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• Predicting performance for an iPhone/iPod Touch App

  - by Avizz

  I don't have an iPhone Developer Program Account yet and will be getting one in the next couple of days. Can instruments be used with the simulator to give a rough estimate on how well my app may perform? Using instruments I checked and fixed all the leaks it was detecting, and it appears that my memory usage maxes out at about 5.77mb. Is there any other tests I could perform with instruments to judge how well my app would perform? I realize there is no way other then the actual device to get a definite answer, it would be nice to get an estimate.

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• Easiest way to combine a dataset and other data in a single file?

  - by Tim Gradwell

  I have a dataset in C# which I can serialise using dataset.WriteXml(filename); but I want the file to contain other data as well (essentially some meta data about the dataset). I could add another table to the dataset which contained the metadata, but I'd prefer to keep it separate, if at all possible. Essentially I think I want to create a 'combination of files' file, that looks something like this: size_of_file1 file1 size_of_file2 file2 ... etc Then, I'd like to load the file into memory, and split the file into separate streams, so that I can feed the dataset into dataset.ReadXml(stream); and the metadata into something else. Sound possible? Can anyone tell me how I can do it? Thanks Tim

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• how to read httpWebRequest's request stream in c#, i got error" the stream is not readable" ?

  - by sam

  hi i want to read request stream from a custom httpWebRequest class that inherits from httpWebRequest and i have tried to read the request stream in different stages but sitll not sure how to archieve that in the class,thanks very much for any help. This custom httpWebRequest is used to serilize soap message and i want to know what request has been sent in string format. I also implemented custom HttpRequestCreator,HttpWebResponse but till cant find a place/stage i can read the request stream. If i output everything in a memory stream then copy the content to request stream, anyone knows which stage i can do it in the constructor, BeginGetRequestStream,EndGetRequestStream or GetRequestStream?

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• How are a session identifiers generated?

  - by Asaf R

  Most web applications depend on some kind of session with the user (for instance, to retain login status). The session id is kept as a cookie in the user's browser and sent with every request. To make it hard to guess the next user's session these session-ids need to be sparse and somewhat random. The also have to be unique. The question is - how to efficiently generate session ids that are sparse and unique? This question has a good answer for unique random numbers, but it seems not scalable for a large range of numbers, simply because the array will end up taking a lot of memory.

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• In C, as free() knows an array size, why isn't there a function that gets the array size? [closed]

  - by user354959

  Possible Duplicate: If free() knows the length of my array, why can’t I ask for it in my own code? Searching around (including here at stackoverflow), I got that malloc() allocates an array and also creates a header to control the array info. In this header, there's also the array size. free() use such information to know how to deallocate that array. So, if the array size info is "there" (somewhere in the memory), why there isn't a function that returns an array size, looking for this at the array header? Or am I missing something?

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• Freeing JavaScript object

  - by pion

  I am looking at the example from http://www.javascriptkit.com/javatutors/oopjs.shtml var person = new Object() person.name = "Tim Scarfe" person.height = "6Ft" But there is no mention how to "free" it in order to avoid memory leak. Will the following code free it? person = null; How do you free a JavaScript Object using "new Object()? How do you free a JavaScript Array allocated using "new Array(10)"? How do you free a JavaScript JSON allocated using "var json = {"width": 480, "height": 640}"? Thanks in advance for your help.

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• Retrieving data from an encrypted text file?

  - by user

  Let's say I have a text file contains my data. data : ab bc de - encrypted data on text file : ba cb ed I want to find bc from text file, so I have to decrypt the text file with this code : SL:=TStringList.create; SL.LoadFromFile(textfile) SLtemp:=TStringList.create; for I := 0 to SL.Count - 1 do SLtemp.Add(ReverseString(SL[i])); //decrypt SL.Free; for I := 0 to SLtemp.Count - 1 do if SLtemp[i] = 'bc' then begin showmessage('found'); break; end; SLtemp.Free; I think my way is wasting resources. I have to load whole file to memory and decrypt them. I need some suggestions here to find quickly a specific line from an encrypted text. Thanks.

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• Could someone give me their two cents on this optimization strategy

  - by jimstandard

  Background: I am writing a matching script in python that will match records of a transaction in one database to names of customers in another database. The complexity is that names are not unique and can be represented multiple different ways from transaction to transaction. Rather than doing multiple queries on the database (which is pretty slow) would it be faster to get all of the records where the last name (which in this case we will say never changes) is "Smith" and then have all of those records loaded into memory as you go though each looking for matches for a specific "John Smith" using various data points. Would this be faster, is it feasible in python, and if so does anyone have any recommendations for how to do it?

