CSC322 C Programming and UNIX - Department of Computer ...

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The execvp() function execvp(const char *file, char *const argv[]) is reaonably easy to use: – First argument is a file name (not containing any /) – The program to be executed is found as by the shell, by looking through all the directories in PATH Second argument is a pointer to an array <strong>of</strong> argument pointers – Same format <strong>and</strong> conventions as argv in main – First argument should be program name – Array should be NULL terminated Upon execution, the new program runs – Keeps old PID, GID, PGID, working directory, . . . – Normal file descriptors stay open (unless the the flag FD CLOEXEC is set using fcntl()) Stephan Schulz 614
#include #include #include #include #include #include #define MAX_LINE 1024 void err_sys(char* message) { perror(message); exit(EXIT_FAILURE); } Example: A mini-Shell Stephan Schulz 615
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CSC322 C Programming and UNIX Steph
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The UNIX Operating System UNIX and
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The UNIX Operating System UNIX and
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UNIX is a big-iron operating system
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UNIX First portable operating syste
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UNIX history tree (simplified) For
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1978 3BSD, adding virtual memory 19
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A Short History of UNIX and C 1991
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Another Opinion UNIX is not an oper
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Upshot You don’t have to grow a b
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Shell UNIX Architecture Libraries U
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Some Concepts UNIX is a multi-user
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UNIX: Provide Tools, Not Policy The
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Default KDE Desktop (SuSE Linux) St
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KDE Desktop with Terminal Applicati
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Text Interface Example (contd.) Mos
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Typical File System Layout / (Root
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More about files We can use the -l
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GNU info files UNIX Online Document
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CSC322 C Programming and UNIX UNIX
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Command Types There are different t
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UNIX User Commands: rm, mkdir, rmdi
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Effective Shell Use: Editing/Comple
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Example: File Handling and Globbing
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UNIX User Commands: cat/more/less c
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Getting into it: vi vi flyby Modal
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Emacs for Everyone Getting into it:
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Emacs for Everyone III Emacs is non
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ed is the standard text editor When
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? ? quit ? exit ? bye ? hello? ? ea
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SO-CALLED "VISUAL" EDITORS HAVE BEE
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Usage: grep . . . UNIX User Comma
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Simple Output Redirection You can r
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Input Redirection You can also redi
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Basic Process Control You can start
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Job Control Example $ emacs & (Star
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CSC322 C Programming and UNIX Progr
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Consider the following C program #i
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#include #include int main(void)
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A Closer Look (4) gcc is the GNU C
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The Fahrenheit-Celsius Example Comp
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Variables “int fahrenheit, celsiu
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A while-loop has the form while()
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UNIX User Commands: cp and mv cp wi
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Flow-Control: if The primary means
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Flow-Control: for The for-loop in C
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for vs. while Note that for is more
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Types: Integers and Characters C ha
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Simple Character I/O The C library
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Exercises Write a programm that con
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Nomination: Most Useless Use of cat
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Example: Word Counting /* Count wor
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Another View at Expressions Express
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Expressions: Associativity of Binar
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Expressions: Logical Operators Logi
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Floating Point Numbers C supports t
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Administrative Notes Please ssh to
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#include #include #include int m
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Initializing Arrays In the example,
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No Safety Belts and No Air Bag! C d
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Functions Functions are the primary
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Function Calling A function is call
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Example: Printing Character Frequen
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Assignment A prime number is a (pos
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A function is a named subroutine Re
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Example: int read int10(void) /* We
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Do we have a Valid Digit? /* Is a c
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Build General Functions! Good progr
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Example: Printing Integers We now w
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Writing a Number in any Base (
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Putting Things Together: A Base Con
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Usage Example $ ./base converter In
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Includes Translates into Is combibe
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The C Preprocessor The C preprocess
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myfile.c: A Poem #include "mary" $
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Simple Macro Definitions: #define T
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Macros with Arguments Macro definit
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#define Caveats Since macros work b
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cond preproc.c: #define hallo #defi
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cond preproc.c: #define hallo #defi
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Combinations of #ifdef and #include
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Definitions and Declarations Defini
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Scoping Rules There are two kinds o
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Limiting Potential Scope By default
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Persistent Local Variables: static
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Example: Static and Automatic Varia
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Implement the libray in its own sou
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Project: An RPN Calculator Aim: A c
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$ ./rpn calc Usage Example 10 8 + S
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Subtasks From the above, we can ide
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The Character I/O Library: Ideas Ma
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The Character I/O Library: Global V
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int LookChar(void) { int c = GetCha
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#include "chario.h" The Integer I/O
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The Integer I/O Library: Helper fun
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The Integer I/O Library: Helper fun
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The Integer I/O Library: Checking f
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Exercises Download the program from
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Recapitulation: Some of our Library
