1. Advanced UNIX progamming
Fall 2002
Instructor: Ashok Srinivasan
Lecture 4
Acknowledgements: The syllabus and power point presentations are modified versions of those by T. Baker and X. Yuan

2. Announcements Assignment 1 announced
Due Sep 13, 2002
Quiz next week, on week 1 & 2 topics
Reading assignment
APUE chapter 1
APUE Chapter 2
Pages 25-30, 44-46

3. Review of week 1 topics UNIX programming environment Editors
C compilers and debuggers
Makefiles

4. Week 2 Topics Review some features of C Review some UNIX system calls
Header files
Command line arguments
Utilities
Review some UNIX system calls
system, etc
Portability
Standards: ANSI, POSIX, etc
32 bit vs 64 bit
Byte order: Little endian vs big endian

5. Week 2 Topics ... continued Introduction to the UNIX API
Environment variables
Exit status
Process ID
User ID
Signals and signal masking
UNIX file system
File system abstraction
Directories
File descriptors
Unix API Programming Examples and Techniques
Example with direct IO
open, close, etc
Variable argument list

6. Review some features of C
Header files
Macros
Command line arguments
Utilities

7. Header files
Usually define interfaces between separately compiled modules
May contain macro definitions, preprocessor directives, declarations of types, and function prototypes
Should not contain variable definitions or executable code

8. Some header file errors
Improper header file use can cause problems
Try compiling example2.c
Including a header file multiple times may cause redefinition errors
Why does including stdio.h twice not cause any problem?
Look at /usr/include/stdio.h

9. Conditional Code in Headers
Preprocessor directives are used to prevent the body of a header file from being used multiple times.
#ifndef MYHEADER
#define MYHEADER
/* the body of the header file */
#endif

10. Macros with and without Parameters
#define MAX_LENGTH 256
... for (i = 0; i < MAX_LENGTH; i++) ...
Macros can have parameters
#define max(a,b) (a > b) ? a : b
What is wrong with the following?
#define sum(a, b) a + b
#define product(a, b) a*b
See example3.c, example3b.c, example3c.c, and example3d.c

11. Some useful functions #include <stdio.h>
int sprintf(char *s, const char *format, ...);
int sscanf(const char *s, const char *format, ...);
How would these be used to get all the fields from the output of the shell command ps?
See example4.c

12. Some Unix System Calls You may use these in your first assignment
mkstemp

13. system #include <stdlib.h> int system(const char *string);
Works as if string is typed into the shell at a terminal
Returns the exit status (see man page for waitpid)
Usually -1 is returned if there is an error

14. mkstemp #include <stdlib.h> int mkstemp(char *template)
template should end in XXXXXX
It replaces XXXXXX with unique file name, and returns an open file descriptor for a file available for reading and writing

15. Portability Standards 32 bit vs 64 bit Byte order
Source code portability: ANSI/ISO C
UNIX standards: POSIX, open group
Internet engineering task force (IETF)
32 bit vs 64 bit
Byte order
Little endian vs big endian

16. Source Code Portability
Standard programming language
Example: ANSI/ISO C
ISO C90 is in use; C99 is latest - should it be used?
Standard libraries
Standard API to operating system
Example: POSIX.1
Auto-configuration mechanisms
Programmer discipline

17. POSIX (IEEE STDS 1003.x and ISO/IEC 9945)
Unix Standards
POSIX (IEEE STDS 1003.x and ISO/IEC 9945)
POSIX.1: System API for C language
POSIX.2: Shell and utilities
POSIX.5: System API for Ada language
POSIX.9: System API for Fortran language
See also and

18. Unix Standards ... continued
The Open Group
A consortium of vendors and user organizations
Consolidation of X/Open and the Open Software Foundation
Controls the UNIX trademark
The Austin Group combined the IEEE, TOG, and ISO standards
See also and

19. Internet Engineering Task Force (IETF)
Network designers, operators, vendors, researchers
Deals with the Internet
Issues RFCs
See also

20. 64-bit vs. 32-bit architecture
Pointers cannot be stored as int
size_t cannot be stored as int
long may not be long enough for size_t and offset_t
Datatype
ILP32
LP64
char 8
short 16
int 32
long 64
pointer
(long long)
Note: ILP32 and LP64 are not the only two models

21. Byte order Little-Endian Big-Endian
Low-order byte is stored at lowest address
Big-Endian
High-order byte is stored at lowest address