C Programming - Declarations and Initializations - Discussion

Please check by running the same program with c compiler, the Garbage value will be printed for i.

When we are changing char array to short array it's not doing the same thing. In my compiler size of int is 4 and short is 2.

Why including only 512?

Kindly help by explaining this.

I think this might not be entirely correct.

Different computers use different orderings for bytes (notice I am not saying bits).
A little endian machine will place the least significant byte first (so ch[0] will come before ch[1]), and a big endian machine will do the reverse.

So the answer cannot be determined without this information.

How does the statement printf("%d %d %d", u.ch[0],u.ch[1],u.i); prints the size of union?

Any variable hold some garbage value without initialization.

Here we din't used sizeof operator too then how its calculating the size and printing. Any one please explain?

Explanation to the given question is as follows. As we know union size is the biggest size of its element, hence integer is considered to be the biggest.

Here integer is considered to be 4 bytes which are equal to 32 bits (GCC compiler). The memory allocation is as follows. 0000000000000000000000010000000011.

Hence from the above figure u.ch[0] = 3 & u.ch[1]=2.

As the character is of 1 byte.

So in that 4 bytes itself u.ch[0] and u.ch[1] can be occupied, as we are considering the biggest element to b integer, in other words, memory is shared.

So when we see u.i value is equivalent to 512 (the value at 10th bit) +2 (the value at 1st bit) +1 (the value at 0th bit). Therefore 512 + 2 + 1 = 515.

Why value of u?

I means the entire size of union? Can someone help me out?

#include<stdio.h>
int main()
{
union a
{
long int i, j;
int ch[2];
};

union a u;
u.ch[0] = 3;
u.i=1;u.j = 2;
u.ch[1] = 5 ;
printf( "%d, %d, %d, %d\n", u.ch[0], u.ch[1], u.j, u.i );
return 0;
}

I am not able to understand. And @Nandini you have a good explanation but I have understood it partially can you explain t more deeply?

I read all question and answer but still I can't get answer of why union share common memory to all data elements.