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Case Distinctions Note: The operato
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The Stack Abstract Datatype A stack
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Pushing things onto the stack: PUSH
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The Main Program: Prelimaries and D
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The Main Loop: Arithmetic operators
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The Main Loop: I/O operators switch
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case ’S’: for(i=0; i
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UNIX User Commands: dc dc is an arb
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Bitwise Operators Bitwise operators
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Example These macros can be used to
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Conditional Expressions Similarly t
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Type Conversion (Casting) As alread
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Order Of Execution In general, the
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Types in C C offers a set of basic
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Defining New Types with typedef The
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Enumerations in C Enumeration data
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enum and typedef Typically, enumera
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Aggregating Data Types Let’s agai
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Consider the following definition:
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Exercises Create a function that ha
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Assume the following problem: Repre
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typedef enum { circle, square, rect
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typedef union { CircleCoord circle_
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Pointers Pointers are derived types
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#include #include void swap(int *
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Why Pointers? The are two main reas
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Exercises Write a program that prin
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Refresher: Pointers A pointer type
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The malloc() function We request a
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More on Dynamic Memory Allocation G
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Example: SecureMalloc() Note: In my
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Example: Linear Lists (of Integers)
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#ifndef INT_LISTS #define INT_LISTS
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Example - Inserting At the End /* I
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Example - Freeing Lists /* Free the
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Example - Main Function int main(vo
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Use this datatype and the functions
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Monday, Oct. 14th, 11:00 - 11:50 To
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Refresher: Dynamic Memory Handling
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int array[10]; int *a, *b; a = arra
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Compiling: gcc -o csc322 csc322.c R
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#include #include #include void
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CSC322 C Programming and UNIX Midte
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The File System / (Root directory)
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Some Important UNIX Commands (1) Or
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Input and Output Redirection, Pipin
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C Compiling with gcc Programs consi
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if...else - Conditional execution s
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C Preprocessor The #include directi
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#include #include #define BUF_SIZ
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Example: Growing the Buffer as Need
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char *cp, *cq; int *ip, *iq; Pointe
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Reading the Command Line: argc and
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#include #include Example: Echoin
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CSC322 C Programming and UNIX Makin
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chario.h The rpn calc Example (Simp
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UNIX User Utilities: make make is a
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Built-In Rules and Makefile Variabl
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Phony Targets Not all targets need
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CSC322 C Programming and UNIX Odds
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Assertions Internal consistency che
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#include #include #include int g
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Search in Loops A frequent use of l
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Selective Operations and Special Ca
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do/while Loops Both while and for l
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E theorem prover Some Loop Statisti
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CSC322 C Programming and UNIX Funct
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Function Pointers We can use the ad
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Example #include #include int add
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C Library Functions: qsort() qsort(
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#include #include Example typedef
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Unsorted: 103 70 105 115 81 127 74
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C Standard Library Organisation - a
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#include #include #include #incl
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CSC322 C Programming and UNIX C Sta
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Some C Character Classes All charac
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#include #include #include int m
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Strings Strings are not part of the
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Example: Duplicating Strings Severa
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String Functions from (3) int strc
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Generic Memory Access Functions The
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Memory Functions from (2) void *me
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Memory Functions from (1) void *me
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Example #include #include #includ
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Input and Output in the Standard Li
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Opening File Streams In addition to
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Simple Stream Based I/O Functions (
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} for(i=1; i
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Exercises Write a version of memmov
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Remark about fgets() char *fgets(ch
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int main(int argc, char *argv[]) {
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$ man man | ./mycat1 Example Output
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Buffering and Flushing Both input a
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#include #include int main(int ar
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More Operations on Files int remove
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Error Functions Each FILE data stru
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A first Example printf("%d divided
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Format Specifiers Format specifiers
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Some Conversion Letters (2) f: Prin
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Size Modifiers Size modifiers are u
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The Flags -: Left-justify output (o
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#include #include Example int mai
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$ arch322 Makefile sort_csc322.c ut
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Processes A UNIX process is an inst
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$ ps PID TTY TIME CMD 1125 pts/3 00
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$ ps aux Interesting ps Example USE
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Signals Signals are a way to signal
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Some UNIX Signals UNIX defines abou
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top is an interactive version of ps
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Catching Signals User programs can
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ANSI C Signal Handling with signal.
