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• Writing at the end of file

  - by user342534

  Hi, I'm working on a system that requires high file I/O performance (with C#). Basically, I'm filling up large files (~100MB) from the start of the file until the end of the file. Every ~5 seconds I'm adding ~5MB to the file (sequentially from the start of the file), on every bulk I'm flushing the stream. Every few minutes I need to update a structure which I write at the end of the file (some kind of metadata). When flushing each one of the bulks I have no performance issue. However, when updating the metadata at the end of the file I get really low performance. My guess is that when creating the file (which also should be done extra fast), the file doesn't really allocates the entire 100MB on the disk and when I flush the metadata it must allocates all space until the end of file. Guys/Girls, any Idea how I can overcome this problem? Thanks a lot!

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• Fastest method for SQL Server inserts, updates, selects

  - by Ian

  I use SPs and this isn't an SP vs code-behind "Build your SQL command" question. I'm looking for a high-throughput method for a backend app that handles many small transactions. I use SQLDataReader for most of the returns since forward only works in most cases for me. I've seen it done many ways, and used most of them myself. Methods that define and accept the stored procedure parameters as parameters themselves and build using cmd.Parameters.Add (with or without specifying the DB value type and/or length) Assembling your SP params and their values into an array or hashtable, then passing to a more abstract method that parses the collection and then runs cmd.Parameters.Add Classes that represent tables, initializing the class upon need, setting the public properties that represent the table fields, and calling methods like Save, Load, etc I'm sure there are others I've seen but can't think of at the moment as well. I'm open to all suggestions.

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• How to do a random-and-unique generator?

  - by javaLearner.java

  I already wrote a random generator which take arguments a and b, where a is minimun and b is maximum value, like this randomGenerator(int a, int b) What I want to do next is: Using a loop, then generate unique number from a to b. Example: I want to have 8 unique numbers, int a = 1; int b = 10; int value; If I do the loop, there is a high % that same number will appear more than once. Any idea how to do it? My own way is: while(int i <= 8){ randomGenerator(a,b); // if value is not in array, then insert into array } I am stuck at the comment part. Is there any way to check if a variable is exists in an array?

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• Conversion of Single to two UInt16 values in .net

  - by Gio

  In the good old days of C. I could cast a float to an int (assuming 32 bit system), do some bit manipluation ( bitwise and, right shift, ect ), and get the upper and lower 16 bit hex representations of the floating point number, which I could then store in two short values. I'm not seeing an easy way of doing this in C#. System.Convert.ToUInt16 just does a float to int convert (even after I shift right), which leaves a vlaue of 0 if the float is less than 0, which is not the desired effect. //useless leaves me witg a value 0f 0 UIN16 s1 = (UInt16)((System.Convert.ToUInt32(d2) & 0xffff0000) >> 16); //capture the high word UInt16 s2 = (UInt16)(System.Convert.ToUInt32(d2) & 0xffff); //capture the low word A basic cast (UInt32) doesn't work either.

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• antlr: How to rewrite only specific

  - by user1293945

  I am sure antlr can solve my problem, but can't figure out how to implement it, even high level. I rapidly got caught into syntax problems of antlr itself. My grammar is quite simple and made of following tokens and rules. Don't really need to go in their details here. The evaluator resolves to expressions, which finally resolve to IDENT: evaluator : expression EOF! ; ... ... term : PARTICIPANT_TYPE(IDENT | '('! expression ')'! | max | min | if_ | NUMBER)+ ; Now, I would like to analyse and rewrite the 'term', so that IDENT tokens (and them only) get re-written with the PARTICIPANT_TYPE. All the others should simply remain the same.

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• How to process credit card by using intuit's (quickbook) ?

  - by Grace Ladder

  How to process credit card by using Hello all, I am doing shopping cart project for my client and one of the requirement is using intuit's (http://www.intuit.com/) product to process credit card in real manner, as the client is going to integrate the online shop with quickbook in later stage. My question is, does intuit products purely payment gateway solution? as in this stage, we are not involved with any dev work about quickbook, the main focus for us is deliver the high quality shopping cart solution, we read something about intuit's web shop solution but seems this one require quickbook running in desktop to sync the data? Very confused now, if anyone had experience before, please help!

