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• 1k of Program Space, 64 bytes of RAM. Is 1 wire communication possible?

  - by Earlz

  (If your lazy see bottom for TL;DR) Hello, I am planning to build a new (prototype) project dealing with physical computing. Basically, I have wires. These wires all need to have their voltage read at the same time. More than a few hundred microseconds difference between the readings of each wire will completely screw it up. The Arduino takes about 114 microseconds. So the most I could read is 2 or 3 wires before the latency would skew the accuracy of the readings. So my plan is to have an Arduino as the "master" of an array of ATTinys. The arduino is pretty cramped for space, but it's a massive playground compared to the tinys. An ATTiny13A has 1k of flash ROM(program space), 64 bytes of RAM, and 64 bytes of (not-durable and slow) EEPROM. (I'm choosing this for price as well as size) The ATTinys in my system will not do much. Basically, all they will do is wait for a signal from the Master, and then read the voltage of 1 or 2 wires and store it in RAM(or possibly EEPROM if it's that cramped). And then send it to the Master using only 1 wire for data.(no room for more than that!). So far then, all I should have to do is implement trivial voltage reading code (using built in ADC). But this communication bit I'm worried about. Do you think a communication protocol(using just 1 wire!) could even be implemented in such constraints? TL;DR: In less than 1k of program space and 64 bytes of RAM(and 64 bytes of EEPROM) do you think it is possible to implement a 1 wire communication protocol? Would I need to drop to assembly to make it fit? I know that currently my Arduino programs linking to the Wiring library are over 8k, so I'm a bit concerned.

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• How much effort do you have to put in to get gains from using SSE?

  - by John

  Case One Say you have a little class: class Point3D { private: float x,y,z; public: operator+=() ...etc }; Point3D &Point3D::operator+=(Point3D &other) { this->x += other.x; this->y += other.y; this->z += other.z; } A naive use of SSE would simply replace these function bodies with using a few intrinsics. But would we expect this to make much difference? MMX used to involve costly state cahnges IIRC, does SSE or are they just like other instructions? And even if there's no direct "use SSE" overhead, would moving the values into SSE registers and back out again really make it any faster? Case Two Instead, you're working with a less OO-based code base. Rather than an array/vector of Point3D objects, you simply have a big array of floats: float coordinateData[NUM_POINTS*3]; void add(int i,int j) //yes it's unsafe, no overlap check... example only { for (int x=0;x<3;++x) { coordinateData[i*3+x] += coordinateData[j*3+x]; } } What about use of SSE here? Any better? In conclusion Is trying to optimise single vector operations using SSE actually worthwhile, or is it really only valuable when doing bulk operations?

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• foreach() error handling - how do make it do nothing?

  - by Jared

  Hey all, This should be very basic, but I am a little stumped! Here is my array: $menu = array( 'Home', 'Stuff'=>array( 'Losta Stuff', 'Less Stuff', 'Ur moms stuff', 'FAQ' ), 'Public Works' ); Here is my logic: echo "<ol>\n"; foreach( (array)$menu as $header ) { echo ' <li><b>'.$header."</b><br />\n"; echo ' <ol>'; foreach( (array)$header as $headers ) { echo ' <li>'.$headers.".</li>\n"; } echo ' </ol>'; } echo "</ol>\n"; As you can see, Home and Public Works don't have data in the them, so I get a Warning: Invalid argument supplied for foreach() in test.php on line ## If I add (array) to $header like this: foreach( (array)$header as $headers ), It no longer gives me the error, but it just displays the $header as the $headers (i.e. Home - Home, Instead of Home - nothing). Basically, if the data is empty, I want it to do nothing!

