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• Float addition promoted to double?

  - by Andreas Brinck

  I had a small WTF moment this morning. Ths WTF can be summarized with this: float x = 0.2f; float y = 0.1f; float z = x + y; assert(z == x + y); //This assert is triggered! (Atleast with visual studio 2008) The reason seems to be that the expression x + y is promoted to double and compared with the truncated version in z. (If i change z to double the assert isn't triggered). I can see that for precision reasons it would make sense to perform all floating point arithmetics in double precision before converting the result to single precision. I found the following paragraph in the standard (which I guess I sort of already knew, but not in this context): 4.6.1. "An rvalue of type float can be converted to an rvalue of type double. The value is unchanged" My question is, is x + y guaranteed to be promoted to double or is at the compiler's discretion? UPDATE: Since many people has claimed that one shouldn't use == for floating point, I just wanted to state that in the specific case I'm working with, an exact comparison is justified. Floating point comparision is tricky, here's an interesting link on the subject which I think hasn't been mentioned.

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• C++ find largest BST in a binary tree

  - by fonjibe

  what is your approach to have the largest BST in a binary tree? I refer to this post where a very good implementation for finding if a tree is BST or not is bool isBinarySearchTree(BinaryTree * n, int min=std::numeric_limits<int>::min(), int max=std::numeric_limits<int>::max()) { return !n || (min < n->value && n->value < max && isBinarySearchTree(n->l, min, n->value) && isBinarySearchTree(n->r, n->value, max)); } It is quite easy to implement a solution to find whether a tree contains a binary search tree. i think that the following method makes it: bool includeSomeBST(BinaryTree* n) { if(!isBinarySearchTree(n)) { if(!isBinarySearchTree(n->left)) return isBinarySearchTree(n->right); } else return true; else return true; } but what if i want the largest BST? this is my first idea, BinaryTree largestBST(BinaryTree* n) { if(isBinarySearchTree(n)) return n; if(!isBinarySearchTree(n->left)) { if(!isBinarySearchTree(n->right)) if(includeSomeBST(n->right)) return largestBST(n->right); else if(includeSomeBST(n->left)) return largestBST(n->left); else return NULL; else return n->right; } else return n->left; } but its not telling the largest actually. i struggle to make the comparison. how should it take place? thanks

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• Oracle Date Format Convert Hour-Minute to Interval and Disregard Year-Month-Day

  - by dlite922

  I need to compare an event's half-way midpoint between a start and stop time of day. Right now i'm converting the dates you see on the right, to HH:MM and the comparison works until midnight. the query says: WHERE half BETWEEN pStart and pStop. As you can see below, pStart and pStap have January 1st 2000 dates, this is because the year month day are not important to me... Valid Data: +-------+--------+-------+---------------------+---------------------+---------------------+ | half | pStart | pStop | half2 | pStart2 | pStop2 | +-------+--------+-------+---------------------+---------------------+---------------------+ | 19:00 | 19:00 | 23:00 | 2012-11-04 19:00:00 | 2000-01-01 19:00:00 | 2000-01-01 23:00:00 | | 20:00 | 19:00 | 23:00 | 2012-11-04 20:00:00 | 2000-01-01 19:00:00 | 2000-01-01 23:00:00 | | 21:00 | 19:00 | 23:00 | 2012-11-04 21:00:00 | 2000-01-01 19:00:00 | 2000-01-01 23:00:00 | | 23:00 | 20:00 | 23:00 | 2012-11-05 23:00:00 | 2000-01-01 20:00:00 | 2000-01-01 23:00:00 | +-------+--------+-------+---------------------+---------------------+---------------------+ Now observe what happens when pStop is midnight or later... Valid Data that breaks it: +-------+--------+-------+---------------------+---------------------+---------------------+ | half | pStart | pStop | half2 | pStart2 | pStop2 | +-------+--------+-------+---------------------+---------------------+---------------------+ | 23:00 | 22:00 | 00:00 | 2012-11-04 23:00:00 | 2000-01-01 22:00:00 | 2000-01-01 00:00:00 | | 23:30 | 23:00 | 02:00 | 2012-11-05 23:30:00 | 2000-01-01 23:00:00 | 2000-01-01 02:00:00 | +-------+--------+-------+---------------------+---------------------+---------------------+ Thus my where clause translates to: WHERE 19:00 BETWEEN 22:00 AND 00:00 ...which returns false and I miss those two correct rows above. Question: Is there a way to show those dates as integer interval so that saying half BETWEEN pStart and pStop are correct? I thought about adding 24 when pStop is less than pStart to make 00:00 into 24:00 but don't know an easy way to do that without long string concatenations and number conversions. This would solve the problem because pStart pStop difference will never be longer than 6 hours. Note: (The Query is much more complex. It has other irrelevant date calculations, but the result are show above. DATE_FORMAT(%H:%i) is applied to the first three columns and no formatting to the last three) Thanks for your help:

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• Which are the RDBMS that minimize the server roundtrips? Which RDBMS are better (in this area) than

  - by user193655

  When the latency is high ("when pinging the server takes time") the server roundtrips make the difference. Now I don't want to focus on the roundtrips created in programming, but the roundtrips that occur "under the hood" in the DB engine, so the roundtrips that are 100% dependant on how the RDBMS is written itself. I have been told that FireBird has more roundtrips than MySQL. But this is the only information I know. I am currently supporting MS SQL but I'd like to change RDBMS (because I use Express Editions and in my scenario they are quite limiting from the performance point of view), so to make a wise choice I would like to include also this point into "my RDBMS comparison feature matrix" to understand which is the best RDBMS to choose as an alternative to MS SQL. So the bold sentence above would make me prefer MySQL to Firebird (for the roundtrips concept, not in general), but can anyone add informations? And MS SQL where is it located? Is someone able to "rank" the roundtrip performance of the main RDBMS, or at least: MS SQL, MySql, Postegresql, Firebird (I am not interested in Oracle since it is not free, and if I have to change I would change to a free RDBMS). Anyway MySql (as mentioned several times on stackoverflow) has a not clear future and a not 100% free license. So my final choice will probably dall on PostgreSQL or Firebird. Additional info: somehow you can answer my question by making a simple list like: MSSQL:3; MySQL:1; Firebird:2; Postgresql:2 (where 1 is good, 2 average, 3 bad). Of course if you can post some links where the roundtrips per RDBMSs are compared it would be great

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• Python Ephem / Datetime calculation

  - by dassouki

  the output should process the first date as "day" and second as "night". I've been playing with this for a few hours now and can't figure out what I'm doing wrong. Any ideas? Edit I assume that the problem is due to my date comparison implementation Output: $ python time_of_day.py * should be day: event date: 2010/4/6 16:00:59 prev rising: 2010/4/6 09:24:24 prev setting: 2010/4/5 23:33:03 next rise: 2010/4/7 09:22:27 next set: 2010/4/6 23:34:27 day * should be night: event date: 2010/4/6 00:01:00 prev rising: 2010/4/5 09:26:22 prev setting: 2010/4/5 23:33:03 next rise: 2010/4/6 09:24:24 next set: 2010/4/6 23:34:27 day time_of_day.py import datetime import ephem # install from http://pypi.python.org/pypi/pyephem/ #event_time is just a date time corresponding to an sql timestamp def type_of_light(latitude, longitude, event_time, utc_time, horizon): o = ephem.Observer() o.lat, o.long, o.date, o.horizon = latitude, longitude, event_time, horizon print "event date ", o.date print "prev rising: ", o.previous_rising(ephem.Sun()) print "prev setting: ", o.previous_setting(ephem.Sun()) print "next rise: ", o.next_rising(ephem.Sun()) print "next set: ", o.next_setting(ephem.Sun()) if o.previous_rising(ephem.Sun()) <= o.date <= o.next_setting(ephem.Sun()): return "day" elif o.previous_setting(ephem.Sun()) <= o.date <= o.next_rising(ephem.Sun()): return "night" else: return "error" print "should be day: ", type_of_light('45.959','-66.6405','2010/4/6 16:01','-4', '-6') print "should be night: ", type_of_light('45.959','-66.6405','2010/4/6 00:01','-4', '-6')

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• Performance impact when using XML columns in a table with MS SQL 2008