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• Number guessing game (3+- guessed result)

  - by Nick Waring

  I've been assigned a task to create a game that generates 4 digits and the user has to guess the digits one at a time to get the correct result. If the number is correct a Y is displayed and if not, a N. This was easy, now the next step was to implement another two responses. If the answer is too high, a H is displayed and too low, an N. Again, was easy - now the third is to use the same design as game 2 but if the number is 3 higher than a H is displayed and same if it's 3 lower than a L is displayed - otherwise an X is displayed. I can't figure out how to do this. Here's my test code for game 2 for just one of the digits - any help is appreciated. (5 was used just for a test.) def guess(): x = 5 g= int(input("Guess the number: ")) if g == x: print("Y") elif g < x: print("L") else: print("H")

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• Android 3.2 HTTP streaming

  - by user1281053

  I'm trying to create an app to stream live TV. Currently the problem I'm facing is that after say 10 minutes of playing, the video will freeze but the audio will carry on. This is on a 1.3mbps stream. I also have lower streams, such as a 384kbps stream, that might last an hour or so, but will still do the same. I've tested this with a local video, that is high quality (file size is 2.3gb) and that has no lag and doesn't freeze at all, so it must be something to do with the way HLS is streamed to android. Does anyone have any idea on how to solve this problem? Thanks

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• Scalable stl set like container for C++

  - by Pqr

  Hi, I need to store large number of integers. There can be duplicates in the input stream of integers, I just need to store distinct amongst them. I was using stl set initially but It went OutOfMem when input number of integers went too high. I am looking for some C++ container library which would allow me to store numbers with the said requirement possibly backed by file i.e container should not try to keep all numbers in-mem. I don't need to store this data persistently, I just need to find unique values amongst it.

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• class member access specifiers and binary code

  - by pdehaan

  I understand what the typical access specifiers are, and what they mean. 'public' members are accessible anywhere, 'private' members are accessible only by the same class and friends, etc. What I'm wondering is what, if anything, this equates to in lower-level terms. Are their any post-compilation functional differences between these beyond the high-level restrictions (what can access what) imposed by the language (c++ in this case) they're used in. Another way to put it - if this were a perfect world where programmers always made good choices (like not accessing members that may change later and using only well defined members that should stay the same between implementations), would their be any reason to use these things?

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• How to check an exectuable's path is correct in PHP?

  - by nickf

  I'm writing a setup/installer script for my application, basically just a nice front end to the configuration file. One of the configuration variables is the executable path for mysql. After the user has typed it in (for example: /path/to/mysql-5.0/bin/mysql or just mysql if it is in their system PATH), I want to verify that it is correct. My initial reaction would be to try running it with "--version" to see what comes back. However, I quickly realised this would lead to me writing this line of code: shell_exec($somethingAUserHasEntered . " --version"); ...which is obviously a Very Bad Thing. Now, this is a setup script which is designed for trusted users only, and ones which probably already have relatively high level access to the system, but still I don't think the above solution is something I want to write. Is there a better way to verify the executable path? Perhaps one which doesn't expose a massive security hole?

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• MySQL query with JOINS and GROUP BY

  - by user1854049

  I'm building a MySQL query but I can't seem to get it right. I have four tables: - customers - orders - sales_rates - purchase_rates There is a 1:n relation 'customernr' between customers and orders. There is a 1:n relation 'ordernr' between orders and sales_rates. There is a 1:n relation 'ordernr' between orders and purchase_rates. What I would like to do is produce an output of all customers with their total purchase and sales amounts. So far I have the following query. SELECT c.customernr, c.customer_name, SUM(sr.sales_price) AS sales_price, SUM(pr.purchase_price) AS purchase_price FROM orders o, customers c, sales_rates sr, purchase_rates pr WHERE o.customernr = c.customernr AND o.ordernr = sr.ordernr AND o.ordernr = pr.ordernr GROUP BY k.bedrijfsnaam The result of the sales_price and purchase_price is far too high. I seem to be getting double counts. What am I doing wrong? Is it possible to perform this in a single query? Thank for your response!

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• What machine learning algorithms can be used in this scenario?

