, student2;
The
above snippet of code would declare a structure by name student and it
initializes two objects student1, student2. Now these objects and their fields
could be accessed by saying student1.roll_number for accesing roll number field
of student1 object, similarly student2.name for accesing name field of student2
object.
6.What
are the differences between a structure and a union?
Structures
and Unions are used to store members of different data types.
STRUCTURE:
a)
Struct
{
Data
type member1;
Data
type member2;
};
b)
Every structure member is allocated
memory when a structure variable is defined.
Example:
memory when a structure variable is defined.
Example:
struct
emp {
char name[5];
int age;
float sal;
};
struct emp e1;
Memory allocated for structure is 1+2+4=7 bytes. 1byte for name, 2 bytes for age and 4 bytes for sal.
char name[5];
int age;
float sal;
};
struct emp e1;
Memory allocated for structure is 1+2+4=7 bytes. 1byte for name, 2 bytes for age and 4 bytes for sal.
c)
All structure variables can be initialized at a time
struct st {
int a;
float b;
};
struct st s = { .a=4, .b=10.5 };
Structure is used when all members are to be
independently used in a program.
struct st {
int a;
float b;
};
struct st s = { .a=4, .b=10.5 };
Structure is used when all members are to be
independently used in a program.
UNION:
a)
union
{
data
type member1;
data type member1;
};
b)
The memory equivalent to the largest item is allocated
commonly for all members.
Example:
commonly for all members.
Example:
Union
emp1
{
char name[5];
int age;
float sal;
};
union emp1 e2;
char name[5];
int age;
float sal;
};
union emp1 e2;
Memory allocated to a union is equal to size of the
largest member. In this case, float is the largest-sized
data type. Hence memory allocated to this union is 4
bytes.
c)
Only one union member can be initialized at a time
union un {
int a;
float b;
};
union un un1 = { .a=10 };
Union is used when members of it are not required to be
accessed at the same time.
union un {
int a;
float b;
};
union un un1 = { .a=10 };
Union is used when members of it are not required to be
accessed at the same time.
7.What are the advantages of unions?
Union is a collection of
data items of different data types. It can hold data of only one member at a
time though it has members of different data types. If a union has two members
of different data types, they are allocated the same memory. The memory
allocated is equal to maximum size of the members. The data is interpreted in
bytes depending on which member is being accessed.
Example:
union pen
{
char name;
float point;
};
Here name and point are union members. Out of these two variables, 'point' is larger variable which is of float data type and it would need 4 bytes of memory. Therefore 4 bytes space is allocated for both the variables. Both the variables have the same memory location. They are accessed according to their type. Union is efficient when members of it are not required to be accessed at the same time.
8.How
can typedef be to define a type of structure?
typedef
declaration
helps to make source code of a C program more readable. Its purpose is to
redefine the name of an existing variable type. It provides a short and
meaningful way to call a data type. typedef is useful when the name of the data
type is long. Use of typedef can reduce length and complexity of data types.
Note: Usually uppercase letters are used to make it clear that we are dealing with our own data type.
Example:
struct employee
{
char name[20];
int age;
};
struct employee e;
The above declaration of the structure would be easy to use when renamed using typedef as:
struct employee
{
char name[20];
int age;
};
typedef struct employee EMP;
EMP e1, e2;
A
function in C can return only one value. If we want the function to return
multiple values, we need to create a structure variable, which has three
integer members and return this structure.
Program: Program with a function to return 3 values
#include<stdio.h>
//sample structure which has three integer variables.
struct sample
{
int a, b, c;
};
//this is function which returns three values.
struct sample return3val()
{
struct sample s1;
s1.a = 10;
s1.b = 20;
s1.c = 30;
//return structure s1, which means return s1.a ,s1.b and s1.c
return s1;
}
int main()
{
struct sample accept3val;
//three values returned are accepted by structure accept3val.
accept3val = return3val();
//prints the values
printf(" \n %d", accept3val.a);
printf("\n %d", accept3val.b);
printf(" \n %d", accept3val.c);
return 0;
}
Output:
10
20
30.
