Question

As per my knowledge, By default 4-byte alignment will be done. say

typedef struct
{
     int data7;  
     unsigned char data8;
     //3 -bytes will be added here.
}Sample1;

so sizeof(Sample1) will be 8.

But for the following structure, why padding is not happened?.

typedef struct
{
     unsigned char data1;
     unsigned char data2;
     unsigned char data3;
     unsigned char data4;
     unsigned char data5;
     unsigned char data6;

}Sample2;

But the sizeof(Sample2) is 6 only. This Sample2 is not a 4 byte aligned structure?

EDIT::

As per Wiki

Data alignment means putting the data at a memory offset equal to some multiple of the word size, which increases the system’s performance due to the way the CPU handles memory.

But members of Sample2 will not be aligned in multiples of two right??

Thanks.

Answer 1

None of the fields in your second struct require 4-byte alignment. unsigned char only needs 1-byte alignment. Therefore, there is no need to actually align it to 4 bytes.

Structs are generally only aligned to the maximum alignment of all the fields.