Is there any C system call for getting the major number and minor number from a device file in solaris?
You can use one of the stat family functions. The numbers are in the st_rdev field. Use the major/minor functions defined in sys/mkdev.h to retrieve them.
Related
I have a read/write operation going on in the Fortran code snippet as follows
OPEN(5,FILE='WKDAT.dat', STATUS='OLD')
OPEN(6,FILE='WKLST.dat', STATUS='UNKNOWN')
I know that by default the unit number 5 is used for input from the keyboard and unit number 6 is used to display on the screen. Also I can use *.
But in the above-mentioned Fortran code unit number is 5 and a file name "WKDAT.dat" is given. So this means that the data is being read from "WKDAT.dat" file. Also there is code unit number 6 and a file name "WKLST.dat" is given. So this means that the data is being written to "WKLST.dat" file.
Is my understanding correct?
As per my basic knowledge:
Unit number 5 is only used to take input from keyboard & unit number 6 is only used to print to console so no files should be involved. But in the code snippet it has both unit number 5, 6 as well as file name.
So both are contradicting :(
In this link http://www.oc.nps.edu/~bird/oc3030_online/fortran/io/io.html they have mentioned the following "When I/O is to a file you must ASSOCIATE a UNIT number (which you choose) with the FILENAME. Use any unit number other than 5 and 6. On some computers, some unit numbers are reserved for use by the computer operating system."
Fortran has no magic unit numbers. The Fortran standard says nothing about 5, 6 or any other valid unit number being used for a special purpose. As such you are free to use the open statement to associate any valid unit number with a file. However traditionally for reasons that pre-date me 5 and 6 have been pre-associated with the keyboard and screen, as you say. Now still you can change the association by use of the open statement and that is fine save for the confusion it can cause, so most people I know recommend avoiding this and using unit numbers of 10 and upwards. Also because 5 and 6 are not guaranteed to be associated with the default input and output devices I would recommend against their use, preferring * or, in more modern code, the named constants input_unit, output_unit and error_unit from the iso_fortran_env intrinsic module.
So in summary you've got the right idea, and I'm not surprised you're confused.
Nothing in the standard says units 5 and 6 have any special meaning although in practice standard input and standard output are often pre-connected to 5 and 6.
Module iso_fortran_env from Fortran 2008 contains constants
INPUT_UNIT
OUTPUT_UNIT
ERROR_UNIT
with the unit numbers where standard input, standard output and standard error are connected. These are allowed to be different than 5 and 6.
Opening a file in unit that is in use causes the unit to be associated with the new file.
For example the Cray Fortran manual says:
Unit numbers 100, 101, and 102 are permanently associated with the
standard input, standard output, and standard error files,
respectively.
That means if you open some other file as unit 5 or 6 standard input and standard output still have some other unit where they are pre-connected and they will not be closed.
ld man here say
-n
--nmagic
Turn off page alignment of sections, and mark the output as "NMAGIC" if possible.
-N
--omagic
Set the text and data sections to be readable and writable. Also, do not page-align the data segment, and disable linking against shared
libraries. If the output format supports Unix style magic numbers,
mark the output as "OMAGIC". Note: Although a writable text section is
allowed for PE-COFF targets, it does not conform to the format
specification published by Microsoft.
--no-omagic
This option negates most of the effects of the -N option. It sets the text section to be read-only, and forces the data segment to be
page-aligned. Note - this option does not enable linking against
shared libraries. Use -Bdynamic for this.
I do understand that theses options are used to make the code (.text) section writable or not, but I don't get the point to align or not the sections, and what is a "NMAGIC" section
On historic (PDP-11) Unix, an executable file's header began with a branch instruction that would jump past the header, to the actual start of the code. When Unix was ported to other processors, that initial PDP-11 branch instruction became fossilized as the "magic number" for the a.out(5) file format. When "pure text" was introduced, initially to allow processes to share their code segments, a new magic number was introduced so that the kernel could tell the difference (there were some important Unix programs that relied on self-modifying code and thus needed to be loaded with writable code segments). The old magic number (0407) was given the name "OMAGIC" -- "old magic" -- and the new magic number (0410) was given the name "NMAGIC", "new magic". The data segment immediately follows the code segment in memory, so when the code segment is made read-only, it must be padded to a page boundary.
Various operating systems and file formats since then introduced other magic numbers; in the last FreeBSD releases to use a.out format, the normal formats were ZMAGIC and QMAGIC, which were introduced to allow page zero in the address space to be unmapped for safety (so that a null-pointer dereference would fault) while still allowing executables to be demand paged (i.e., mmap()ed into the process's address space).
So to answer your question more directly: NMAGIC and OMAGIC are different formats of executable files, not of individual sections. They indicate the desired correspondence between the in-memory and on-disk layouts of the executable. (The reason these numbers are traditionally written in octal rather than hex or decimal is that octal is a natural representation for the instruction format on the PDP-11.) GNU ld uses these names (only) as references to executable formats that have analogous features, even when you are not generating traditional a.out format -- which of course is quite rare today. One particular benefit to using OMAGIC format is that it is more compact than any other format, which may matter in cases like boot loaders where space is limited, there is no demand paging, and there is also no room for any sort of padding.
I'm trying to get a "retro-computing" class open and would like to give people the opportunity to finish projects at home (without carrying a 3kb monstrosity out of 1980 with them) I've heard that repl.it has every programming language, does it have QuickBasic and how do I use it online? Thanks for the help in advance!
