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• C++: is it safe to read an integer variable that's being concurrently modified without locking?

  - by Hongli

  Suppose that I have an integer variable in a class, and this variable may be concurrently modified by other threads. Writes are protected by a mutex. Do I need to protect reads too? I've heard that there are some hardware architectures on which, if one thread modifies a variable, and another thread reads it, then the read result will be garbage; in this case I do need to protect reads. I've never seen such architectures though. This question assumes that a single transaction only consists of updating a single integer variable so I'm not worried about the states of any other variables that might also be involved in a transaction.

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• How to determine the radius and center of a circle when only three noncollinear points are known?

  - by Bob

  I'm working on a C# program that deals with Oracle Spatial geometry. When circle data is stored in a geometry field only three non-collinear points are stored to represent the circle. The problem is that I need to use this data on a Google Maps web page and need the center point and radius of the circle (since my circle drawing function uses that information). Can anyone help with the math involved and translating said math to C#? I think this page may hold the answer, but I'm having a hard time following it. There are formulas for radius and center given three points, but then they define the variables as matrices and I get lost at that point. How would I solve that in code?

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• How can I write faster JavaScript?

  - by a paid nerd

  I'm writing an HTML5 canvas visualization. According to the Chrome Developer Tools profiler, 90% of the work is being done in (program), which I assume is the V8 interpreter at work calling functions and switching contexts and whatnot. Other than logic optimizations (e.g., only redrawing parts of the visualization that have changed), what can I do to optimize the CPU usage of my JavaScript? I'm willing to sacrifice some amount of readability and extensibility for performance. Is there a big list I'm missing because my Google skills suck? I have some ideas but I'm not sure if they're worth it: Limit function calls When possible, use arrays instead of objects and properties Use variables for math operation results as much as possible Cache common math operations such as Math.PI / 180 Use sin and cos approximation functions instead of Math.sin() and Math.cos() Reuse objects when passing around data instead of creating new ones Replace Math.abs() with ~~ Study jsperf.com until my eyes bleed Use a preprocessor on my JavaScript to do some of the above operations

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• The case of the mysterious MySQL caching across restarts

  - by shanusmagnus

  I found a very slow MySQL query in my web app. The weird thing is that the query is only slow the first time it's executed, despite the fact that the query_cache is set to its default (query_cache_size 0) like so: mysql> show variables like 'query%'; +------------------------------+---------+ | Variable_name | Value | +------------------------------+---------+ | query_alloc_block_size | 8192 | | query_cache_limit | 1048576 | | query_cache_min_res_unit | 4096 | | query_cache_size | 0 | | query_cache_type | ON | | query_cache_wlock_invalidate | OFF | | query_prealloc_size | 8192 | +------------------------------+---------+ The even weirder thing is that this speedup persists even after the MySQL server has been stopped and restarted (I'm using OSX, and perform this restart using the system preferences pane.) The only way I can re-create the poor performance of the initial query is by rebooting the system. So my question is: how is this happening? Obviously some sort of caching at work, but where? And how does it persist across database restarts? This query is mediated through our web app, which comes via PHP/Apache, but there are no extra bells and whistles, and the curious caching also persists across Apache restarts. Help?

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• How can I implement a login wall for expired or inappropriate pages?

  - by Redandwhite

  I am writing a website that very explicitly requires a login wall. Visitors should be required to log in before they are allowed to view a page. The page being built depends very much on the user's "ID". I am not sure how or where to store the user's login. I am not sure whether I should use a session variable (e.g. Session["userId"]), or some other method. The problem I see with session variables is that it's difficult to time out sessions. Note: I'm using C# 3.5 with ASP.NET in Visual Studio 2008.

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• Are there any pitfalls to having two different Models from two different assemblies? (EF)

  - by Jonn

  I have two projects, both of them data access layers, and both using EF. I have another project calling services related to the two different assemblies. Are there any pitfalls on using two different models on two different databases linked to the same database? I'm asking this because I've been getting this generic "EntitySqlException" could not be resolved in the current scope or context. Make sure that all referenced variables are in scope, that required schemas are loaded, and that namespaces are referenced correctly., near escaped identifier. that does not appear when are run separately but appear when under the same project.

