Yashavant kanetkar understanding pointer in C, Chepter 1, Question 6.

Question

6. Would the following program compile?

main( )
{
int a = 10, *j;
void *k;
j = k = &a;
j++ ;
k++;
printf ("\n %u %u", j, k ) ;
}

Please explain above program with some examples..

Comments

whatever address it stores , it is pointing to next memory location.

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K++ ===> K=K+1 ===> K is void pointer then how to say for which datatype it is matching?

if you are saying K internally have it?

then why you type cast when you have to print the value at K,

 

i mean,

int i=2;

void *ptr;

ptr=i;

printf("%d\n",*(int *)ptr); ====> ptr is typecasted to int pointer ====> next Dereferenced

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Please check the answer now

Answer 1

The reason we define type of pointer is that during arithmetic of pointers it should know by how much size it should increment or decrement. Now j and k storing address of a (eg address of a is 100). but when we do j++ and k++ j will be j=j+4(sizeof(int)=4 just example) whereas k will be incremented by one. So output will be j=104 and k=101.

Arithmetic with void pointer doesn't make sense.

https://stackoverflow.com/questions/16336757/why-does-incrementing-a-void-pointer-by-1-moves-one-byte-ahead-but-its-4-bytes

Comments

My question is that when we print the value which pointed by void pointer, typecasting is not required explicitly but when we make increment in void pointer, typecasting is required why?

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who says,   " when we print the value which pointed by void pointer, typecasting is not required explicitly "

 

it's require when you want to print the value which is pointed by void pointer using void pointer.

 

but for assigning void pointer to any specific pointer, it is not needed to typecast why because 

expression j = k means convert ( k ) into type of j.

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@ Tushar Patil, 

arithmetic on void pointer is lead to undefined behavior, it means it is compiler dependent.

then how you say k=101 ?

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just an example bro. even the size of int is compiler dependent :) . Conclusion is the code will compile successfully but it doesn't make any sense doing arithmetic on void pointers