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  • Assigning a default value to a final variable in case of an exception in Java

    - by frenetisch applaudierend
    Why won't Java let me assign a value to a final variable in a catch block after setting the value in the try block, even if it is not possible for the final value to be written in case of an exception. Here is an example that demonstrates the problem: public class FooBar { private final int foo; private FooBar() { try { int x = bla(); foo = x; // In case of an exception this line is never reached } catch (Exception ex) { foo = 0; // But the compiler complains // that foo might have been initialized } } private int bla() { // You can use any of the lines below, neither works // throw new RuntimeException(); return 0; } } The problem is not hard to work around, but I would like to understand why the compiler does not accept this. Thanks in advance for any inputs!

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  • Multiple actions upon a case statement in Haskell

    - by Schroedinger
    One last question for the evening, I'm building the main input function of my Haskell program and I have to check for the args that are brought in so I use args <- getArgs case length args of 0 -> putStrLn "No Arguments, exiting" otherwise -> { other methods here} Is there an intelligent way of setting up other methods, or is it in my best interest to write a function that the other case is thrown to within the main? Or is there an even better solution to the issue of cases. I've just got to take in one name.

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  • Storing unique values into an array and comparing against a loop - PHP

    - by Aphex22
    I'm writing a PHP report which is designed to be exported purely as a CSV file, using commma delimiters. There are three columns relating to product_id, these three columns are as follows: SKU Parent / Child Parent SKU 12345 parent 12345 12345_1 child 12345 12345_2 child 12345 12345_3 child 12345 12345_4 child 12345 18099 parent 18099 18099_1 child 18099 Here's a link to the full CSV file: http://i.imgur.com/XELufRd.png At the moment the code looks like this: $sql = "select * from product WHERE on_amazon = 'on' AND active = 'on'"; $result = mysql_query($sql) or die ( mysql_error() );?> <? // set headers echo " Type, SKU, Parent / Child, Parent SKU, Product name, Manufacturer name, Gender, Product_description, Product price, Discount price, Quantity, Category, Photo 1, Photo 2, Photo 3, Photo 4, Photo 5, Photo 6, Photo 7, Photo 8, Color id, Color name, Size name <br> "; // load all stock while ($line = mysql_fetch_assoc($result) ) { ?> <?php // Loop through each possible size variation to see whether any of the quantity column has stock > 0 $con_size = array (35,355,36,37,375,38,385,39,395,40,405,41,415,42,425,43,435,44,445,45,455,46,465,47,475,48,485); $arrlength=count($con_size); for($x=0;$x<$arrlength;$x++) { // check if size is available if($line['quantity_c_size_'.$con_size[$x].'_chain'] > 0 ) { ?> <? echo 'Shoes'; ?>, <?=$line['product_id']?>, , , <?=$line['title']?>, <? $brand = $line['jys_brand']; echo ucfirst($brand); ?>, <? $gender = $line['category']; if ($gender == 'Mens') { echo 'H'; } else{ echo 'F'; } ?>, <?=preg_replace('/[^\da-z]/i', ' ', $line['amazon_desc']) ?>, <?=$line['price']?>, <?=$line['price']?>, <?=$line['quantity_c_size_'.$con_size[$x].'_chain']?>, <? $category = $line['style1']; switch ($category) { case "ankle-boots": echo "10013"; break; case "knee-high-boots": echo "10011"; break; case "high-heel-boots": echo "10033"; break; case "low-heel-boots": echo "10014"; break; case "wedge-boots": echo "10014"; break; case "western-boots": echo "10032"; break; case "flat-shoes": echo "10034"; break; case "high-heel-shoes": echo "10039"; break; case "low-heel-shoes": echo "10039"; break; case "wedge-shoes": echo "10035"; break; case "ballerina-shoes": echo "10008"; break; case "boat-shoes": echo "10018"; break; case "loafer-shoes": echo "10037"; break; case "work-shoes": echo "10039"; break; case "flat-sandals": echo "10041"; break; case "low-heel-sandals": echo "10042"; break; case "high-heel-sandals": echo "10042"; break; case "wedge-sandals": echo "10042"; break; case "mule-sandals": echo "10038"; break; case "mary-jane-shoes": echo "10039"; break; case "sports-shoes": echo "10026"; break; case "court-shoes": echo "10035"; break; case "peep-toe-shoes": echo "10035"; break; case "flat-boots": echo "10609"; break; case "mid-calf-boots": echo "10014"; break; case "trainer-shoes": echo "10009"; break; case "wellington-boots": echo "10012"; break; case "lace-up-boots": echo "10609"; break; case "chelsea-and-jodphur-boots": echo "10609"; break; case "desert-and-chukka-boots": echo "10032"; break; case "lace-up-shoes": echo "10034"; break; case "slip-on-shoes": echo "10043"; break; case "gibson-and-derby-shoes": echo "10039"; break; case "oxford-shoes": echo "10039"; break; case "brogue-shoes": echo "10039"; break; case "winter-boots": echo "10021"; break; case "slipper-shoes": echo "10016"; break; case "mid-heel-shoes": echo "10039"; break; case "sandals-and-beach-shoes": echo "10044"; break; case "mid-heel-sandals": echo "10042"; break; case "mid-heel-boots": echo "10014"; break; default: echo ""; } ?>, http://www.getashoe.co.uk/full/<?=$line['product_id']?>_1.jpg, http://www.getashoe.co.uk/full/<?=$line['product_id']?>_2.jpg, http://www.getashoe.co.uk/full/<?=$line['product_id']?>_3.jpg, http://www.getashoe.co.uk/full/<?=$line['product_id']?>_4.jpg, , , , , <? $colour = preg_replace('/[^\da-z]/i', ' ', $line['colour']); if( preg_match( '/white.*/i', $colour)) { echo '1'; } elseif( preg_match( '/yellow.*/i', $colour)) { echo '4'; } elseif( preg_match( '/orange.*/i', $colour)) { echo '7'; } elseif( preg_match( '/red.*/i', $colour)) { echo '8'; } elseif( preg_match( '/pink.*/i', $colour)) { echo '13'; } elseif( preg_match( '/purple.*/i', $colour)) { echo '15'; } elseif( preg_match( '/blue.*/i', $colour)) { echo '19'; } elseif( preg_match( '/green.*/i', $colour)) { echo '25'; } elseif( preg_match( '/brown.*/i', $colour)) { echo '28'; } elseif( preg_match( '/grey.*/i', $colour)) { echo '35'; } elseif( preg_match( '/black.*/i', $colour)) { echo '38'; } elseif( preg_match( '/gold.*/i', $colour)) { echo '41'; } elseif( preg_match( '/silver.*/i', $colour)) { echo '46'; } elseif( preg_match( '/multi.*/i', $colour)) { echo '594'; } elseif( preg_match( '/beige.*/i', $colour)) { echo '6887'; } elseif( preg_match( '/nude.*/i', $colour)) { echo '6887'; } else { echo '534'; } ?>, <?=$line['colour']?>, <?=$con_size[$x]?> <br> <? // finish checking if size is available } } ?> So at the moment this is simply echoing out the product_ID into the SKU column. The code would need to enter the product_id into an array and check whether it is unique. If the product_id is unique to the array, then the product_id is echoed out unaltered, and parent is echoed out to the 'Parent/Child' column and then the product_id is repeated to the 'Parent SKU' column. However, if the array is checked and the product_id already exists in the array, then the product_id is echoed out to the 'SKU' column with a suffix i.e. _1. Then child is echoed to the 'Parent / Child' column and the original parent product_id echoed to the 'Parent SKU' column. HOWEVER - the same SKU cannot be repeated with the same suffix i.e. 12345_1, 12345_1 - so presumably there would be to be another array for the suffixed SKUs to be checked against. If anybody could help, it would be great. Thanks --- UPDATE ANSWER --- I managed to solved this myself and thought I would share my solution for future reference. /* * Array to collect product_ids and check whether unique. * If unique product_id becomes parent SKU * If not product_id becomes child of previous parent and suffixed with _1, _2 etc... */ if (!in_array($line['product_id'], $SKU)) { $SKU[] = $line['product_id']; $parent = $line['product_id']; $a = 0; ?> <? echo 'Shoes'; ?>, <? echo $parent; ?>, <? echo "Parent"; ?>, <? echo $parent; ?>, <? } else { $child = $line['product_id'] . "_" . $a; ?> <? echo 'Shoes'; ?>, <? echo $child; ?>, <? echo "Child"; ?>, <? echo $child; <? // increment suffix value for child SKU $a++; ?>

