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• Which NoSQL db to use with C?

  - by systemsfault

  Hello all, I'm working on an application that I'm going to write with C and i am considering to use a nosql db for storing timeseries data with at most 8 or 9 fields. But in every 5 minutes there will huge write operations such as 2-10 million rows and then there will be reads(but performance is not as crucial in read as in the write operation). I'm considering to use a NoSQL db here in order to store the data but couldn't decide on which one to use. Couchdb seems to have a stable driver called pillowtalk for C; but Mongo's driver doesn't look as promising as pillowtalk. I'm also open to other suggestions. What is your recommendation?

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• What exactly is a variable in C++?

  - by FredOverflow

  The standard says A variable is introduced by the declaration of an object. The variable's name denotes the object. But what does this definition actually mean? Does a variable give a name to an object, i.e. are variables just a naming mechanism for otherwise anonymous objects? Or is a variable the name itself? Or is a variable a named object in the sense that every variable is also an object? Or is a variable just a "proxy" with a name that "delegates" all operations to the real object? To confuse things further, many C++ books seem to treat variables and objects as synonyms. What is your take on this?

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• sortable + draggable demo - how to get access to dropped item?

  - by user246114

  Hi, I have a sortable list. When a new item is dropped into the list (from a draggable), I'd like to get access to it to perform some operations on it. This is what I have: $("#mySortableList").sortable({ receive: function(event, ui) { alert("this is the dropped item: " + ui.item.toString()); } }).disableSelection(); so "ui.item" is the element that was dropped, but it's not the duplicated item that will now be part of my list. How do I get access to the new item that was dropped? I am using the exact demo from the jquery-ui site here: http://jqueryui.com/demos/draggable/#sortable Thanks

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• Best way to manage the persistence of a form state, to and from a database

  - by Laurent.B

  In a JSP/Servlet webapp, I have to implement a functionality that allows a user to save or restore a form state, that latter containing for instance some search criteria. In other words, the user must be able to save or restore field values of a form, at any time. On the same page that contains that form, there's also another little form that allows him to name his form state before saving it. Then, later he'll be able to recall that state, via a combobox, and refill dynamically the form with the state he selected. I know how to implement that by hand but I would prefer not to reinvent the wheel then I'd like to know if there are some frameworks managing that kind of functionality ? A mix between JSP taglib, filter class, jQuery or other JavaScript frameworks... My research has not give anything yet. Thank you in advance.

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• Speed of interpolation algorithms, C# and C++ working together.

  - by Kaminari

  Hello. I need fast implementation of popular interpolation algorithms. I figured it out that C# in such simple algorithms will be much slower than C++ so i think of writing some native code and using it in my C# GUI. First of all i run some tests and few operations on 1024x1024x3 matrix took 32ms in C# and 4ms in C++ and that's what i basicly need. Interpolation however is not a good word because i need them only for downscaling. But the question is: Will it be faster than C# methods in Drawing2D Image outputImage = new Bitmap(destWidth, destHeight, PixelFormat.Format24bppRgb); Graphics grPhoto = Graphics.FromImage(outputImage); grPhoto.InterpolationMode = InterpolationMode.*; //all of them grPhoto.DrawImage(bmp, new Rectangle(0, 0, destWidth, destHeight), Rectangle(0, 0, sourceWidth, sourceHeight), GraphicsUnit.Pixel); grPhoto.Dispose(); Some of these method run in 20ms and some in 80. Is there a way to do it faster?

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• Download File from Web C++ (with winsock?)

  - by Lienau

  I need to download files/read strings from a specified url in C++. I've done some research with this, cURL seems to be the most popular method. Also, I've used it before in PHP. The problem with cURL is that the lib is huge, and my file has to be small. I think you can do it with winsock, but I can't find any simple examples. If you have a simple winsock example, a light cURL/Something else, or anything that could get the job done. I would greatly appreciated. Also, I need this to work with native C++.

