SE250:lab-2:rwan064

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Introduction

I am sick with the flu so doing the lab exercise on my laptop at home instead of the GCL lab computers. I also managed to log into the Linux server using PuTTY so got some results for Linux too.

Results

Results from different compilers and environments

Windows Vista: cygwin

These are the results from Vista Business on my laptop. Specs on my laptop:

  • Intel Core 1.66 GHz
  • 1 GB RAM

That should be enough.

Task 1

int *ip;
char *cp;
float *fp;
double *dp;
short *sp;
long *lp;

printf( "sizeof( int* ) = %d\n", sizeof( ip ) );
printf( "sizeof( char* ) = %d\n", sizeof( cp ) );
printf( "sizeof( float* ) = %d\n", sizeof( fp ) );
printf( "sizeof( double* ) = %d\n", sizeof( dp ) );
printf( "sizeof( short* ) = %d\n", sizeof( sp ) );
printf( "sizeof( long* ) = %d\n", sizeof( lp ) );

Results: 

$ ./main.exe
sizeof( int* ) = 4
sizeof( char* ) = 4
sizeof( float* ) = 4
sizeof( double* ) = 4
sizeof( short* ) = 4
sizeof( long* ) = 4
  • Are all pointers the same size? YES
  • What other data types in C are the same size? int

Task 2

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

Results: 

$ ./main.exe
&x = 0x22cca4, &y = 0x22cca0, diff = 1
&x = 0x22cca4, &y = 0x22cca0, diff = 4
  • What is the difference between (long)&x - (long)&y and (long)(&x - &y)?

Task 3

int x;
char arr[4];
int y;
printf( "sizeof( arr ) = %d\n", sizeof( arr ) );
printf( "&arr = %p\n", &arr );
printf( "arr+4 = %p\n", arr+4 );
printf( "&arr[4] = %p\n", &arr[4] )

Results: 

sizeof( arr ) = 4
&arr = 0x22cca0
arr+4 = 0x22cca4
&arr[4] = 0x22cca4

What does sizeof report as the size of the array? The number of elements in the array

Differences between &x and &y for varing size of arr: 

int x;
char arr[0];
int y;
printf( "&x = %p, &y = %p, diff = %ld\n", &x, &y, (long)(&x - &y) );
printf( "&x = %p, &y = %p, diff = %ld\n", &x, &y, (long)&x - (long)&y );

Results: 

For sizeof( arr ) = 0 ----------------------------
&x = 0x22cc9c, &y = 0x22cc7c, diff = 8
&x = 0x22cc9c, &y = 0x22cc7c, diff = 32

For sizeof( arr ) = 1 ----------------------------
&x = 0x22cca4, &y = 0x22cc9c, diff = 2
&x = 0x22cca4, &y = 0x22cc9c, diff = 8

For sizeof( arr ) = 2 ----------------------------
&x = 0x22cca4, &y = 0x22cc9c, diff = 2
&x = 0x22cca4, &y = 0x22cc9c, diff = 8

For sizeof( arr ) = 3 ----------------------------
&x = 0x22cc9c, &y = 0x22cc7c, diff = 8
&x = 0x22cc9c, &y = 0x22cc7c, diff = 32

For sizeof( arr ) = 4 ----------------------------
&x = 0x22cca4, &y = 0x22cc9c, diff = 2
&x = 0x22cca4, &y = 0x22cc9c, diff = 8

For sizeof( arr ) = 5 ----------------------------
&x = 0x22cc9c, &y = 0x22cc7c, diff = 8
&x = 0x22cc9c, &y = 0x22cc7c, diff = 32

For sizeof( arr ) = 6 ----------------------------
&x = 0x22cc9c, &y = 0x22cc7c, diff = 8
&x = 0x22cc9c, &y = 0x22cc7c, diff = 32

For sizeof( arr ) = 7 ----------------------------
&x = 0x22cc9c, &y = 0x22cc7c, diff = 8
&x = 0x22cc9c, &y = 0x22cc7c, diff = 32

For sizeof( arr ) = 8 ----------------------------
&x = 0x22cca4, &y = 0x22cc94, diff = 4
&x = 0x22cca4, &y = 0x22cc94, diff = 16

For sizeof( arr ) = 9 ----------------------------
&x = 0x22cc9c, &y = 0x22cc7c, diff = 8
&x = 0x22cc9c, &y = 0x22cc7c, diff = 32

