PRINCIPLES OF OPERATING SYSTEMS

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1 PRINCIPLES OF OPERATING SYSTEMS Tutorial-1&2: C Review CPSC 457, Spring 2015 May 20-21, 2015 Department of Computer Science, University of Calgary

2 Connecting to your VM Open a terminal (in your linux machine) Go to cloud-key folder Type ssh i cpsc457.key fedora@<vm-ip-address> 2

3 Install Packages Change to root: sudo -i Use yum package manager eg: yum install gcc ( to install C compiler) You may install and use a text editor of your preference Some of the packages you may want to install: g++, vim, emacs, man-pages, make, wget,. 3

4 Download Sample C files Download sameplecodesc.zip wget Unpack unzip sameplecodesc.zip 4

5 Why should I learn C now? High level language Low level: machine languages Gives more control over low level mechanisms Memory management, memory location management, mixing assembly code, device management, direct access to OS primitives Procedural language Small and generic Applications: Most OS code (eg. Linux) is written in C Compilers and application software Some downside Requires careful memory management. You may have to write more lines of code. 5

6 Outline Compiling and executing a C program Linux man page gcc Command line arguments Preprocessing Data types and operators Control flow Pointers Call by value and Call by reference Makefile Arrays Structures Strings File I/O Tutorial-1 Tutorial-2 6

7 Hello World! Step 1: Write code using your favorite editor #include <stdio.h> int main(int argc, char * argv[]) { printf("hello World!\n"); } return 0; Reference: Sample program hello.c 7

8 Hello World! Step 2: Compile 1. Make sure gcc is installed (use yum for installation) 2. Change current directory to where the C source file is saved 3. Compile your program gcc hello.c o hello (By default, the executable program is under the name a.out. The o option allows you to change the name) 4. Run your program:./hello 8

9 Linux manual page Install yum install man-pages Use man command to access manual page eg: # man 3 printf (3 is the section number) Sections 1: Linux commands 2: System calls 3: Library calls You will use this feature extensively in this course 9

10 gcc Common parameters for gcc Please get familiarized with gcc using the manual page # man gcc -o file output file for object or executable -Wall all warnings use always! -c compile source file (don t link) -g insert debugging code (gdb) -l library 10

11 Command-Line Arguments Number of arguments The array of arguments int main(int argc, char * argv[]) Return value of the program: 0 = success, others = some error Can also be declared as void, i.e., no return value Try the following steps and understand the o/p # gcc args.c o args #./args #./args 1 2 hello Reference: Sample program args.c 11

12 Text Replacement Preprocessing By defining macros #define MAX_LEN 100 Header file inclusion #include <head-file.h> eg: I/O Library #include <stdio.h> Reference: Sample program preprocess.c 12

13 Primitive Data Types bool (not boolean) char: a single character short, int, long, long long: integers float, double: floating point number You can also define your own types using typedef typedef unsigned char byte 13

14 Lets find the size of some of the data types What is the size of char short int long int long long int Hint: use sizeof unary operator Reference: Sample program datatype.c 14

15 Operators Arithmetic: +, -, *, /, =, ++, --, % - Conditional: <, <=, ==,!=, >=, > - Boolean: &&,,! - Bitwise: ~, &,, ^, <<, >> 15

16 Control Flow For loop eg: for(int i=1; i<10; i++) printf( %d\n, i); While loop eg: i = 1; while (i < 10) { printf( %d\n, i); i++; } 16

17 If-else i = 1; if (i > 1) i++; else printf( do nothing ); switch Multi-way decision Break : break from loop Continue: continue next iteration of the loop Reference: Sample program control.c 17

18 Pointers Pointers store memory address (not value) Example code-1: int *variable = NULL; // Declaration int i = 10; //This is a different variable variable = &i; // &i gets the address of i int another_variable = *variable; // *variable gets the value *variable = 2; // pointed by variable What is the value of i and another_variable now? Example code-2: Reference: Sample program pointers.c 18

19 Call by value and Call by Reference If data is passed by value, the data is copied from the variable used in a function x to a variable used by a function y If data is passed by reference, a pointer to the data is copied instead of data itself Reference: Sample program argument_passing.c 19

20 Makefile make command (install make using yum ) Help tp organize code compilation Create a file called makefile (no extensions) Use f option to specify makefile name of your choice Format: target: dependencies [tab] system command Eg: all: hello hello: hello.c [tab] gcc o hello hello.c 20

21 Constants in makefile Remove files using make clean CC=gcc CFLAGS=-Wall all: hello hello: hello.c [tab] $(CC) $(CFLAGS) o hello hello.c clean: [tab] rm hello Reference: Sample file makefile 21

22 Arrays Declaration: int array[size] Index starts from zero Common logical error: Array out of bound int input[10]; input[10] = 20; input[-1] = 5; When passing an array to a function, typically you have to pass the array size as a separate argument as well. eg: foo(array, size); Reference: Sample program array.c 22

23 Structures (struct) C struct is a way to logically group related types Structure definition struct student { int studentid; float mark; }; Reference: Sample program structure.c 23

24 Pointers Revisited Memory Allocation: int *p = malloc(sizeof(int)); int *p = (int *) malloc(10 * sizeof(int)) p now contains the beginning of the address space for the uninitialized dynamically allocated memory chunk Deallocation: clear the allocated memory when you are done using it. Otherwise, Memory Leak!!! free(p) 24

25 Pointers - structs and arrays Pointers to a struct Student * s = new Student; //a pointer to student s1->id = 1235; Pointers to an array //struct //access element id of student int size = 3; //size of array int array[size]; //create array int *ptr = array; *ptr = 1; ptr++; *ptr = 2; What is the value of array[0] and array[1]? Reference: Sample program pointers2.c and pointers3.c 25

26 Strings In C, string is an array of char ended with \0 (a null terminator) char s[10]; // Character array char *str; // Pointer to char str = hello ; // str points to a string constant Make use of string library for string manipulations #include <string.h> Copying a string strcpy(s, t); Length of the string strlen(s) - Explore other string library functions Reference: Sample program strings.c 26

27 File I/O Open a file: File * fd = fopen (filename, mode); e.g., File * fd = fopen ( test.txt, r ); r - open for reading w - open for writing a - open for appending r+ - open for reading and writing, start at beginning w+ - open for reading and writing a+ - open for reading and writing Close a file: fclose(fd); Writing to a file: fprintf(fd, Hello\n ); Reading from a file: fscanf(fd, %s, str); Return a special value EOF when reading the end of a file It is also possible to read and write character by character from and to a file using fgetc() and fputc(), respectively. Reference: Sample program fileio1.c and fileio2.c 27

28 References C for Java programmers: va_programmers.pdf C for Java Programmers Tutorial orjavaprogrammers.ppt C Library CPSC 457 Fall

29 Questions? 29

CS 326 Operating Systems C Programming. Greg Benson Department of Computer Science University of San Francisco

CS 326 Operating Systems C Programming Greg Benson Department of Computer Science University of San Francisco Why C? Fast (good optimizing compilers) Not too high-level (Java, Python, Lisp) Not too low-level