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• Parse usable Street Address, City, State, Zip from a string

  - by Rob Allen

  Problem: I have an address field from an Access database which has been converted to Sql Server 2005. This field has everything all in one field. I need to parse out the individual sections of the address into their appropriate fields in a normalized table. I need to do this for approximately 4,000 records and it needs to be repeatable. Here are the rules for this exercise: 1 - no whining about how this should have been separate fields in the first place, we are often confronted with less than ideal situations and have to make the best of them 2- for this post, use any language you want 3- feel free to play code golf 4 - Assume an address in the US (for now) 5 - assume that the input string will sometimes contain an addressee (the person being addressed) and/or a second street address (i.e. Suite B) 6 - states may be abbreviated 7 - zip code could be standard 5 digit or zip+4 8 - there are typos in some instances UPDATE: In response to the questions posed, standards were not universally followed, I need need to store the individual values, not just geocode and errors means typo (corrected above) Sample Data: A. P. Croll & Son 2299 Lewes-Georgetown Hwy, Georgetown, DE 19947 11522 Shawnee Road, Greenwood DE 19950 144 Kings Highway, S.W. Dover, DE 19901 Intergrated Const. Services 2 Penns Way Suite 405 New Castle, DE 19720 Humes Realty 33 Bridle Ridge Court, Lewes, DE 19958 Nichols Excavation 2742 Pulaski Hwy Newark, DE 19711 2284 Bryn Zion Road, Smyrna, DE 19904 VEI Dover Crossroads, LLC 1500 Serpentine Road, Suite 100 Baltimore MD 21 580 North Dupont Highway Dover, DE 19901 P.O. Box 778 Dover, DE 19903

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• How to simulate OutOfMemory exception

  - by Gacek

  I need to refactor my project in order to make it immune to OutOfMemory exception. There are huge collections used in my project and by changing one parameter I can make my program to be more accurate or use less of the memory... OK, that's the background. What I would like to do is to run the routines in a loop: Run the subroutines with the default parameter. Catch the OutOfMemory exception, change the parameter and try to run it again. Do the 2nd point until parameters allow to run the subroutines without throwing the exception (usually, there will be only one change needed). Now, I would like to test it. I know, that I can throw the OutOfMemory exception on my own, but I would like to simulate some real situation. So the main question is: Is there a way of setting some kind of memory limit for my program, after reaching which the OutOfMemory exception will be thrown automatically? For example, I would like to set a limit, let's say 400MB of memory for my whole program to simulate the situation when there is such an amount of memory available in the system. Can it be done?

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• EC2 persistence of machine

  - by Seagull

  I want to 'persist' my Amazon EC2 images. My scenario: I have a range of Windows and Linux machines Some machines are EBS backed, whereas others are S3 backed. I need to be able to persist a machine (put it to sleep), preferably keeping all settings active I had them when the machine was running. I need to be able to quickly wake up a machine from sleep [Ideally with an SLA of less than 2 min to turn-on, if such an SLA is available with Amazon]. Here's the stuff that confuses me: AWS allows me to put EBS backed machines to sleep, but not S3 backed. I believe I can put S3 machines into some sort of persistence mode. But this involves shutting down the machine, writing it to S3 storage and then recovering from there (not a real sleep mode, but at least I don't continue to get billed for CPU). S3 backing seems to take a long time to either writing a machine to disk, or to recover (turn on a machine). I can't tell immediately which machines are EBS backed and which are S3 backed? It seems like I can instantiate either type, but it's not immediately clear how Amazon decided whether a given machine should be EBS or S3 backed. Advice?

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• Clustered index - multi-part vs single-part index and effects of inserts/deletes

  - by Anssssss

  This question is about what happens with the reorganizing of data in a clustered index when an insert is done. I assume that it should be more expensive to do inserts on a table which has a clustered index than one that does not because reorganizing the data in a clustered index involves changing the physical layout of the data on the disk. I'm not sure how to phrase my question except through an example I came across at work. Assume there is a table (Junk) and there are two queries that are done on the table, the first query searches by Name and the second query searches by Name and Something. As I'm working on the database I discovered that the table has been created with two indexes, one to support each query, like so: --drop table Junk1 CREATE TABLE Junk1 ( Name char(5), Something char(5), WhoCares int ) CREATE CLUSTERED INDEX IX_Name ON Junk1 ( Name ) CREATE NONCLUSTERED INDEX IX_Name_Something ON Junk1 ( Name, Something ) Now when I looked at the two indexes, it seems that IX_Name is redundant since IX_Name_Something can be used by any query that desires to search by Name. So I would eliminate IX_Name and make IX_Name_Something the clustered index instead: --drop table Junk2 CREATE TABLE Junk2 ( Name char(5), Something char(5), WhoCares int ) CREATE CLUSTERED INDEX IX_Name_Something ON Junk2 ( Name, Something ) Someone suggested that the first indexing scheme should be kept since it would result in more efficient inserts/deletes (assume that there is no need to worry about updates for Name and Something). Would that make sense? I think the second indexing method would be better since it means one less index needs to be maintained. I would appreciate any insight into this specific example or directing me to more info on maintenance of clustered indexes.

