Odd behavior of a struct

[akshaycjoshi]

the STRANGE THING ABOUT THE PROGRAM IS THAT WHEN WE LEAVE ONLY THE d variable(a char)
in the structure, the structure size is 1 while when we add the char d in the structure
along with other variables, the size of the structure increases by 8 bytes!



Can someone tell me the reason for this strange behavior? Is word boundary thing a possible reason for this? If yes then how?

[weaknessforcats]

Post your struct, please.

[akshaycjoshi]

[code=c]//this program shows the size of the inbuilt structure

#include <stdio.h>
#include <conio.h>

struct test
{
int a; //4 byte taken
float b; //4byte taken
double c; //8 byte taken
char d;// ? what is the problem with this?
}test_struct;

int main()
{
int x=sizeof(test_s truct);
printf("%d", x);
getch();
return 0;
}[/code]

[weaknessforcats]

Because of the double member, the compiler is aligning on double word boundaries. So the int and float are in the first double word (8 bytes), the double is in the second double word (8 bytes) and the char is in a third double word (1 byte + 7 slack bytes). The size is 24.

Take out the char and the size is 16.