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• Book resources for x86/x64 assembly programming on Win platform

  - by Scott Davies

  Hello, I ran a search for assembly language resources on stackoverflow.com and found some interesting results, but they seemed to boil down to two groups: 1) Assembly references to old ia32 architecture, such as the 80386 to Pentium 2) Windows agnostic books. Most of the commenters make the point that assembler is CPU dependent and that the OS is irrelevant, but it seems pointless to me to pick a book that has assembly examples that refer to MS-DOS interrupts and memory layouts. Likewise, learning assembler on Linux would seem to produce Linux executables Are there any: 1) Modern 2) x86/x64 3) on Windows platform - book resources available ? The reason I am targeting the Win platform is I would like to do low-level, OS internals programming, to supplement my Win C/C++ work. Thanks

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• Is it faster to use a complicated boolean to limit a ResultSet at the MySQL end or at the Java end?

  - by javanix

  Lets say I have a really big table filled with lots of data (say, enough not to fit comfortably in memory), and I want to analyze a subset of the rows. Is it generally faster to do: SELECT (column1, column2, ... , columnN) FROM table WHERE (some complicated boolean clause); and then use the ResultSet, or is it faster to do: SELECT (column1, column2, ... , columnN) FROM table; and then iterate over the ResultSet, accepting different rows based on a java version of your boolean condition? I think it comes down to whether the Java iterator/boolean evaluator is faster than the MySQL boolean evaluator.

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• Garbage Collection Java

  - by simion

  On the slides i am revising from it says the following; Live objects can be identified either by maintaining a count of the number of references to each object, or by tracing chains of references from the roots. Reference counting is expensive – it needs action every time a reference changes and it doesn’t spot cyclical structures, but it can reclaim space incrementally. Tracing involves identifying live objects only when you need to reclaim space – moving the cost from general access to the time at which the GC runs, typically only when you are out of memory. I understand the principles of why reference counting is expensive but do not understand what "doesn’t spot cyclical structures, but it can reclaim space incrementally." means. Could anyone help me out a little bit please? Thanks

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• storing an integer constant other than zero in a pointer variable

  - by benjamin button

  int main() { int *d=0; printf("%d\n",*d); return 0; } this works fine. >cc legal.c > ./a.out 0 if i change the statement int *d=0; to int *d=1; i see the error. cc: "legal.c", line 6: error 1522: Cannot initialize a pointer with an integer constant other than zero. so its obvious that it will allow only zero.i want to know what happens inside the memory when we do this int *d=0 which is making it valid syntax. I am just asking this out of curiosity!

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• OpenGL texture not showing up on some computers, problem with auxDIBImageLoad?

  - by CptanPanic

  I have a simple openGL GUI that has uses a bmp as a texture. The problem is on some computers the texture doesn't show up. But on ones with newer OpenGL drivers it works. How can I make it more compatible. I think the problem may be with auxDIBImageLoad. When I inspect the result, I see the x,y correct, but the data pointer points to memory bank with all zeros. What could be wrong?

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• Forcing a templated object to construct from a pointer

  - by SalamiArmi

  I have a fictional class: template<typename T> class demonstration { public: demonstration(){} ... T *m_data; } At some point in the program's execution, I want to set m_data to a big block of allocated memory and construct an object T there. At the moment, I've been using this code: void construct() { *m_data = T(); } Which I've now realised is probably not the best idea... wont work under certain cirumstances, if T has a private assignment operator for example. Is there a normal/better way to do what I'm attempting here?

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• How do I choose a database?

  - by liamzebedee

  I need a comparison table of some sort for database varieties (MySQL, SQLite etc.). I can't find one. My use case is, I am implementing storage of objects in a distributed hash table. I need a database solution that is: Fast for sorting Simplistic (no users, preferably no additional structures like multiple tables etc.) Concurrent (if possible) Multi-platform File based (not stored in memory primarily) Centralized I will be programming in Go. As I understand, I believe I need what is called a Document Orientated Database, because I am storing objects, identified by keys. EDIT: While I am implementing a DHT, I will also be storing metadata about the objects, such as access counts etc. It would also be preferable to have TLL (time to live)

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• how can i set mTextView to show on button click

  - by Ajay Pandey

  i have a UITextView object which i have created in interface builder with it's hidden property unmarked.Now i want this textView to be invisible when my application launches and first view appears.Further i want it to be displayed when a particular method is called.Now this is what i have written in view did load [mTextView setHidden:YES]; self.mTextView=[[UITextView alloc] init]; it hides the textView ats the first view appears but when my desired method is called and i write [mTextView setHidden:NO]; it does not show it again.. Is it like we cant change the appearance of a textView once it is assigned because after assigning memory as self.mTextView=[[UITextView alloc] init]; and then writing [mTextView setHidden:YES]; it does not hide textView in viwDidLoad either.....