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  • Manipulating the case of the build macros in Visual Studio: $(TargetDir)

    - by miked
    I've come across a weird problem today in Visual Studio 2005. If I create a new configuration "NewConfiguration" for one of my projects. The output directory referred to by the project in $(TargetDir) is "/path/to/build/area/newconfiguration". Note the loss of capital letters, I'd expect it to be in "/path/to/build/area/NewConfiguration". In another project that I created yesterday, the capital letters are there. Normally this would be a problem, but it's part of a fairly complicated build system where some of it's on unix and we need to worry about case sensitive filename. Does anyone know where the source string for the Visual Studio macros like $(TargetDir) are stored so that I can get the case to be consistent and match what we need for our build system?

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  • Keeping messages in queue in case of receiver crash

    - by John Doe
    Hi, We've a Spring JMS message listener container for receiving messages asynchronously. Using DefaultMessageListenerContainer and in sessionTransacted mode. I understand being in sessionTransacted mode means in case of an exception the message will be put back into the queue. But how can I make sure the message won't be deleted from the queue even if the receiver (which is picked the message) crashes or just the machine running it looses power? At first I thought CLIENT_ACKNOWLEDGE acknowledge mode should save me, but apparently it's not the case, Spring calls .acknowledge() no matter what. So here's my question, how can I guarantee the delivery? Using a custom MessageListenerContainer? Using a transaction manager?

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  • How to find the formula of best case and worst case of my algorithm?

    - by rachel7660
    I was given a task. Write an algorithm so that, the input of 2 lists of data, will have at least one in common. So, this is my algorithm: (I write the code in php) $arrayA = array('5', '6', '1', '2', '7'); $arrayB = array('9', '2', '1', '8', '3'); $arrayC = array(); foreach($arrayA as $val){ if(in_array($val, $arrayB)){ array_push($arrayC, $val); } } Thats my own algo, not sure if its a good one. So, based on my algorithm, how to find the formula of best case and worst case (big O)? Note: Please do let me know, if my algorithm is wrong. My goal is " input of 2 lists of data, will have at least one in common."

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  • Simplest one-to-many Map case in Hibernate doesn't work in MySQL

    - by Malvolio
    I think this is pretty much the simplest case for mapping a Map (that is, an associative array) of entities. @Entity @AccessType("field") class Member { @Id protected long id; @OneToMany(cascade = CascadeType.ALL, fetch=FetchType.LAZY) @MapKey(name = "name") private Map<String, Preferences> preferences = new HashMap<String, Preferences>(); } @Entity @AccessType("field") class Preferences { @ManyToOne Member member; @Column String name; @Column String value; } This looks like it should work, and it does, in HSQL. In MySQL, there are two problems: First, it insists that there be a table called Members_Preferences, as if this were a many-to-many relationship. Second, it just doesn't work: since it never populates Members_Preferences, it never retrieves the Preferences. [My theory is, since I only use HSQL in memory-mode, it automatically creates Members_Preferences and never really has to retrieve the preferences map. In any case, either Hibernate has a huge bug in it or I'm doing something wrong.]

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  • Zend Studio 7.1 PHPUnit Test Case wizard does not populate "Element to Test"

    - by Mike
    When I follow the instructions in ZS documentation to create a phpunit test case, the wizard returns no objects to select on the "Element to Test" line. Selecting "browse" provides an empty dialog box. The PHPUnit path in my preferences shows "/Applications/zend/zs710/plugins/com.zend.php.phpunit_7.1.0.v20091120-0900/resources/library/". What else can I check to see why I cannot create a test case? I'm new to ZS and PHP, so I have no idea how to troubleshoot this. Thanks.

