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• Recommendations with hierarchical data on non-relational databases?

  - by Luki

  I'm developing an web application that uses a non-relational database as a backend (django-nonrel + AppEngine). I need to store some hierarchical data (projects/subproject_1/subproject_N/tasks), and I'm wondering which pattern should I use. For now I thought of: Adjacency List (store the item's parent id) Nested sets (store left and right values for the item) In my case, the depth of nesting for a normal user will not exceed 4-5 levels. Also, on the UI, I would like to have a pagination for the items on the first level, to avoid to load too many items at the first page load. From what I understand so far, nested sets are great when the hierarchy is used more for displaying. Adjacency lists are great when editing on the tree is done often. In my case I guess I need the displaying more than the editing (when using nested sets, even if the display would work great, the above pagination could complicate things on editing). Do you have any thoughts and advice, based on your experience with the non-relational databases?

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• Using .dll methods to load data from file in C# code

  - by Espinas.iss

  I want to use in C# these methods: * int LibRaw::open_datastream(LibRaw_abstract_datastream *stream) * int LibRaw::open_file(const char *rawfile) * int LibRaw::open_buffer(void *buffer, size_t bufsize) * int LibRaw::unpack(void) * int LibRaw::unpack_thumb(void) that are stored in a libraw.dll. These functions one by one load data from file... I've been reading about P/Invoke but i'm not sure how to invoke them. Can anyone show me an example how to use all of these functions together in C# to load file (raw image stored in folder) or just how to PIvoke one of them. Thanx!

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• Visit neighbor of a position in a 2d-array

  - by Martin

  I have the following two dimensional array: static int[,] arr = new int[5, 5] { { 00, 00, 00, 01, 00 }, { 00, 00, 01, 01, 00 }, { 00, 00, 01, 01, 00 }, { 00, 00, 01, 01, 00 }, { 00, 00, 00, 01, 00 }, }; I have to a implement a method called Hit(int x, int y). When we hit a 0 in the array (i.e. Hit(0, 0), Hit(1, 1), but not Hit(3, 0)) I would like all the adjacent zeros to the zero we hit to be incremented by 10. So if I call Hit(1, 1), the array should become the following. static int[,] arr = new int[5, 5] { { 10, 10, 10, 01, 00 }, { 10, 10, 01, 01, 00 }, { 10, 10, 01, 01, 00 }, { 10, 10, 01, 01, 00 }, { 10, 10, 10, 01, 00 }, }; Any idea how I could implement that? It sounds to me like a Depth First Search/Recursive sort-of algorithm should do the job, but I haven't been able to implement it for an 2d array. Thanks for the help!

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• How do you determine using stat() whether a file is a symbolic link?

  - by hora

  I basically have to write a clone of the UNIX ls command for a class, and I've got almost everything working. One thing I can't seem to figure out how to do is check whether a file is a symbolic link or not. From the man page for stat(), I see that there is a mode_t value defined, S_IFLNK. This is how I'm trying to check whether a file is a sym-link, with no luck (note, stbuf is the buffer that stat() returned the inode data into): switch(stbuf.st_mode & S_IFMT){ case S_IFLNK: printf("this is a link\n"); break; case S_IFREG: printf("this is not a link\n"); break; } My code ALWAYS prints this is not a link even if it is, and I know for a fact that the said file is a symbolic link since the actual ls command says so, plus I created the sym-link... Can anyone spot what I may be doing wrong? Thanks for the help!

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• design patterns for hierarchical structures

  - by JLBarros

  Anyone knows some design patterns for hierarchical structures? For example, to manage inventory categories, accounting chart of accounts, divisions of human resources, etc.. Thank you very much in advance EDIT: Thanks for your interest. I am looking for a better way of dealing with hierarchical items to which they should apply operations depending on the level of hierarchy. I have been studying the patterns by Martin Fowler, for example Accounting, but I wonder if there are other more generic. The problem is that operations apply to the items must be possible to change even at run time and may depend on other external variables. I thought of a kind of strategy pattern but would like to combine it with the fact that it is a hierarchical scheme. I would appreciate any reference to hierarchical patterns and you'll take care of them in depth.

