I know this is possible, because I have a binary I wrote a couple years ago to do exactly this. Unfortunately, I didn't save the source code.
I know that it was written in pure C, and I called against an OS X API and was able to lock the screen. Googling for "pure C OS X lock screen" and similar strings isn't getting me much; I saw documentation on how to do it in Objective C but that's not what I'm looking for.
Anyone have any idea how I accomplished this previously?
One way to do this is by using a call to system():
#include <stdlib.h>
int main(void) {
system("/System/Library/CoreServices/Menu\\ Extras/User.menu/Contents/Resources/CGSession -suspend");
return 0;
}
You're probably thinking of CGSCreateLoginSession() -- it's a private function and not documented by Apple. See this question for an example of its use.
Related
during this year in school my teacher showed us this function:
#include<Windows.h>
void gotoxy(int x,int y)
{
COORD punto;punto.X=x;punto.Y=y;
SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE),punto);
}
And looking in here some posts I read about this one based on ANSI escape codes
#include<stdio.h>
void gotoxy(int x, int y)
{
// <ESC>[(ROW);(COLUMN)f
printf("\x1B[%i;%if",y,x);
}
I kind of like the second one more, I feel I understand it better. But I wanted to ask here which of them is better because I know I'm probably missing something. What do you think?
If you write code for Windows then definitely use the first version. It always works on Windows but it does not work on other OSes (it does not even compile because other OSes do not provide these functions).
The second version is not tight to an OS. It works on any OS as long as the application runs in a terminal emulator that understands ANSI escape codes (most of them do).
I am trying to create a new system call in Minix 3.3. At first i just want to create simple printmsg() call that will write "Hello World" on screen.
I looked various tutorials on internet and still couldn't find out solution.
I defined my sys call number in callnr.h like this #define PM_PRINTMSG (PM BASE + 48) and i increased number of sys calls #define NR_PM_CALLS 49.
In table.c I added CALL(PM_PRINTMSG) = doprintmsg.
In proto.h I described function prototype `int do_printmsg(void);
Function implementation is written in misc.c. I added #include <stdio.h> and made Hello World function int do printmsg(){ printf("I am a system call"); return 0; }
When I test my system call in user program _syscall(PM_PROC_NR, PM_PRINTMSG, &m); I don't get any errors but no printf is displayed.
So, is it possible to printf messages from system calls since i had to add <stdio.h> myself in misc.c or i missed some steps. I forgot to mention that i go in /usr/src/releasetools and type make services and make install respectively to recompile kernel.
I figured out what was the problem, so i will post answer if someone needs this in future. I did everything well in this example but i failed to compile kernel.
The location was correct which is usr/src/releasetools, but command needed is make hdboot. Also i figured out my PC somehow wasnt working well with this virtual machines and i had many errors while compiling even though i didn't change anything. When i switched to laptop everything worked fine.
My conclusion is sometimes there is just something wrong on your machine so you should try and test problems on different ones
In my opinion, with the continuous evolution of MINIX 3 and its series, it will be wise to only follow the developer's guide directly from the minix3.org website here
Although you managed to solve the problem yourself, the latest version of MINIX3 (MINIX 3.4) will follow a more advanced and suitable approach.
Please visit the link to learn more.
Many regards.
Ola
I have a Lisp reader written in Java that I'm thinking of translating into C. (Or perhaps C++.) It's a fairly complete and useful hack, so the main issue is doing the dynamic-storage allocation in a language without garbage collection. If someone has already thought this through I'd rather borrow their code than figure it out myself. (C is not my favorite language.)
Of course, having a Lisp reader makes no sense unless you're planning to do something with the things you read, so perhaps I should have phrased the question, Where do I find a simple Lisp core written in C?, but in my experience the hardest unavoidable part of writing a Lisp (somewhat surprisingly) is the reader. Plus, I don't want to have a garbage collector; I'm anticipating an application where the list structures will be freed more or less by hand.
Gary Knott's Interpreting Lisp is very nice.
You may also try others, like Jim Mayfield's Lisp. There are probably lots of little Lisps out there...
You mentioned that you don't like C. Maybe you'd like Haskell -- in which case you could try "Write yourself a Scheme in 48 hours", an interesting tutorial (you get to write a Scheme interpreter in Haskell).