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  • Regular expression Not working properly n case of multiple trailing ]]]]

    - by ronan
    I have the requirement that in a textbox a user can jump to the next word enclosed in [] on a tab out for example Hi [this] is [an] example. Testing [this] So when my cursor is at Hi and I do a tab out , the characters enclosed in the [this] are highlighted and when I again do a tabl out th next characters enclosed in following [an] are highlighted. This works fine Now the requirement is whatever the text including the special chars between [] needs to be highlighted case 1: when I have trailing ]]], it only highlights leading [[[ and ignores ]]]] e.g case 2: In case of multiple trailing ] e.e [this]]]] is [test], ideally one a single tabl out from this , it should go to next text enclosed in [] but a user has to tab out 4 times one tab per training ] to go to next [text] strong text The code is $(document).ready(function() { $('textarea').highlightTextarea({ color : '#0475D1', words : [ "/(\[.*?\])/g" ], textColor : '#000000' }); $('textarea').live('keydown', function(e) { var keyCode = e.keyCode || e.which; if (keyCode == 9) { var currentIndex = getCaret($(this).get(0)) selectText($(this), currentIndex); return false; } }); }); function selectText(element, currentIndex) { var rSearchTerm = new RegExp(/(\[.*?\])/); var ind = element.val().substr(currentIndex).search(rSearchTerm) currentIndex = (ind == -1 ? 0 : currentIndex); ind = (ind == -1 ? element.val().search(rSearchTerm) : ind); currentIndex = (ind == -1 ? 0 : currentIndex); var lasInd = (element.val().substr(currentIndex).search(rSearchTerm) == -1 ? 0 : element.val().substr(currentIndex).indexOf(']')); var input = element.get(0); if (input.setSelectionRange) { input.focus(); input.setSelectionRange(ind + currentIndex, lasInd + 1 + currentIndex); } else if (input.createTextRange) { var range = input.createTextRange(); range.collapse(true); range.moveEnd('character', lasInd + 1 + currentIndex); range.moveStart('character', ind + currentIndex); range.select(); } } function getCaret(el) { if (el.selectionEnd) { return el.selectionEnd; } else if (document.selection) { el.focus(); var r = document.selection.createRange(); if (r == null) { return 0; } var re = el.createTextRange(), rc = re.duplicate(); re.moveToBookmark(r.getBookmark()); rc.setEndPoint('EndToStart', re); return rc.text.length; } return 0; } Please let me know to handle two above cases

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  • Java - Set Color by switch case function

    - by user369150
    I want to set the color of the TextView by the function getcolorss. I tried a lot of different ways but i cant get in it. Please help me i think the solution is easy. import java.awt.*; import android.graphics.Color; public class test extends Activity { TextView text1 = (TextView) findViewById(R.id.text1); text1.setTextColor(getcolorss(1)); public Color getcolorss(int x) { switch(x) { case 1: return Color.BLUE; case 2: return Color.RED; } } }

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  • Insert Statment with Case for avoid duplicate record insertion

    - by rama
    I have written the below SP for Precheck for Duplicate records before insert into Table . but it is not allow me yo write insert staement inside the CASE . how can I write Stored Procedure for fist Check the value @Ordername into table After that if it is not present then it should inserted into Database . CREATE PROCEDURE [Test Procedure ] ( @section varchar(70), @mark varchar(70), @qty decimal(18,2), @Weight decimal(18,2), @dateupdateremark int, @OrderName varchar(70) ) AS BEGIN SET NOCOUNT ON; select case(@OrderName) when (select OrderName from dbo.tbl_insertxmldetails where(@OrderName) not in (select OrderName from tbl_insertxmldetails)) then insert into dbo.tbl_insertxmldetails (Section, Mark, QTY,Weight,Dateupdateremark ,OrderName,SystemDate) values (@Section, @Mark, @QTY,@Weight, @Dateupdateremark,@OrderName,GETDATE()) else 'File already Exists' end

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  • How to find the exact name of the view in asp.net mvc (including the case)

    - by Charles Prakash Dasari
    I have a control in ASP.NET MVC that spits out JavaScript in the page header (in the view page). I derive some values from the current view name (including its case). Let's say we are talking about the path: /Home/Index - my control spits out JavaScript to call a function with the view name - in its exact case - e.g. someFunction('Index'). Now when I try to navigate to my view using '/home/index', the view name is returned as 'index' which is causing issues in my JavaScript as I rely on the casing for it on the JS side. Is there any way to know the exact view name (as it was defined) from the path that got mapped into this view.