Explanation:
In
this program, we use C structure to return multiple values from a function.
Here we have a structure holding three int variables and a function which
returns it. 'return3val' is a function which assigns 10, 20, 30 to its integer variables
and returns this structure. In this program, 'accept3val' is a structure used
to accept the values returned by the function. It accepts those values and
shows the output.
10.In
code snippet below: struct Date { int yr; int day; int month; } date1,date2;
date1.yr = 2004; date1.day = 4; date1.month = 12; Write a function that assigns
values to date2. Arguments to the function must be pointers to the structure,
Date and integer variables date, month, year?
Date
is a structure with three int variables as members. set_date(..) is a function
used to assign values to the structure variable.
Program: Program to illustrate a function that assigns value to the structure.
#include<stdio.h>
#include<stdlib.h>
//declare structure Date
struct Date
{
int yr;
int day;
int month;
}
int yr;
int day;
int month;
}
date1, date2;
//declare function to assign date to structure variable
void set_date(struct Date *dte, int dt, int mnt, int year)
//declare function to assign date to structure variable
void set_date(struct Date *dte, int dt, int mnt, int year)
{
dte->day = dt;
dte->yr = year;
dte->month = mnt;
}
int main(void)
dte->day = dt;
dte->yr = year;
dte->month = mnt;
}
int main(void)
{
date1.yr = 2004;
date1.day = 4;
//assigning values one by one
date1.month = 12;
//assigning values in a single statement
set_date(&date2, 05, 12, 2008);
//prints both dates in date/month/year format
printf("\n %d %d %d ", date1.day, date1.month, date1.yr);
printf("\n %d %d %d ", date2.day, date2.month, date2.yr);
return 0;
}
date1.yr = 2004;
date1.day = 4;
//assigning values one by one
date1.month = 12;
//assigning values in a single statement
set_date(&date2, 05, 12, 2008);
//prints both dates in date/month/year format
printf("\n %d %d %d ", date1.day, date1.month, date1.yr);
printf("\n %d %d %d ", date2.day, date2.month, date2.yr);
return 0;
}
Output:
4 12 2004
5 12 2008
5 12 2008
Explanation:
Two
variables of type Date are created and named 'date1', 'date2'. 'date2' is
assigned by using the function set_date(..). Address of 'date2' is passed to
set_date function.
iii) Functions
1.
What is the purpose of main() function?
In
C, program execution starts from the main() function. Every C program must
contain a main() function. The main function may contain any number of
statements. These statements are executed sequentially in the order which they
are written.
The main function can in-turn call other functions. When main calls a function, it passes the execution control to that function. The function returns control to main when a return statement is executed or when end of function is reached.
In C, the function prototype of the 'main' is one of the following:
int main(); //main with no arguments
int main(int argc, char *argv[]); //main with arguments
The parameters argc and argv respectively give the number and value of the program's command-line arguments.
Example:
#include<stdio.h>
/* program section begins here */
int main()
{
// opening brace - program execution starts here
printf("Welcome to the world of C");
return 0;
}
// closing brace - program terminates here
Output:
Welcome to the world of C
2.Explain command line arguments of
main function?
In
C, we can supply arguments to 'main' function. The arguments that we pass to
main ( ) at command prompt are called command line arguments. These arguments
are supplied at the time of invoking the program.
The main ( ) function can take arguments as: main(int argc, char *argv[]) { }
The
first argument argc is known as 'argument counter'. It represents the number of
arguments in the command line. The second argument argv is known as 'argument
vector'. It is an array of char type pointers that points to the command line
arguments. Size of this array will be equal to the value of argc.