  - by Sam Dahan

  I am using a simple table with 6 columns, 3 of which are of XML type, not schema-constrained. When the table reaches a size around 120,000 or 150,000 rows, I see a dramatic performance cost in doing any query in the table. For comparison, I have another table, which grows in size at about the same rate, but only contain scalar types (int, datetime, a few float columns). That table performs perfectly fine even after 200,000 rows. And by the way, I am not using XQuery on the xml columns, i am only using regular SQL query statements. Some specifics: both tables contain a DateTime field called SampleTime. a statement like (it's in a stored procedure but I show you the actual statement) SELECT MAX(sampleTime) SampleTime FROM dbo.MyRecords WHERE PlacementID=@somenumber takes 0 seconds on the table without xml columns, and anything from 13 to 20 seconds on the table with XML columns. That depends on which drive I set my database on. At the moment it sits on a different spindle (not C:) and it takes 13 seconds. Has anyone seen this behavior before, or have any hint at what I am doing wrong? I tried this with SQL 2008 EXPRESS and the full-blown SQL Server 2008, that made no difference. Oh, one last detail: I am doing this from a C# application, .NET 3.5, using SqlConnection, SqlReader, etc.. I'd appreciate some insight into that, thanks! Sam

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• What can cause my code to run slower when the server JIT is activated?

  - by durandai

  I am doing some optimizations on an MPEG decoder. To ensure my optimizations aren't breaking anything I have a test suite that benchmarks the entire codebase (both optimized and original) as well as verifying that they both produce identical results (basically just feeding a couple of different streams through the decoder and crc32 the outputs). When using the "-server" option with the Sun 1.6.0_18, the test suite runs about 12% slower on the optimized version after warmup (in comparison to the default "-client" setting), while the original codebase gains a good boost running about twice as fast as in client mode. While at first this seemed to be simply a warmup issue to me, I added a loop to repeat the entire test suite multiple times. Then execution times become constant for each pass starting at the 3rd iteration of the test, still the optimized version stays 12% slower than in the client mode. I am also pretty sure its not a garbage collection issue, since the code involves absolutely no object allocations after startup. The code consists mainly of some bit manipulation operations (stream decoding) and lots of basic floating math (generating PCM audio). The only JDK classes involved are ByteArrayInputStream (feeds the stream to the test and excluding disk IO from the tests) and CRC32 (to verify the result). I also observed the same behaviour with Sun JDK 1.7.0_b98 (only that ist 15% instead of 12% there). Oh, and the tests were all done on the same machine (single core) with no other applications running (WinXP). While there is some inevitable variation on the measured execution times (using System.nanoTime btw), the variation between different test runs with the same settings never exceeded 2%, usually less than 1% (after warmup), so I conclude the effect is real and not purely induced by the measuring mechanism/machine. Are there any known coding patterns that perform worse on the server JIT? Failing that, what options are available to "peek" under the hood and observe what the JIT is doing there?

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• visualising piano performance evaluation

  - by Dolphin

  I need to develop a performance evaluator for piano playing. Based on a midi generated from sheet music, I need to evaluate the midi of the actual playing (midi keyboard). I'm planning to evaluate the playing based on note pitch, duration and loudness. The evaluation is I suppose a comparison of the notes of the sheet music and playing in midi. But I have no idea how I can visualise (i.e. show where the person have gone wrong) this evaluation process. i.e. maybe show both the notation and highlight which note has gone wrong. But how can I show any of this in some graphical form? Or more precisely on a stave (a music score) itself. I have note details (pitch, duration) and score details (key and time signature) stored in a table, and I'm using Java. But I have no clue as in how I can put all this into graphical form. Any insight is most gratefully appreciated. Advance thanks

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• Character Set Issues when Upgrading from Symfony 2.0.* to Symfony 2.1.*?

  - by Adam Stacey

  I have recently upgraded my staging test site to the latest version of Symfony and updated all the vendors using composer as instructed in the upgrade document that comes with the download. Everything has all updated fine, but I have noticed now that some bits of HTML are not displaying in the Twig templates. I did a comparison with the current live site and it appears to be a character set issue. As an example I had a drop down list that had the following value in: Kitchen Ducting > Ducting Kits > Ducting Kit 4” / 100mm In the updated site the drop-down list item just appeared blank. When I used Twig's raw function it then displayed the item again, but with the dreaded question mark in a black diamond. Kitchen Ducting > Ducting Kits > Ducting Kit 4? / 100mm Things that you should know that may help: The staging test site and live site are both on the same server. In my httpd.conf file I have 'AddDefaultCharset utf-8'. In my php.ini file I have 'default_charset = "utf-8"'. The HTML file served has the Content-Type meta tag 'content="text/html; charset=utf-8"' My database is InnoDB and uses 'utf8' as the default character set and 'utf8_general_ci' as default collation. All tables in the database also use the defaults. I looked into BOM with UTF8, but could not work out if that was a problem or not?

