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  • How to sum up an array of integers in C#

    - by Filburt
    Is there a better shorter way than iterating over the array? int[] arr = new int[] { 1, 2, 3 }; int sum = 0; for (int i = 0; i < arr.Length; i++) { sum += arr[i]; } clarification: Better primary means cleaner code but hints on performance improvement are also welcome. (Like already mentioned: splitting large arrays). It's not like I was looking for killer performance improvement - I just wondered if this very kind of syntactic sugar wasn't already available: "There's String.Join - what the heck about int[]?".

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  • Database indexes and their Big-O notation

    - by miket2e
    I'm trying to understand the performance of database indexes in terms of Big-O notation. Without knowing much about it, I would guess that: Querying on a primary key or unique index will give you a O(1) lookup time. Querying on a non-unique index will also give a O(1) time, albeit maybe the '1' is slower than for the unique index (?) Querying on a column without an index will give a O(N) lookup time (full table scan). Is this generally correct ? Will querying on a primary key ever give worse performance than O(1) ? My specific concern is for SQLite, but I'd be interested in knowing to what extent this varies between different databases too.

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  • Extract a sentence out of sentences separated by delimitors

    - by Laura
    Below is a sample line I have extracted from a website: below a satisfactory level; &quot;an off year for tennis&quot;; &quot;his performance was off&quot; The output displays as: below a satisfactory level; "an off year for tennis"; "his performance was off" I want to get only the first sentence "below a satisfactory level"; Here is the code I have tried after exploring many stackoverflow posts: $data=explode('; ',$str); echo $data[0]; But somehow it is not working. Thanks in advance.

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  • Mac OSX: Passing a link to file from user process to kernel module.

    - by Inso Reiges
    Hello, I need to pass a link to file from a user process to the OSX kernel driver. By link i mean anything that uniquely identifies a file on the local filesystem. I need that link to do I/O on that file in kernel. The most obvious solution seems to pass a file name and use a VFS vnode lookup. However i noticed, that Apple Disk Images helper process passes a raw data array for image-path property to driver when attaching a disk image file: <2f 56 6f 6c 75 6d 65 73 2f 73 74 6f 72 61 67 65 2f 74 65 73 74 32 2e 64 6d 67> What is that diskimages-helper passes to the kernel driver? Some serialized type perhaps? If yes, what type is it and how can i use it?

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  • Remove items from SWT tables

    - by Dima
    This is more of an answer I'd like to share for the problem I was chasing for some time in RCP application using large SWT tables. The problem is the performance of SWT Table.remove(int start, int end) method. It gives really bad performance - about 50msec per 100 items on my Windows XP. But the real show stopper was on Vista and Windows 7, where deleting 100 items would take up to 5 seconds! Looking into the source code of the Table shows that there are huge amount of windowing events flying around in this call.. That brings the windowing system to its knees. The solution was to hide the damn thing during this call: table.setVisible(false); table.remove(from, to); table.setVisible(true); That does wonders - deleting 500 items on both XP & Windows7 takes ~15msec, which is just an overhead for printing out time stamps I used. nice :)

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  • Mac OSX: Passing a file from user process to kernel module.

    - by Inso Reiges
    Hello, I need to pass a link to file from a user process to the OSX kernel driver. By link i mean anything that uniquely identifies a file on the local filesystem. I need that link to do I/O on that file in kernel. The most obvious solution seems to pass a file name and use a VFS vnode lookup. However i noticed, that Apple Disk Images helper process passes a raw data array for image-path property to driver when attaching a disk image file: <2f 56 6f 6c 75 6d 65 73 2f 73 74 6f 72 61 67 65 2f 74 65 73 74 32 2e 64 6d 67> What is that diskimages-helper passes to the kernel driver? Some serialized type perhaps? If yes, what type is it and how can i use it?

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  • which is better, creating a materialized view or a new table?

    - by Carson
    I have some demanding mysql queries that are needed to grap same up-to-date datasets from 5-7 mysql tables. I am thinking of creating a table or materialized view to gather all demanding columns from other tables, so as to increase performance. If I create that table, I may need to do extra insert / update / delete operation each time other tables updated. if I create materialized view, I am worrying if the performance can be greatly improved. Because data from other tables are changing very frequently. Most likely, the view may need to be created first everytime before selecting it. Any ideas? e.g. how to cache? other extra measures I can do?