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• running Hadoop software on office computers (when they are idle)

  - by Shahbaz

  Is there a project which helps setup a Hadoop cluster on office desktops, when they are idle? I'd like to experiment with Hadoop/MR/hbase but don't have acces to 5-10 computers. The computers at work are idle after hours and are connected to each other through a very high speed connection. What's more, data on these computers stays within our network so there is no privacy issue. In order for this to work I need a fairly light weight monitor running on each machine. When the computer has been idle for X hours, it will join the cluster. If the user logs on, it has to drop out of the cluster and return all CPU/memory back. Does something like this exist?

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• Excel workbooks produced by POI don't work when linked

  - by Eric Nicolas

  Here is what I'm doing : Create a workbook in memory (book = new HSSFWorkbook(), ...) Save it to disk (book.write(...)) Open in Excel (ok) Create another workbook in Excel, which links to the first one (=PoiWorkbook?xls!A1) Close Excel Then everytime I open the second workbook again, all the links are #N/A, unless I also open the POI-generated workbook at the same time. I never saw this behaviour with standard workbooks created in Excel. Anyone has seen this and found a workaround ? Thanks.

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• Application disappears after starting - C++ linking managed code dll

  - by Axarydax

  Hello, we have a problem with our applications. We have recently upgraded our toolchain to Visual Studio 2010 and friends, it all works fine on Windows Vista + Windows 7 developer machines and Windows 7 customer machines. (all x86) Today we did a first installation to a client PC running Windows XP SP3 x86, and all applications linking managed code dll do not work. After starting the .exe seemingly nothing happens, no window pops up, no memory gets eaten, no task shows in task manager, nothing, nada. Event log is empty, everything is just as if the application returned to the OS right after the start. I am at loss about this, I really don't know how should I start even debugging this problem. I don't want to install VS2010 and everything onto a Windows XP box, I'd like to try something less time intensive first. This all is happening just to native C++ apps that link managed c++ DLL. Pure managed C# apps do work. Pure native C++ apps do work.

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• Unit testing with serialization mock objects in C++

  - by lhumongous

  Greetings, I'm fairly new to TDD and ran across a unit test that I'm not entirely sure how to address. Basically, I'm testing a couple of legacy class methods which read/write a binary stream to a file. The class functions take a serializable object as a parameter, which handles the actual reading/writing to the file. For testing this, I was thinking that I would need a serialization mock object that I would pass to this function. My initial thought was to have the mock object hold onto a (char*) which would dynamically allocate memory and memcpy the data. However, it seems like the mock object might be doing too much work, and might be beyond the scope of this particular test. Is my initial approach correct, or can anyone think of another way of correctly testing this? Thanks!

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• What segments does C compiled program use?

  - by b-gen-jack-o-neill

  Hi, I read on OSDev wiki, that protected mode of x86 architecture allow you to create separate segments for code and data, while you cannot write into code section. That Windows (yes, this is the platform) loads new code into code segment, and data are created on data segment. But, if this is the case, how does program know it must switch segments to the data segment? Becouse if I understand it right, all adress instructions point to the segment you run the code from, unless you switch the descriptor. But I also read, that so colled flat memory model allows you to run code and data within one segment. But I read this only in connection to assembler. So, please, what is the case with C compiled code on Windows? Thanks.

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• Quick way to do data lookup in PHP

  - by Ghostrider

  I have a data table with 600,000 records that is around 25 megabytes large. It is indexed by a 4 byte key. Is there a way to find a row in such dataset quickly with PHP without resorting to MySQL? The website in question is mostly static with minor PHP code and no database dependencies and therefore fast. I would like to add this data without having to use MySQL if possible. In C++ I would memory map the file and do a binary search in it. Is there a way to do something similar in PHP?

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• Objective-C: Initializing char with char at index of string.

  - by Mr. McPepperNuts

  unichar myChar = [myString characterAtIndex:0]; [myNSMutableArray addObject:myChar]; I am trying to insert the first char of a string into an array, to create an array of chars. the first line does not give me an error. The second line however, provides the following error: warning: passing argument 1 of 'addObject:' makes pointer from integer without a cast This also crashes the application with a "bad address" error. I thought this error was due to a problem with memory allocation. Can someone shed some light on this.

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• Why does UITableViewCell have a contentView property?

  - by mystify

  What's the point of this contentView property? I mean: Why aren't all the subviews just added to self? Let me get that right: Every cell is a view (UITabvleViewCell is a UIView subclass). And this fat view has another fat view with same bounds sitting on top of it, called contentView. That contentView then carries all those other subviews. Now why didn't they save that extra chunk of memory? Is there any genius logic behind this decision? Would love to understand the reason for this.

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• How does Photoshop (Or drawing programs) blit?

  - by user146780

  I'm getting ready to make a drawing application in Windows. I'm just wondering, do drawing programs have a memory bitmap which they lock, then set each pixel, then blit? I don't understand how Photoshop can move entire layers without lag or flicker without using hardware acceleration. Also in a program like Expression Design, I could have 200 shapes and move them around all at once with no lag. I'm really wondering how this can be done without GPU help. I don't think super efficient algorithms could justify that? Thanks

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