System Programming with C and Unix

1. System Programmingwith C and Unix CSCI 1730 April 1st, 2014

2. Materials • Class notes • slides & some “plain old” html & source code examples • linked from course calendar • board notes & diagrams • Textbook (Hoover) • http://www.amazon.com/System-Programming-Unix-Adam-Hoover/dp/0136067123 • Buy new / buy used / rent / eTextbook

3. Text • System Programming with C and Unix by Hoover • Ch 1: Introduction • Ch 2: Bits, Bytes and Data Types • Ch 3: Arrays and Strings • Ch 4: Pointers and Structures • Ch 5: Input/Output • Ch 6: Program Management • Ch 7: System Calls • Ch 8: Libraries • Ch 9: Scripting Languages

4. The UNIX operating system • kernel + shell + system calls • kernel: • provides access to H/W resources of computer • manages memory and CPU • shell: • provides command-line interface to services • system calls: • provide method-call interface to services

5. Overview of UNIX portion of course We'll (try to) cover: • basic concepts and terminology • files and directories • processes • interprocess communication • signals and signal handling • pipes • shared memory, messages, semaphores • X terminal i/o • sockets • standard i/o library

6. Basics: Files and Processes • info stored in files • while files have logical structure to programs that create and use them, at the UNIX level they are just a sequence of bytes • no record terminators, no file terminators, no special file types • names < 256 characters • < 14 to be backward compatible

7. Directories, pathnames • directories have hierarchical, tree-like structure • each directory can contain files and subdirectories • full names of UNIX files are pathnames, including directories • /users/faculty/eileen/junk.txt /users … Faculty … eileen junk.txt …

8. Example /users/faculty/eileen/junk.txt (absolute pathname) if _current working directory_ is /users/faculty/eileen • can use junk.txt (relative pathname) if _current working directory_ is /users/faculty • can use eileen/junk.txt (also a relative pathname)

9. Ownership, permissions • each file has an owner • that owner is a member of a _group_ • each file has 3 sets of permissions: • read/write/execute • one set for owner, one set for group, one set for public -rwxr-xr-x. 1 eileen users 50 Mar 31 20:29 play.exe -rw-r--r--. 1 eileen users 50 Mar 31 20:28 junk3.txt -rw-r-----. 1 eileen users 50 Mar 31 20:28 junk2.txt

10. Devices • UNIX treats devices like files. • filenames exist that represent devices like a keyboard or printer. To write to the printer, you can just write to the file that represents it... for example • cat fileX > /dev/rmt0 causes the contents of fileX to be written to the tape drive associated with the rmt0 file in the /devdirectory

11. Processes • process = instance of an executing program • When you type: > ls • at the command line, the shell process creates a process to run the ls program. • UNIX is multitasking • more than one process can run at the same time • i.e., multiple processes share the CPU

12. IPC: Interprocess Communication • Consists of mechanisms that allow processes to send info to one another • Methods differ in : • type/amount of info • number of processes • whether processes need to exist at the same time • whether processes need to be on the same machine

13. IPC: InterProcess Communication • pipes • output of one program is input of another • signals • processes that exist at same time on same machine can send integer signals • shared memory • processes that exist at same time can share variables • semaphores control access to shared memory • sockets • processes that exist at the same time on same or different machines can communicate arbitrary info

14. The shell supports pipes: >ls | more • output of the ls program is input to the more program >ls | grep notes | more • output of the ls program is input to the grep program • notes is a command line parameter to • output of grep is input to more

15. System calls and library functions • kernel • memory resident program, deals with process scheduling and i/o control • system calls • the interface to the kernel and the resources it controls. • invoked like library subroutines (but typically more efficient, lower level, run in 'kernel mode' rather than 'user mode'). • Library routines are a layer between user code and system calls.

16. Common shell commands • cd • pwd • set • which

17. Common system commands • grep • ls • man • more • time • sort

18. A “review” of C

19. C review – 4 data types /* A review of the basic data types in C. */ #include <stdio.h> int main() { intx,y; char a; float f,e; double d; x=4; y=7; a='H'; f=-3.4; d=54.123456789; e=54.123456789; printf("%d %c %f %lf\n",x,a,e,d); printf("%d %c %.9f %.9lf\n",x,a,e,d); }

20. C review – arithmetic /* A review of the basic arithmetic operators in C. */ #include <stdio.h> int main() { intx,y; int r1,r2,r3,r4,r5; x=4; y=7; r1=x+y; r2=x-y; r3=x/y; r4=x*y; printf("%d %d %d %d\n",r1,r2,r3,r4); r3++; r4--; r5=r4%r1; printf("%d %d %d\n",r3,r4,r5); }

21. C review – loops #include <stdio.h> /* A review of the loop types in C. */ int main() { inti,x; x=0; for (i=0; i<4; i++) { x=x+i; printf("%d\n",x); } while (i<7) { x=x+i; i++; printf("%d\n",x); } do { x=x+i; i++; printf("%d\n",x); } while (i<9); }

22. C review – blocks /* A review of conditionals and blocks in C. */ #include <stdio.h> int main() { inti,x; x=0; for (i=0; i<5; i++) { if (i%2 == 0 || i == 1) x=x+i; else x=x-i; printf("%d\n",x); } }

23. C review – flow control /* A review of flow control statements in C. */ #include <stdio.h> int main() { inti,x; x=0; for (i=0; i<5; i++) { if (i%2 == 0) continue; x=x-i; if (i%4 == 0) break; printf("%d\n",x); } }

24. System Programming Chapter 2

25. ASCII /* This program shows the dual interpretations of char and ** unsigned char data types. */ #include <stdio.h> main() { char a; unsigned char b; a='A'; b='B'; printf("%c %c %d %d\n",a,b,a,b); a=183; b=255; printf("%d %d\n",a,b); }

26. sizeof() operator /* This program demonstrates the sizeof() operator. */ #include <stdio.h> main() { int i; char c; double d; printf("%d %d %d %d\n",sizeof(i),sizeof(c),sizeof(d),sizeof(float)); }

27. Bitwise NOT /* This program demonstrates the bitwise not operator. */ #include <stdio.h> main() { unsigned char a; a=17; a=~a; printf("%d\n",a); }

28. Bitwise AND /* This program demonstrates the bitwise and operator. */ #include <stdio.h> main() { unsigned char a,b; a=17; b=22; a=a & b; printf("%d\n",a); }

29. Bitwise OR /* This program demonstrates the bitwise or operator. */ #include <stdio.h> main() { unsigned char a,b; a=17; b=22; a=a | b; printf("%d\n",a); }

30. Bit operators (variables and constants) /* This program demonstrates using the bitwise operators ** with variables and constants. */ #include <stdio.h> main() { char x,y; x=7; y=6; x=x&y; y=x|16; printf("%d %d\n",x,y); }