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• Allow paste in worksheet without overwriting locked cells

  - by jjeaton

  I have a protected worksheet that users would like to copy and paste into. I have no control over the workbook they are copying from. The protected worksheet has some rows that are available for data entry, and other rows that are locked and greyed out to the user. The users would like to be able to paste over the top of the entire worksheet from another random workbook and have all the cells available for data entry filled in, while the locked cells are undisturbed. In the current state, the user gets an error when they try to paste, because it cannot paste over the locked cells. Example: Worksheet 1: Act1 100 100 100 Act2 100 100 100 Act3 100 100 100 Worksheet 2: (The second row is locked) Act1 300 300 300 Act2 200 200 200 Act3 100 100 100 After copying/pasting Worksheet 2 should look like this: Act1 100 100 100 Act2 200 200 200 Act3 100 100 100 The values from worksheet 1 are populated and the locked rows are undisturbed. I've been thinking along the lines of having a hook where on paste, the locked cells are unlocked so that the paste can happen, and then are reverted to their original values and relocked. Is there some way I can loop through the cells in the clipboard and only paste cells where the target isn't locked? It is preferable to not create a separate button for paste, so there is less impact on the users, but if that's the only way, I'm not opposed to it. Currently, I plan on grouping the locked rows together, so that the data entry cells are contiguous, but then the accounts will be out of order, which is not preferred.

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• How do I left join tables in unidirectional many-to-one in Hibernate?

  - by jbarz

  I'm piggy-backing off of http://stackoverflow.com/questions/2368195/how-to-join-tables-in-unidirectional-many-to-one-condition. If you have two classes: class A { @Id public Long id; } class B { @Id public Long id; @ManyToOne @JoinColumn(name = "parent_id", referencedColumnName = "id") public A parent; } B - A is a many to one relationship. I understand that I could add a Collection of Bs to A however I do not want that association. So my actual question is, Is there an HQL or Criteria way of creating the SQL query: select * from A left join B on (b.parent_id = a.id) This will retrieve all A records with a Cartesian product of each B record that references A and will include A records that have no B referencing them. If you use: from A a, B b where b.a = a then it is an inner join and you do not receive the A records that do not have a B referencing them. I have not found a good way of doing this without two queries so anything less than that would be great. Thanks.

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• Cross-reference js-object variables when creating object

  - by Ivar Bonsaksen

  Summary: I want to know if it is possible to do something like this: {a: 'A',b: this.a} ...by using some other pointer like {a: 'A',b: self.a} or {a: 'A',b: own.a} or anything else... Full question: I'm trying to extend MyBaseModule using Ext.extend, and need to cross-reference values in the extension object passed to Ext.extend(). Since I'm not yet in context of MyModule, I'm not able to use this to reference the object (See example below line 12). Is there any other way to reference values like this without creating the object first? 1 MyModule = Ext.extend(MyBaseModule, { 2 dataStores: { 3 myDataStore: new Ext.data.Store({...}) 4 }, 5 6 myGridDefinition: { 7 id: 'myGridDefinitionPanel', 8 bodyBorder: false, 9 items: [{ 10 xtype: 'grid', 11 id: 'myGridDefinitionGrid', 12 store: this.dataStores.myDataStore 13 }] 14 } 15 }); Or is the following the only solution? I would like to avoid this if possible, as I find it less readable for large extension definitions. 1 var extensionObject = { 2 dataStores: { 3 myDataStore: new Ext.data.Store({...}) 4 }, 5 6 myGridDefinition: { 7 id: 'myGridDefinitionPanel', 8 bodyBorder: false, 9 items: [{ 10 xtype: 'grid', 11 id: 'myGridDefinitionGrid' 12 }] 13 } 14 }; 15 16 extensionObject.locationsGrid.items[0].store = extensionObject.dataStores.locations; 17 18 MyModule = Ext.extend(MyBaseModule, extensionObject);