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  • undefined index mode, which is the variable that case statement is looking for

    - by Brad
    receiving error: PHP Notice: Undefined index: mode in /web/ee_web/include/form-modal.php on line 51 line 51 switch($_GET["mode"]) { block of code it is in: switch($_GET["mode"]) { case "login": login_user(); break; case "logout": session_destroy(); print "<p>You are now logged out.</p>"; print "<p><input type=\"submit\" id=\"closeButton\" name=\"closeButton\" value=\"Close\" onclick=\"self.parent.tb_remove(); parent.location.reload(1);\" /></p>"; break; default: login_user(); //print "<p>How'd you end up here?</p>"; break; } The URL for the page is index.php?mode=logout, that is how I am passing the value into mode. Any way I could resolve this error message?

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  • Dynamically set the result of a TSQL query using CASE WHEN

    - by Name.IsNullOrEmpty
    SELECT MyTable.Name,(SELECT CASE WHEN ISNULL(SUM(TotalDays), 0) <= 0 THEN 0 ELSE SUM(TotalDays) END AS Total FROM Application AS Applications WHERE (ID = MyTable.id)) - MIN(Assignments) AS Excesses FROM MyTable The above TSQL statement is a subquery in a main query. When i run it, if TotalDays is NULL or <=0, then Total is set to 0 (zero). What i would like to do here is to set the result of the whole query(Excesses) to 0. I want (Excesses) which is the result of Total - Min(Assignments) to be set to 0 if its NULL or <=0. I want the CASE WHEN to apply to the whole query but am struggling to get it right.

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  • PHP Case Insensitive Word Replacement

    - by zuk1
    Ok I'm trying to make search terms bold in this search script I'm making, except I can't get it to work case insensitive. function highlight($term,$target){ $terms = explode(" ", $term); foreach($terms as $term){ $result = (eregi_replace($term, "<strong>$term</strong>", $target)); } return $result; } That is the function I have so far.. It says on PHP.net that eregi_replace is case insensitive matching but it's obviously not working for some reason. (I'm a noob). Any ideas? :D

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  • Conditional Statements - If Then vs. Select Case

    - by cloyd800
    I'm a bit new to programming, and based on the few sources I've read both on the web and the books I'm learning to teach myself they are able to define what IF THEN and SELECT CASE conditional statements are, but have failed to give a comparison as to why I would use one over the other and what best practices decide this. If I'm understanding these conditional statements correctly, then both are based on a set of conditions with an outcome based around meeting these conditions, and if no conditions are met then an alternative outcome can be defined. I'm having trouble in understanding when I would use an IF THEN statement, and when I'd use a SELECT CASE statement, and what best practices are used to define this decision. Any insight on this would be greatly appreciated!

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  • Change find method in database search so that it isn't case sensitive in Rails app

    - by Ryan
    Hello, I am learning Rails and have created a work-in-progress app that does one-word searches on a database of shortcut keys for various programs (http://keyboardcuts.heroku.com/shortcuts/home). The search method in the Shortcut model is the following: def self.search(search) search_condition = "%" + search + "%" find(:all, :conditions => ['action LIKE ? OR application LIKE ?', search_condition, search_condition]) end ...where 'action' and 'application' are columns in a SQLite table. (source: https://we.riseup.net/rails/simple-search-tutorial) For some reason, the search seems to be case sensitive (you can see this by searching 'Paste' vs. 'paste'). Can anyone help me figure out why and what I can do to make it not case sensitive? If not, can you at least point me in the right direction? Database creation: I first copied shortcuts from various website into Excel and saved it as a CSV. Then I migrated the database and filled it with the data using db:seed and a small script I wrote (I viewed the database and it looked fine). To get the SQLite database to the server, I used Taps as outline by the Heroku website (http://blog.heroku.com/archives/2009/3/18/push_and_pull_databases_to_and_from_heroku/). I am using Ubuntu. Please let me know if you need more information. Thanks in advance for you help, very much appreciated! Ryan

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  • USE case to Class Diagram - How do I?