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• ArrayList.Sort should be a stable sort with an IComparer but is not?

  - by Kaleb Pederson

  A stable sort is a sort that maintains the relative ordering of elements with the same value. The docs on ArrayList.Sort say that when an IComparer is provided the sort is stable: If comparer is set to null, this method performs a comparison sort (also called an unstable sort); that is, if two elements are equal, their order might not be preserved. In contrast, a stable sort preserves the order of elements that are equal. To perform a stable sort, you must implement a custom IComparer interface. Unless I'm missing something, the following testcase shows that ArrayList.Sort is not using a stable sort: internal class DisplayOrdered { public int ID { get; set; } public int DisplayOrder { get; set; } public override string ToString() { return string.Format("ID: {0}, DisplayOrder: {1}", ID, DisplayOrder); } } internal class DisplayOrderedComparer : IComparer { public int Compare(object x, object y) { return ((DisplayOrdered)x).DisplayOrder - ((DisplayOrdered)y).DisplayOrder; } } [TestFixture] public class ArrayListStableSortTest { [Test] public void TestWeblinkCallArrayListIsSortedUsingStableSort() { var call1 = new DisplayOrdered {ID = 1, DisplayOrder = 0}; var call2 = new DisplayOrdered {ID = 2, DisplayOrder = 0}; var call3 = new DisplayOrdered {ID = 3, DisplayOrder = 2}; var list = new ArrayList {call1, call2, call3}; list.Sort(new DisplayOrderedComparer()); // expected order (by ID): 1, 2, 3 (because the DisplayOrder // is equal for ID's 1 and 2, their ordering should be // maintained for a stable sort.) Assert.AreEqual(call1, list[0]); // Actual: ID=2 ** FAILS Assert.AreEqual(call2, list[1]); // Actual: ID=1 Assert.AreEqual(call3, list[2]); // Actual: ID=3 } } Am I missing something? If not, would this be a documentation bug or a library bug? Apparently using an OrderBy in Linq gives a stable sort.

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• Alternatives to the Entity Framework for Serving/Consuming an OData Interface

  - by Egahn

  I'm researching how to set up an OData interface to our database. I would like to be able to pull/query data from our DB into Excel, as a start. Eventually I would like to have Excel run queries and pull data over HTTP from a remote client, including authentication, etc. I've set up a working (rickety) prototype so far, using the ADO.NET Entity Data Model wizard in Visual Studio, and VSTO to create a test Excel worksheet with a button to pull from that ADO.NET interface. This works OK so far, and I can query the DB using Linq through the entities/objects that are created by the ADO.NET EDM wizard. However, I have started to run into some problems with this approach. I've been finding the Entity Framework difficult to work with (and in fact, also difficult to research solutions to, as there's a lot of chaff out there regarding it and older versions of it). An example of this is my being unable to figure out how to set the SQL command timeout (as opposed to the HTTP request timeout) on the DataServiceContext object that the wizard generates for my schema, but that's not the point of my question. The real question I have is, if I want to use OData as my interface standard, am I stuck with the Entity Framework? Are there any other solutions out there (preferably open source) which can set up, serve and consume an OData interface, and are easier to work with and less bloated than the Entity Framework? I have seen mention of NHibernate as an alternative, but most of the comparison threads I've seen are a few years old. Are there any other alternatives out there now? Thanks very much!

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• What's the recommended implementation for hashing OLE Variants?