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• PHP Redirection with Post Parameters

  - by arik-so

  Hello, I have a webpage. This webpage redirects the user to another webpage, more or less the following way: <form method="post" action="anotherpage.php" id="myform"> <?php foreach($_GET as $key => $value){ echo "<input type='hidden' name='{$key}' value='{$value}' />"; } ?> </form> <script> document.getElementById('myform').submit(); </script> Well, you see, what I do is transferring the GET params into POST params. Do not tell me it is bad, I know that myself, and it is not exactly what I really do, what is important is that I collect data from an array and try submitting it to another page via POST. But if the user has JavaScript turned off, it won't work. What I need to know: Is there a way to transfer POST parameters by means of PHP so the redirection can be done the PHP way (header('Location: anotherpage.php');), too? It is very important for me to pass the params via POST. I cannot use the $_SESSION variable because the webpage is on another domain, thus, the $_SESSION variables differ. Anyway, I simply need a way to transfer POST variables with PHP ^^ Thanks in advance!

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• Correct Time Display

  - by Matthew

  Guys, I''m looking to get this correct and i'm getting a bit fustrated with this. What I want to do is get hours and days and weeks correct. Example: if this post is < 60min old then have it read: Posted Less then 1 minute ago if this post is < 120min old then have it read: Posted 1 hour ago if this post is 120min old then have it read: Posted 1 hours ago if this post is < 1440min old then have it read: Posted 1 day ago if this post is 1440min old then have it read: Posted 2 days ago Is that right?? This is what I have so far: if (lapsedTime < 60) { return '< 1 mimute'; } else if (lapsedTime < (60*60)) { return Math.round(lapsedTime / 60) + 'minutes'; } else if (lapsedTime < (12*60*60)) { return Math.round(lapsedTime / 2400) + 'hr'; } else if (lapsedTime < (24*60*60)) { return Math.round(lapsedTime / 3600) + 'hrs'; } else if (lapsedTime < (7*24*60*60)) { return Math.round(lapsedTime / 86400) + 'days'; } else { return Math.round(lapsedTime / 604800) + 'weeks'; }

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• How can I force a ListView with a custom panel to re-measure when the ListView width goes below the

  - by Scott Whitlock

  Sorry for the long winded question (I'm including background here). If you just want the question, go to the end. I have a ListView with a custom Panel implementation that I'm using to implement something similar to a WrapPanel, but not quite. I'm overriding the MeasureOverride and ArrangeOverride methods in the custom panel. If I do the naive implementation of a WrapPanel in the MeasureOverride method it doesn't work when the ListView is resized. Let's say the custom panel does a measure and the constraint is a width of 100 and let's say I have 3 items that are 40 wide each. The naive approach is to return a size of 80,80 but when I resize the window that the ListView is in, down to say 75, it just turns on the horizontal scrollbar and never calls measure or arrange again (it does keep measuring and arranging if the width is greater than 80). To get around this, I hard coded the measurement to only have a width of the widest item. Then in the arrange, it gives me more space than I asked for and I use as much horizontal space as I can before wrapping. If I resize the window smaller than the smallest item in the ListView, then it turns on the scrollbar, which is great. Unfortunately this is causing a big problem when I have one of these ListViews with a custom panel nested inside of another one. The outside one works ok, but I can't get the inside one to "take as much as it needs". It always sizes to the smallest item, and the only way around it is to set the MinWidth to be something greater than zero. Anyway, stepping back for a second, I think the real way to fix this is to go back to the Naive implementation of the WrapPanel but force it to re-measure when the ListView width goes below the Size I previously returned as a measurement. That should solve my problem with the nested one. So, that's my question: I have a ListView with a custom panel If I return a measurement width on the panel and the ListView is resized to less than that width, it stops calling MeasureOverride How can I get it to continue calling MeasureOverride?