You can do it (hint: search for QBasic; it shares syntax with QuickBASIC), but you should be aware that it has some limitations as it's running on an incomplete JavaScript implementation. For completeness, I'll reproduce the info from the original blog post:
What works
Only text mode is supported. The most common commands (enough to run
nibbles) are implemented. These include:
Subs and functions
Arrays
User types
Shared variables
Loops
Input from screen
What doesn't work
Graphics modes are not supported
No statements are allowed on the same line as IF/THEN
Line numbers are not supported
Only the built-in functions used by NIBBLES.BAS are implemented
All subroutines and functions must be declared using DECLARE
This is far from being done. In the comments, AC0KG points out that
P=1-1 doesn't work.
In short, it would need another 50 or 100 hours of work and there is
no reason to do this.
One caveat that I haven't been able to determine is a statement like INPUT or LINE INPUT... They just don't seem to work for me on repl.it, and I don't know where else one might find qb.js hosted.
My recommendation: FreeBASIC
I would recommend FreeBASIC instead, if possible. It's essentially a modern reimplementation coded in C++ (last I knew) with additional functionality.
Old DOS stuff like the DEF SEG statement and VARSEG function are no longer applicable since it is a modern BASIC implementation operating on a 32-bit flat address space rather than 16-bit segmented memory. I'm not sure what the difference between the old SADD function and the new StrPtr function is, if there is any, but the idea is the same: return the address of the bytes that make up a string.
You could also disable some stuff and maintain QB compatibility using #lang "qb" as the first line of a program as there will be noticeable differences when using the default "fb" dialect, or you could embrace the new features and avoid the "qb" dialect, focusing primarily on the programming concepts instead; the choice is yours. Regardless of the dialect you choose, the basic stuff should work just fine:
DECLARE SUB collatz ()
DIM SHARED n AS INTEGER
INPUT "Enter a value for n: ", n
PRINT n
DO WHILE n <> 4
collatz
PRINT n
LOOP
PRINT 2
PRINT 1
SUB collatz
IF n MOD 2 = 1 THEN
n = 3 * n + 1
ELSE
n = n \ 2
END IF
END SUB
A word about QB64
One might argue that there is a much more compatible transpiler known as QB64 (except for some things like DEF FN...), but I cannot recommend it if you want a tool for students to use. It's a large download for Windows users, and its syntax checking can be a bit poor at times, to the point that you might see the QB code compile only to see a cryptic message like "C++ compilation failed! See internals\temp\compile.txt for details". Simply put, it's usable and highly compatible, but it needs some work, like the qb.js script that repl.it uses.
An alternative: DOSBox and autorun
You could also find a way to run an actual copy of QB 4.5 in something like DOSBox and simply modify the autorun information in the default DOSBox.conf (or whatever it's called) to automatically launch QB. Then just repackage it with the modified DOSBox.conf in a nice installer for easy distribution (NSIS, Inno Setup, etc.) This will provide the most retro experience beyond something like a FreeDOS virtual machine as you'll be dealing with the 16-bit segmented memory, VGA, etc.—all emulated of course.
OS has 2 modes i.e user and kernel mode.What is the need of these two modes to protect PCB?
Here's a good read on the differences:
http://blog.codinghorror.com/understanding-user-and-kernel-mode/
Basically, you want to keep user mode code from doing anything that could harm the computer ("harm" being defined as overwriting memory other processes are using, sending malicious/dangerous input to hardware, etc). But at the same time, you need to have access to these functions of the computer (i.e, you want your program to be able to open / read / write to files, etc) By segregating these functions to another program that runs in kernel mode (the "kernel" of your OS), you can do this.
I recently got some Fortran code, which successfully ran on Mac OS. This code along with input files were later sent to me to get compiled. I precisely used the same code and the same input files but an error "array bounds exceeded" appeared. I am using CVF 6.6 on Windows XP.
I wanted to know the following things:
Is this a compiler or OS problem?
Shall I arrange a Mac OS to get them compiled?
After surfing so much on internet I think the wise thing to do is to get my data "format free". But I don't how to do that when my data is a time series with time in one column and voltage in the second.
The error message array bounds exceeded always (I think) indicates that your code has tried to access an array element outside the bounds of an array, for example element 25 in an array with 24 elements. This can only occur at run-time, and your compiler/run-time will only spot it if, when compiling, you set on the compiler option(s) for array bounds checking; your compiler documentation will tell you what those options are.
The error message should have been accompanied by some more information telling you where in the program the error occurred and the index of the out-of-bounds array access.
Given that your source code and your input data are identical how could this have occurred ? Since you have compiled the program on 2 different platforms your compilations cannot have been identical, it is entirely possible that array bounds checking is switched off on your Mac and on on your Windows PC.
Fortran programs may execute apparently successfully despite making accesses to out-of-bounds array elements. If the memory address of array element 25 out of 24 holds a value which is meaningful and the address is within your program's space the computation is likely to continue. It is also likely to be useless, but you can go for many years before finding that out.
I suggest that you go back to the Mac, recompile with array bounds checking, and run again, see what happens.
It's also possible that the routines which read your file find a different number of values on XP and Mac; I suspect that can be caused by different line ending characters, even by whether or not the input file has a newline at the end. Check this too.