Example: at the command prompt if we give:
C:\> fruit.exe apple mango
then
argc
would contain value 3
argv
[0] would contain base address of string " fruit.exe" which is the
command name that invokes the program.
argv
[1] would contain base address of string "apple"
argv
[2] would contain base address of string "mango"
here
apple and mango are the arguments passed to the program fruit.exe
Program:
#include<stdio.h>
int main(int argc, char *argv[])
{
int n;
printf("Following are the arguments entered in the command
line");
for (n = 0; n < argc; n++)
{
printf("\n %s", argv[n]);
}
printf("\n Number of arguments entered are\n %d\n",
argc);
return 0;
}
Output:
Following are the arguments entered in the command line
C:\testproject.exe
apple
mango
Number of arguments entered are 3
3.What are header files?Are functions
declared or defined in header files?
Functions
and macros are declared in header files. Header files would be included in
source files by the compiler at the time of compilation.
Header files are included in source code using #include directive. #include<some.h> includes all the declarations present in the header file 'some.h'.
Header files are included in source code using #include directive. #include<some.h> includes all the declarations present in the header file 'some.h'.
A header file may contain declarations of sub-routines, functions, macros and also variables which we may want to use in our program. Header files help in reduction of repetitive code.
Syntax of include directive:
#include<stdio.h> //includes the header file stdio.h, standard input output header into the source code Functions can be declared as well as defined in header files. But it is recommended only to declare functions and not to define in the header files. When we include a header file in our program we actually are including all the functions, macros and variables declared in it.
In case of pre-defined C standard library header files ex(stdio.h), the functions calls are replaced by equivalent binary code present in the pre-compiled libraries. Code for C standard functions is linked and then the program is executed. Header files with custom names can also be created.
Program: Custom header files example
/****************
Index: restaurant.h
****************/
int billAll(int food_cost, int tax, int tip);
/****************
Index: restaurant.c
****************/
#include<stdio.h>
int billAll(int food_cost, int tax, int tip)
{
int result;
result = food_cost + tax + tip;
printf("Total bill is %d\n",result);
return result;
}
/****************
Index: main.c
****************/
#include<stdio.h>
#include"restaurant.h"
int main()
{
int food_cost, tax, tip;
food_cost = 50;
tax = 10;
tip = 5;
billAll(food_cost,tax,tip);
return 0;
}
4.What
are the differences between formal arguments and actual arguments of a
function?
Argument:
An
argument is an expression which is passed to a function by its caller (or macro
by its invoker) in order for the function (or macro) to perform its task. It is
an expression in the comma-separated list bound by the parentheses in a
function call expression.
Actual arguments:
The arguments that are passed in a function call are called actual arguments. These arguments are defined in the calling function.
Formal arguments:
The formal arguments are the parameters/arguments in a function declaration. The scope of formal arguments is local to the function definition in which they are used. Formal arguments belong to the called function. Formal arguments are a copy of the actual arguments. A change in formal arguments would not be reflected in theactual arguments.
Example:
#include<stdio.h>
void sum(int i, int j, int k);
/* calling function */
int main()
{
int a = 5;
// actual arguments
sum(3, 2 * a, a);
return 0;
}
/* called function */
/* formal arguments*/
void sum(int i, int j, int k)
{
int s;
s = i + j + k;
printf("sum is %d", s);
}
Here 3,2*a,a are actual arguments and i,j,k are formal arguments.
5.
What is pass by value in functions?
Pass
by Value:
In
this method, the value of each of the actual arguments in the calling function
is copied into corresponding formal arguments of the called function. In pass
by value, the changes made to formal arguments in the called function have no
effect on the values of actual arguments in the calling function.
Example:
#include<stdio.h>
void swap(int x, int y)
{
int t;
t = x;
x = y;
y = t;
}
int main()
{
int m = 10, n = 20;
printf("Before executing swap m=%d n=%d\n", m, n);
swap(m, n);
printf("After executing swap m=%d n=%d\n", m, n); return 0;
}
Output:
Before executing swap m=10 n=20
After executing swap m=10 n=20
Explanation:
In the main function, value of variables m, n are not changed though they are passed to function 'swap'. Swap function has a copy of m, n and hence it cannot manipulate the actual value of arguments passed to it.