For sizeof( arr ) = 10 ----------------------------
&x = 0x22cc9c, &y = 0x22cc7c, diff = 8
&x = 0x22cc9c, &y = 0x22cc7c, diff = 32

Putting values into the variables: 

int x = 0;
char arr[4];
int y = 0;

arr[4] = 10;

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

Results: 

$ ./main.exe
&x = 0x22cca4, &y = 0x22cc9c, diff = 2
&x = 0x22cca4, &y = 0x22cc9c, diff = 8
x = 10, y = 0

Task 4

Differences between &x and &y for varying sizes of arr: 

int x;
int y;

int main( void )
{
    char arr[0];
    printf( "&x = %p, &y = %p, diff = %ld\n", &x, &y, (long)(&x - &y) );
    printf( "&x = %p, &y = %p, diff = %ld\n", &x, &y, (long)&x - (long)&y );
    return 0;
}

Results: 

For sizeof( arr ) = 0 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

For sizeof( arr ) = 1 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

For sizeof( arr ) = 2 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

For sizeof( arr ) = 3 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

For sizeof( arr ) = 4 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

For sizeof( arr ) = 5 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

For sizeof( arr ) = 6 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

For sizeof( arr ) = 7 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

For sizeof( arr ) = 8 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

For sizeof( arr ) = 9 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

For sizeof( arr ) = 10 ----------------------------
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16

Putting values into variables: 

int x;
int y;

int main( void )
{
    char arr[4];
    arr[4] = 10;
    x = 0;
    y = 0;
    printf( "&x = %p, &y = %p, diff = %ld\n", &x, &y, (long)(&x - &y) );
    printf( "&x = %p, &y = %p, diff = %ld\n", &x, &y, (long)&x - (long)&y );
    printf( "x = %d, y = %d\n", x, y );
    return 0;
}

Results: 

$ ./main.exe
&x = 0x403030, &y = 0x403020, diff = 4
&x = 0x403030, &y = 0x403020, diff = 16
x = 0, y = 0

Task 5

int *p1, *p2;
printf( "Un-initializd pointers:\n" );
printf( "p1 = %p, p2 = %p\n", p1, p2 );
printf( "\n" );
{
    int q;
    p1 = &q;
    printf( "Inside first scope:\n" );
    printf( "&q = %p\n", &q );
    printf( "p1 = %p, p2 = %p\n", p1, p2 );
    printf( "\n" );
}
{
    int r;
    p2 = &r;
    printf( "Inside second scope:\n" );
    printf( "&r = %p\n", &r );
    printf( "p1 = %p, p2 = %p\n", p1, p2 );
    printf( "\n" );
}

printf( "p1 = %p, p2 = %p\n", p1, p2 );
printf( "*p1 = %d, *p2 = %d\n", *p1, *p2 );

Results: 

$ ./main.exe
Un-initializd pointers:
p1 = 0x401450, p2 = 0x611021a0

Inside first scope:
&q = 0x22ccbc
p1 = 0x22ccbc, p2 = 0x611021a0

Inside second scope:
&r = 0x22ccb8
p1 = 0x22ccbc, p2 = 0x22ccb8

p1 = 0x22ccbc, p2 = 0x22ccb8
*p1 = 0, *p2 = 1628704768

Task 6

Results: 

$ ./main.exe
sp = 0x22cc90(456)
sp = 0x22cc90(efg)
sp = 0x402000(tuvwxyz)
sp = 0xda0170(hijklmn)

Results with extra printf strcpy and printf: 

$ ./main.exe
sp = 0x22cc90(456)
sp X'd = 0x22cc90(-0@)
sp = 0x22cc90(efg)
sp X'd = 0x22cc90(-0@)
sp = 0x402000(tuvwxyz)
sp X'd = 0x402000(XXXXXXX)
sp = 0xda0170(hijklmn)
sp X'd = 0xda0170(XXXXXXX)

Task 7

Results: 

$ ./main.exe
&my_struct = 0x0
offsets:
my_char: 0
my_short: -2
my_int: -4
my_long: -8
my_float: -12
my_double: -16

Task 8

Results: 

$ ./main.exe
&my_struct = 0x0
offsets:
my_char: 0
my_short: 0
my_int: 0
my_long: 0
my_float: 0
my_double: 0