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• looping and arrays

  - by user1838418

  Hi I'm trying to construct a loop to execute 16 states of the 8 4 2 1 code in (C++) while( condition) { double Bubble[16], Bubble1[16]; Bubble[0] = ( a-2 - (b-2) ) + ( c-2 - (d-2)); // represents 0000 Bubble[1] = ( a-2 - (b-2) ) + ( c-2 - (d+2)); // represents 0001 Bubble[2] = ( a-2 - (b-2) ) + ( c+2 - (d-2)); // represents 0010 Bubble[3] = ( a-2 - (b-2) ) + ( c+2 - (d+2)); //represents 0011 ....... Bubble[15] =(a+2 - (b+2) ) + ( c+2 - (d+2)); //represents 1111 } Is there an easy way of coding using for loops? instead of writing bubble[] every time? 0 stands for -2 and 1 stands for +2. So I have 4 variables and each one need to be incremented and/or decremented. Can this be done using for loop? Appreciate your help

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• making a programming language

  - by None

  I was wondering which way would create a faster programming language, because I have tried both. Writing code that takes the text, splits it by whitespace or newlines or something, then processes each line and has a dictionary for variables. Or writing code that takes text and converts it to another programming language. This is an example of how a very simple version of the first way would be programmed in python: def run(code): text = code.split(";") for t in text: if t == "hello": print "hi" second: def run(code): rcode = "" text = code.split(";") for t in text: if t == "hello": rcode += "print 'hi'"

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• MS VC++ 6 class wizard

  - by Shane MacLaughlin

  Ok, I'm developing an application that has been in pretty much continous development over the last 16 years, from C in DOS, through various flavours of C++ and now is largely based around C++ with MFC and StingRay GUIs and various other SDKs. While I use VS 2005 for the release builds, I still use MSVC 6 for much of the GUI building, simply because ClassWizard is so much quicker in this environment than the weak equivalent tools that followed. Note that I am using ClassWizard to automatically generate code for my own user defined types (see Custom DDXs) and I like to add a lot of member variables and methods in one go. Creating them one at a time as per later versions of Visual Studio for me is a big backward step. At the same time, working with multiple IDEs is also a pain. My question is in two parts; Is there any way of getting ClassWizard to work is VS 2005 or VS 2008? Is there any drop in replacement, or alternative IDE, that provides similar levels of productivty for old C++ hacks such as myself?

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• What is the difference between the * and the & operators in c programming?

  - by Wesley

  I am just making sure I understand this concept correctly. With the * operator, I make a new variable, which is allocated a place in memory. So as to not unnecessarily duplicate variables and their values, the & operator is used in passing values to methods and such and it actually points to the original instance of the variable, as opposed to making new copies...Is that right? It is obviously a shallow understanding, but I just want to make sure I am not getting them mixed up. Thanks!

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• Problems reading text file data in Java

  - by user1828401

  I have this code: BufferedReader br =new BufferedReader(new FileReader("userdetails.txt")); String str; ArrayList<String> stringList = new ArrayList<String>(); while ((str=br.readLine())!=null){ String datavalue [] = str.split(","); String category = datavalue[0]; String value = datavalue[1]; stringList.add(category); stringList.add(value); } br.close(); it works when the variables category and value do not have a comma(,),however the values in the variable value does contain commas.Is there a way that I can split the index of the without using comma?

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• How do I pass in config info to CKEditor using the jQuery adapter?