Update: I know that a Lisper would hardly feel comfortable using Haskell, but hey, it's much more comfortable than C (at least for me)! Besides that, HAskell has a good FFI, so it should be easy to use the Haskell-made Lisp-reader as a C-compatible library.
Update 2: If you want to use XLisp, as suggested by another user, you will probably need src/xlread.c (863 lines) and include/xlisp.h (1379 lines) -- but I could be wrong...
Update 3: If you use Gary Knott's Lisp (one single C file with 942 lines), the function signature is int32 sread(void). This would be my choie if I didn't need anything fancy (like read macros) or highly optimized (there is a PDF paper that describes how the code is implemented, so you won't have to find your way in a labyrinth). The documentation for the function is:
This procedure scans an input string g using a lexical token scanning
routine, e(), where e() returns
1 if the token is '('
2 if the token is '''
3 if the token is '.'
4 if the token is ')' or a typed pointer d to an
atom or number stored in row ptrv(d) in the atom or number tables.
Due to the typecode (8 or 9) of d, d is a negative 32-bit integer. The
token found by e() is stripped from the front of g.
SREAD constructs an S-expression and returns a typed pointer to it as
its result.
See that Gary's Lisp is old and you'll need to change it so it compiles. Instead of including linuxenv.h, include:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <setjmp.h>
Also, it does not work in 64-bit machines (the documentation of sread should tell you why...)
Update 4: There's also the Scheme implementations by Nils Holm (there are books describing the internals)
Lisp500 http://code.google.com/p/lisp5000
ThinLisp http://www.thinlisp.org
lispreader is a simple Lisp file parser done in plain C.
If you want C++, you can dig around in the SuperTux source code, it contains a Lisp file parser written in C++.
When you want an actual implementation of Lisp instead of just a parser you could have a look at Abuse, which contains a small one as the games scripting language.
MIT Professor Rivest published a set of small readers for s-expressions back in 1997 http://people.csail.mit.edu/rivest/sexp.html as part of his DARPA supported research on public key cryptography. The code only does reading and printing and is well described in a document written in the style of an internet RFC.
there are lots of embeddable Scheme implementations, off the top of my head: SIOD, Guile, ChickenScheme, Scheme48....
I know there are many tutorials out there for getting started in C. However Its hard for me to apply the knowledge. The way I've always started out in languages is by writing scripts. Of course C is not a scripting language.
My question isn't so much about learning C as much as it is about how to get started applying C. Great I can write a temperature converter or a text-based rpg. Maybe its because in python I just write up the code in somefile.py and chmod +x somefile.py && somefile.py . I do not really have an equivalent process for C. Every time I read about C its a different compiling process with different flags. Can someone just give me some definite direction on best ways to apply C when you already work with higher-level dynamic scripting languages?
Btw. .. I'm asking about C and not C++.
I usually am on either OpenSuse 11 or Ubuntu 9.04 . "What compiler do i use" is part of the problem. In python there is no choice its just "python somefile.py" same with php or ruby. I didn't know there were choices.
write w.c
#include <stdio.h>
int main(int argc, char *argv[]) {
int i;
for (i = 0; i < argc; ++i) {
printf("Param %d is '%s'\n", i, argv[i]);
}
return 0;
}
and compile with
gcc -Wall -o w w.c
run
./w
As rogeriopvl wrote in a comment, the compilation process is really simple. Just write up the code in somefile.c and
gcc -o somefile somefile.c && ./somefile
(if you're using GCC, and if not, your compiler of choice can probably be invoked similarly) Unless/until you start getting into more complicated projects, it's barely any more complicated than a scripting language. (Well... okay, you may need to link some libraries, once you get beyond the basics. But still, not a huge deal.)
In fact, I did write myself a little shell script that allows me to use C as a scripting language. But the process for setting it up is a little more complicated than what you may want to get into at this stage - it's simpler to just run the compiler each time. Still, if you're interested, I can look up the directions (for Linux) and put them here.
C code needs to be compiled before the program can be run. The exact process is different depending on which platform and compiler you are working on.
For the most part, using an IDE (such as Visual studio, Eclipse, MonoDevelop, and a bunch of others) will do the nasty work for you so that you just have to press a button or click an icon. Download one of these
I asked myself this question when I was learning C. The problem here, if I can say this is a problem, is that C can be used in a broad range of applications and in a broad range of environments, which one with its own IDEs or compilers and libraries. Some examples where you can use C for real staff.