  - by Barry Kelly

  OLE Variants, as used by older versions of Visual Basic and pervasively in COM Automation, can store lots of different types: basic types like integers and floats, more complicated types like strings and arrays, and all the way up to IDispatch implementations and pointers in the form of ByRef variants. Variants are also weakly typed: they convert the value to another type without warning depending on which operator you apply and what the current types are of the values passed to the operator. For example, comparing two variants, one containing the integer 1 and another containing the string "1", for equality will return True. So assuming that I'm working with variants at the underlying data level (e.g. VARIANT in C++ or TVarData in Delphi - i.e. the big union of different possible values), how should I hash variants consistently so that they obey the right rules? Rules: Variants that hash unequally should compare as unequal, both in sorting and direct equality Variants that compare as equal for both sorting and direct equality should hash as equal It's OK if I have to use different sorting and direct comparison rules in order to make the hashing fit. The way I'm currently working is I'm normalizing the variants to strings (if they fit), and treating them as strings, otherwise I'm working with the variant data as if it was an opaque blob, and hashing and comparing its raw bytes. That has some limitations, of course: numbers 1..10 sort as [1, 10, 2, ... 9] etc. This is mildly annoying, but it is consistent and it is very little work. However, I do wonder if there is an accepted practice for this problem.

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• Validating Login / Changing User settings / Php Mysql

  - by Marcelo

  Hi everyone, my questions are about login, and changing already saved data. (Q1) 'Till now I've only saved input in the tables of the database (registration steps), now I need to check if the input (login steps), are the same of my table in database, in fact I have 3 types of users, then I'll have to check 3 kind of tables. Then if the input data matches with one of those 3 tables I will redirect the user to his specific area. I'm thinking about saved the submitted data $login=$_REQUEST['login']; and $password=$_REQUEST['password']; and compare with the login column in the database. Then if the login matches, I'll compare the password submitted with the one in the row, not in the column. But I don't know how to do this search and comparison,neither what to use. Then if both matches I'll redirect the user. Else I'll send an login error message. (this I know how to do) (Q2) What if need to change an already saved user ? For example to change an email address. My changing user's data web page is exactly the same like the registration user web page. Can I load the already saved options and values of registration (table user for example). Then the user will change whatever he thinks it's necessary, and then when he submits the new information, they would not create a new row in my table, but just be overwritten the old information? How can I do this? Sorry for any mistake in English, and Thanks for the attention.

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• c# "==" operator : compiler behaviour with different structs

  - by Moe Sisko

  Code to illustrate : public struct MyStruct { public int SomeNumber; } public string DoSomethingWithMyStruct(MyStruct s) { if (s == null) return "this can't happen"; else return "ok"; } private string DoSomethingWithDateTime(DateTime s) { if (s == null) return "this can't happen"; // XX else return "ok"; } Now, "DoSomethingWithStruct" fails to compile with : "Operator '==' cannot be applied to operands of type 'MyStruct' and '<null>'". This makes sense, since it doesn't make sense to try a reference comparison with a struct, which is a value type. OTOH, "DoSomethingWithDateTime" compiles, but with compiler warning : "Unreachable code detected" at line marked "XX". Now, I'm assuming that there is no compiler error here, because the DateTime struct overloads the "==" operator. But how does the compiler know that the code is unreachable ? e.g. Does it look inside the code which overloads the "==" operator ? (This is using Visual Studio 2005 in case that makes a difference). Note : I'm more curious than anything about the above. I don't usually try to use "==" on structs and nulls.

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• URL equals and checking Internet access

  - by James P.

  On http://java.sun.com/j2se/1.5.0/docs/api/java/net/URL.html it states that: Compares this URL for equality with another object. If the given object is not a URL then this method immediately returns false. Two URL objects are equal if they have the same protocol, reference equivalent hosts, have the same port number on the host, and the same file and fragment of the file. Two hosts are considered equivalent if both host names can be resolved into the same IP addresses; else if either host name can't be resolved, the host names must be equal without regard to case; or both host names equal to null. Since hosts comparison requires name resolution, this operation is a blocking operation. Note: The defined behavior for equals is known to be inconsistent with virtual hosting in HTTP. According to this, equals will only work if name resolution is possible. Since I can't be sure that a computer has internet access at a given time, should I just use Strings to store addresses instead? Also, how do I go about testing if access is available when requested?