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• How to use C# nested structures to access tree of data

  - by zotty

  I'm importing some XML to C#, and want to be able to access data from the XML in the form of what I think is a nested structure. (I may be wrong!) What I have in my XML is in the following form: <hardwareSettings initial="true> <cameraSettings width="1024" height="768" depth="8" /> <tiltSettings theta="35" rho="90"> </hardwareSettings> I can import each setting alright, so I have them all in individual ints, but I would like to be able to access it in the form int x=hardwaresettings.camerasettings.width; int rho=hardwaresettings.tiltsettings.rho; I've tried various arrangements of structs within structs, but I don't seem able to cast a new object (hardwaresettings) that contains the appropriate children (camerasettings.width & tiltsettings.rho). Sorry if I'm not using the right lingo... I'm reading myself in circles here!

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• SDL+OpenGL app: blank screen

  - by Lococo

  I spent the last three days trying to create a small app using SDL + OpenGL. The app itself runs fine -- except it never outputs any graphics; just a black screen. I've condensed it down to a minimal C file, and I'm hoping someone can give me some guidance. I'm running out of ideas. I'm using Windows Vista, MinGW & MSYS. Thanks in advance for any advice! #include <SDL/SDL.h> #include <SDL_opengl.h> size_t sx=600, sy=600, bpp=32; void render(void) { glEnable(GL_DEPTH_TEST); // enable depth testing glClearColor(0.0f, 0.0f, 0.0f, 0.0f); // clear to black glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // clear color/depth buffer glLoadIdentity(); // reset modelview matrix glColor3b(255, 0, 0); // red glLineWidth(3.0); // line width=3 glRecti(10, 10, sx-10, sy-10); // draw rectangle glFlush(); SDL_GL_SwapBuffers(); } int input(void) { SDL_Event event; while (SDL_PollEvent(&event)) if (event.type == SDL_QUIT || (event.type == SDL_KEYUP && event.key.keysym.sym == SDLK_ESCAPE)) return 0; return 1; } int main(int argc, char *argv[]) { SDL_Surface* surf; if (SDL_Init(SDL_INIT_EVERYTHING) != 0) return 0; if (!(surf = SDL_SetVideoMode(sx, sy, bpp, SDL_HWSURFACE|SDL_DOUBLEBUF))) return 0; glViewport(0, 0, sx, sy); // reset the viewport to new dimensions glMatrixMode(GL_PROJECTION); // set projection matrix to be current glLoadIdentity(); // reset projection matrix glOrtho(0, sx, sy, 0, -1.0, 1.0); // create ortho view glMatrixMode(GL_MODELVIEW); // set modelview matrix glLoadIdentity(); // reset modelview matrix for (;;) { if (!input()) break; render(); SDL_Delay(10); } SDL_FreeSurface(surf); SDL_Quit(); exit(0); } UPDATE: I have a version that works, but it changes orthographic to perspective. I'm not sure why this works and the other doesn't, but for future reference, here's a version that works: #include <SDL/SDL.h> #include <SDL_opengl.h> size_t sx=600, sy=600, bpp=32; void render(void) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); // set location in front of camera glTranslated(0, 0, -10); glBegin(GL_QUADS); // draw a square glColor3d(1, 0, 0); glVertex3d(-2, 2, 0); glVertex3d( 2, 2, 0); glVertex3d( 2, -2, 0); glVertex3d(-2, -2, 0); glEnd(); glFlush(); SDL_GL_SwapBuffers(); } int input(void) { SDL_Event event; while (SDL_PollEvent(&event)) if (event.type == SDL_QUIT || (event.type == SDL_KEYUP && event.key.keysym.sym == SDLK_ESCAPE)) return 0; return 1; } int main(int argc, char *argv[]) { SDL_Surface *surf; if (SDL_Init(SDL_INIT_EVERYTHING) != 0) return 0; if (!(surf = SDL_SetVideoMode(sx, sy, bpp, SDL_OPENGL))) return 0; glViewport(0, 0, sx, sy); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspective(45.0, (float)sx / (float)sy, 1.0, 100.0); glMatrixMode(GL_MODELVIEW); glClearColor(0, 0, 0, 1); glClearDepth(1.0); glEnable(GL_DEPTH_TEST); for (;;) { if (!input()) break; render(); SDL_Delay(10); } SDL_FreeSurface(surf); SDL_Quit(); return 0; }

