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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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• 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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• How does a cmdlet know when it really should call WriteVerbose()?

  - by Roman Kuzmin

  How does a cmdlet know when it really should call WriteVerbose(), WriteDebug() and etc.? Perhaps I miss something simple but I cannot find the answer. All cmdlet implementations I have seen so far just call WriteVerbose() without any hesitation. I know that it is correct to do so, but it is not effective. Performance suffers when verbose mode is off but a cmdlet still prepares data for WriteVerbose() call, that is, for nothing. In other words, in a cmdlet I would like to be able to: if (<VerboseMode>) { .... data preparation, sometimes expensive ... WriteVerbose(...); } But I don't know how to get this if (<VerboseMode>). Any ideas?

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• I want to make a wrapped acces type for certain internals of one of classes and I have some performa

  - by Alex

  I am writing an abstract matrix class (and some concrete subclasses) for use on very differing hardwares/architectures, etc. and I want to write a row and column type that provides a transparent reference to the rows and columns of the matrix. However, I want to tune for performance, so I'd like this class to be essentially a compiler construct. In other words, I'm willing to sacrifice some dev time to making the overhead of these classes as small as possible. I assume all (small) methods would want to be virtual? Keep the structure small? Any other suggestions?

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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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• java virtual machine - how does it allocate resources?

  - by Will

  I am testing the performance of a data streaming system that supports continuous queries. This is how it works: - There is a polling service which sends data to my system. - As data passes into the system, each query evaluates based on a window of the stream at the current time. - The window slides as data passes in. My problem is this, when I add more queries to the system, I should expect the throughput to decrease because it can't cope the data rate. However, I actually observe an increase in throughput. I can't understand why this is the case and I am guessing that it's something to do with the way the JVM allocates CPU, memory etc. Can anyone shed any light to my problem?

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• scrollTop issue on constant moving div

  - by joe

  I have a FLASH object that I mouse over which in turn calls the following function to scroll a div. It works but due to the constant high speed scrolling it would throw up NULLS. This in turn caused IE to open a new page through my FLASH ActionScript 2.0 I found that by creating the SC variable and throwing in the condition "if it exists" keeps FLASH from causing IE to open a new page. However, it still creates an error behind the scenes of "Object Required". Although my application works I do not want load up memory with errors. Any thoughts? var SC; function pP(PT){ SC=document.getElementById('P'+PT).offsetTop; if(SC){document.getElementById('CBOX').scrollTop=SC;} }

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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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• Fastest way to convert a binary file to SQLite database

  - by chown

  I've some binary files and I'm looking for a way to convert each of those files to a SQLite database. I've already tried C# but the performance is too slow. I'm seeking an advice on how and what programming language should be the best to perform this kind of conversion. Though I prefer any Object Oriented Language more (like C#, Java etc), I'm open for any programming language that boosts up the conversion. I don't need a GUI frontend for the conversion, running the script/program from console is okay. Thanks in advance

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• Eclipse debug - line: not available

  - by Mike

  I can't seem to find anything on google telling me why this might be and what the resolution is. I'm Stepping through third party code (that I have the source for) and would really like to see the current line being executed... Looking at javac compile flags, I see the -g:none flag. If this flag is set, would this be enough to explain why I'm not able to see line numbers? If so, why would someone do this, are there performance implications? Do I need to recompile the jar myself to attach the missing debug info (if possible)? Thanks!

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• Language D compared to C++?

  - by Henrik

  Anyone here with experience of the language D? I was just reading through its presentation at http://www.d-programming-language.org/ and at Wikipedia and it seems like a good (better) alternative to C++. With good/better I mean that it seem simpler yet it has all the good stuff within C/C++. But without some of the difficulties that make C++ more difficult to learn and use in a good and efficient way. So anyone with comments/experience with the language D? Performance?

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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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• CouchDB: How to change view function via javascript?

  - by osti

  Hello Guys, I am playing around with CouchDB to test if it is "possible" [1] to store scientific data (simulated and experimental raw data + metadata). A big pro is the schema-less approach of CouchDB: we have to be very flexible with the metadata, as the set of parameters changes very often. Up to now I have some code to feed raw data, plots (both as attachments), and hierarchical metadata (as JSON) into CouchDB documents, and have written some prototype Javascript for filtering and showing. But the filtering is done on the client side (a.k.a. browser): The map function simply returns everything. How could I change the (or push a second) map function of a specific _design-document with simple browser-JS? I do not think that a temporary view would yield any performance gain... Thanks for your time and answers. [1]: of course it is possible, but is it also useful? feasible? reasonable?