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  • Why do people still use C these days? [closed]

    - by Joshua
    C++ is clearly a far superior language than C, since it has many features that C lacks (although, C++'s object model isn't as ideal as say C#'s). With the coming off the new C++0x standard, why hasn't C been phased out to obscurity? C++ has been around for so long, since the '80s. The Linux kernel has already been ported to C++ with negligible performance differences. I believe, with no evidence, that larger program structures benefit in performance if written in C++ than in C, if only because of object interaction. Don't get me started on "objects-in-C!" libraries, which are all a terrible hack. (Not that C++'s object model is the most ideal, but it is almost up to snuff with C# using common ad-hoc techniques.)

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  • What is the optimal number of threads for performing IO operations in java?

    - by marc
    In Goetz's "Java Concurrency in Practice", in a footnote on page 101, he writes "For computational problems like this that do not I/O and access no shared data, Ncpu or Ncpu+1 threads yield optimal throughput; more threads do not help, and may in fact degrade performance..." My question is, when performing I/O operations such as file writing, file reading, file deleting, etc, are there guidelines for the number of threads to use to achieve maximum performance? I understand this will be just a guide number, since disk speeds and a host of other factors play into this. Still, I'm wondering: can 20 threads write 1000 separate files to disk faster than 4 threads can on a 4-cpu machine?

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  • Warning in gdb,while run application in device mode

    - by dragon
    Warning in gdb, while run application in device mode... The warning message is warning: UUID mismatch detected with the loaded library - on disk is: /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.2.sdk/System/Library/PrivateFrameworks/MBX2D.framework/MBX2D =uuid-mismatch-with-loaded-file,file="/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.2.sdk/System/Library/PrivateFrameworks/MBX2D.framework/MBX2D" warning: UUID mismatch detected with the loaded library - on disk is: /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.2.sdk/usr/lib/libxml2.2.dylib =uuid-mismatch-with-loaded-file,file="/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.2.sdk/usr/lib/libxml2.2.dylib" The application not loaded in ipod ? the blackscreen shown for long time ... How can i fix this ? can any one help me? Thanks in advance.....

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  • Resolving Assemblies, the fuzzy way

    - by David Rutten
    Here's the setup: A pure DotNET class library is loaded by an unmanaged desktop application. The Class Library acts as a plugin. This plugin loads little baby plugins of its own (all DotNET Class Libraries), and it does so by reading the dll into memory as a byte-stream, then Assembly asm = Assembly.Load(COFF_Image); The problem arises when those little baby plugins have references to other dlls. Since they are loaded via the memory rather than directly from the disk, the framework often cannot find these referenced assemblies and is thus incapable of loading them. I can add an AssemblyResolver handler to my project and I can see these referenced assemblies drop past. I have a reasonably good idea about where to find these referenced assemblies on the disk, but how can I make sure that the Assmebly I load is the correct one? In short, how do I reliably go from the System.ResolveEventArgs.Name field to a dll file path, presuming I have a list of all the folders where this dll could be hiding)?

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  • Is a program compiled with -g gcc flag slower than the same program compiled without -g?

    - by e271p314
    I'm compiling a program with -O3 for performance and -g for debug symbols (in case of crash I can use the core dump). One thing bothers me a lot, does the -g option results in a performance penalty? When I look on the output of the compilation with and without -g, I see that the output without -g is 80% smaller than the output of the compilation with -g. If the extra space goes for the debug symbols, I don't care about it (I guess) since this part is not used during runtime. But if for each instruction in the compilation output without -g I need to do 4 more instructions in the compilation output with -g than I certainly prefer to stop using -g option even at the cost of not being able to process core dumps. How to know the size of the debug symbols section inside the program and in general does compilation with -g creates a program which runs slower than the same code compiled without -g?

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  • How can I position QDockWidgets as the screen shot shows using code?