Embedded software. In this case you will probably use some lib.
Network programming (take a look at this book.
Device driver development.
Libraries (both for Linux/Windows and other OSs)
Well this list is endless.
O don't know if I help you with this question. If you give more details about what are you interested in, could be helpful
Good luck
The best advice I can give here is find a topic you're interested in, see if you can make a program to do what you want/assist in doing what you want/adding functionality to the interest of choice, and start coding.
This gives the bonus of doing something you're interested in, and at the same time making something that directly influences it. It should give the motivation to keep steaming onward with the learning process.
I'm working with C a lot at the moment with Linux Kernel modules and am relatively new to C. I've found this rewarding which I think is what's important for this sort of hobby 'temperature converter or a text-based rpg' type programming.
I also struggle finding an application of programming skills. Balance of challenge and reward is important I think.
I know that standard C doesn't give me any ability to do anything with folders, but I would like a fairly portable and cross-platform way to access folders. At this time, all I need to do is make a folder, check if a folder exists, and possibly delete a folder. I can forsee needing to read files from a folder in the near future, but that's not a very pressing need.
Anyway, I was wondering if there was a good cross-platform C library for working with directories. In an absolute pinch I can probably roll my own to work on POSIX and Windows, but I was wondering if there were any good ones already out there. I've been considering GLib or the Apache Portable Runtime, but both of those come with a lot more stuff than I really need, and I'd like to keep this fairly lightweight. I've also considered using the internals of a popular scripting language, like Perl or Python, but that also seems like a lot of overhead just for directory functions.
If anyone has anything to add to this list that I should look into, or wants to make a good case for one of the options I've already listed, please tell me. I don't want to sound like I'm asking for code, but if you posted a simple function like int direxist(char *dirname) that returned true if the directory exists and false otherwise, just to illustrate the API for your library of choice, that would be really awesome, and I imagine not too hard. If you want to advocate using POSIX/rolling my own, do that too, because I'm a sucker for learning new stuff like this by doing it myself.
Just to make sure, I want C, not C++. I'm sure boost is good, but I'm not interested in C++ solutions.
I would jump on the APR bandwagon. It does give you a lot more than directory access, but it is the best multi-platform C library that I've used. Chances are that you will find yourself needing some of the other components of it in the future anyway, so you might as well have them handy.
The other option is to implement the POSIX API set over Win32 and just write everything in POSIX. The bonus here is that the Windows is quickly becoming the only modern OS that does not include a POSIX runtime implementation.
I've been considering GLib or the Apache Portable Runtime, but both of those come with a lot more stuff than I really need, and I'd like to keep this fairly lightweight.
It's quite probable that GLib will already be installed (on GNU/Linux, at least). The only problem is that it will add a dependency.
I've also considered using the internals of a popular scripting language, like Perl or Python, but that also seems like a lot of overhead just for directory functions.
I would rather use Python in the first place, and possibly use C for specific parts of code.
>>> def direxist(dirname):
... return os.path.isdir(dirname)
...
>>> direxist('/')
True
>>> direxist('/home')
True
>>> direxist('/home/bastien/Petites leçons de typographie.pdf')
False
About writing your own C function, it would go something like this:
#include <stdio.h>
#ifdef _WIN32
#include <windows.h>
#else
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#endif
int direxist(const char* dirname)
{
#ifdef _WIN32
/* ... */
#else
struct stat fileinfo;
int ret = -1;
if (stat(dirname, &fileinfo) == -1)
{
perror("direxist");
}
else
{
if (S_ISDIR(fileinfo.st_mode))
{
ret = 1;
}
else
{
ret = 0;
}
}
return ret;
#endif
}
int
main (void)
{
printf("%d\n", direxist("/"));
return 0;
}
I don't how to do it with Win32, so you'll to find that yourself.
However, I would strongly recommend using an external library. You don't go far with just the C library or by reinventing the wheel.
I think you should use APR or something in the same vein. Designing a POSIX API and then implement it for windows does not work well in my experience (which is quite limited I must confess).
File IO, and related semantics are just too different, so you have to design your API to deal with windows right away. There are also different constraints on what can be put in the public API. One example of such a problem is the python C API for file handling. It was clearly designed with a POSIX POV, and it is very difficult to use it on windows because of things like sharing C runtimes objects, etc...