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2008-11-03T05:19:13Z

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== 1 ==
Using the code

printf("%d\n", sizeof(ip))

on the pointer variable '''ip''' returned a value of 4 on both the linux and PC.

Pointers are 4 bytes in memory.

== 2 ==
printf("&x = %p, &y = %p, diff = %ld\n", &x, &y, (long)(&x - &y));

returned a difference of 4 on PC and 1 on linux.

I am not sure what this result means. Why would the pointers take up less space on linux?

The difference between '''(long)&x - (long)&y and (long)(&x - &y)''' is that the latter converts the answer from the

subtraction to type '''long''' while the former does the conversion to long '''before''' the subtraction.

== 3 ==
Declaring an array of '''type char''' and '''size 4''' between the integer declarations x and y

int x;
char arr[ 4 ];
int y;

Sizeof(arr) showed 4 as output. This was expected.

The address of '''&arr''' was 4 bytes in front of the address of '''&arr[ 4 ]'''.

This means that '''&arr''' points to the first value in the array, something I should have known.

My initial thoughts were that the difference between the addresses of x and y would be bigger, due to the new

array taking up room in the memory. But

== 5 ==
using the code

int *p1, *p2;
int q;
p1 = &q;
int r;
p2 = &r;

Gave outputs for p1/p2 as huge values on the PC. On linux it gave huge '''negative''' numbers as outputs.

== 7 ==
After initialising a structure containing one of every variable type and running

printf("&my_struct = %p\n", my_struct);
printf("offsets:\n"
"my_char: %ld\n"
"my_short: %ld\n"
"my_int: %ld\n"
"my_long: %ld\n"
"my_float: %ld\n"
"my_double: %ld\n",

(long)&my_struct - (long)&my_struct.my_char,
(long)&my_struct - (long)&my_struct.my_short,
(long)&my_struct - (long)&my_struct.my_int,
(long)&my_struct - (long)&my_struct.my_long,
(long)&my_struct - (long)&my_struct.my_float,
(long)&my_struct - (long)&my_struct.my_double);

The output was

'''char 0''' - meaning the char variable is first in the memory.
'''short -2''' - followed by variable type short. Type char takes up 2 bytes.
'''int -4''' - Short also takes up 2 bytes.
'''long -8''' - Int takes up 4 bytes.
'''float -12''' - Long takes up 4 bytes.
'''double -16''' - I was told that a structure had size 24. Double takes up 8 bytes.

== 8 ==
Using a '''union''' the output was

'''char 0'''
'''short 0'''
'''int 0'''
'''long 0'''
'''float 0'''
'''double 0'''

I was a bit confused by this. Perhaps it means all the variable types are placed together in memory?

Need to know more about '''union'''s

SE250:lab-2:tlou006 - Revision history

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