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ANSI C Signal Handers A signal hand
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int main(int argc, char* argv[]) {
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Exercises Start a long running proc
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UNIX philosophy: Everything is a fi
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FIFOs (named pipes) UNIX File Types
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The stat() Functions (2) All three
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} Example Continued else if(S_ISLNK
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Example Output (of device directory
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Links (2) Soft links create indirec
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Exercises Read man stat and extend
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All files have an owner (a user) Fi
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User Groups Groups are used in UNIX
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UNIX User Utilities: chown and chgr
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Symbolic Encoding ls -l prints a st
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Examples rw-r--r-- is the most comm
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chmod Examples chmod ugo+rwx myfile
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Exercises Read the man and info pag
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File Decriptors Files are identifie
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Option flags for open() Note: All o
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Notes on open() and close() The mod
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} Example Continued while((count =
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Cheating with fdopen() Formatted, b
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CSC322 C Programming and UNIX More
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FILE* myfile Standard IO Library Th
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Manipulating File Descriptors: fcnt
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if(flags & O_APPEND) { printf("Appe
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Multiplexing I/O Often, a program h
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select() Arguments fd set is define
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$ ./select_example 2 file descripto
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CSC322 C Programming and UNIX Basic
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Networking Stephan Schulz 517
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Networking Concepts Is communicatio
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Level 2 protocol (Hardware-Agnostic
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The Transmission Control Protocol (
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A server offers a certain service C
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The Client Side for TCP Connections
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Creating Sockets with socket() (2)
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Socket Adresses for IPv4 For IPv4 a
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Connecting to a Remote Port: connec
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Example (2) sock = socket(PF_INET,
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The Server Side A server has a more
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Naming a Socket (Binding a Socket t
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Accepting Connections To finally es
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Example (2) if(argc!=2) { fprintf(s
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man pages: - man socket - man 2 bin
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CSC322 C Programming and UNIX Proce
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Process Properties For each process
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Exiting There are three normal ways
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Cleaning up: atexit() ANSI C allows
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Example (2) int main(void) { if(ate
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Running other Programs: system() Th
Page 563 and 564: Termination Status Interpretation T
Page 565 and 566: Example: Executing Commands int mai
Page 567 and 568: Exercises Write a program that prin
Page 569 and 570: Creating new Processes: fork() The
Page 571 and 572: } Example if(child_pid == 0) { pid
Page 573 and 574: Comments on fork() Order of executi
Page 575 and 576: #include int main(int argc, char*
Page 577 and 578: FILE* myfile Standard IO Library I/
Page 579 and 580: Example: Bufferd I/O and Forking /*
Page 581 and 582: Waiting for Children to Die As stat
Page 583 and 584: Example (2) for(i=0; i
Page 585 and 586: Output: Example Output Parent. My P
Page 587 and 588: CSC322 C Programming and UNIX Proce
Page 589 and 590: Getting and Changing Process Groups
Page 591 and 592: Example (2) res = setpgid(0,0); if(
Page 593 and 594: Example Output $ ./pg example Paren
Page 595 and 596: Is this good for Something? There a
Page 597 and 598: Example (2) pid = getpid(); pgid =
Page 599 and 600: Example Output with kill Queen bee:
Page 601 and 602: Waiting for Termination: waitpid()
Page 603 and 604: Exercises Write a program that keep
Page 605 and 606: Process Environment Each UNIX proce
Page 607 and 608: $ printenv Example: Part of my Envi
Page 609 and 610: Accessing the Environment from a Pr
Page 611 and 612: The POSIX Interface to the Environm
Page 613: The 6 exec Functions #include int
Page 617 and 618: int count_words(char* line) { int w
Page 619 and 620: } Example (5) for(i=0; i
Page 621 and 622: int main(void) { pid_t child_pid; c
Page 623 and 624: } { /* Parent */ setpgid(child_pid,
Page 625 and 626: # ls * Command: ls Arguments: ls *
Page 627 and 628: CSC322 C Programming and UNIX Final
Page 629 and 630: Pointers and Dynamic Arrays Arrays
Page 631 and 632: New Flow Control Constructs break i
Page 633 and 634: Standard Library: Characters and St
Page 635 and 636: Standard Library: Buffered I/O Stan
Page 637 and 638: Processes and Signals Processes are
Page 639 and 640: UNIX: Everything is a file File typ
Page 641 and 642: File Descriptors and select() File
Page 643 and 644: TCP/IP (v4) Connections Reliable, s
Page 645 and 646: Process Environment and Program Exe
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