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• xcode project-/target-settings-syntax for linker flag force_load on iPhone

  - by Kaiserludi

  Hi all. I am confronted with the double bind, that on the one hand for one of the 3rd party static libraries, my iPhone application uses, the linker flag -all_load has to be set in the application project- or target settings, otherwise the app crashes at runtime not finding some symbols, called internally from the lib, on the other hand for another 3rd party static lib -all_load must not be set on application level, or the app won't build thanks to a "duplicate symbols"-linker error. To solve this issue I now want to use force_load instant of load_all, as it due to documentation it does the same like all_load, but only for the passed path or lib-file, instead of all libs. The problem with force_load is, I do not have a clue, how to pass a path or file as parameter with it, when passing it via xcode project- or target-settings. All syntax-possibilities coming to my mind either lead into xcode thinking its another linker flag instead of a parameter to the previous one, or the linker is throwing syntax related errors or the flag simply does nothing at all in comparison to not being set. I also opened the .pbxproj-file in a text-editor to edit it to the correct command line syntax manually, but when reloading the project with xcode, it auto changes the syntax into interpreting the parameter to force_load as a separate flag. Anyone having an idea on this issue? Thx, Kaiserludi.

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• Resolving the WMI DNS Host Name

  - by Stephen Murby

  I am trying to make a comparison between a machine name i have retrieved from AD, and the DNS Host Name i want to get using WMI from the machine. I currently have: foreach (SearchResult oneMachine in allMachinesCollected) { pcName = oneMachine.Properties["name"][0].ToString(); ConnectionOptions setupConnection = new ConnectionOptions(); setupConnection.Username = USERNAME; setupConnection.Password = PASSWORD; setupConnection.Authority = "ntlmdomain:DOMAIN"; ManagementScope setupScope = new ManagementScope("\\\\" + pcName + "\\root\\cimv2", setupConnection); setupScope.Connect(); ObjectQuery dnsNameQuery = new ObjectQuery("SELECT * FROM Win32_ComputerSystem"); ManagementObjectSearcher dnsNameSearch = new ManagementObjectSearcher(setupScope, dnsNameQuery); ManagementObjectCollection allDNSNames = dnsNameSearch.Get(); string dnsHostName; foreach (ManagementObject oneName in allDNSNames) { dnsHostName = oneName.Properties["DNSHostName"].ToString(); if (dnsHostName == pcName) { shutdownMethods.ShutdownMachine(pcName, USERNAME, PASSWORD); MessageBox.Show(pcName + " has been sent the reboot command"); } } } } But i get a ManagementException dnsHostName = oneName.Properties["DNSHostName"].ToString(); << here saying not found. Any ideas?

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• Vector [] vs copying

  - by sak

  What is faster and/or generally better? vector<myType> myVec; int i; myType current; for( i = 0; i < 1000000; i ++ ) { current = myVec[ i ]; doSomethingWith( current ); doAlotMoreWith( current ); messAroundWith( current ); checkSomeValuesOf( current ); } or vector<myType> myVec; int i; for( i = 0; i < 1000000; i ++ ) { doSomethingWith( myVec[ i ] ); doAlotMoreWith( myVec[ i ] ); messAroundWith( myVec[ i ] ); checkSomeValuesOf( myVec[ i ] ); } I'm currently using the first solution. There are really millions of calls per second and every single bit comparison/move is performance-problematic.

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• Comparing two images from the clipboard class

  - by VeXe

  In a C# winform app. I'm writing a Clipboard log manager that logs test to a log file, (everytime a Ctrl+c/x is pressed the copied/cut text gets appended to the file) I also did the same for images, that is, if you press "prtScreen", the screen shot you took will also go to a folder. I do that by using a timer, inside I have something which 'looks' like this: if (Clipboard.ContainsImage()) { if (IsClipboardUpdated()) { LogData(); UpdateLastClipboardData(); } } This is how the rest of the methods look like: public void UpdateLastClipboardData() { // ... other updates LastClipboardImage = Clipboard.GetImage(); } // This is how I determine if there's a new image in the clipboard... public bool IsClipboardUpdated() { return (LastClipboardImage != Clipboard.GetImage()); } public void LogData() { Clipboard.GetImage().Save(ImagesLogFolder + "\\Image" + now_hours + "_" + now_mins + "_" + now_secs + ".jpg"); } The problem is: inside the update method, "LastClipboardImage != Clipboard.GetImage()" is always returning true! I even did the following inside the update method: Image img1 = Clipboard.GetImage(); Image img2 = Clipboard.GetImage(); Image img3 = img2; bool b1 = img1 == img2; // this returned false. WHY?? bool b2 = img3 == img2; // this returned true. Makes sense. Please help, the comparison isn't working... why?