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• Making simple tabs in android

  - by user2910566

  I am new to Android. I am making a tab Activity that has 3 tabs in it. . I came across reading some interesting articles that tab can be made in three ways:: Regular TabHost Using simple Fragments Using Action Bar Sherlock I have a set of questions Which is a better choice & why ? Which gives more flexibility, efficiency & performance ? Which would be the preferd choice in case of requirement changes happen in future ? My research indicate :: ActionBarsherlock is better ! Is there something better than this ? If so what is it ?

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• When is a program limited by the memory bandwidth?

  - by hanno

  I want to know if a program that I am using and which requires a lot of memory is limited by the memory bandwidth. When do you expect this to happen? Did it ever happen to you in a real life scenario? I found several articles discussing this issue, including http://www.cs.virginia.edu/~mccalpin/papers/bandwidth/node12.html http://www.cs.virginia.edu/~mccalpin/papers/bandwidth/node13.html http://ispass.org/ucas5/session2_3_ibm.pdf The first link is a bit old, but suggests that you need to perform less than about 1-40 floating point operations per floating point variable in order to see this effect (correct me if I'm wrong). How can I measure the memory bandwidth that a given program is using and how do I measure the (peak) bandwidth that my system can offer? I don't want to discuss any complicated cache issues here. I'm only interested in the communication between the CPU and the memory.

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• What types of conditions can be used for conditional compilation in C++?

  - by user1002288

  This is an exam question for C++: Which of the following statements accurately describe the condition that can be used for conditional compilation in C++? A. The condition can depend on the value of environment variables. B. The condition can depend on the value of any const variables. C. The condition can depend on the value of program variables. D. The condition can use the sizeof() operator to make decision about compiler-dependent operations based on the size of standard data type. E. The condition must evaluate to either a 0 or 1 during preprocessing. I think the answer is E. Is this correct?

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• finding character in string C language

  - by iSight

  Hi, I am searching a character at first occurence in string using the following code. But, it is taking some time when the character is too long or the character that i am searching is at far extend, which makes delay in other operations. How could i tackle with this problem. The code is below here. Note: attrPtr is a char* which holds a reference to a string containing '"' character at far extend. int position = 0; char qolon = '"';//character to search while (*(attrPtr + position++) != qolon); char* attrValue = NULL; attrValue = (char*)malloc(position * sizeof(char)); strncpy(attrValue, attrPtr, position-1);

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• How to group rows into two groups in sql?

  - by user1055638

  Lets say I have such a table: id|time|operation 1 2 read 2 5 write 3 3 read 4 7 read 5 2 save 6 1 open and now I would like to do two things: Divide all these records into two groups: 1) all rows where operation equals to "read" 2) all other rows. Sum the time in each group. So that my query would result only into two rows. What I got so far is: select sum(time) as total_time, operation group by operation ; Although that gives me many groups, depending on the number of distinct operations. How I could group them only into two categories? Cheers!

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• Special simple random number generator

  - by psihodelia

  How to create a function, which on every call generates a random integer number? This number must be most random as possible (according to uniform distribution). It is only allowed to use one static variable and at most 3 elementary steps, where each step consists of only one basic arithmetic operation of arity 1 or 2. Example: int myrandom(void){ static int x; x = some_step1; x = some_step2; x = some_step3; return x; } Basic arithmetic operations are +,-,%,and, not, xor, or, left shift, right shift, multiplication and division. Of course, no rand(), random() or similar staff is allowed.

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• how to check if ssl exists on a webserver through php?

  - by sarmenhb

  i have this function here that i have in a class function enable_ssl() { if ($_SERVER[HTTPS]!="on") { $domain = "https://".$_SERVER['HTTP_HOST']."/".$_SERVER['SCRIPT_NAME']; header("Location: {$domain}"); } } but the problem is when the server doesnt have ssl installed and i have this function initiating the page redirects to a 404 page. i was wondering how i can have this function work only when ssl is installed and working is it possible? thanks. ps: did some google research and couldnt find much of anything.