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• Javascript Rich Display WYSIWYG Component/Methodology

  - by Laramie

  quick back story-- I am working on ASP.Net based template editor that lets authors create text templates using Javascript inserted placeholder tags that will be filled in with dynamic text when the templates are used to display the final results. For example the author might create a template like The word [%12#add] was generated dynamically. The application would eventually replace the tag with a dynamic word down the road (though it's not specifically relevant to this post) The word foo was generated dynmamically. Depending on the circumstances, the template may be created in a text input, textarea or a modified version of the Ajax Control Toolkit HTML Editor. There might be 40 or more of these editable elements on the page, so using lots of stripped down or modified HTML editors would probably bog the page down too much. The problem is that the tags such as [%12#add] are displayed inline with the user text and the result is confusing and aesthetically gross. The goal is parse the contens of the source element and when a tags such as [%12#add] are encountered, display something prettier and less cryptic to the user such as a stylable element or image wherever tags such as [%12#add] occur. The application still needs the template text with the tags on postback. So the user might see The word tag placeholder was generated dynamically. but the original template would still be the value of the text input box The word [%12#add] was generated dynamically. It seems HTML editors like the ACT version and FckEditor accomplish this by rendering their output in an IFrame, but rather than kill myself trying to roll a lighter specialized version myself, I thought I'd ask if anyone knows of an existing free component or approach that has already tackled this. With good reason, I don't think S.O. allows HTML formatting, but the bold "tag placeholder" above would ideally be something like tag placeholder.

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• Password hashing, salt and storage of hashed values

  - by Jonathan Leffler

  Suppose you were at liberty to decide how hashed passwords were to be stored in a DBMS. Are there obvious weaknesses in a scheme like this one? To create the hash value stored in the DBMS, take: A value that is unique to the DBMS server instance as part of the salt, And the username as a second part of the salt, And create the concatenation of the salt with the actual password, And hash the whole string using the SHA-256 algorithm, And store the result in the DBMS. This would mean that anyone wanting to come up with a collision should have to do the work separately for each user name and each DBMS server instance separately. I'd plan to keep the actual hash mechanism somewhat flexible to allow for the use of the new NIST standard hash algorithm (SHA-3) that is still being worked on. The 'value that is unique to the DBMS server instance' need not be secret - though it wouldn't be divulged casually. The intention is to ensure that if someone uses the same password in different DBMS server instances, the recorded hashes would be different. Likewise, the user name would not be secret - just the password proper. Would there be any advantage to having the password first and the user name and 'unique value' second, or any other permutation of the three sources of data? Or what about interleaving the strings? Do I need to add (and record) a random salt value (per password) as well as the information above? (Advantage: the user can re-use a password and still, probably, get a different hash recorded in the database. Disadvantage: the salt has to be recorded. I suspect the advantage considerably outweighs the disadvantage.) There are quite a lot of related SO questions - this list is unlikely to be comprehensive: Encrypting/Hashing plain text passwords in database Secure hash and salt for PHP passwords The necessity of hiding the salt for a hash Clients-side MD5 hash with time salt Simple password encryption Salt generation and Open Source software I think that the answers to these questions support my algorithm (though if you simply use a random salt, then the 'unique value per server' and username components are less important).

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• Should I go for Arrays or Objects in PHP in a CouchDB/Ajax app?