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• Is it a good idea to use an integer column for storing US ZIP codes in a database?

  - by Yadyn

  From first glance, it would appear I have two basic choices for storing ZIP codes in a database table: Text (probably most common), i.e. char(5) or varchar(9) to support +4 extension Numeric, i.e. 32-bit integer Both would satisfy the requirements of the data, if we assume that there are no international concerns. In the past we've generally just gone the text route, but I was wondering if anyone does the opposite? Just from brief comparison it looks like the integer method has two clear advantages: It is, by means of its nature, automatically limited to numerics only (whereas without validation the text style could store letters and such which are not, to my knowledge, ever valid in a ZIP code). This doesn't mean we could/would/should forgo validating user input as normal, though! It takes less space, being 4 bytes (which should be plenty even for 9-digit ZIP codes) instead of 5 or 9 bytes. Also, it seems like it wouldn't hurt display output much. It is trivial to slap a ToString() on a numeric value, use simple string manipulation to insert a hyphen or space or whatever for the +4 extension, and use string formatting to restore leading zeroes. Is there anything that would discourage using int as a datatype for US-only ZIP codes?

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• Good way to identify similar images?

  - by Nick

  I've developed a simple and fast algorithm in PHP to compare images for similarity. Its fast (~40 per second for 800x600 images) to hash and a unoptimised search algorithm can go through 3,000 images in 22 mins comparing each one against the others (3/sec). The basic overview is you get a image, rescale it to 8x8 and then convert those pixels for HSV. The Hue, Saturation and Value are then truncated to 4 bits and it becomes one big hex string. Comparing images basically walks along two strings, and then adds the differences it finds. If the total number is below 64 then its the same image. Different images are usually around 600 - 800. Below 20 and extremely similar. Are there any improvements upon this model I can use? I havent looked at how relevant the different components (hue, saturation and value) are to the comparison. Hue is probably quite important but the others? To speed up searches I could probably split the 4 bits from each part in half, and put the most significant bits first so if they fail the check then the lsb doesnt need to be checked at all. I dont know a efficient way to store bits like that yet still allow them to be searched and compared easily. I've been using a dataset of 3,000 photos (mostly unique) and there havent been any false positives. Its completely immune to resizes and fairly resistant to brightness and contrast changes.

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• MinGW-gcc PCH not speeding up wxWidget build times. Is my setup correct?

  - by Victor T.

  Hi all, I've been building wxMSW 2.8.11 with the latest stable release of mingw-gcc 4.5.1 and I'm trying to see if the build could be sped up using precompiled headers. My initial attempts at this doesn't seem to work. I basically followed the given instructions here. I created a wxprec.h precompiled header with the following: g++ -O2 -mthreads -DHAVE_W32API_H -D__WXMSW__ -DNDEBUG -D_UNICODE -I..\..\lib\gcc_dll\mswu -I..\..\include -W -Wall -DWXBUILDING -I..\.. \src\tiff -I..\..\src\jpeg -I..\..\src\png -I..\..\src\zlib -I..\..\src \regex -I..\..\src\expat\lib -DwxUSE_BASE=1 -DWXMAKINGDLL -Wno-ctor- dtor-privacy ../../include/wx/wxprec.h That does successfully create a wxprec.h.gch that's about ~1.6meg in size. Now I proceed to build wxmsw using the follow make command from cmd.exe shell: mingw32-make -f makefile.gcc While, the build does succeed I noticed no speedup whatsoever then if pch wasn't used. To make sure gcc was actually using the pch I added -H in the config.gcc and did another rebuild. Indeed, the outputted include list does show a '!' next to the wxprec.h so gcc is supposely using it. What's the reason for pch not working? Did I setup the precompiled headers correctly or am I missing a step? Just for reference comparison, here's the compile times I get when building wxmsw 2.8.11 with the other compilers(visual studio 2010 and C++ Builder 2007). The time savings is pretty significant. | | release, pch | release, nopch | debug, nopch ------------------------------------------------------- | gcc451 | 8min 33sec | 8min 17sec | 8min 49sec | msc_1600 | 2min 23sec | 13min 11sec | -- | bcc593 | 0min 59sec | 2min 29sec | -- Thanks

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• Is .NET 4.0 just a show?