    - by 01010011
    Hi, I would like your guidance on how to create classes and their relationships (generalization, association, aggregation and composition) accurately from my USE case diagram (please see below). I am trying to create this class diagram so I can use it to create a simple online PHP application that allows the user to register an account, login and logout, and store, search and retrieve data from a MySQL database. Are my classes correct? Or should I create more classes? And if so, what classes are missing? What relationships should I use when connecting the register, login, logout, search_database and add_to_database to the users? I'm new to design patterns and UML class diagrams but from my understanding, the association relationship relates one object with another object; the aggregation relationship is a special kind of association that allows "a part" to belong to more than one "whole" (e.g. a credit card and its PIN - the PIN class can also be used in a debit card class); and a composition relationship is a special form of aggregation that allows each part to belong to only one whole at a time. I feel like I have left out some classes or something because I just can't seem to find the relationships from my understanding of relationships. Any assistance will be really appreciated. Thanks in advance. USE CASE DIAGRAM CLASS DIAGRAM

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  • The fallacies of all these Studies Linking one thing to another&hellip;

    - by Shawn Cicoria
    Are pesticides really the link?  Or is it hereditary?  Pesticides in kids linked to ADHD http://www.msnbc.msn.com/id/37156010/ns/health-kids_and_parenting/ You’ve got to think this one through.  If the parents already have ADHD, and they buy fruits, don’t have the “patience” to wash the fruit, and the kids end up with larger detectible amounts of pesticides in their bodies – are the pesticides really the cause or is it hereditary? I say, switch the kids around for the real test – sure, let the kids go live at a parent’s house w/ out ADHD for 10 years [clearly I’m kidding] who then consciously chooses NOT to wash the fruit. I read this story and all I could think was that the parents already have ADHD and they end up not washing these fruits and vegetables

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  • Problem while executing test case in VS2008 test project

    - by sukumar
    Hi all I have the situation as follows I have develpoed one test project in visual studio 2008 to test my target project. I was getting the following exception when i ran test case in my PC System.IO.FileNotFoundException: The specified module could not be found. (Exception from HRESULT: 0x8007007E) at System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) at System.Reflection.Assembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) at System.Reflection.Assembly.InternalLoad(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) at System.Reflection.Assembly.InternalLoadFrom(String assemblyFile, Evidence securityEvidence, Byte[] hashValue, AssemblyHashAlgorithm hashAlgorithm, Boolean forIntrospection, StackCrawlMark& stackMark) at System.Reflection.Assembly.LoadFrom(String assemblyFile) at Microsoft.VisualStudio.TestTools.TestTypes.Unit.UnitTestExecuter.GetType(UnitTestElement unitTest, String type) at Microsoft.VisualStudio.TestTools.TestTypes.Unit.UnitTestExecuter.ResolveMethods(). but the same project runs successfully in my colleague PC. as per my Understanding System.IO.FileNotFoundException will occur in case of missing out the dlls. i checked up with dependency walker to trace out the missed dll.dependency walke traced out the following dlls 1)MFC90D.dll 2)mSvcr90d.dll 3)msvcp90d.dll i copied this dlls to C:\windows\system32 from Microsoft visual studio 9.0 dir and again i ran the dependency walker.this time dependency walker is able to open the given testproject dll with 0 errors .even then the same exception comes up when i ran the test. i got fed up with this. can any one tell why it is behaving as PC dependent.is there any thing that i still missing? any suggestion can be helpfull Thakns in Advance Sukumar i

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  • Organization &amp; Architecture UNISA Studies &ndash; Chap 5