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• Flushing stdin after every input - which approach is not buggy?

  - by Aseem Bansal

  While using scanf() in C there is always the problem of extra input lying in the input buffer. So I was looking for a function that I call after every scanf call to remedy this problem. I used this, this, this and this to get these answers //First approach scanf("%*[^\n]\n"); //2ndapproach scanf("%*[^\n]%*c"); //3rd approach int c; while((c = getchar()) != '\n' && c != EOF) /* discard */ ; All three are working as far as I could find by hit-and-trial and going by the references. But before using any of these in all of my codes I wanted to know whether any of these have any bugs?

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• Oracle PL/SQL: Dump query result into file

  - by CC

  Hi. I'm working on a pl sql stored procedure. What I need is to do a select, use a cursor and for every record build a string using values. At the end I need to write this into a file. I try to use dbms_output.put_line("toto") but the buffer size is to small because I have about 14 millions lines. I call my procedure from a unix ksh. I'm thinking at something like using "spool on" (on the ksh side) to dump the result of my procedure, but I don' know how to do it (if this is possible) Anyone has any idea? Thank alot. C.C.

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• emacs: is there a semantic-jump-to-declaration (using semantic.el)?

  - by Cheeso

  Suppose I am editing a buffer containing C code. I have started semantic with semantic-load-enable-code-helpers . I have point placed on the name of a function . If I then invoke senator-jump I can jump to the place where that fn is first declared, in that module. What if it is an extern? Is it possible to use senator to jump to the definition of the fn, which resides in a separate module? Thanks.

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• Write to pipe deadlocking program

  - by avs3323

  Hi, I am having a problem in my program that uses pipes. What I am doing is using pipes along with fork/exec to send data to another process What I have is something like this: //pipes are created up here if(fork() == 0) //child process { ... execlp(...); } else { ... fprintf(stderr, "Writing to pipe now\n"); write(pipe, buffer, BUFFER_SIZE); fprintf(stderr, "Wrote to pipe!"); ... } This works fine for most messages, but when the message is very large, the write into the pipe deadlocks. I think the pipe might be full, but I do not know how to clear it. I tried using fsync but that didn't work. Can anyone help me?

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• How to run shell script with live feedback from PHP?

  - by Highway of Life

  How would I execute a shell script from PHP while giving constant/live feedback to the browser? I understand from the system function documentation: The system() call also tries to automatically flush the web server's output buffer after each line of output if PHP is running as a server module. I'm not clear on what they mean by running it as a 'server module'. I attempted to run the script in the cgi-bin, but either I'm doing it wrong, or that's not what they mean. Example PHP code: <?php system('/var/lib/script_test.sh'); Example shell code: #!/bin/bash echo "Start..." for i in {1..10} do echo "$i..." sleep 1 done echo "Done."

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• Strange behaviour with fputs and a loop.

  - by Jonathan

  When running the following code I get no output but I cannot work out why. # include <stdio.h> int main() { fputs("hello", stdout); while (1); return 0; } Without the while loop it works perfectly but as soon as I add it in I get no output. Surely it should output before starting the loop? Is it just on my system? Do I have to flush some sort of buffer or something? Thanks in advance.

