In the following C code, the union size is decided by?

Akash Lawaniya • 9.58K Points
Tutor III

Q. In the following C code, the union size is decided by?

Code:

union temp
    {
        char ch;
        int n;
        float f;
    };

(A) float
(B) int
(C) both float and int
(D) char

Correct Answer - Option(A)
Views: 184
Filed under category C Programming

Explanation by: Mr. Dubey

The correct answer is:
✅ (A) float
Explanation:
In a union, all members share the same memory space, and its size is determined by the largest data type inside it.
In this case, the union contains:char ch; → 1 byte
int n; → typically 4 bytes
float f; → typically 4 bytes
How is Union Size Determined?
A union only allocates one memory block large enough to store the largest member.
Here, both int and float require 4 bytes each (assuming standard memory sizes).
So, the union size is determined by float, which is the largest.
If padding is involved (architecture-specific), it might be slightly larger to align the memory.
Example Code:
#include <stdio.h>

union temp {
    char ch;
    int n;
    float f;
};

int main() {
    printf("Size of union: %lu\n", sizeof(union temp));
    return 0;
}
Expected Output:
Size of union: 4
(If there's padding, it might be 8 bytes on some architectures.)
Final Answer:
✅ (A) float