    - by MarkPearl
    Learning Outcomes Describe the operation of a memory cell Explain the difference between DRAM and SRAM Discuss the different types of ROM Explain the concepts of a hard failure and a soft error respectively Describe SDRAM organization Semiconductor Main Memory The two traditional forms of RAM used in computers are DRAM and SRAM DRAM (Dynamic RAM) Divided into two technologies… Dynamic Static Dynamic RAM is made with cells that store data as charge on capacitors. The presence or absence of charge in a capacitor is interpreted as a binary 1 or 0. Because capacitors have natural tendency to discharge, dynamic RAM requires periodic charge refreshing to maintain data storage. The term dynamic refers to the tendency of the stored charge to leak away, even with power continuously applied. Although the DRAM cell is used to store a single bit (0 or 1), it is essentially an analogue device. The capacitor can store any charge value within a range, a threshold value determines whether the charge is interpreted as a 1 or 0. SRAM (Static RAM) SRAM is a digital device that uses the same logic elements used in the processor. In SRAM, binary values are stored using traditional flip flop logic configurations. SRAM will hold its data as along as power is supplied to it. Unlike DRAM, no refresh is required to retain data. SRAM vs. DRAM DRAM is simpler and smaller than SRAM. Thus it is more dense and less expensive than SRAM. The cost of the refreshing circuitry for DRAM needs to be considered, but if the machine requires a large amount of memory, DRAM turns out to be cheaper than SRAM. SRAMS are somewhat faster than DRAM, thus SRAM is generally used for cache memory and DRAM is used for main memory. Types of ROM Read Only Memory (ROM) contains a permanent pattern of data that cannot be changed. ROM is non volatile meaning no power source is required to maintain the bit values in memory. While it is possible to read a ROM, it is not possible to write new data into it. An important application of ROM is microprogramming, other applications include library subroutines for frequently wanted functions, System programs, Function tables. A ROM is created like any other integrated circuit chip, with the data actually wired into the chip as part of the fabrication process. To reduce costs of fabrication, we have PROMS. PROMS are… Written only once Non-volatile Written after fabrication Another variation of ROM is the read-mostly memory, which is useful for applications in which read operations are far more frequent than write operations, but for which non volatile storage is required. There are three common forms of read-mostly memory, namely… EPROM EEPROM Flash memory Error Correction Semiconductor memory is subject to errors, which can be classed into two categories… Hard failure – Permanent physical defect so that the memory cell or cells cannot reliably store data Soft failure – Random error that alters the contents of one or more memory cells without damaging the memory (common cause includes power supply issues, etc.) Most modern main memory systems include logic for both detecting and correcting errors. Error detection works as follows… When data is to be read into memory, a calculation is performed on the data to produce a code Both the code and the data are stored When the previously stored word is read out, the code is used to detect and possibly correct errors The error checking provides one of 3 possible results… No errors are detected – the fetched data bits are sent out An error is detected, and it is possible to correct the error. The data bits plus error correction bits are fed into a corrector, which produces a corrected set of bits to be sent out An error is detected, but it is not possible to correct it. This condition is reported Hamming Code See wiki for detailed explanation. We will probably need to know how to do a hemming code – refer to the textbook (pg. 188 – 189) Advanced DRAM organization One of the most critical system bottlenecks when using high-performance processors is the interface to main memory. This interface is the most important pathway in the entire computer system. The basic building block of main memory remains the DRAM chip. In recent years a number of enhancements to the basic DRAM architecture have been explored, and some of these are now on the market including… SDRAM (Synchronous DRAM) DDR-DRAM RDRAM SDRAM (Synchronous DRAM) SDRAM exchanges data with the processor synchronized to an external clock signal and running at the full speed of the processor/memory bus without imposing wait states. SDRAM employs a burst mode to eliminate the address setup time and row and column line precharge time after the first access In burst mode a series of data bits can be clocked out rapidly after the first bit has been accessed SDRAM has a multiple bank internal architecture that improves opportunities for on chip parallelism SDRAM performs best when it is transferring large blocks of data serially There is now an enhanced version of SDRAM known as double data rate SDRAM or DDR-SDRAM that overcomes the once-per-cycle limitation of SDRAM

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