  - by karlthorwald

  I find myself converting between array and object all the time in PHP application that uses couchDB and Ajax. Of course I am also converting objects to JSON and back (for sometimes couchdb but mostly Ajax), but this is not so much disturbing my workflow. At the present I have php objects that are returned by the CouchDB modules I use and on the other hand I have the old habbit to return arrays like array("error"="not found","data"=$dataObj) from my functions. This leads to a mixed occurence of real php objects and nested arrays and I cast with (object) or (array) if necessary. The worst thing is that I know more or less by heart what a function returns, but not what type (array or object), so I often run into type errors. My plan is now to always cast arrays to objects before returning from a function. Of course this implies a lot of refactoring. Is this the right way to go? What about the conversion overhead? Other ideas or tips? Edit: Kenaniah's answer suggests I should go the other way, this would mean I'd cast everything to arrays. And for all the Ajax / JSON stuff and also for CouchDB I would use $myarray = json_decode($json_data,$assoc = true); //EDIT: changed to true, whcih is what I really meant Even more work to change all the CouchDB and Ajax functions but in the end I have better code.

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• Destructors not called when native (C++) exception propagates to CLR component

  - by Phil Nash

  We have a large body of native C++ code, compliled into DLLs. Then we have a couple of dlls containing C++/CLI proxy code to wrap the C++ interfaces. On top of that we have C# code calling into the C++/CLI wrappers. Standard stuff, so far. But we have a lot of cases where native C++ exceptions are allowed to propagate to the .Net world and we rely on .Net's ability to wrap these as System.Exception objects and for the most part this works fine. However we have been finding that destructors of objects in scope at the point of the throw are not being invoked when the exception propagates! After some research we found that this is a fairly well known issue. However the solutions/ workarounds seem less consistent. We did find that if the native code is compiled with /EHa instead of /EHsc the issue disappears (at least in our test case it did). However we would much prefer to use /EHsc as we translate SEH exceptions to C++ exceptions ourselves and we would rather allow the compiler more scope for optimisation. Are there any other workarounds for this issue - other than wrapping every call across the native-managed boundary in a (native) try-catch-throw (in addition to the C++/CLI layer)?

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• PHP: tips/resources/patterns for learning to implement a basic ORM

  - by BoltClock

  I've seen various MVC frameworks as well as standalone ORM frameworks for PHP, as well as other ORM questions here; however, most of the questions ask for existing frameworks to get started with, which is not what I'm looking for. (I have also read this SO question but I'm not sure what to make of it, and the answers are vague.) Instead, I figured I'd learn best by getting my hands dirty and actually writing my own ORM, even a simple one. Except I don't really know how to get started, especially since the code I see in other ORMs is so complicated. With my PHP 5.2.x (this is important) MVC framework I have a basic custom database abstraction layer, that has: Very simple methods like connect($host, $user, $pass, $base), query($sql, $binds), etc Subclasses for each DBMS that it supports A class (and respective subclasses) to represent SQL result sets But does not have: Active Record functionality, which I assume is an ORM thing (correct me if I'm wrong) I've read up a little about ORM, and from my understanding they provide a means to further abstract data models from the database itself by representing data as nothing more than PHP-based classes/objects; again, correct me if I am wrong or have missed out in any way. Still, I'd like some simple tips from anyone else who's dabbled more or less with ORM frameworks. Is there anything else I need to take note of, simple example code for me to refer to, or resources I can read? Thanks a lot in advance!

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• Template compiling errors on iPhone SDK 3.2

  - by Didier Malenfant

  I'm porting over some templated code from Windows and I'm hitting some compiler differences on the iPhone 3.2 SDK. Original code inside a class template's member function is: return BinarySearch<uint32, CSimpleKey<T> >(key); where BinarySearch is a method inherited from another template. This produces the following error: csimplekeytable.h:131: error: no matching function for call to 'BinarySearch(NEngine::uint32&)' The visual studio compiler seems to walk up the template hierarchy fine but gcc needs me to fully qualify where the function comes from (I have verified this by fixing the same issues with template member variables that way). So I now need to change this into: return CSimpleTable<CSimpleKey<T> >::BinarySearch<uint32, CSimpleKey<T> >(key); Which now produces the following error: csimplekeytable.h:132: error: expected primary-expression before ',' token csimplekeytable.h:132: error: expected primary-expression before '>' token After some head scratching, I believe what's going on here is that it's trying to resolve the '<' before BinarySearch as a 'Less Than' operator for some reason. So two questions: - Am I on the right path with my interpretation of the error? - How do I fix it? -D

