Bissoy.com
Doctors Medicines MCQs Q&A

Suppose you are compiling on a machine with 1-byte chars, 2-byte shorts, 4-byte ints, and 8-byte doubles, and with alignment rules that require the address of every primitive data element to be an integer multiple of the element's size. Suppose further that the compiler is not permitted to reorder fields: padding is used to ensure alignment. How much space will be consumed by the following array? struct { short s; char c; short t; char d; double r; int i; } A[10]; /*10-element array of structs*/

Suppose you are compiling on a machine with 1-byte chars, 2-byte shorts, 4-byte ints, and 8-byte doubles, and with alignment rules that require the address of every primitive data element to be an integer multiple of the element's size. Suppose further that the compiler is not permitted to reorder fields: padding is used to ensure alignment. How much space will be consumed by the following array? struct { short s; char c; short t; char d; double r; int i; } A[10]; /*10-element array of structs*/ Correct Answer 240 bytes

The correct answer is option 3.

Key Points

  • "alignment rules" that "require the address of every primitive data element to be an even multiple of the element’s size". It's not very interesting that we're talking about alignment rules; we knew that already.
  • "require the address" of "every primitive data element" to be "an even multiple of the element’s size". Now we're getting somewhere. We have a requirement and a scope:
  • Requirement: The address is an even multiple of the element's size.
  • Scope: Every primitive data element.
  • So, every time we position an element, we must impose the requirement. It may also mean "even" as in "integral" rather than "multiple of two" 

That would make the array:

Offset Variable Size Range
 0                s        2  0-1
 4      c                1     2-2
 8       t                  2     4-5
12      d                1     6-6
16      r                 8   8-15
24      i                  4   16-19
28      *                4   20-23
       
 32     s     2   24-25
 34      c                1   26-26
36      t                 2   28-29
 38      d                1   30-30
48      r                 8   32-39
56      i                 4   40-43
60      *               4   44-47

 

In that case, you have 24 bytes per element for a total of 240 bytes. Again, you need padding to ensure that r is aligned correctly.

∴ Hence the correct answer is 240 bytes.

Related Questions

Following declaration of an array of struct, assumes size of byte, short, int and long are 1, 2, 3 and 4 respectively. Alignment rule stipulates that n-type field must be located at an address divisible by n. the fields in a struct are not rearranged, padding is used to ensure alignment. All elements of array should be of same size. Struct complx                 Short s                 Byte b                 Long l                 Int i End complx Complx C[10] Assuming C is located at an address divisible by 8, what is the total size of C, in bytes?
Which of the following should be used for freeing the memory allocated in the following C code?
#include struct p{ struct p *next; int x;};int main(){ struct p *p1 = (struct p*)malloc(sizeof(struct p)); p1->x = 1; p1->next = (struct p*)malloc(sizeof(struct p)); return 0;}
Which of the following statements are correct? (i) All elements of an array are ints (ii) All elements of an array are floats (iii) Some elements of an array can be ints and other floats (iv) All elements of an array are chars 
What is the output of following program? abstract class Sum { public abstract int sumOfTwo(int n1, int n2); public abstract int sumOfThree(int n1, int n2, int n3); public void disp( ){ System.out.println("Method of class Sum"); } } class DemoAbstract1 extends Sum { public int sumOfTwo(int num1, int num2) { return num1+num2; } public int sumOfThree(int num1, int num2, int num3) { return num1+num2+num3; } public static void main(String args[ ]){ Sum obj = new DemoAbstract1( ); System.out.println(obj.sumOfTwo(3, 7)); System.out.println(obj.sumOfThree(4, 3, 19)); obj.disp( ); } }
Which among the following is correct syntax to declare a 2D array using new operator? = new char; b) char (pchar) = new char; c) char (*char) = new char; d) char (*char)= new char;
What is the output of this program? #include
using namespace std;
struct sec {
int a;
char b;
};
int main()
{
struct sec s ={25,50};
struct sec *ps =(struct sec *)&s;
cout << ps->a << ps->b;
return 0;
}
What is the output of this program ? #include
using namespace std;
int n(char, int);
int (*p) (char, int) = n;
int main()
{
(*p)('d', 9);
p(10, 9);
return 0;
}
int n(char c, int i)
{
cout << c << i;
return 0;
}
Consider the following C function in which size is the number of elements in the array E: int MyX(int *E, unsigned int size) {       int Y = 0;       int Z;       int i, j, k;       for(i = 0; i < size; i++) Y = Y + E[i];       for(i = 0; i < size; i++) for(j = i; j < size; j++) {       Z = 0;       for(k = i; k <= j; k++) Z = Z + E[k];       if (Z > Y) Y = Z; }       return Y; } The value returned by the function MyX is the
Consider the following two C code segment. Y and X are one- and two-dimensional arrays of size n and n × n respectively, where 2 ≤ n ≤ 10. Assume that in both code segments, elements of y are initialized to 0 and each element X[i] [j] of array X is initialized to i + j. Further assume that when stored in main memory all elements of x are in same main memory page frame. Code segment 1:                 //initialize elements of y to 0                 //initialize elements X[i] [j] of X to i+j                       for (i = 0; i < n; i++)                                 Y[i] += X[0] [i]; Code Segment 2:                 //initialize elements of Y to 0                 //initialize elements X[i] [j] of X to i+j                        for (i = 0; i < n; i++)                                 Y[i] += X[i] [0]; Which of the following statements is/are correct? S1: Final contents of array Y will be same in both code segments S2: Elements of array X accessed inside the for loop shown in code segment 1 are contiguous in main memory S3: Elements of array X accessed inside the for loop shown in code segment 2 are contiguous in main memory
Calculate the % of memory saved when bit-fields are used for the following C structure as compared to with-out use of bit-fields for the same structure? (Assuming size of int = 4)
struct temp{ int a : 1; int b : 2; int c : 4; int d : 4;}s;