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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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  • Horizontally Flip a One Bit Bitmap Line

    - by roygbiv
    I'm looking for an algorithm to flip a 1 Bit Bitmap line horizontally. Remember these lines are DWORD aligned! I'm currently unencoding an RLE stream to an 8 bit-per-pixel buffer, then re-encoding to a 1 bit line, however, I would like to try and keep it all in the 1 bit space in an effort to increase its speed. Profiling indicates this portion of the program to be relatively slow compared to the rest. Example line (Before Flip): FF FF FF FF 77 AE F0 00 Example line (After Flip): F7 5E EF FF FF FF F0 00

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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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  • 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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  • measuring uncertainty in matlabs svmclassify

    - by Mark
    I'm doing contextual object recognition and I need a prior for my observations. e.g. this space was labeled "dog", what's the probability that it was labeled correctly? Do you know if matlabs svmclassify has an argument to return this level of certainty with it's classification? If not, matlabs svm has the following structures in it: SVM = SupportVectors: [11x124 single] Alpha: [11x1 double] Bias: 0.0915 KernelFunction: @linear_kernel KernelFunctionArgs: {} GroupNames: {11x1 cell} SupportVectorIndices: [11x1 double] ScaleData: [1x1 struct] FigureHandles: [] Can you think of any ways to compute a good measure of uncertainty from these? (Which support vector to use?) Papers/articles explaining uncertainty in SVMs welcome. More in depth explanations of matlabs SVM are also welcome. If you can't do it this way, can you think of any other libraries with SVMs that have this measure of uncertainty?

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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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  • Trying to draw textured triangles on device fails, but the emulator works. Why?

    - by Dinedal
    I have a series of OpenGL-ES calls that properly render a triangle and texture it with alpha blending on the emulator (2.0.1). When I fire up the same code on an actual device (Droid 2.0.1), all I get are white squares. This suggests to me that the textures aren't loading, but I can't figure out why they aren't loading. All of my textures are 32-bit PNGs with alpha channels, under res/raw so they aren't optimized per the sdk docs. Here's how I am loading my textures: private void loadGLTexture(GL10 gl, Context context, int reasource_id, int texture_id) { //Get the texture from the Android resource directory Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(), reasource_id, sBitmapOptions); //Generate one texture pointer... gl.glGenTextures(1, textures, texture_id); //...and bind it to our array gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[texture_id]); //Create Nearest Filtered Texture gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_NEAREST); gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR); //Different possible texture parameters, e.g. GL10.GL_CLAMP_TO_EDGE gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_REPEAT); gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_REPEAT); //Use the Android GLUtils to specify a two-dimensional texture image from our bitmap GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0); //Clean up bitmap.recycle(); } Here's how I am rendering the texture: //Clear gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT); //Enable vertex buffer gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY); gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer); gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer); //Push transformation matrix gl.glPushMatrix(); //Transformation matrices gl.glTranslatef(x, y, 0.0f); gl.glScalef(scalefactor, scalefactor, 0.0f); gl.glColor4f(1.0f,1.0f,1.0f,1.0f); //Bind the texture gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[textureid]); //Draw the vertices as triangles gl.glDrawElements(GL10.GL_TRIANGLES, indices.length, GL10.GL_UNSIGNED_BYTE, indexBuffer); //Pop the matrix back to where we left it gl.glPopMatrix(); //Disable the client state before leaving gl.glDisableClientState(GL10.GL_VERTEX_ARRAY); gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY); And here are the options I have enabled: gl.glShadeModel(GL10.GL_SMOOTH); //Enable Smooth Shading gl.glEnable(GL10.GL_DEPTH_TEST); //Enables Depth Testing gl.glDepthFunc(GL10.GL_LEQUAL); //The Type Of Depth Testing To Do gl.glEnable(GL10.GL_TEXTURE_2D); gl.glEnable(GL10.GL_BLEND); gl.glBlendFunc(GL10.GL_SRC_ALPHA,GL10.GL_ONE_MINUS_SRC_ALPHA); Edit: I just tried supplying a BitmapOptions to the BitmapFactory.decodeResource() call, but this doesn't seem to fix the issue, despite manually setting the same preferredconfig, density, and targetdensity. Edit2: As requested, here is a screenshot of the emulator working. The underlaying triangles are shown with a circle texture rendered onto it, the transparency is working because you can see the black background. Here is a shot of what the droid does with the exact same code on it: Edit3: Here are my BitmapOptions, updated the call above with how I am now calling the BitmapFactory, still the same results as below: sBitmapOptions.inPreferredConfig = Bitmap.Config.RGB_565; sBitmapOptions.inDensity = 160; sBitmapOptions.inTargetDensity = 160; sBitmapOptions.inScreenDensity = 160; sBitmapOptions.inDither = false; sBitmapOptions.inSampleSize = 1; sBitmapOptions.inScaled = false; Here are my vertices, texture coords, and indices: /** The initial vertex definition */ private static final float vertices[] = { -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, -1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f }; /** The initial texture coordinates (u, v) */ private static final float texture[] = { //Mapping coordinates for the vertices 0.0f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f }; /** The initial indices definition */ private static final byte indices[] = { //Faces definition 0,1,3, 0,3,2 }; Is there anyway to dump the contents of the texture once it's been loaded into OpenGL ES? Maybe I can compare the emulator's loaded texture with the actual device's loaded texture? I did try with a different texture (the default android icon) and again, it works fine for the emulator but fails to render on the actual phone. Edit4: Tried switching around when I do texture loading. No luck. Tried using a constant offset of 0 to glGenTextures, no change. Is there something that I'm using that the emulator supports that the actual phone does not? Edit5: Per Ryan below, I resized my texture from 200x200 to 256x256, and the issue was NOT resolved. Edit: As requested, added the calls to glVertexPointer and glTexCoordPointer above. Also, here is the initialization of vertexBuffer, textureBuffer, and indexBuffer: ByteBuffer byteBuf = ByteBuffer.allocateDirect(vertices.length * 4); byteBuf.order(ByteOrder.nativeOrder()); vertexBuffer = byteBuf.asFloatBuffer(); vertexBuffer.put(vertices); vertexBuffer.position(0); byteBuf = ByteBuffer.allocateDirect(texture.length * 4); byteBuf.order(ByteOrder.nativeOrder()); textureBuffer = byteBuf.asFloatBuffer(); textureBuffer.put(texture); textureBuffer.position(0); indexBuffer = ByteBuffer.allocateDirect(indices.length); indexBuffer.put(indices); indexBuffer.position(0); loadGLTextures(gl, this.context);