  - by alex

  I'm using the latest CKeditor with jQuery adapter. I have successfully got it to work, and display. However, as I am completely new to CKeditor, how do I pass in config variables using the jQuery method? This is what I've got $( '#input-content' ).ckeditor('', { toolbar: 'basic' }); I think from what I've read, the first argument is meant to be a callback, and the 2nd the config. But doing this has not changed the editor at all. How do I use these config properties etc using the jQuery adapter? Thanks

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• Postback of delimited text from javascript and parsing on server side

  - by Alt_Doru

  In my ASP.NET page, I have a Javascript object, like this: var args = new Object(); args.Data1 = document.getElementById("Data1").value; args.Data2 = document.getElementById("Data2").value; args.Data3 = document.getElementById("Data3").value; The object is populated on client side using user input data. I am passing the data to a C# method, through an Ajax request: someObj.AjaxRequest(argsData1 + "|" + argsData2 + "|" + argsData3) Finally, I need to obtain the data in my C# code: string data1 = [JS args.Data1] string data2 = [JS args.Data2] string data3 = [JS args.Data3] My question is what's the best solution for this? As i am concatenating bits of user input, I don't think it's best to use "|" as a delimiter. Also, it's not clear to me how to actually parse the data in my C# code to populate the three variables with the original data.

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• Foreach wont split a string

  - by Luke

  //assign variables string measurementIn; //read in file in array string[] lines = File.ReadAllLines("../../convert.txt"); //ask user for date Console.WriteLine("Enter the conversion in the form (amount,from,to)"); measurementIn = Console.ReadLine(); //array for splitting input string[] conversionArray = measurementIn.Split(','); Console.WriteLine("{0} , {1} , {2}", conversionArray[0], conversionArray[1], conversionArray[2]); Console.ReadLine(); //check lines for conversion foreach (string line in lines) { //array for the measurement string[] measurementArray = line.Split(','); Console.WriteLine("{0}", measurementArray[0]);

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• What should I name instances of a twisted.internet.defer.Deferred?

  - by slacy

  I'm writing code using Twisted, and having trouble coming up with a sensible variable name for my twisted internet deferred's. Here are my candidates: d : Too generic, too short, violates pylint rule C0103. def : Conflicts with function defintion builtin. defer : Conflicts with module twisted.internet.defer deferred : OK but pretty long cb : Still too short, violates pylint C0103, conflicts with many callback method names. cback : Too Weird? callback : Conflicts with method Deferred.callback() I'm looking for other suggestions. It seems like most of the Twisted example code uses "d" which is fine for simple invocations, but when you're passing Deferred's around to methods and storing them as member variables, it's really far too descriptive.

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• Duel Masters game in Java

  - by Arun Ramasubramanian

  I was trying to make a Duel Masters card game in Java using BlueJ, and came up with a lot of ideas. However, I could not exactly figure out how to sort a deck on basis of the card names in the game. I have an array of Card objects(each has, as its instance variables: String name, int cost, int civ), and I want to sort them based on name. ie: if I have the cards "Pyrofighter Magnus", "Bazagazeal Dragon" and another "Pyrofighter Magnus" in the array, the cards should be sorted on basis of their names. I know that I could use compareTo(), but is there an easier method? Anyone? Remember, the method that sorts the cards should be a modifier.

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• Build a Sitemap but webpages don't use links

  - by THX1138.6

  Folks I am trying to build a sitemap (we need one badly) for a huge multi-page web app. Technically its not much more than a collection of php/MySQL web forms that use javascript instead of traditional linkage to access the many pages. >td width="100" align="center" ONMOUSEOVER="this.className='bgover'" ONMOUSEOUT="this.className='bgout'" onclick="location.href='../main.php'">Main Page</td> Above is code sample of how the links are currently managed. I know I can search through the various pages, nearly a 1000, and find these "location.href" variables and that will help me a sitemap for each section. But maybe there is an easier way? WE use Trac and SVN so perhaps I am going about this the wrong way? Any advice would be appreciated.

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• Reference Paramters in C++: VERY basic example please.

  - by Sagistic

  I am trying to understand how to use reference parameters. There are several examples in my text, however they are too complicated for me to understand why and how to use them. Could anyone give me the MOST basic example of how/why to use one, and perhaps the difference with or without it (what would happen if you didn't attach the '&'). for example, if I've created a function: int doSomething(int& a, int& b), what would be the consequences of not putting in that '&.' I understand that reference variables are used in order to change a formal-reference, which then allows a two-way exchange of parameters. However, that is the extent of my knowledge, and a more concrete example would be of much help. Thank you.