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• Event(s) for opening the workbook AND worksheets

  - by KeyMs92

  I'm looking for an elegant solution to trigger an event for opening the workbook as well as opening different worksheets. I don't need seperate operations for each worksheet: they all trigger the same method. I know I can use the events Workbook_Activate / Workbook_Open and Workbook_SheetActivate at the same time but I don't know if this is 'the official way' to do it. Perhaps there's a way to do this with one event. I was also wondering if it is relevant in this matter where I put the code. I now have all the code inside "ThisWorkbook" and not in a "Module"...

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• Low-overhead way to access the memory space of a traced process?

  - by vovick

  Hello all. I'm looking for an efficient way to access(for both read and write operations) the memory space of my ptraced child process. The size of blocks being accessed may vary from several bytes up to several megabytes in size, so using the ptrace call with PTRACE_PEEKDATA and PTRACE_POKEDATA which read only one word at a time and switch context every time they're called seems like a pointless waste of resources. The only one alternative solution I could find, though, was the /proc/<pid>/mem file, but it has long since been made read only. Is there any other (relatively simple) way to do that job? The ideal solution would be to somehow share the address space of my child process with its parent and then use the simple memcpy call to copy data I need in both directions, but I have no clues how to do it and where to begin. Any ideas?

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• How online-game clients are able to exchange data through internet so fast?

  - by Kirzilla

  Hello, Let's imagine really simple game... We have a labirinth and two players trying to find out exit in real time through internet. On every move game client should send player's coordinates to server and accept current coordinates of another client. How is it possible to make this exchange so fast (as all modern games do). Ok, we can use memcache or similar technology to reduce data mining operations on server side. We can also use fastest webserver etc., but we still will have problems with timings. So, the questions are... What protocol game clients are usually using for exchanging information with server? What server technologies are coming to solve this problem? What algorithms are applied for fighting with delays during game etc. PS: Sorry for my English and I hope that my question is clear. Thank you.

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• Asp.net static object behaviour

  - by Circadian

  I have the following class as part of an asp.net application. public sealed class SomeClass { private static string appId = Guid.NewGuid().ToString(); public static ReadSomethingFromDb(){} public static WriteSomethingToDb(){} } There are more than one application instances in the same application pool, and they all access the same database. I want the operations performed by the above class to be uniquely tied to the instance that performed it, hence the use of the appId. So adding a record to the database would for example contain a name, address and appId. This has been simplified for discussion purposes. Assuming that I have two instances running at mysite.a and mysite.b the above class would generate two different guids. My problem is that mysite.a sometimes produces more than one guid, which is unexpected. Thank you in advance

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• Add 64 bit offset to a pointer

  - by Novox

  In F#, there's the NativePtr module, but it seems to only support 32 bit offsets for its’ add/get/set functions, just like System.IntPtr does. Is there a way to add a 64 bit offset to a native pointer (nativeptr<'a) in F#? Of course I could convert all addresses to 64 bit integers, do normal integer operations and then convert the result again to nativeptr<'a, but this would cost additional add and imul instructions. I really want the AGUs to perform the address calculations. For instance, using unsafe in C# you could do something like void* ptr = Marshal.AllocHGlobal(...).ToPointer(); int64 offset = ...; T* newAddr = (T*)ptr + offset; // T has to be an unmanaged type Well actually you can't, because there is no "unmanaged" constraint for type parameters, but at least you can do general pointer arithmetic in a non-generic way. In F# we finally got the unmanaged constraint; but how do I do the pointer arithmetic?

