Unit 2
- 1. UNIT -2 UNIX FILES Prepared By, Darshan.K.R Lecturer,SJBIT Kengeri,Bangalore
- 2. The ANSI/ISO C++ standard Objective: “ To make writing good programs easier and more pleasant for individual programmer ” 1980’s by Bjarne Stroustrup at AT & T Bell Labs ANSI C++ standard developed by WG21 committee of ISO & ANSI X3J16 in 1994
- 3. Difference between ANSI C and C++ All functions must be declared or defined before they can be referenced. int foo(); ANSI C : int foo(…); C++: int foo(void); C++ encrypts external function names for type-safe linkage.
- 4. The POSIX standards IEEE society in 1980’s formed a special Task Force called POSIX for creating standards for OS interfacing. POSIX.1 : Basic OS APIs for manipulation of files and processes. POSIX.1b : Standard APIs for real-time OS interface. It includes Interprocess Communication. POSIX.1c: Standards for multi-threaded programming interface.
- 5. The POSIX standards To ensure a user program confirms to POSIX.1 standard, #define _POSIX_SOURCE OR % cc -D_POSIX_SOURCE *.c POSIX.1b standard , _POSIX_C_SOURCE 198808L 199009L 199309L _POSIX_VERSION in the <unistd.h>
- 6. Show Posix Version #define _POSIX_SOURCE #define _POSIX_C_SOURCE 199309L #include <iostream.h> #include <unistd.h> int main() { #ifdef _POSIX_VERSION cout<<“System confirms to POSIX”<<_POSIX_VERSION<<endl; #else cout<<“_POSIX_VERSION is undefined”; #endif return 0; }
- 7. The POSIX Environment #include <header_file_name> Each #included file need not be a physical file The /user/include directory does not have to exist. POSIX standards do not mandate that all systems support the concept of supervisor. Userid of Zero does not have any special privilege.
- 8. The POSIX Feature Test Macros _POSIX_JOB_CONTROL _POSIX_SAVED_IDS _POSIX_CHOWN_RESTRICTED _POSIX_NO_TRUNC _POSIX_VDISABLE
- 9. Show test macros #define _POSIX_SOURCE #define _POSIX_C_SOURCE 199309L #include <iostream.h> #include <unistd.h> int main() { #ifdef _POSIX_JOB_CONTROL cout<<“System supports job control\n”; #else cout<<“System does not support job control\n”; #endif }
- 10. Limits Checking <limits.h> - has the set of configuration limits _POSIX_CHILD_MAX _POSIX_NAME_MAX _POSIX_PATH_MAX …… .
- 11. APIs for configuration limits #include <unistd.h> long sysconf(const int limit_name); long pathconf(const char * pathname, int flimit_name); long fpathconf(const int fdesc, int flimit_name); limit_name in <unistd.h> has values _SC_CHILD_MAX _SC_OPEN_MAX…..etc flimit_name in <unistd.h> has values _PC_PATH_MAX _PC_NAME_MAX
- 12. #define _POSIX_SOURCE #define _POSIX_C_SOURCE 199309L #include <stdio.h> #include<iostream.h> #include <unistd.h> int main() { int res; if((res=sysconf(_SC_OPEN_MAX)) == -1) perror(“sysconf”); else cout<<“OPEN_MAX:”<<res<<endl; } Test Config
- 13. The POSIX.1 FIPS Standard FIPS: Federal Information Processing Standard POSIX.1 FIPS - Developed by NIST (National Institute of Standard and Technology) _POSIX_JOB_CONTROL _POSIX_SAVED_IDS _POSIX_NO_TRUNC _POSIX_CHOWN_RESTRICTED _POSIX_VDISABLE NGROUP_MAX = 8 Read and write APIs should return the no of bytes after signals. Group ID – Inherit that of the parent
- 14. The X/Open Standards X/Open organization was formed by a group of European companies to propose a common OS interface for their computing systems. XPG3 – 1989 XPG4 – 1994 COSE (Common Open software Environment) formed in 1993 by HP, IBM, Novell, OSF and Sun Microsystems SPEC 1179 Incorporated in XPG4 as part of X/Open Common Application Environment
- 15. UNIX and POSIX APIs System Calls Determine system Config and user info Files manipulation Process creation and control Interprocess Communication Network Communication
- 16. System Calls User mode : is the normal execution context of any user process. It allows the process to access its process-specific data only. Kernel mode : Is a protective execution environment that allows a user to access kernels data in a restricted manner. Context switching
- 17. The UNIX and POSIX Development Environment <unistd.h> APIs /usr/include/sys headers <stdio.h> - perror function - Called by a user process when API execution fails. It prints the system-defined diagnostic message for any failure. lib.a & lib.so libsocket.a & libsocket.so – Socket APIs
- 18. API Common Characteristics APIs - return an integer value indicating the termination status of execution. - return –1 if API execution has failed. - set a global variable errno in <errno.h> - user process can call perror/strerror Error Status Code EACCESS EPERM EIO……etc
- 19. Question Bank Give the difference between ANSI C and C++. What are the major differences between ANSI ‘C’ and K & R ‘C’? Explain each with examples. What is POSIX? List few POSIX standards. Name a few POSIX APIs. Give the differences between POSIX and UNIX. Give the different POSIX feature test macros. Explain with a program and also give the output of the program. Give the prototype and explain with an example the following APIs. sysconf pathconf fpathconf Expand FIPS. Describe the characteristics of POSIX. 1 FIPS standard and X/open standard. What are the different features to be implemented in all FIPS conforming systems? Explain the common characteristics of API and describe the error status codes.