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• C# .NET 2.0 components

  - by Ervin

  How can I check what objects, tools, variables, anything... are used from .NET 2.0 in a C# application. How can I get a C# application run without .NET 2.0 ? UPDATE: sorry, I didn't clarify enought. Here's my situation: I have developed a pretty simple application in C#: embeded browser which displayes static webpages with an option of searching inside of these html pages. I'm using simple textbox, buttons components for this. The application will be distribuited for people wich have very old PCs, even with windows 95. I would like the app to be runable on it, or at least on win 98, without telling the people to install .NET 2.0, as the users don;t really have PC usage skills :) .

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• Perl array and hash manipulation using map

  - by somebody

  I have the following test code use Data::Dumper; my $hash = { foo => 'bar', os => 'linux' }; my @keys = qw (foo os); my $extra = 'test'; my @final_array = (map {$hash->{$_}} @keys,$extra); print Dumper \@final_array; The output is $VAR1 = [ 'bar', 'linux', undef ]; Shouldn't the elements be "bar, linux, test"? Why is the last element undefined and how do I insert an element into @final_array? I know I can use the push function but is there a way to insert it on the same line as using the map command? Basically the manipulated array is meant to be used in an SQL command in the actual script and I want to avoid using extra variables before that and instead do something like: $sql->execute(map {$hash->{$_}} @keys,$extra);

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• Where does static variable work in C# page. At Application level or Page Level

  - by Shantanu Gupta

  I had an interview today and every thing was going very good, but then an interviewer asked me a question Where Does Static Variable Work in C#- At Application Level or At Page Level. I was not very much clear about this answer as I only knew that static variables are stored on heap and I didn't knew anything about web related thing about it. Then tried to make me more clear by giving an example that in a page I am using static variable and three users are accessing the page one of the user updates the value of static variable, What value will be visible to remaining two users an old copy or the update will be reflected.

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• When and why does an EventHandler require objects to be final?

  - by Michiel Borkent

  I have the following code from a GWT Project that is part of the onModuleLoad() method (similar to Java's main method, if you don't know GWT): final TextBox t1 = new TextBox(); final Label lt1 = new Label(); t1.addKeyUpHandler(new KeyUpHandler() { @Override public void onKeyUp(KeyUpEvent event) { // TODO Auto-generated method stub if (!(t1.getText().matches("\\w{2}-\\w{2}-\\w{2}"))) lt1.setText("Invalid."); else lt1.setText("OK."); } }); Why do the two local variables have to be final here?

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• Insert date and time into Mysql

  - by Jerry

  Hi..guys I am trying to insert date and time into mysql datetime field. When a user select a date and time, it will generate two POST variables. I have searched internet but still not sure how to do it. My code. //date value is 05/25/2010 //time value is 10:00 $date=$_POST['date']; $time=$_POST['time']; $datetime=$date.$time If I insert $datetime into mysql, the date appears to be 0000-00-00:00:00:00 I appreciate it if anyone could help me about this. Thanks.

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• Absolute URL Path for PHP Website

  - by kakaajee

  Hi friends, I am working on a website in a CMS site. I have provided a link in my footer file e.g blogs.php. This page is at the root like "http://www.example.com/new_cms/blogs.php" When I moves to other files link like "http://www.example.com/new_cms/forums" the footer link is changed to "http://www.example.com/new_cms/forums/blogs.php" but the blogs.php page resides at path "http://www.example.com/new_cms/" . I tried different $_SERVER[] variables but got no luck to get the above path "http://www.example.com/new_cms/" means the server name with the directory where the project is currently running from. Any one have idea how to get it done will be a great help. Thanks

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• how to set and access variable values from another classess

  - by BittenApple

  I am modifying QuartzDemo example app and want to do set and read values of integer type variables in other classes which are already included. For example, in MainViewController.m I want to set a numeric value (simple numbers from 1-100) to a variable which is then going to be called (read) in file QuartzImages.m. Question is how to define variable properly, set and access (read) the value. I am a beginner with Obj C and iPhone SDK in general and have some experience with Delphi and VB but this doesn't help at all :) Thank you, whoever and wherever you are, person who will take me out of this endless googling loop.

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