C Programming - Structures, Unions, Enums - Discussion

The difference between structure and union is the size of the structure is the sum of the size of its data members, whereas the size of the union is the size of the largest element.

All members of the union share the same memory space.
size of union = size of largest datatype element
So here the size of the union is 4 bytes and shared by integer and char array, so redeclaration should overwrite the values.

union a z2 = {0, 2}; // gives warning: excess elements in union initializer.

printf("%d\n",z1);// if we print z1 it prints 512.

z1.i =16961; / / redeclare z1 will overwrite its value because its a union.
z1.ch; / / array will store the same value but split it bitwise.


0100 0010 0100 0001 =16961 (16384 + 512 + 64 +1)

0100 0010 =66(64+2) 0100 0001=65(64+1)
B (ch[1]) A (ch[0])

printf("%d\n",z1); //now if we print z1 it prints 16961.
printf("%c %c\n",z1.ch[0],z1.ch[1]); // it prints A B.

This is how the union works as per my knowledge.

Program compiles normally but issues a warning of trying to assign more than one value at a time for a union.

All of you read this here. Union is not a problem, in this union has two members one is 'int' and another is 'char' all of you may know how to initialize character must be placed in between two double quotes hear z2 character initialization is error correct is '2' this.

In unions we can initialize only one member at the declaring of object/variable for the union.

I am not understanding this.

#include<stdio.h>
int main()
{
union a
{
int i;
char ch[2];
};
union a z1 = {512};
union a z2[2] = {5,6};
return 0;
}

@Bnr.

You are correct. Thank you.

Union allocates at only once time for memory allocation at the same type of union and overwrite allocate in one value.

Can anyone explain the concepts of pointer structure and union clearly?

Union denotes singularity hence only one value at a time is permitted for the init. Hence the answer.