C Programming - Pointers - Discussion

Explanation :
printf ("%c", * (int*) vp) ;
Here vp is a void pointer (void * vp)that can hold address of all type of variable.
Lets take an example
void *vp; // void pointer declaration
int a=5; // declaration of variable and assigned to 5
vp=&a;
Normally to show the value of the variable through pointer, we are just appending * before pointer i.e printf("%d",*p) that means it will show value at p . but here it will not show if we will declare like the above. Because vp is a void pointer that means it can hold all data type address .if we simply place *vp then compiler does not identify ..So for that we have to type cast ie (int *)vp ..it indicates vp hold the integer address only .if we wan to see that value just place * (int *)vp..
Then you will get the value of variable..but here %c format specifier used so it will convert that integer value to character value
A-Z(65-90)
a-z (92-122)
0-9 (48-57)

Thanks

Pointer always store integer value so cp will store the memory address of location where string "jack " is stored.

Step 1 : vp = &ch;
/*Will store address of ch in vp so while we print content in printf it will print asccii value of 74 i.e "J"*/

Step 2 : vp = &j;
/* It will assign address of j to vp again it will print ascii value of 65 as "A"*/

Step 3 : vp = cp;
/* In this step cp is pointing to memory locatioon where string jack is stored and we r incrementing it by two so it will point to "C" from sring "JACK" and since we hava given %S in printf so it will print content from c onwords ie "CK"*/

So final combined output will be JACK.

Hi sourav,
Typecasting is making a variable of one type, such as an int, act like another type, a char, for one single operation. To typecast something, simply put the type of variable you want the actual variable to act as inside parentheses in front of the actual variable. (char)a will make 'a' function as a char.

#include <iostream>

using namespace std;

int main()
{
cout<< (char)65 <<"\n";
// The (char) is a typecast, telling the computer to interpret the 65 as a
// character, not as a number. It is going to give the character output of
// the equivalent of the number 65 (It should be the letter A for ASCII).
cin.get();
}

ch=74 which is the ASCII value of J
j=65 which is the ASCII value of A
vp a void pointer contains the address of ch so it can be type casted to any type of pointer.
printf("%c", *(char*)vp);
(char*)vp type castes void type vp to char type and prints the value pointed by vp which is J.
vp=&j;
printf("%c", *(int*)vp);
Now vp contains the address of j.
*(int*)vp it type castes void type pointer vp to int type and prints the value pointed by vp which is A
vp=cp;
printf("%s", (char*)vp+2);
Now vp contains the value of cp. pointer vp is incremented by 2.so now it points to the letter C of JACK and prints the string CK.

So finally JACK is printed.

#include<stdio.h>
int main()
{
void *vp;
char ch=74, *cp="JACK";
int j=65;
vp=&ch;
printf("%c", *(char*)vp);
vp=&j;
printf("%c", *(int*)vp);
vp=cp;
printf("%s", (char*)vp+2);
return 0;
}

A ASCII value is 65 and J ASCII value is 75.
and printf function in vp++2 so JACK first two letters are eliminated and ASCII values are replaced.

For @Lucky:

ch is a character variable. From the character set, we can assign any kind of values to the character variable. The character set consists of floating point no. s, integers, characters, special characters etc. which when given charater datatype behave as character.

Hi satya.

This mens, the pronunciation of pointer alwys strt from right to left, so firstly we typecast the vp because vp is othr datatype of pointer nd we want to intgr pointer so we use typecasting nd aftr tht we solve *vp (mens value at vp or value at adress stored in vp).

@Manasa.

Because vp is void pointer. When we use void pointer for any data type then we have to typecast that void pointer with the datatype of the variable whose address is stored into that void pointer.

q = (int**)&p;
Here void ptr is casted into integer ptr.

this was d explantion given for typecasting in 1 of the discussion...

*(char*)vp-dis is also typecasting.. but both differs..

Hello friends!

Will anyone explain the meaning of

printf ("%c", * (int*) vp) ;

As I am new in this field, will anyone took mercy on me and explain it ?