Is there any database which can work without any Operating System.
My requirement is, i need to port some code on an embedded device, which runs without OS on a microcontroller. Suggest me the best database or alternate for this scenario.
I think you will implement it on an embedded system. If you write your application using C/C++ try use SQLite. There are SQLite API for C/C++
What you need is a simple key value store, is my guess. It is better you write a small package for the same as conventional databases may be too heavy for your applications.
BTW most higher end embedded systems (routers/switches) these days seem to be using sqite
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Is there a lightweight (in size and memory usage), portable (that i can copy and paste it to another computer without reconfiguration, or rsync it with ease), cross-platform (that runs on windows and linux, at least at data level), client-server (because there would be more than one user write at the same time, so i wont use sqlite or any other embedded database) database?
what are my options?
i don't care if it's sql or nosql, i don't care about the security too..
How about Apache Derby? It would require a JRE (Java), but other than that, it should do exactly what you want.
Alternatively, you could write a small wrapper for SQLite (or any other embedded database) and just ship that instead. Your wrapper would expose some sort of network-level API of your choosing.
I'm interested in studying the 9P FS, currently been reading the source available from these implementations: http://9p.cat-v.org/implementations
Is 9P obsolete? Are you using it for some application?
(also I've found this, some perfomance test between 9P and NFS: http://graverobbers.blogspot.com/2007/08/v9fs-performance-versus-nfs.html)
No, 9P isn't obsolete; I don't know of a protocol that does what it does and is clean and well defined enough to be implemented correctly in almost any language that exists.
9P is used in a variety of systems. A couple of recent uses in arm-js (an ARM emulator) and 9webdraw (a GSoC project that implements the Plan 9 /dev/draw). Both are HTML5 Javascript implementations.
Just to add a bit, both the Linux client implementation and several servers are under active development, so I'd say that's a pretty clear sign that folks still have use for it. One of the areas its seen heavy use more recently is the virtio-9P (aka virtfs) which is part of qemu/kvm and can be used for direct guest to host file access. It's also been used in several experimental operating systems projects (Libra, PROSE, FusedOS) and incorporated into other operating systems (BSD, MacOSX, Windows, Linux) and hypervisors (in addition to the KVM instance above, its also been incorporated in various ways into Xen). 9P is actually being used in supercomputing deployments (both for Plan 9 and Linux, see the diod project on Sourceforge).
I think the reason is that the protocol is quite simple, so implementations also tend to be quite simple and easy to integrate elsewhere (there are several applications both inside and outside the Plan 9 world which use 9P as an interface to the application, in much the same way that some web developers use RESTful interfaces).
The protocol has a couple of different variations including the 9P.L variant which was developed specifically to match the Linux VFS API better. It adds a bit of complexity to the protocol in the addition of operations, but removes some of the complexity of mapping Linux VFS API -> 9P and vice versa.
It is used in Erlang-on-Xen both as a storage protocol for goofs http://erlangonxen.org/blog/goofs-simple-filesystem
It is the way erlang on xen instances in other ways too, see here:
http://erlangonxen.org/more/9p2000e
Also, it's used by libvirt stuff with QEMU.
http://wiki.qemu.org/Documentation/9psetup
9p, to me, is like the Scheme of network protocols. For the most part, it is very simple, but people see need to extend it to fit their environments. Luckily this is done in ways that are often backwards compatible.
In addition to everything mentioned in the other answers, Microsoft is using 9P as part of their Windows Subsystem for Linux.
They add a 9P server to each Linux distribution that is running as a guest, so that Windows can mount the Linux filesystem over 9P, and Windows processes can transparently access the files on Linux's ext4 partition.
I have a small program written in c and i am planning to convert it to a web service module. Is there any web server(Linux or Windows platform) where i can embed the c program directly. I googled and found some of the web servers which supports c code are Apache, mongoose etc. But i don't know how to implement it?
You are looking for CGI. See the docs for more info:
http://httpd.apache.org/docs/2.0/howto/cgi.html
G-WAN is one of the fastest Web Servers, and it supports running C-programs directly (gwan.com). It's much faster on multi-core CPUs than other webservers.
Basically, you can just run any C/C++ (or many other) files just by placing them in /csp directory.
http://monkey-project.com/ is able to do what you want and probably the simplest solution to your problem. http://gwan.com/ might also be interesting, depending on what exactly you want to do.
What things should be kept most in mind when writing cross-platform applications in C? Targeted platforms: 32-bit Intel based PC, Mac, and Linux. I'm especially looking for the type of versatility that Jungle Disk has in their USB desktop edition ( http://www.jungledisk.com/desktop/download.aspx )
What are tips and "gotchas" for this type of development?