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  • Handling of data truncation (short reads/writes) in FUSE

    - by Vi
    I expect any good program should do all their reads and writes in a loop until all data written/read without relying that write will write everything (even with regular files). Am I right? Implemented simple FUSE filesystem which only allows reading and writing with small buffers, very often returning that it is written less bytes that in a buffer (using -o direct_io). Some programs work, some not (notably mountlo). Are them buggy or programs should not expect truncated writes and reads from the regular files? In general, are seekable file descriptors expected to truncate data like sockets and pipes?

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  • XML Parsing Error: no element found

    - by Anilkumar
    XML Parsing Error: no element found Line Number 1, Column 1: I want to download a Excel file. I wrote the data in a html table format and appending to the response. The code is following : Response.Buffer = false; Response.Expires = 0; Response.Clear(); Response.ContentType = "application/vnd.ms-excel"; Response.AddHeader("Content-Disposition", "attachment; filename=" + FileName); Response.Write(str); Response.End();

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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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  • In what circumstances can large pages produce a speedup ?

    - by timday
    Modern x86 CPUs have the ability to support larger page sizes than the legacy 4K (ie 2MB or 4MB), and there are OS facilities (Linux, Windows) to access this functionality. The Microsoft link above states large pages "increase the efficiency of the translation buffer, which can increase performance for frequently accessed memory". Which isn't very helpful in predicting whether large pages will improve any given situation. I'm interested in concrete, preferably quantified, examples of where moving some program logic (or a whole application) to use huge pages has resulted in some performance improvement. Anyone got any success stories ? There's one particular case I know of myself: using huge pages can dramatically reduce the time needed to fork a large process (presumably as the number of TLB records needing copying is reduced by a factor on the order of 1000). I'm interested in whether huge pages can also benefit more mundane applications though.

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  • Regex pattern help (I almost have it, just need a bit of expertise to finish it)

    - by Mohammad
    I need to match two cases js/example_directory/example_name.js and js/example_directory/example_name.js?12345 (where 12345 is a digit string of unknown length and the directory can be limitless in depth or not exist at all) I need to capture in both cases everything between js/ and .js and if ? exists capture the digit string after ? This is what I have so far ^js/(.*).js\??(\d+)? This works except it also captures js/example_directory/example_name.js12345 I want the regex to ignore that. Any suggestions? Thank you all! Test your patterns here

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  • C++: Avoid .cpp files with only an empty (de)constructor

    - by Martijn Courteaux
    Hi, When I have a header file like this: #ifndef GAMEVIEW_H_ #define GAMEVIEW_H_ #include <SDL/SDL.h> class GameView { public: GameView(); virtual ~GameView(); virtual void Update() = 0; virtual void Render(SDL_Surface* buffer) = 0; }; #endif /* GAMEVIEW_H_ */ I need to create a .cpp file like this: #include "GameView.h" GameView::~GameView() { } GameView::GameView() { } This is a bit stupid. Just a .cpp file for an empty constructor and deconstructor. I want to implement that method simply in the header file. That is much cleaner. How to do this?