Task 9

char *sp1, *sp2, *sp3;
printf( "Declared\nsp1 = %p, sp2 = %p, sp3 = %p\n\n", sp1, sp2, sp3 );
sp1 = malloc( 10 );
printf( "sp1 mallocd\nsp1 = %p, sp2 = %p, sp3 = %p\n\n", sp1, sp2, sp3 );
sp2 = malloc( 10 );
printf( "sp2 mallocd\nsp1 = %p, sp2 = %p, sp3 = %p\n\n", sp1, sp2, sp3 );
free( sp1 );
printf( "sp1 freed\nsp1 = %p, sp2 = %p, sp3 = %p\n\n", sp1, sp2, sp3 );
sp3 = malloc( 10 );
printf( "sp3 mallocd\nsp1 = %p, sp2 = %p, sp3 = %p\n\n", sp1, sp2, sp3 );

Results: 

$ ./main.exe
Declared
sp1 = 0x401420, sp2 = 0x611021a0, sp3 = 0x0

sp1 mallocd
sp1 = 0x1030170, sp2 = 0x611021a0, sp3 = 0x0

sp2 mallocd
sp1 = 0x1030170, sp2 = 0x1030180, sp3 = 0x0

sp1 freed
sp1 = 0x1030170, sp2 = 0x1030180, sp3 = 0x0

sp3 mallocd
sp1 = 0x1030170, sp2 = 0x1030180, sp3 = 0x1030170
  • What can you say about the pointers returned by malloc?
  • What will happen if sp1 is used after it has been freed?

Task 10

Results: 

$ ./main.exe
local_str = 0x401050

Linux server

Task 1

sizeof( int* ) = 4
sizeof( char* ) = 4
sizeof( float* ) = 4
sizeof( double* ) = 4
sizeof( short* ) = 4
sizeof( long* ) = 4

Task 2

&x = 0xffd4278c, &y = 0xffd42788, diff = 1
&x = 0xffd4278c, &y = 0xffd42788, diff = 4

Task 3

sizeof( arr ) = 4
&arr = 0xffd23784
arr+4 = 0xffd23788
&arr[4] = 0xffd23788

&x = 0xffdf878c, &y = 0xffdf8788, diff = 1
&x = 0xffdf878c, &y = 0xffdf8788, diff = 4

&x = 0xffaa9788, &y = 0xffaa9784, diff = 1
&x = 0xffaa9788, &y = 0xffaa9784, diff = 4

&x = 0xfff0b788, &y = 0xfff0b784, diff = 1
&x = 0xfff0b788, &y = 0xfff0b784, diff = 4

&x = 0xfface788, &y = 0xfface784, diff = 1
&x = 0xfface788, &y = 0xfface784, diff = 4

&x = 0xffebc78c, &y = 0xffebc784, diff = 2
&x = 0xffebc78c, &y = 0xffebc784, diff = 8

&x = 0xffcb078c, &y = 0xffcb0788, diff = 1
&x = 0xffcb078c, &y = 0xffcb0788, diff = 4

&x = 0xff81878c, &y = 0xff818788, diff = 1
&x = 0xff81878c, &y = 0xff818788, diff = 4

&x = 0xffc8178c, &y = 0xffc81788, diff = 1
&x = 0xffc8178c, &y = 0xffc81788, diff = 4

&x = 0xffd9f780, &y = 0xffd9f77c, diff = 1
&x = 0xffd9f780, &y = 0xffd9f77c, diff = 4

&x = 0xfff2077c, &y = 0xfff20778, diff = 1
&x = 0xfff2077c, &y = 0xfff20778, diff = 4

&x = 0xfff3077c, &y = 0xfff30778, diff = 1
&x = 0xfff3077c, &y = 0xfff30778, diff = 4

&x = 0xffd4178c, &y = 0xffd41784, diff = 2
&x = 0xffd4178c, &y = 0xffd41784, diff = 8
x = 167772160, y = 0

Task 4

&x = 0x10010aa4, &y = 0x10010aa8, diff = -1
&x = 0x10010aa4, &y = 0x10010aa8, diff = -4

&x = 0x10010aa4, &y = 0x10010aa8, diff = -1
&x = 0x10010aa4, &y = 0x10010aa8, diff = -4

&x = 0x10010aa4, &y = 0x10010aa8, diff = -1
&x = 0x10010aa4, &y = 0x10010aa8, diff = -4