I maintained for a number of years an ANSI C networking library that was ported to close to 30 different OS's and compilers. The library didn't have any GUI components, which made it easier. We ended up abstracting out into dedicated source files any routine that was not consistent across platforms, and used #defines where appropriate in those source files. This kept the code that was adjusted per platform isolated away from the main business logic of the library. We also made extensive use of typedefs and our own dedicated types so that we could easily change them per platform if needed. This made the port to 64-bit platforms fairly easy.
If you are looking to have GUI components, I would suggest looking at GUI toolkits such as WxWindows or Qt (which are both C++ libraries).
Try to avoid platform-dependent #ifdefs, as they tend to grow exponentially when you add new platforms. Instead, try to organize your source files as a tree with platform-independent code at the root, and platform-dependent code on the "leaves". There is a nice book on the subject, Multi-Platform Code Management. Sample code in it may look obsolete, but ideas described in the book are still brilliantly vital.
Further to Kyle's answer, I would strongly recommend against trying to use the Posix subsystem in Windows. It's implemented to an absolute bare minimum level such that Microsoft can claim "Posix support" on a feature sheet tick box. Perhaps somebody out there actually uses it, but I've never encountered it in real life.
One can certainly write cross-platform C code, you just have to be aware of the differences between platforms, and test, test, test. Unit tests and a CI (continuous integration) solution will go a long way toward making sure your program works across all your target platforms.
A good approach is to isolate the system-dependent stuff in one or a few modules at most. Provide a system-independent interface from that module. Then build everything else on top of that module, so it doesn't depend on the system you're compiling for.
XVT have a cross platform GUI C API which is mature 15+ years and sits on top of the native windowing toollkits. See WWW.XVT.COM.
They support at least LINUX, Windows, and MAC.
Try to write as much as you can with POSIX. Mac and Linux support POSIX natively and Windows has a system that can run it (as far as I know - I've never actually used it). If your app is graphical, both Mac and Linux support X11 libraries (Linux natively, Mac through X11.app) and there are numerous ways of getting X11 apps to run on Windows.
However, if you're looking for true multi-platform deployment, you should probably switch to a language like Java or Python that's capable of running the same program on multiple systems with little or no change.
Edit: I just downloaded the application and looked at the files. It does appear to have binaries for all 3 platforms in one directory. If your concern is in how to write apps that can be moved from machine to machine without losing settings, you should probably write all your configuration to a file in the same directory as the executable and not touch the Windows registry or create any dot directories in the home folder of the user that's running the program on Linux or Mac. And as far as creating a cross-distribution Linux binary, 32-bit POSIX/X11 would probably be the safest bet. I'm not sure what JungleDisk uses as I'm currently on a Mac.
There do exist quite few portable libraries just examples I've worked within the past
1) glib and gtk+
2) libcurl
3) libapr
Those cover nearly every platform and so they are extremly useful tool.
Posix is fine on Unices but well I doubt it's that great on windows, besides we do not have any stuff for portable GUIs there.
I also second the recommendation to separate code for different platforms into different modules/trees instead of ifdefs.
Also I recommend to check beforehand what are the differences in you platforms and how you could abstract them. E.g. this is some OS related stuff (e.g. the annoying CR,CRLF,LF in text files), or hardware stuff. E.g. the previous mentioned posix compability doesnt stop you from
int c;
fread(&c, sizeof(int), 1, file);
But on different hardware platforms the internal memory layout can be complete different (endianess), forcing you to use conversion functions on some of the target platforms.
You can use NAppGUI for both console and desktop apps. The SDK uses ANSI-C and your code will work on Windows/macOS/Linux.
https://www.nappgui.com
It's free and OpenSource.
I'm new to windows programming and I'm trying to get notified of all changes to the file system (similar to the information that FileMon from SysInternals displays, but via an API). Is a FindFirstChangeNotification for each (non-network, non-substed) drive my best bet or are there other more suitable C/C++ APIs?
FindFirstChangeNotification is fine, but for slightly more ultimate power you should be using ReadDirectoryChangesW. (In fact, it's even recommended in the documentation!)
It doesn't require a function pointer, it does require you to manually decode a raw buffer, it uses Unicode file names, but it is generally better and more flexible.
On the other hand, if you want to do what FileMon does, you should probably do what FileMon does and use IFS to create and install a file system filter.
There are other ways to do it, but most of them involve effort on your part (or take performance from your app, or you have to block a thread to use them, etc). FindFirstChangeNotification is a bit complicated if you're not used to dealing with function pointers, etc, but it has the virtue of getting the OS to do the bulk of the work for you.
Actually FileSystemWatcher works perfectly with shared network drives. I am using it right now in an application which, among other things, monitors the file system for changes. (www.tabbles.net).
You can use FileSystemWatcher class. Very efficient but cannot work with Network shared drives.