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• Spring 3.0 vs J2EE 6.0

  - by StudiousJoseph

  Hi everybody, I'm confronted with a situation... I've been asked to give an advise regarding which approach to take, in terms of J2EE development between Spring 3.0 and J2EE 6.0. I was, and still am, a promoter of Spring 2.5 over classic J2EE 5 development, specially with JBoss, I even migrated old apps to Spring and influenced the re-definition of the development policy here to include Spring specific APIs, and helped the development of a strategic plan to foster more lightweight solutions like Spring + Tomcat, instead of the heavier ones of JBoss, right now, we're using JBoss merely as a Web container, having what i call the "container inside the container paradox", that is, having Spring apps, with most of its APIs, running inside JBoss, So we're in the process of migrating to tomcat. However, with the coming of J2EE 6.0 many features, that made Spring attractive at that time, easy deployment, less-coupling, even some sort of D.I, etc, seems to have been mimicked, in one way or the other. JSF 2.0, JPA 2.0, WebBeans, WebProfiles, etc. So, the question goes... From your point of view, how save, and logical, it is to continue to invest in a non-standard J2EE development framework like Spring given the new perspectives offered by J2EE 6.0? Can we talk about maybe 3 or 4 more years of Spring development, or do you recommend early adoption of J2EE 6.0 APIs and it's practices? I'll appreciate any insights with this...

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• Is XMLReader a SAX parser, a DOM parser, or neither?

  - by Renesis

  I am testing various methods to read (possibly large, and very often) XML configuration files in PHP. No writing is ever needed. I have two successful implementations, one using SimpleXML (which I know is a DOM parser) and one using XMLReader. I know that a DOM reader must read the whole tree and therefore uses more memory. My tests reflect that. I also know that A SAX parser is an "event-based" parser that uses less memory because it reads each node from the stream without checking what is next. XMLReader also reads from a stream with the cursor providing data about the node it is currently at. So, it definitely sounds like XMLReader (http://us2.php.net/xmlreader) is not a DOM parser, but my question is, is it a SAX parser, or something else? It seems like XMLReader behaves the way a SAX parser does but does not throw the events themselves (in other words, can you construct a SAX parser with XMLReader?) If it is something else, does the classification it's in have a name?

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• POST variables to web server?

  - by OverTheRainbow

  Hello I've been trying several things from Google to POST data to a web server, but none of them work: I'm still stuck at how to convert the variables into the request, considering that the second variable is an SQL query so it has spaces. Does someone know the correct way to use a WebClient to POST data? I'd rather use WebClient because it requires less code than HttpWebRequest/HttpWebResponse. Here's what I tried so far: Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim wc = New WebClient() 'convert data wc.Headers.Add("Content-Type", "application/x-www-form-urlencoded") Dim postData = String.Format("db={0}&query={1}", _ HttpUtility.UrlEncode("books.sqlite"), _ HttpUtility.UrlEncode("SELECT id,title FROM boooks")) 'Dim bytArguments As Byte() = Encoding.ASCII.GetBytes("db=books.sqlite|query=SELECT * FROM books") 'POST query Dim bytRetData As Byte() = wc.UploadData("http://localhost:9999/get", "POST", postData) RichTextBox1.Text = Encoding.ASCII.GetString(bytRetData) Exit Sub Dim client = New WebClient() Dim nv As New Collection nv.Add("db", "books.sqlite") nv.Add("query", "SELECT id,title FROM books") Dim address As New Uri("http://localhost:9999/get") 'Dim bytRetData As Byte() = client.UploadValues(address, "POST", nv) RichTextBox1.Text = Encoding.ASCII.GetString(bytRetData) Exit Sub 'Dim wc As New WebClient() 'convert data wc.Headers.Add("Content-Type", "application/x-www-form-urlencoded") Dim bytArguments As Byte() = Encoding.ASCII.GetBytes("db=books.sqlite|query=SELECT * FROM books") 'POST query 'Dim bytRetData As Byte() = wc.UploadData("http://localhost:9999/get", "POST", bytArguments) RichTextBox1.Text = Encoding.ASCII.GetString(bytRetData) Exit Sub End Sub Thank you.