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• FtpWebResponse and StreamReader - specifying an offset

  - by AJ

  Hi, I am using the FtpWebRequest / FtpWebResponse objects in C# to download files from a server - so far, so good. I create a StreamReader object from the response stream and use a StreamWriter to create a local file. Now, the file I am reading happens to be in a very simple 'archive' format - there is a small TOC at the start of the file followed by the actual file data. I can therefore read the TOC and get a file offset and size of the data I want to download. My question is: Supposing the offset is 1024. I would use StreamReader.Read(buffer, 1024, length), but will .NET and the FTP protocol actually allow me to skip bytes 0-1023, or does the reader still go through the (relatively) slow process of downloading and discarding the bytes I don't need? This may make the difference between whether I want to use a single archive file, or a TOC file with the data files stored separately. As a bit of a secondary question, would my mileage vary using the Http classes instead of Ftp? Cheers, Adam

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• php multidimensional array problem

  - by ntan

  Hi to all, i am trying to setup a multidimensional array but my problem is that i can not get the right order from incoming data. Explain $x[1][11]=11; $x[1]=1; var_dump($x); In the above code i get only x[1]. To right would be $x[1]=1; $x[1][11]=11; var_dump($x); But in my case i can dot ensure that x[1] will come first, and x[1][11] will come after. Is there any way that i can use the first example and get right the array. Keep in mind that the array depth is large. Thats

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• Increase the TCP receive window for a specific socket

  - by rursw1

  Hi, How to increase the TCP receive window for a specific socket? - I know how to do so for all the sockets by setting the registry key TcpWindowSize, but how do do that for a specific one? According to MSFT's documents, the way is Calling the Windows Sockets function setsockopt, which sets the receive window on a per-socket basis. But in setsockopt, it is mentioned about SO_RCVBUF : Specifies the total per-socket buffer space reserved for receives. This is unrelated to SO_MAX_MSG_SIZE and does not necessarily correspond to the size of the TCP receive window. So is it possible? How? Thanks.

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• Using the windows api and C++, how could I load an exe from the hard drive and run it in its own thread?

  - by returneax

  For the sake of learning I'm trying to do what the OS does when launching a program ie. parsing a PE file and giving it a thread of execution. If I have two exe's one called foo.exe and the other bar.exe, how could I have foo.exe load the contents of bar.exe into memory then have it execute from there in its own thread? I know how to get it into memory using MapViewOfFile or by simple loading the contents on the hard drive into a buffer. I'm assuming simply copying the contents of bar.exe on disk into its own suspended thread and running it wouldn't work. I am semi-familiar with PE file internals. All help is very much appreciated, of course :)

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• ASP.net web page still displaying cached versions

  - by user279521

  My web page is still displaying a previously cached versions of the page. I have this in the page_load event: Response.Clear(); Response.Buffer = true; Response.ExpiresAbsolute = DateTime.Now.AddDays(-1d); Response.Expires = -1; Response.CacheControl = "no-cache"; Response.Cache.SetCacheability(HttpCacheability.NoCache); I have this in the Page_Init: protected void Page_Init(object Sender, EventArgs e) { Response.Cache.SetCacheability(HttpCacheability.NoCache); Response.Cache.SetExpires(DateTime.Now.AddDays(-1)); } Any idea what I might be missing?

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• The implicit function __strcpy_chk() call

  - by Summer_More_More_Tea

  Hi everyone: I'm now performing a stack buffer overflow attack test on my own PC( Ubuntu 9.10, gcc-4.4.1 ) based on the article http://www.tenouk.com/Bufferoverflowc/Bufferoverflow4.html. Yet I haven't achieved the goal. Each time a segfault is thrown accompanied with some error informaiton. I compile the source code, and wanna get further information using objdump. Function __strcpy_chk is invoked in the assembly code dumped out, and it's said that "The __strcpy_chk() function is not in the source standard; it is only in the binary standard." Does this the mechanism a compiler employed to protect runtime stack? To finish my test, how can I bypass the protection? Regards.

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• How i store the images pixels in matrix form?