&x = 0x10010aa4, &y = 0x10010aa8, diff = -1
&x = 0x10010aa4, &y = 0x10010aa8, diff = -4

&x = 0x10010aa4, &y = 0x10010aa8, diff = -1
&x = 0x10010aa4, &y = 0x10010aa8, diff = -4

&x = 0x10010aa4, &y = 0x10010aa8, diff = -1
&x = 0x10010aa4, &y = 0x10010aa8, diff = -4

&x = 0x10010aa4, &y = 0x10010aa8, diff = -1
&x = 0x10010aa4, &y = 0x10010aa8, diff = -4

&x = 0x10010aa4, &y = 0x10010aa8, diff = -1
&x = 0x10010aa4, &y = 0x10010aa8, diff = -4

&x = 0x10010b18, &y = 0x10010b1c, diff = -1
&x = 0x10010b18, &y = 0x10010b1c, diff = -4

&x = 0x10010b18, &y = 0x10010b1c, diff = -1
&x = 0x10010b18, &y = 0x10010b1c, diff = -4

&x = 0x10010b18, &y = 0x10010b1c, diff = -1
&x = 0x10010b18, &y = 0x10010b1c, diff = -4

&x = 0x10010af4, &y = 0x10010af8, diff = -1
&x = 0x10010af4, &y = 0x10010af8, diff = -4
x = 0, y = 0

Task 5

Un-initializd pointers:
p1 = 0xff929a24, p2 = 0x1

Inside first scope:
&q = 0xff929784
p1 = 0xff929784, p2 = 0x1

Inside second scope:
&r = 0xff929784
p1 = 0xff929784, p2 = 0xff929784

p1 = 0xff929784, p2 = 0xff929784
*p1 = -7169520, *p2 = -7169520

Task 6

sp = 0xffb01754(�þîÐ�)
sp = 0xffb01754(abcdefg)
sp = 0x10010cd4(tuvwxyz)
sp = 0x10011008(hijklmn)

sp = 0xffcf4754(�þîÐ�)
sp X’d = 0xffcf4754(XXXXXXX)
sp = 0xffcf4754(abcdefg)
sp X’d = 0xffcf4754(XXXXXXX)
sp = 0x10010dc0(tuvwxyz)
sp X’d = 0x10010dc0(XXXXXXX)
sp = 0x10011008(hijklmn)
sp X’d = 0x10011008(XXXXXXX)

Task 7

&my_struct = 0xffab5770
offsets:
my_char: 0
my_short: -2
my_int: -4
my_long: -8
my_float: -12
my_double: -16

Task 8

&my_struct = 0xffec6788
offsets:
my_char: 0
my_short: 0
my_int: 0
my_long: 0
my_float: 0
my_double: 0

Task 9

Declared
sp1 = 0xffa49a10, sp2 = 0xffa49a24, sp3 = 0x1

sp1 mallocd
sp1 = 0x10011008, sp2 = 0xffa49a24, sp3 = 0x1

sp2 mallocd
sp1 = 0x10011008, sp2 = 0x10011018, sp3 = 0x1

sp1 freed
sp1 = 0x10011008, sp2 = 0x10011018, sp3 = 0x1

sp3 mallocd
sp1 = 0x10011008, sp2 = 0x10011018, sp3 = 0x10011008

Task 10

local_str = 0x100004ac

Memory Map

local variables
0x22CCA4
0x22CCA0

static variables
0x403030
0x403020

malloc'd variables
0x402000
0xDA0170

Image of memory locations: <html> <embed src="http://www.rajithaonline.com/SE250/map.png" width="270" height="494" /> </html>

Conclusions & Discussion

I had to read through the lab instructions a couple of times till I understood properly exactly what I need to do. It was quite a lot of work re-typing, compiling and running multiple times. I started off with using Cygwin to run the programs on my Windows machine. This wasn't too hard for many of the exercises since all I need to do was copy and paste the code and run it. But it was quite annoying doing Task 3 and 4 because I had to edit, compile and run MANY times!

For the Linux machine I logged into the server (login.cs.auckland.ac.nz) using PuTTY. The problem I had now was to find a way to easily get the results from the server. I don't want to have to edit, compile and run about 20 times because I will also have to upload the edited file that many times since I was at home. So I made multiple files which has everything I need to run. Then I wrote a shell script to automatically compile and run all of the files and output the results into a file instead of the screen.

But overall the lab wasn't too challenging but it was a lot of work.

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