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• asp.net sharepoint development

  - by Daniel

  Hi all, Im my current project we need to interface with sharepoint to store and retrieve various documents. This has previously been done by referencing the Microsoft.Sharepoint dlls directly and going from there. As I don't know a lot about sharepoint yet I have been doing some research. Most of the examples I find actually refer to using the Sharepoint web services themselves (the various vti_bin ones shown in http://www.sharepointmonitor.com/2007/01/sharepoint-web-service/). I cant seem to find the differences in approaches. This current project was written a few years ago so maybe the web services weren't available then? Cheers

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• Use AJAX to check for a new message

  - by Luke

  Quite simply, I need to alert the end user when they have a new private message. From a combination of research and other opinion, I realise I need to use AJAX for this. The mysql query would be SELECT id FROM tbl_messages WHERE to_viewed = 1 So when someone sends a message, I want an alert to popup on the screen to inform the user without a page reload. I have absolutely no idea what I am doing, but know what I want. Really need help with this, AJAX is definitely something I want to improve as it opens up greater possibilities! Thanks

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• Common strategies to deal with rounding errors in currency-intensive soft?

  - by Max

  What is your advice on: compensation of accumulated error in bulk math operations on collections of Money objects. How is this implemented in your production code? (things like variable rounding, etc...) theory behind rounding in accountancy. any literature on topic. I currently read Fowler. He mentions Money type, but says nothing on strategies. Older posts on money-rounding (here, and here) do not provide a details and formality I need. Thanks for help.

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• Best neural network for certain type of pattern analysis?

  - by fred basset

  Hi All, I'm working on a system that will send telemetry data on machine operation back to a central server for analysis. One of the machine parameters we're measuring is motor current drawn vs time. After an operation is finished we plan to send back an array of currents vs time to the server. A successful operation would have a pattern like a trapezoid, problematic operations would have a pattern completely different, more like a large spike in values. Can anyone recommend a type of neural network that would be good at classifying these 1D vectors of current values into a pass/fail type output? Thanks, Fred

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• How often does memcache on Google AppEngine lose data?

  - by Freed

  Memcache in general and on AppEngine in specific is unreliable in the sense that my data may be deleted from the cache for whatever reason at any point in time. However, in some cases there might be cases where a small risk may be worth the added performance using memcache could give, such as updating some data in memcache that gets saved periodically to some other, more reliable storage. Are there any numbers from Google that could give me an indication of the actual probability that a memcache entry would be lost from the cache before its expiration time, given that I keep within my quotas? Are there any reasons other than hardware failure and administrative operations such as machines at the data centers being upgraded/moved/replaced that would cause entries to be removed from memcache prematurely?

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• Merge 2 lines into one

  - by shantanuo

  I have a text file starts with 9 digits college code and ends with of 5 digits course code. 512161000 EN5121 K. K. Jorge Institute of Engineering Education and Research, Nashik 61220 Mechanical Engineering [Second Shift] XOPENH 1 116 16978 517261123 EN5172 R. C. Rustom Institute of Technology, Shirpur 61220 Mechanical Engineering [Second Shift] YOPENH 1 100 29555 617561234 EN6175 abc xyz Education Trust, abc xyz College of Engineering, Pune 61220 Mechanical Engineering [Second Shift] ZOPENH 2 105 25017 There are some entries where there is a line break as shown in the 3 example above. I need to merge 3rd and 4th line into one just like 1st and 2nd line, so that I can easily use command like grep, awk etc.

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• How to define an array inside a function in C?

  - by Arunav Dev

  So in my source file I have the folowin function: void update(state* old_state, state* measurement, uint32_t size) { state new_state[size]; //some function using measurement and old_state and returning the result in newstate arm_fadd_32(measurement,old_state,newstate,size); // rest of the code } Now the compiler throws an error saying that error#28:expression must have a constant value. I think it's due to the fact that even though inside the method the size local variable is not changing the compiler is expecting a constant while defining the size. I have tried the following: int const a = size; and then tried to reinitialize it says constant value is not known. I did some research in internet and it appears that there is no easier way without using malloc, which I don't want to since I am using the code for some embedded application. Is there a way to avoid this problem without really using malloc? Thanks in advance guys!

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