  - by ExceptionHandler

  My data consists of objects as follows. Obj1 - Color - shape - size - price - ranking So I want to be able to predict what combination of color/shape/size/price is a good combination to get high ranking. Or even a combination could work like for eg: in order to get good ranking, the alg predicts best performance for this color and this shape. Something like that. What are the advisable algorithms for such a prediction? Also may be if you can briefly explain how I can approach towards the model building I would really appreciate it. Say for eg: my data looks like Blue pentagon small $50.00 #5 Red Squre large $30.00 #3 So what is a useful prediction model that I should look at? What algorithm should I try to predict like say highest weightage is for price followed by color and then size. What if I wanted to predict in combinations like a Red small shape is less likely to higher rank compared to pink small shape . (In essence trying to combine more than one nominal values column to make the prediction)

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• Extendable accessing of sqlite database on android platform

  - by mscriven

  Hi, I am fairly new to the android sdk and databases and have been searching for an answer to this quite some time. I am trying to build an app which has multiple tables within a database. e.g. one for weapons, armours etc. However, my DatabaseManager class which handles all of my table creating, DatabaseHelper inner class and populating of data is creating for an extremely large class requiring high maintenance. Every time I would like to add or remove a table column I need to change quite a few areas of code, - Every reference to the addition of a row in that table with data - The method that the above calls - The method returning all of the database rows - The code in the helper class creating the table - Any specific update methods My question is this: Surely there must be some better way of coding this system, maybe using a database isn't the best way to go, or am i just not used to such large classes having only learned java at university and my largest class consisting of a mere 400-600 lines of code. Thanks for any help!

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• How can I update a column in a table with the result of a select statement that uses row being updat

  - by Sailing Judo

  This SQL statement example is very close to what I think I need... update table1 set value1 = x.value1 from (select value1, code from table2 where code = something) as x However, what I need to do is change the "something" in the above example to a value from the row that is being updated. For example, I tried this but it didn't work: update table1 A set value1 = x.value1 from (select value1, code from table2 where code = A.something) as x This is a one time operation to update an existing table and I'm not really looking for high performance way to do this. Any solution that gets the task done is good enough.

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• class member access specifiers

  - by pdehaan

  I understand what the typical access specifiers are, and what they mean. 'public' members are accessible anywhere, 'private' members are accessible only by the same class and friends, etc. What I'm wondering is what, if anything, this equates to in lower-level terms. Are their any post-compilation functional differences between these beyond the high-level restrictions (what can access what) imposed by the language (c++ in this case) they're used in. Another way to put it - if this were a perfect world where programmers always made good choices (like not accessing members that may change later and using only well defined members that should stay the same between implementations), would their be any reason to use these things?

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• Configuring jdbc-pool (tomcat 7)

  - by john

  i'm having some problems with tomcat 7 for configuring jdbc-pool : i`ve tried to follow this example: http://www.tomcatexpert.com/blog/2010/04/01/configuring-jdbc-pool-high-concurrency so i have: conf/server.xml <GlobalNamingResources> <Resource type="javax.sql.DataSource" name="jdbc/DB" factory="org.apache.tomcat.jdbc.pool.DataSourceFactory" driverClassName="com.mysql.jdbc.Driver" url="jdbc:mysql://localhost:3306/mydb" username="user" password="password" /> </GlobalNamingResources> conf/context.xml <Context> <ResourceLink type="javax.sql.DataSource" name="jdbc/LocalDB" global="jdbc/DB" /> <Context> and when i try to do this: Context initContext = new InitialContext(); Context envContext = (Context)initContext.lookup("java:/comp/env"); DataSource datasource = (DataSource)envContext.lookup("jdbc/LocalDB"); Connection con = datasource.getConnection(); i keep getting this error: javax.naming.NameNotFoundException: Name jdbc is not bound in this Context at org.apache.naming.NamingContext.lookup(NamingContext.java:803) at org.apache.naming.NamingContext.lookup(NamingContext.java:159) pls help tnx

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• How to switch data pins on/off on parallel port?

  - by Matt

  I want to simply switch certain data pins on and off, so that they can control a set of relays. I'm not asking about the hardware bit (should be easy), but I don't know where to begin writing the software. I don't want a high level library that can send bytes to a device - I literally want to switch on/off certain pins. I'm running Linux and I want to do this in Java, so would I just need a library? It would be nice if the library has good documentation and is easy to use, but if not then a short example code will help me get started.