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  • check whether fgets would block

    - by lv
    Hi, I was just wondering whether in C is it possible to peek in the input buffer or perform similar trickery to know whether a call to fgets would block at a later time. Java allows to do something like that by calling BufferedReader.ready(), this way I can implement console input something like this: while (on && in.ready()) { line = in.readLine(); /* do something with line */ if (!in.ready()) Thread.sleep(100); } this allows an external thread to gracefully shutdown the input loop by setting on to false; I'd like to perform a similar implementation in C without resorting to non portable tricks, I already know I can make a "timed out fgets" under unix by resorting to signals or (better, even though requering to take care of buffering) reimplement it on top of recv/select, but I'd prefer something that would work on windows too. TIA

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  • Performing regex on a stream

    - by takoi
    I have some large text files which im going to preform consecutive matching on (just capturing, not replacing). Im thinking its not such a good idea to keep the whole file in memory, but rather use a Reader. What i know about the input is that if there's a match, its not going to span more than 5 lines. So my idea was to have some sort of buffer which just keeps these 5 lines, or so, do the first search, and continue. But it has to "know" where the regex match ended for this to work. e.g if the match ends at line 2 it should start the next search from here. Is it possible to do something like this in an efficient way?

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  • Can jQuery perform a compound select against the top level only? (a.k.a. "How to avoid chaining chil

    - by harpo
    Basically, is there a way to write a.children('.outer').children('.inner') without the intermediate selector? I can't write $('.outer > .inner', a) because I don't want to do full-depth search against a — I know that the .outer elements are immediate children of a. It's partly a matter of "elegance", but partly because I'm trying to avoid "throwaway" element sets. Yes, jQuery may in effect do the same thing, but it has a better chance of optimizing (at least in theory), when it knows the full query's intent.

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  • C# Serial Communications - Received Data Lost

    - by Jim Fell
    Hello. Received data in my C# application is getting lost due to the collector array being over-written, rather than appended. private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e) { try { pUartData_c = serialPort1.ReadExisting().ToCharArray(); bUartDataReady_c = true; } catch ( System.Exception ex ) { MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); } } In this example pUartData_c is over-written every time new data is received. On some systems this is not a problem because the data comes in quickly enough. However, on other systems data in the receive buffer is not complete. How can I append received data to pUartData_c, rather than over-write it. I am using Microsoft Visual C# 2008 Express Edition. Thanks.

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  • C++'s unordered_map / hash_map / Google's dense_hash - how to input binary data (buf+len) and insert

    - by shlomif
    Hi all, I have two questions about Google's dense_hash_map, which can be used instead of the more standard unordered_map or hash_map: How do I use an arbitrary binary data memory segment as a key: I want a buffer+length pair, which may still contain some NUL (\0) characters. I can see how I use a NUL-terminated char * string , but that's not what I want. How do I implement an operation where I look if a key exists, and if not - insert it and if it does return the pointer to the existing key and let me know what actually happened. I'd appreciate it if anyone can shed any light on this subject. Regards, -- Shlomi Fish

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  • Texture repeats even with GL_CLAMP_TO_EDGE set [FIXED]

    - by Lliane
    Hi, i'm trying to put a translucing texture on a face which uses points 1 to 4 (don't mind the numbers) on the following screenshot Sadly as you can see the texture repeats herself in both dimensions, I tried to switch the TEXTURE_WRAP_S from REPEAT to CLAMP_to_EDGE but it doesn't change anything. Texture loading code is here : gl.glBindTexture(gl.GL_TEXTURE_2D, mTexture.get(4)); gl.glActiveTexture(4); gl.glTexParameterf(gl.GL_TEXTURE_2D, gl.GL_TEXTURE_MIN_FILTER, gl.GL_LINEAR); gl.glTexParameterf(gl.GL_TEXTURE_2D, gl.GL_TEXTURE_MAG_FILTER, gl.GL_LINEAR); gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_CLAMP_TO_EDGE); gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_CLAMP_TO_EDGE); gl.glTexImage2D(gl.GL_TEXTURE_2D, 0, gl.GL_RGBA, shadowbmp.width, shadowbmp.height, 0, gl.GL_RGBA, gl.GL_UNSIGNED_SHORT_4_4_4_4, shadowbmp.buffer); Texture coordinates are the following : float shadow_bot_text[] = { 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f, 1.0f }; Thanks