    - by Nathan
    I want a Qt window to come up with the following arrangement of dock widgets on the right. Qt allows you to provide an argument to the addDockWidget method of QMainWindow to specify the position (top, bottom, left or right) but apparently not how two QDockWidgets placed on the same side will be arranged. Here is the code that adds the dock widgets. this uses PyQt4 but it should be the same for Qt with C++ self.memUseGraph = mem_use_widget(self) self.memUseDock = QDockWidget("Memory Usage") self.memUseDock.setObjectName("Memory Usage") self.memUseDock.setWidget(self.memUseGraph) self.addDockWidget(Qt.DockWidgetArea(Qt.RightDockWidgetArea),self.memUseDock) self.diskUsageGraph = disk_usage_widget(self) self.diskUsageDock = QDockWidget("Disk Usage") self.diskUsageDock.setObjectName("Disk Usage") self.diskUsageDock.setWidget(self.diskUsageGraph) self.addDockWidget(Qt.DockWidgetArea(Qt.RightDockWidgetArea),self.diskUsageDock) When this code is used to add both of them to the right side, one is above the other, not like the screen shot I made. The way I made that shot was to drag them there with the mouse after starting the program, but I need it to start that way.

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  • What's the best way to match a query to a set of keywords?

    - by Ryan Detzel
    Pretty much what you would assume Google does. Advertisers come in and big on keywords, lets say "ipod", "ipod nano", "ipod 60GB", "used ipod", etc. Then we have a query, "I want to buy an ipod nano" or "best place to buy used ipods" what kind of algorithms and systems are used to match those queries to the keyword set. I would imagine that some of those keyword sets are huge, 100k keywords made up of one or more actual words. on top of that queries can be 1-n words as well. Any thoughts, links to wikipedia I can start reading? From what I know already I would use some stemmed hash in disk(CDB?) and a bloom filter to check to see if I should even go to disk.

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  • How to view existing data in Core Data?

    - by mshsayem
    Well, may be this question is silly, but I couldn't find a way (except programmatically). I built a project (for iPhone OS 3.0) which uses Core Data. The xcdatamodel file shows the schema description, but I want to see the data in tabular form (like the management studio for mssql server or phpmyadmin for mysql). Is there any way (except coding)? What is that? Also, which file (in disk/device) those data are stored into? [ I built the tutorial (from apple) on Core Data, named Locations. They used this line somewhere in the code: NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"Locations.sqlite"]]; But, I did not see any "xxxxx.sqlite" file in project location (nor in the disk).]

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  • installing Delphi5 pro in windows 64b

    - by Larry
    Please dont laugh . Over the past 15 years or so I've written all the software that runs my medical practice in D5. Last week when I went to DelphiArea to update a component I got attacked and my disk became unbootable/unrecoverable. I have my original D5p disk and all the components backed up but I want to migrate to W7. I don't care if my delphi apps look like vista/7, I just want to be able to install it and code on the machine again for maintenance purposes. 1) are there any tricks to install D5 so it works in W7? 2) is using a vm program really the only/best way? if so, which is suggested. Thanks in advance. My new Gateway zx6800-03 arrives tomorrow! Larry [email protected]

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  • What Use are Threads Outside of Parallel Problems on MultiCore Systesm?

    - by Robert S. Barnes
    Threads make the design, implementation and debugging of a program significantly more difficult. Yet many people seem to think that every task in a program that can be threaded should be threaded, even on a single core system. I can understand threading something like an MPEG2 decoder that's going to run on a multicore cpu ( which I've done ), but what can justify the significant development costs threading entails when you're talking about a single core system or even a multicore system if your task doesn't gain significant performance from a parallel implementation? Or more succinctly, what kinds of non-performance related problems justify threading? Edit Well I just ran across one instance that's not CPU limited but threads make a big difference: TCP, HTTP and the Multi-Threading Sweet Spot Multiple threads are pretty useful when trying to max out your bandwidth to another peer over a high latency network connection. Non-blocking I/O would use significantly less local CPU resources, but would be much more difficult to design and implement.

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  • Why does C++ linking use virtually no CPU?

    - by John
    On a native C++ project, linking right now can take a minute or two, yet during this time CPU drops from 100% during compilation to virtually zero. Does this mean linking is primarily a disk activity? If so, is this the main area an SSD would make big changes? But, why aren't all my OBJ files (or as many as possible) kept in RAM after compilation to avoid this? With 4Gb of RAM I should be able to save a lot of disk access and make it CPU-bound again, no?

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  • how to get apache log like debugging in Android logcat

    - by Nav
    I am currently using a webview to load a webpage which contains lots of javascript and having lots of trouble debugging what exactly gets loaded and when in the webview . Then I saw this post where the op seems to be using apache log to monitor webpage load events in his webview. Enhance webView performance (should be the same performance as native Web Browser) Can I get a similar utility plugin or anything so that I can use it with logcat in ddms view. If possible please provide some resource as to how to configure it for android.

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