  - by Rajendra Bhole

  Hi, I developing an application in which the pixelize image i want to be store in matrix format. The code is as follows. struct pixel { //unsigned char r, g, b,a; Byte r, g, b; int count; }; (NSInteger) processImage1: (UIImage*) image { // Allocate a buffer big enough to hold all the pixels struct pixel* pixels = (struct pixel*) calloc(1, image.size.width * image.size.height * sizeof(struct pixel)); if (pixels != nil) { // Create a new bitmap CGContextRef context = CGBitmapContextCreate( (void*) pixels, image.size.width, image.size.height, 8, image.size.width * 4, CGImageGetColorSpace(image.CGImage), kCGImageAlphaPremultipliedLast ); NSLog(@"1=%d, 2=%d, 3=%d", CGImageGetBitsPerComponent(image), CGImageGetBitsPerPixel(image),CGImageGetBytesPerRow(image)); if (context != NULL) { // Draw the image in the bitmap CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), image.CGImage); NSUInteger numberOfPixels = image.size.width * image.size.height; I confusing about how to initialize the 2-D matrix in which the matrix store data of pixels.

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• Buffering db inserts in multithreaded program

  - by Winter

  I have a system which breaks a large taks into small tasks using about 30 threads as a time. As each individual thread finishes it persists its calculated results to the database. What I want to achieve is to have each thread pass its results to a new persisance class that will perform a type of double buffering and data persistance while running in its own thread. For example, after 100 threads have moved their data to the buffer the persistance class then the persistance class swaps the buffers and persists all 100 entries to the database. This would allow utilization of prepared statements and thus cut way down on the I/O between the program and the database. Is there a pattern or good example of this type of multithreading double buffering?

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• FFmpeg + iPhone - Interesting (incorrect?) video encoding results

  - by jtrim

  I'm encoding some video on the iPhone by running the png image data through swscale to get YUV420P data then encoding that frame using the MSMPEG4V1 codec. In the api docs, avcodec_encode_video should return the number of bytes used from the output buffer by that encode operation. There are 234,000 bytes going into the encoder, but the result returned by avcodec_encode_video is simply "4". The result is exactly the same over 24 frames. Something seems fishy here...any insight? Here's a pastebin link to the code: http://pastebin.com/ht94FWva (sorry for the link away from SO, I just didn't want to have the code duplicated in several places) EDIT: Also, I've set up a custom log callback for ffmpeg to use and I have the log level set to "Verbose" (libavutil/log.h), so libavcodec should be logging any goofs to the console, but avcodec is quiet throught he whole operation. (note: I did test to make sure my log callback was working)

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• Named keywords in decorators?

  - by wheaties

  I've been playing around in depth with attempting to write my own version of a memoizing decorator before I go looking at other people's code. It's more of an exercise in fun, honestly. However, in the course of playing around I've found I can't do something I want with decorators. def addValue( func, val ): def add( x ): return func( x ) + val return add @addValue( val=4 ) def computeSomething( x ): #function gets defined If I want to do that I have to do this: def addTwo( func ): return addValue( func, 2 ) @addTwo def computeSomething( x ): #function gets defined Why can't I use keyword arguments with decorators in this manner? What am I doing wrong and can you show me how I should be doing it?

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• What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

  - by fabrizioM

  I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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• What is the best method of assessment for computer science students?

  - by Gavimoss

  This question is a bit more philosophical so feel free to remove if you like but it's been bugging me for the last 4 years! As a final year student I find that exams can be often be passed with a couple of days of cramming, without necessarily retaining or understanding the content i.e. a regurgitation of lecture notes is often enough to gain high marks. A friend of mine is about to graduate with an honours degree whose final year evaluation was based solely on practical work (a project, assignment marks and the creation of a poster) yet all of this work could have been completed by a third party. Personally I don't think either of these methods of assessment is sufficient as I am currently on track for a 1st class honours in artificial intelligence and computer science and believe this is mostly due to my skill in passing exams not my skill as a programmer or my vast in depth knowledge of any of the subjects I have "studied". Surely there is a better way to assess our skills - isn't there?

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