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• Find MySQL entries with same set of column B values for their common column A value

  - by nnsd44g

  I have: +----+------+------+ | id | A | B | +----+------+------+ | 1 | 1 | 1 | < | 2 | 1 | 2 | < | 3 | 2 | 2 | | 4 | 2 | 3 | | 5 | 3 | 1 | < | 6 | 3 | 2 | < | 7 | 4 | 4 | | 8 | 4 | 5 | +----+------+------+ I need to select the entries that have the same set of B values for their common A value. So, in this case, I need ids 1, 2 and 5, 6 because in those cases the sequence of B values is 1, 2. Is this possible? Thanks!

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• C++ performance, optimizing compiler, empty function in .cpp

  - by Dodo

  I've a very basic class, name it Basic, used in nearly all other files in a bigger project. In some cases, there needs to be debug output, but in release mode, this should not be enabled and be a NOOP. Currently there is a define in the header, which switches a makro on or off, depending on the setting. So this is definetely a NOOP, when switched off. I'm wondering, if I have the following code, if a compiler (MSVS / gcc) is able to optimize out the function call, so that it is again a NOOP. (By doing that, the switch could be in the .cpp and switching will be much faster, compile/link time wise). --Header-- void printDebug(const Basic* p); class Basic { Basic() { simpleSetupCode; // this should be a NOOP in release, // but constructor could be inlined printDebug(this); } }; --Source-- // PRINT_DEBUG defined somewhere else or here #if PRINT_DEBUG void printDebug(const Basic* p) { // Lengthy debug print } #else void printDebug(const Basic* p) {} #endif

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• How much faster are register based architectures than stack architectures?

  - by drozzy

  Studying compilers course, I am left wondering why use registers at all. It is often the case that the caller or callee must save the register value and then restore it. In a way they always end up using the stack anyway. Is creating additional complexity by using registers really worth it? Excuse my ignorance. Update: Please, I know that registers are faster than RAM and other types of cache. My main concern is that one has to "save" the value that is in the register and the "restore" it to. In both cases we are accessing some kind of cache. Would it not be better to use cache in the first place?

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• Style question about existing piece of code (C/C++)

  - by Leif Ericson

  I just hope the following doesn't seem to you like redundant jabber :) Anyway, there is that: for (p = fmt; *p; p++) { if (*p != '%') { putchar(*p); continue; } switch (*++p) { /* Some cases here */ ... } } And I wondered why the writer (Kernighan / Ritchie) used the continue in the if statement. I thought it was for the mere reason that he deemed it would be more elegant than indenting the whole switch under an else statement, what do you think?

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• Ignoring "Content is not allowed in trailing section" SAXException

  - by Paul J. Lucas

  I'm using Java's DocumentBuilder.parse(InputStream) to parse an XML document. Occasionally, I get malformed XML documents in that there is extra junk after the final > that causes a SAXException: Content is not allowed in trailing section. (In the cases I've seen, the junk is simply one or more null bytes.) I don't care what's after the final >. Is there an easy way to parse an entire XML document in Java and have it ignore any trailing junk? Note that by "ignore" I don't simply mean to catch and ignore the exception: I mean to ignore the trailing junk, throw no exception, and to return the Document object since the XML up to an including the final > is valid.

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• Best practices: displaying text that was input via multi-line text box

  - by chris

  I have a multi-line text box. When users simply type away, the text box wraps the text, and it's saved as a single line. It's also possible that users may enter line breaks, for example when entering a "bulleted" lists like: Here are some suggestions: - fix this - remove that - and another thing Now, the problem occurs when I try to display the value of this field. In order to preserve the formatting, I currently wrap the presentation in <pre> - this works to preserve user-supplied breaks, but when there's a lot of text saved as a single line, it displays the whole text block as single line, resulting in horizontal scrolling being needed to see everything. Is there a graceful way to handle both of these cases?

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• my output parameters are always null when i use BeginExecuteNonQuery

  - by CharlesO

  I have a stored procedure that returns a varchar(160) as an output parameter of a stored procedure. Everything works fine when i use ExecuteNonQuery, i always get back the expected value. However, once i switch to use BeginExecuteNonQuery, i get a null value for the output. I am using connString + "Asynchronous Processing=true;" in both cases. Sadly the BeginExecuteNonQuery is about 1.5 times faster in my case...but i really need the output parameter. Thanks!

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• Get averages from pre-aggregated reports in mongodb

  - by Chris

  I've got a database with pre-aggregated metrics similar to the one outlined in this use case: http://docs.mongodb.org/manual/use-cases/pre-aggregated-reports/ I have a daily collection with a subdocument for hour and minute metrics, and a 'metadata.date' entry for midnight on the day it represents. I also have a monthly collection with a day subdocument for each day. If I want to get an average of a metric over the past eight or so days how can I do that with the aggregation framework? Is the aggregation framework not the right tool for this since it's already pre-aggregated?