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  • How to name variables which are structs

    - by evilpie
    Hello, i often work on private projects using the WinApi, and as you might know, it has thousands of named and typedefed structs like MEMORY_BASIC_INFORMATION. I will stick to this one in my question, what still is preferred, or better when you want to name a variable of this type. Is there some kind of style guide for this case? For example if i need that variable for the VirtualQueryEx function. Some ideas: MEMORY_BASIC_INFORMATION memoryBasicInformation; MEMORY_BASIC_INFORMATION memory_basic_information; Just use the name of the struct non capitalized and with or without the underlines. MEMORY_BASIC_INFORMATION basicInformation; MEMORY_BASIC_INFORMATION information; Short form? MEMORY_BASIC_INFORMATION mbi; I often see this style, using the abbreviation of the struct name. MEMORY_BASIC_INFORMATION buffer; VirtualQueryEx defines the third parameter lpBuffer (where you pass the pointer to the struct), so using this name might be an idea, too. Cheers

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  • How do I bind a key to "the function represented by the following key sequence"?

    - by katrielalex
    I'm just starting to learn emacs (woohoo!) and I've been mucking around in my .emacs quite happily. Unfortunately, I don't know Lisp yet, so I'm having issues with the basics. I've already remapped a few keys until I fix my muscle memory: (global-set-key (kbd "<f9>") 'recompile) That's fine. But how can I tell a key to 'simulate pressing several keys'? For instance, I don't know, make <f1> do the same as C-u 2 C-x } (widen buffer by two chars). One way is to look up that C-x } calls shrink-window-horizontally, and do some sort of lambda thing. This is of course the neat and elegant way (how do you do this?). But surely there's a way to define <f1> to send the keystrokes C-u 2 C-x }?

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  • How to refresh a folder's data in asp.net 2.0 using c#

    - by vedactive
    Again i rewrite my question with more details i.e. I am developing a website in Asp.net 2.0 in that i'm tracking the user's some details like their id,no of page hitted and time of hitting etc, in a LogfileDate(the LogfileDate contains whole day summary of all users) saved inside a folder(Folder is inside my project). And at another day when a new logfileDate created i want to mail the previous day Logfile and delete that file after sending. Everything happened but when It is going to delete its shows file is accessed by another process. So I need to refresh that folder after sending mail so that it got free with buffer. I'm not using IIS and i dont want it to use.

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  • SVG Animation in Python? - Any options other than Things! 0.4?

    - by ThantiK
    I recently gave my daughter some time on the computer, and she really likes a program called 'BabySmash!', and I also have another program that came with a keyboard attachment called 'Laugh, Smile & Learn' from playschool I think. I'm not a python guru by any stretch of the imagination and I kind of have it in my head that I want to create some sort of program in the spirit of these two, with vector animation and sounds. Thing is, it doesn't look like there are many options for vector animation in python. I found a library called Things! 0.4, but it's lacking in-depth documentation and seems to be more of an experiment in vector animation rather than a full blown solution. Are there any options that I'm not immediately finding? What other animation-libraries do you recommend? Even if the library isn't vector-based, ease of use is probably the strongest factor in my use.

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  • Binding in ContentControl Crash

    - by ImJames
    Can anyone tell me why this crashes my app? There seems to be some endless recursion by I can't figure out why. I get this exception Logical tree depth exceeded while traversing the tree. This could indicate a cycle in the tree <ContentControl Content="{Binding}"> <ContentControl.ContentTemplate> <DataTemplate> <Button Content="{Binding MyString}"/> </DataTemplate> </ContentControl.ContentTemplate> </ContentControl> And this is all I have as Source public MainWindow() { InitializeComponent(); MyString = "Test"; this.DataContext = this; } public string MyString { get; set; }

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  • Excel + Web Data

    - by user348152
    I've spent hours scouring the net for anything to do with VBA calling data from the web in excel and nothing provides a tutorial on how to do so, only complicated examples un-related to what I want to do. I want to pull data from either a .html or .xml site, doesn't matter, via Excel and find specific points in that data. I can find specific points but don't know how to get the data or scroll through multiple lines. I've done this exact sort of thing in mIRC (sort of C code). http://eve-central.com/home/quicklook.html?typeid=438 http://api.eve-central.com/api/quicklook?typeid=438 Those are two examples, using roughly the same data I'd like to retrieve. It'd be FAR more specific with at most 100 or so different values. I'd like to be TAUGHT how to do it, not given the code to do it, or if you must explain each part with comments in-depth please. Thanks Nick

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