Forum: D2L Discussion
- Participation is expected

Deadlock vs Starvation
- Under starvation, some, but not all processes are unable to make progress.
- Under deadlock, the system (all processes) can't make progress.

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File|I/O Device Representation

C++|Java:	Streams (object)
- Standard: cin, cout, cerr
- Library: <iostream>
- Seek: seekg, seekp (g=get, p=put)
- Open: <fstream>, <ifstream>, <ofstream>

C:		File Pointer (address)
- Standard: stdin, stdout, stderr
- Library: <stdio.h>, in C++ referred to as <cstdio> (by g++)
- Seek: fseek() - stdio library call
- Open: fopen - stdio library call

Unix (System): 		File descriptor (int)
- Standard: 0, 1, 2
- Library:  None. These are system calls, i.e. they are built into the operating system.
- Seek: lseek
- Open: open

Compilers: 
- g++ for C++; can handle Unix/C
- gcc for Unix/C

C and Unix are coupled. The system language of Unix IS C.

Permissions on files are set from the shell using chmod. 
- The system call open() requires permissions to be specified on newly created files. 
- Others use a default value set in the shell

Most system calls return 0=success, -1=failure

Unix open() examples/exercises, with C/stdio & C++ equivalent - assume fstream file:
1. Open a file named abc.txt for writing, only if it exists. If it does, the present contents should be preserved, and writing should occur after the present contents.

result=open("abc.txt",O_WRONLY|O_APPEND);

C++:
file.open("abc.txt",ios::read);
if (file.is_open()) {
  file.close();  
  file.open("abc.txt",ios::write|ios::app);

Notes: 
- For an fstream, ios::write does not automatically clobber (i.e. truncate). 
- For an ofstream, ios::write does truncate unless or'd with ios::ate or ios::app
  * ate means you can start writing at the end if you like
  * app means that the location pointer seeks to eof before any write takes place.
	
stdio.h:
FILE *fPtr;
fPtr=fopen(("abc.txt","r");
if (fPtr) {
  fclose(fPtr);
  fPtr= fopen("abc.txt","a");
}


Give an open() command equivalent to the C++ command Dest.open(“abc.txt”), where Dest is an ofstream