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• which is the cleaner way to do this simple while?

  - by user363834

  I'm learning c++ and I want to make clean and readable code and I was wondering which way is better (while is supposed to make the factorial of 9) : 1 - int main(){ int i = 1,r = i; while (i < 10) { r *= ++i; } 2 - int main(){ int i = 1,r = i; while (i < 10) { i++ r *= i } 1 may be harder to understand but it's 1 less line, is it worth it? and what about performance. Obviously it wouldn't matter in such a trivial example but it would be a good practice to make fast code from the begining.

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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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• Simulators for thread scheduling on multicore

  - by shijie xu

  I am seeking a simulator for thread scheduling at multi-core architecture, that is mapping threads to the cores at runtime. During runtime, simulator collects overall cache and IPC statistics. I checked below simulators, but seems there are not sufficient for me: Simplescalar: A simulator only for single core. SESC: multiprocessor simulator with detailed power, thermal, and performance models, QSim: provides instruction-level control of the emulated environment and detailed information about the executing instruction stream. It seems both SESC and QSim supports instructions scheduling instead of thread scheduling on the cores? Anyone can help provide some clues or share experience for this part?

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• "Volkswagen Passat" Navigation

  - by joe_midi

  http://web.vw.com/all-new-passat-experience/ The navigation on this .swf is very impressive, and I was wondering how I would go about replicating it. The way each of the sections Design / Technology / Safety / Performance I want to know how each section can expand and still fit together. I've started with MOUSE_OVER events, but I'm not entirely sure how to order them so each section is the right size for every mouse over Event. This is the code I have for each "Section", I have created a movie clip with a Mask that expands on mouse over and brings the selected clip to the highest depth. this.firstButton01.addEventListener(MouseEvent.MOUSE_OVER, firstButton01OVER) function firstButton01OVER(e:Event):void { this.firstButton01.gotoAndPlay(2); this.setChildIndex(firstButton01,this.numChildren-1); }

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• What language should I use to parse a lot of text?

  - by BicMan

  My company's proprietary software generates a log file that is much easier to use if it is parsed. The log parser we all use was written by another employee as a side project, and it has horrible performance. These log files can grow to 10s of megabytes very quickly, and the parser we currently use has issues if a log file is bigger than 1 megabyte. So, I want to write a program that can parse this massive amount of text in the shortest amount of time possible. We use Windows exclusively, so running on Windows is a must. Our current implementation runs on a local web server, and I'm convinced that running it as an application would have to be faster. All suggestions will be helpful. Thanks.

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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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• C# Why does calling an interface member from a class generate an error?

  - by Jack

  So I have an interface: interface IFoo { int Bar(); int this[int i] {get; set;} } And a class that derives from it class Foo : IFoo { public int IFoo.Bar() { //Implementation { public int IFoo.this[int i] { //Implementation } } Now, I try to do this: var fooey = new Foo(); int i = Fooey.Bar(); or this: int i = Fooey[4]; I would expect these to work properly. However, the compiler generates an error as if such members don't exist. Why is that? I am aware I can cast Foo as IFoo, but I am also aware that casting is costly to performance, which is often the reason to use interfaces in the first place. EDIT 1: These are the errors generated 'Foo' does not contain a definition for 'Bar' and no extension method 'Bar' accepting a first argument of type 'Foo' could be found (are you missing a using directive or an assembly reference?) "Cannot apply indexing to an expression of type 'Foo'"

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• Any efficient way to read datas from large binary file?

  - by limi

  Hi, I need to handle tens of Gigabytes data in one binary file. Each record in the data file is variable length. So the file is like: <len1><data1><len2><data2>..........<lenN><dataN> The data contains integer, pointer, double value and so on. I found python can not even handle this situation. There is no problem if I read the whole file in memory. It's fast. But it seems the struct package is not good at performance. It almost stuck on unpack the bytes. Any help is appreciated. Thanks.

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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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• try finally block around every Object.Create?

  - by max

  Hi, I have a general question about best practice in OO Delphi. Currently, I but a try finally block around everywhere, where I create an object, to free that object after usage (to avoid memory leaks). E.g.: aObject := TObject.Create; try aOBject.AProcedure(); ... finally aObject.Free; end; instead of: aObject := TObject.Create; aObject.AProcedure(); .. aObject.Free; To you think, it is good practice, or too much overhead? And what about the performance?

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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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