What is the difference between struct and union in c programming

Answer 1

hope these helps..

https://www.sololearn.com/discuss/96904/?ref=app
https://www.sololearn.com/discuss/117597/?ref=app
https://www.sololearn.com/discuss/2692638/?ref=app
https://www.sololearn.com/discuss/2053833/?ref=app

Answer 2

A struct holds members that will not be overwritten, a union holds members that share a memory location thus they get overwritten.

struct my_data{
char a;
int x;
}

sets in memory

1 byte for the char & 2 or 4 bytes (depending on your system) for the int such:

[char a][int x][int x][int x][int x] <-- reserved on stack or heap depending on how you initialize it.

union my_data{
char a;
int x;
}

Sets in memory the most memory needed for any of the members and reuses it such:

[my_data][my_data][my_data][my_data] <-- used if setting or getting the char or int. Only the last set will be saved.

Here is an example for union:
#include <stdio.h>
#include <stdlib.h>

union my_data{
char a;
int x;
};

int main(void){

union my_data My_Data;

My_Data.a = 'c';

printf("char a is = %c\n", My_Data.a); //Both are still valid names.
printf("int x is = %i\n", My_Data.x);
puts("");

My_Data.x = 5;

printf("char a is = %c\n", My_Data.a); //Both are still valid names, but data was overwritten
printf("int x is = %i\n", My_Data.x);
return 0;
}

outputs:
char a is = c
int x is = 99

char a is =
int x is = 5