6.
What is pass by reference in functions?
Pass
by Reference:
In
this method, the addresses of actual arguments in the calling function are
copied into formal arguments of the called function. This means that using
these addresses, we would have an access to the actual arguments and hence we
would be able to manipulate them. C does not support Call by reference. But it
can be simulated using pointers.
Example:
#include<stdio.h>
/* function definition */
void swap(int *x, int *y)
{
int t;
t = *x; /* assign the value at address x to t */
*x = *y; /* put the value at y into x */
*y = t; /* put the value at to y */
}
int main()
{
int m = 10, n = 20;
printf("Before executing swap m=%d n=%d\n", m, n);
swap(&m, &n);
printf("After executing swap m=%d n=%d\n", m, n);
return 0;
}
Output:
Before executing swap m=10 n=20
After executing swap m=20 n=10
Explanation:
In the main function, address of variables m, n are sent as arguments to the function 'swap'. As swap function has the access to address of the arguments, manipulation of passed arguments inside swap function would be directly reflected in the values of m, n.
7.
Out of the functions fgets() and gets(), which one is safer to use and why?
Out
of functions fgets( ) and gets( ), fgets( ) is safer to use. gets( ) receives a
string from the keyboard and it is terminated only when the enter key is hit.
There is no limit for the input string. The string can be too long and may lead
to buffer overflow.
Example:
gets(s) /* s is the input string */
Whereas fgets( ) reads string with a specified limit, from a file and displays it on screen.The function fgets( )
takes three arguments.
First argument : address where the string is stored.
Second argument : maximum length of the string.
Third argument : pointer to a FILE.
Example:
fgets(s,20,fp); /* s: address of the string, 20: maximum length of string, fp: pointer to a file */
The second argument limits the length of string to be read. Thereby it avoids overflow of input buffer. Thus fgets( ) is preferable to gets( ).
8.
What is the difference between the functions strdup() and strcpy()?
strcpy
function:
It
copies a source string to a destination defined by user. In strcpy function
both source and destination strings are passed as arguments. User should make
sure that destination has enough space to accommodate the string to be copied.
'strcpy' sounds like short form of "string copy".
Syntax:
strcpy(char *destination, const char *source);
Source string is the string to be copied and destination string is string into which source string is copied. If successful, strcpy subroutine returns the address of the copied string. Otherwise, a null pointer is returned.
Example Program:
#include<stdio.h>
#include<string.h>
int main() {
char myname[10];
//copy contents to myname
strcpy(myname, "techtechniquesonline.blogspot.com");
//print the string
puts(myname);
return 0;
}
Output: techtechniquesonline.blogspot.com
Explanation:
If the string to be copied has more than 10 letters, strcpy cannot copy this string into the string 'myname'. This is because string 'myname' is declared to be of size 10 characters only.
In the above program, string "nodalo" is copied in myname and is printed on output screen.
strdup function: duplicates a string to a location that will be decided by the function itself. Function will copy the contents of string to certain memory location and returns the address to that location. 'strdup' sounds like short form of "string duplicate"
Syntax:
strdup (const char *s);
strdup returns a pointer to a character or base address of an array. Function returns address of the memory location where the string has been copied. In case free space could not be created then it returns a null pointer. Both strcpy and strdup functions are present in header file
Program: Program to illustrate strdup().
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int main() {
char myname[] = " techtechniquesonline.blogspot.com ";
//name is pointer variable which can store the address of memory location of string
char* name;
//contents of myname are copied in a memory address and are assigned to name
name = strdup(myname);
//prints the contents of 'name'
puts(name);
//prints the contents of 'myname'
puts(myname);
//memory allocated to 'name' is now freed
free(name);
return 0;
}
Output: techtechniquesonline.blogspot.com
techtechniquesonline.blogspot.com
Explanation:
String myname consists of "techtechniquesonline.blogspot.com" stored in it. Contents of myname are copied in a memory address and memory is assigned to name. At the end of the program, memory can be freed using free(name);