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• Showing a loading page in a google chrome extension

  - by user1092042

  I have searched high and low for this but whatever i do this simply does not seem to work. I have a google chrome extension which send an XHR request using a background.js file. Now my requirement is that i need to show a small loading icon while the xhr request is proceeding. Are there any tutorials out there which explains how to do this. I have tried an iframe but it looks ugly when it expands as the entire popup.html expands. Is jquery my only option here because that would mean adding a lot of size to my current project just for a simple animation.

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• c++ projects for beginners

  - by JohnWong

  So I know this is a frequent question, but I still can't find a good one. It's a 3-week internship where I get to teach high school students. I would cover basic c++ first week, and start the project second week. What I need is a project that is doable (for them) in 2 weeks. It is interesting. Somehow I want it to be interactive (something that's cool, something that we get to use a lot or something like that)? Any idea?

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• Desired features for C++

  - by bytepusher

  I am a full time C++ developer, and I really like the language. I think it is suited for almost any kind of application. Some people claim Java and C# are better suited for high level programming, but I'm not so sure about this. I have worked with all three languages, and when using C++, it happens only now and then I come across something that might be improved. What features would you like to see added to C++? I'm talking about big improvements, not details like typesafe enums.

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• Optimal ASP.Net cache duration for a large site?

  - by HeroicLife

  I've read lots of material on how to do ASP.Net caching but little on the optimal duration that pages should be cached for. Let's say that I have a popular site with 50,000 pages. The content does not change frequently, so I could cache pages for up to an hour if I wanted. The server has 16 GB of RAM, but database connections are limited. How long should pages be cached for? My thinking is that if I set the cache duration too high (let's say 60 minutes), I will fill up memory with a fraction of the total content, which will continually be shuffled in and out of memory. Furthermore, let's say that 10% of the pages are responsible for 90% of traffic. If the popular pages are hit every second, and the unpopular ones every hour, then a 60 second cache would only keep the load-intensive content cached without sacrificing freshness. Should numerous but rarely-accessed content be cached at all?

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• How to manage memory for ios with large csv files?

  - by Pell000

  I'm new to ios development, and I'm running into issues relating to memory management and my approaches to dealing with large datasets. Right now, I am loading the csv files and storing the relevant data as objects in memory at app initialization. Some of the csv files are larger than 1MB, and in total, my app uses about 180MB of memory. This is obviously way too high of a number (unless the info I found is wrong and this is an acceptable number, then please let me know). I feel as though there is a fundamental flaw in my approach: is there a way I can avoid storing the csv files in the project itself? Or, is there a kind of "lazy" loading I can do so that I can simply look up info in the csv file, as opposed to loading all of the data from it at once? Any help would do. I think that I need a new perspective in how to manage this more efficiently.

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• Action(Of T) in Visual Basic in List(Of T).ForEach

  - by Jason

  I have searched high and low for documentation on how to use this feature. While the loop I could write would be simple and take no time, I really would like to learn how to use this. Basically I have a class, say, Widget, with a Save() sub that returns nothing. So: Dim w as New Widget() w.Save() basically saves the widget. Now let's say I have a generic collection List(Of Widget) name widgetList(Of Widget) and I want to run a Save() on each item in that list. It says I can do a widgetList.ForEach([enter Action(Of T) here]) ....but how in the F does this work??? There is no documentation anywhere on the intrablags. Help would be much much appreciated.

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• Need to sync two lists with atrribute time, but times aren't equal

  - by virgula24

  I gonna try to describe my problem the best i can. I have two lists, one with audio frames and other with color frames (not relevant). Both of them have timestamps, they were captured at the same moment but at different instants. So, i have like this: index COLOR AUDIO 0 841 846 1 873 897 2 905 948 3 940 1000 the frames start at high numbers because they were captured and then trimmed to specific parts, but im shot, frame 0 is synced with only 5ms apart(timestamp in ms). On every case i have, the audio frames count is less than the color count. I need to make them have the same count. The stating frames may be coloraudio, color

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