  - by Will Marcouiller

  I went to a presentation about the .NET Framework and Visual Studio 2010, last night. The topis were: ASP.NET 4 - Some of the new features of ASP.NET 4 More control over ClientID's in WebForms; Output Caching; ... // Some other stuff I don't really remember being more in framework and WinForms world. Entity Framework 2.0 (.NET 4.0) T4 Templates; Domain driven development; Data driven development; Contexts (edmx files); Some of real-world limitations of EF4 (projects with over 70 to 75 tables); Better POCO support, despite there are still these hidden EntityObject and StructuralObject, but used differently in comparison to EF 1.0 so that it doesn't take off your inheritance; Allows to easily choose how to persist the hierarchy into the underlying database; Code only (start working with EF4 directly from your code!); Design by Contract (DbC). The most interesting feature is, and only, as far as I'm concerned, all related to parallelism made easier. Which really works! No additional assembly references to add. In conclusion, I'm far from impressed about .NET Framework 4.0, apart that it makes some things easier to do. But when you're used to make it a way, it doesn't really change much, in my opinion. Is it me who cannot foresee what .NET 4.0 has to offer? What would you guys base your decision on to migrate to .NET 4.0, in a practical way?

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• How to "push" updates to individual cells in a (ASP.NET) web page table/grid?

  - by dommer

  I'm building something similar to a price comparison site. This will be developed in ASP.NET/WebForms/C#/.NET 3.5. The site will be used by the public, so I have no control over the client side - and the application isn't so central to their lives that they'll go out of their way to make it work. I want to have a table/grid that displays products in rows, vendors in columns, and prices in the cells. Price updates will be arriving (at the server) continuously, and I'd like to "push" any updates to the clients' browsers - ideally only updating what has changed. So, if Vendor A changes their price on Product B, I'd want to immediately update the relevant cell in all the browsers that are viewing this information. I don't want to use any browser plug-ins (e.g. Silverlight). Javascript is fine. What's the best approach to take? Presumably my options are: 1) have the client page continuously poll the server for updates, locate the correct cell and update it; or 2) have the server be able to send updates to all the open browser pages which are listening for these updates. The first one would seem the most plausible, but I don't want to constrain the assembled wisdom of the SO community. I'm happy to purchase any third party components (e.g. a grid) that might help with this. I already have the DevExpress grid/ajax components if they provide anything useful.

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• DB Design to store custom fields for a table

  - by Fazal

  Hi All, this question came up based on the responses I got for the question http://stackoverflow.com/questions/2785033/getting-wierd-issue-with-to-number-function-in-oracle As everyone suggested that storing Numeric values in VARCHAR2 columns is not a good practice (which I totally agree with), I am wondering about a basic Design choice our team has made and whether there are better way to design. Problem Statement : We Have many tables where we want to give certain number of custom fields. The number of required custom fields is known, but what kind of attribute is mapped to the column is available to the user E.g. I am putting down a hypothetical scenario below Say you have a laptop which stores 50 attribute values for every laptop record. Each laptop attributes are created by the some admin who creates the laptop. A user created a laptop product lets say lap1 with attributes String, String, numeric, numeric, String Second user created laptop lap2 with attributes String,numeric,String,String,numeric Currently there data in our design gets persisted as following Laptop Table Id Name field1 field2 field3 field4 field5 1 lap1 lappy lappy 12 13 lappy 2 lap2 lappy2 13 lappy2 lapp2 12 This example kind of simulates our requirement and our design Now here if somebody is lookinup records for lap2 table doing a comparison on field2, We need to apply TO_NUMBER. select * from laptop where name='lap2' and TO_NUMBER(field2) < 15 TO_NUMBER fails in some cases when query plan decides to first apply to_number instead of the other filter. QUESTION Is this a valid design? What are the other alternative ways to solve this problem One of our team mates suggested creating tables on the fly for such cases. Is that a good idea How do popular ORM tools give custom fields or flex fields handling? I hope I was able to make sense in the question. Sorry for such a long text.. This causes us to use TO_NUMBER when queryio

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