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CS 416- Fall 2008Session 02

TA: Tuan PhanEmail: tphan@cs.rutgers.edu

732-445-6450 (ext 9644) : Just leaving msg( prefer using Email, with HEADER:

[CS416] …)

Recitation: TH :3:35pm – 4:30 PM @ SEC 202Office Hour: TH 5:00 – 6:00 PM @ Hill 367

Another place to find me: PANIC LAB, CORE 340

Extra: Email to setup appointment on Monday afternoon.

TA’s Web Site: http://paul.rutgers.edu/~tphan/cs416/Slides for recitation, Useful Links

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What will be in recitations

• Summary of lectures

• Projects

• Sample Questions / Home work

• More technical stuff

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Recommend Tools for CS416

• PuTTy : ssh client without GUI

http://www.chiark.greenend.org.uk/~sgtatham/putty/

• XManager: ssh client with GUI

• WinSCP: to upload files to CEREAL clusters

http://winscp.net/

• IDE: emacs, vi …

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CEREAL cluster / iLab

• Link: http://ilab.rutgers.edu/ – Use Linux machines; DO NOT use Sun

machines (including cereal.rutgers.edu)

• iLab: Hill 248 - 250– Use Rutgers ID– Transfer students: use temporary ID– Problem: meet Robert Toth @ CoRE 232

Homework: Create/Activate an account on iLab

Today’s topics

• Communication Channels with TA• Quick Introduction about C• Prepare for project 1

– General Information– Calling Stack– Pointers in C– Dynamic Memory Allocation– Fork()– Others…

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C Programming

• Links: – http://paul.rutgers.edu/~tphan/cs416/2_IntroC.pdf– http://www.cs.cf.ac.uk/Dave/C/

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Example of Process Creation Using Fork

• The UNIX shell is command-line interpreter whose basic purpose is for user to run applications on a UNIX system

• cmd arg1 arg2 ... argn

Creating, Compiling and Running Your C Program

• Create: myprog.c

• Compile(1) cc myprog.c

(2) cc -o myprog myprog.c

• Running(1) ./a.out

(2) ./myprog

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Compiler Options-llibrary

Link with object libraries.

cc calc.c -o calc -lm

-Ldirectory

Add directory to the list of directories containing object-library routines.

cc prog.c -L/home/myname/mylibs mylib.a

-Ipathname Add pathname to the list of directories in which to search for #include files with relative filenames

    cc prog.c -I/home/myname/myheaders

-g invoke debugging option.

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A Simple C Program#include <stdio.h>

#define STOP 0

/* Function: main */

/* Description: counts down from user input to STOP */

main()

{

/* variable declarations */

int counter; /* an integer to hold count values */

int startPoint; /* starting point for countdown */

/* prompt user for input */

printf("Enter a positive number: ");

scanf("%d", &startPoint); /* read into startPoint */

/* count down and print count */

for (counter=startPoint; counter >= STOP; counter--)

printf("%d\n", counter);

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Fred Kuhns (04/20/23) CSE332– Object Oriented Programming Lab

Another Simple C Programint main (int argc, char **argv) { int i; printf(“There are %d arguments\n”, argc); for (i = 0; i < argc; i++) printf(“Arg %d = %s\n”, i, argv[i]);

return 0;}

• Notice that the syntax is similar to Java•What’s new in the above simple program?

– of course you will have to learn the new interfaces and utility functions defined by the C standard and UNIX

– Pointers will give you the most trouble

What Happens When There Is More Than One Running Process?

OS

Code

Globals

Stack

Heap

P0

P1

P2

Run-Time Stack

main() main() main()

foo()

Memory Memory Memory

Before call During call After call

Notes: Each box represents an activation record of a function.

Activation Record

• Activation Record: – information about each function

– stored in run-time stack

int foo(int a, int b)

{

int w, x, y;

.

.

.

return y;

}

b

a

Return value

Return Address

Dynamic link

w

x

y

parameters

Local variables

bookeeping

Passing pointers into a function (1)

void Swap(int a, int b) {

int tmp;

tmp=a;

a=b;

b=tmp;

printf(“Inside SWAP(): a=%d b=%d”, a, b);

}

main()

{int x=2,y=3;

Swap(x,y);

printf(“x=%d y=%d”, x,y);

}

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Pointers in Cint I;

int *ptr;

i=4; // Store the value 4 into the memory location associated with i.

ptr= &i; // Store the address of I into the memory location associated with ptr

*ptr = *ptr + 1;

-----

int a[10], x;

int *pa;  

pa = &a[0]; /* pa pointer to address of a[0] */

x = *pa; /* x = contents of pa (a[0] in this case) */

// &a[i] ~ a + i a[i] ~ *(a+i)

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Passing pointers into a function (2)

void Swap(int *a, int *b) {

int tmp;

tmp=*a;

*a=*b;

*b=tmp;

printf(“Inside SWAP(): a=%d b=%d\n”, *a, *b);

}

main()

{int x=2,y=3;

Swap(&x,&y);

printf(“x=%d y=%d”, x,y);

}

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Dynamic Memory Allocation• void *malloc(size_t number_of_bytes)

Ex: char *cp; cp = malloc(100);

int *ip; ip = (int *) malloc(100*sizeof(int));

• void *calloc(size_t num_elements, size_t element_size};int *ip; ip = (int *) calloc(100, sizeof(int));

Malloc does not initialise memory (to zero) in any way. If you wish to initialise memory then use calloc.

• free(pointer).• kmalloc() & kfree()

• void * kmalloc (size_t size, int priority); void kfree (void * __ptr);  

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