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• When to choose which machine learning classifier?

  - by LM

  Suppose I'm working on some classification problem. (Fraud detection and comment spam are two problems I'm working on right now, but I'm curious about any classification task in general.) How do I know which classifier I should use? (Decision tree, SVM, Bayesian, logistic regression, etc.) In which cases is one of them the "natural" first choice, and what are the principles for choosing that one? Examples of the type of answers I'm looking for (from Manning et al.'s "Introduction to Information Retrieval book": http://nlp.stanford.edu/IR-book/html/htmledition/choosing-what-kind-of-classifier-to-use-1.html): a. If your data is labeled, but you only have a limited amount, you should use a classifier with high bias (for example, Naive Bayes). [I'm guessing this is because a higher-bias classifier will have lower variance, which is good because of the small amount of data.] b. If you have a ton of data, then the classifier doesn't really matter so much, so you should probably just choose a classifier with good scalability. What are other guidelines? Even answers like "if you'll have to explain your model to some upper management person, then maybe you should use a decision tree, since the decision rules are fairly transparent" are good. I care less about implementation/library issues, though. Also, for a somewhat separate question, besides standard Bayesian classifiers, are there 'standard state-of-the-art' methods for comment spam detection (as opposed to email spam)? [Not sure if stackoverflow is the best place to ask this question, since it's more machine learning than actual programming -- if not, any suggestions for where else?]

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• Your favourite C++ Standard Library wrapper functions?

  - by Neil Butterworth

  This question, asked this morning, made me wonder which features you think are missing from the C++ Standard Library, and how you have gone about filling the gaps with wrapper functions. For example, my own utility library has this function for vector append: template <class T> std::vector<T> & operator += ( std::vector<T> & v1, const std::vector <T> v2 ) { v1.insert( v1.end(), v2.begin(), v2.end() ); return v1; } and this one for clearing (more or less) any type - particularly useful for things like std::stack: template <class C> void Clear( C & c ) { c = C(); } I have a few more, but I'm interested in which ones you use? Please limit answers to wrapper functions - i.e. no more than a couple of lines of code.

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• gcc, strict-aliasing, and horror stories

  - by Joseph Quinsey

  In http://stackoverflow.com/questions/2906365/gcc-strict-aliasing-and-casting-through-a-union I asked whether anyone had encountered problems with union punning through pointers. So far, the answer seems to be No. This question is broader: do you have any horror stories about gcc and strict-aliasing? Background: Quoting from AndreyT's answer in http://stackoverflow.com/questions/2771023/c99-strict-aliasing-rules-in-c-gcc/2771041#2771041: "Strict aliasing rules are rooted in parts of the standard that were present in C and C++ since the beginning of [standardized] times. The clause that prohibits accessing object of one type through a lvalue of another type is present in C89/90 (6.3) as well as in C++98 (3.10/15). ... It is just that not all compilers wanted (or dared) to enforce it or rely on it." Well, gcc is now daring to do so, with its -fstrict-aliasing switch. And this has caused some problems. See, for example, the excellent article http://davmac.wordpress.com/2009/10/ about a Mysql bug, and the equally excellent discussion in http://cellperformance.beyond3d.com/articles/2006/06/understanding-strict-aliasing.html. Some other less-relevant links: http://stackoverflow.com/questions/1225741/performance-impact-of-fno-strict-aliasing http://stackoverflow.com/questions/754929/strict-aliasing http://stackoverflow.com/questions/262379/when-is-char-safe-for-strict-pointer-aliasing http://stackoverflow.com/questions/725138/how-to-detect-strict-aliasing-at-compile-time So to repeat, do you have a horror story of your own? Problems not indicated by -Wstrict-aliasing would, of course, be preferred. And other C compilers are also welcome.

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