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• Best choice for off-site backup: dd vs tar

  - by plok

  I have two 1TB single-partition hard disks configured as RAID1, of which I would like to make an off-site backup on a third disk, which I am still to buy. The idea is to store the backup at a relative's house, considerably far away from my place, in the hope that all the information will be safe in the case of a global thermonuclear apocalypse. Of course, this backup would be well encrypted. What I still have to decide is whether I am going to simply tar the entire partition or, instead, use dd to create an image of the disks. Is there any non-trivial difference between these two approaches that I could be overlooking? This off-site backup would be updated no more than two or three times a year, in the best of the cases, so performance should not be a factor to be pondered at all. What, and why, would you use if you were me? dd, tar, or a third option?

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• Setting baseurl in cakephp

  - by Aruna

  Hi, I am working on an appliication which is running in cakephp and i am using ajax query inbetween. In all the cases for all the ajax post i have used the url as var ht = $.ajax({ type: "GET", url: "http://172.20.52.99/FormBuilder/index.php/forms/viewChoices/"+attribute_id, async: false }).responseText; var myObject = eval('(' + ht + ')'); is there any way in cakephp where i can give my base url as http://172.20.52.99/FormBuilder/index.php/ and to call the baseurl in all the places i want. Please give some suggestions . Thank you..

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• Jython: Is there any difference between adding to sys.path vs passing -D?

  - by trinth

  I have a python application that is trying to load some Java libraries (specifically Axis2 web services). When I add the necessary jars in Eclipse via PyDev Project Source Folders, everything seems to work fine. However, I want to be able to do this at run time by adding to sys.path, but then my application doesn't seem to work. In both cases I can load the jars just fine, but something must be different for there to be different results. My question is, is there a difference between adding jars via the sys.path at run time with sys.path.append() versus passing -D to the jython interpreter?

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• Is it guaranteed that new Integer(i) == i in Java?

  - by polygenelubricants

  Consider the following snippet: int i = 99999999; byte b = 99; short s = 9999; Integer ii = Integer.valueOf(9); // should be within cache System.out.println(new Integer(i) == i); // "true" System.out.println(new Integer(b) == b); // "true" System.out.println(new Integer(s) == s); // "true" System.out.println(new Integer(ii) == ii); // "false" It's obvious why the last line will ALWAYS prints "false": we're using == reference identity comparison, and a new object will NEVER be == to an already existing object. The question is about the first 3 lines: are those comparisons guaranteed to be on the primitive int, with the Integer auto-unboxed? Are there cases where the primitive would be auto-boxed instead, and reference identity comparisons are performed? (which would all then be false!)

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• Access static constant variable from multiple threads in C

  - by user325519

  I have some experience with multithread programming under Linux (C/C++ & POSIX threads), however most obvious cases are sometimes very complicated. I have several static constant variables (global and function local) in my code, can I access them simultaneously from multiple threads without using mutexes? Because I don't modify them it should be ok, but it's always better to ask. I have to do heavy speed optimization, so even as fast operations as mutex lock/unlock are quite expensive for me, especially because my application is going to access these variables form long loops.

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• Is it possible to retrieve only a single property from a CSS class?

  - by werner5471

  Example CSS File: .testClass { color: black; background: red; } Now in an HTML file, I would like to have something like <span class="testClass:color">Text in black but without red background</span> to only apply the color property of that class. Is there a way to do this? The purpose behind it (for people asking themselves "Why the hell would he want that, that's not clean CSS usage!") is that I use jQuery UI themes, and I would like the entire page to fit a theme upon change. As not all kinds of elements (e.g. the color of a link) are covered by those themes, in those cases I would like to "steal" the color property (but not more) of some other CSS class of the jQuery UI theme. If there is another way to do this, of course I'm glad to hear it as well!

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• Handling the distinction between undefined- and null-parameters in JavaScript

  - by Jakob

  I know very well that null and undefined are distinct in JavaScript. However, I can't seem to decide whether or not use that fact when my own functions are passed one of those as its argument. Or, expressed in a different way, should myFoo(undefined) return the same thing as myFoo(null) or is everything fine if it doesn't? Or, in yet another case, since myBar(1, 2, 3) is the same thing as myBar(1, 2, 3, undefined, undefined), should myBar(1, 2, 3, null, null) return the same thing as myBar(1, 2, 3)? I feel that there's potential for confusion in both cases and that a library should probably follow a convention when handling null/undefined. I'm not really asking for personal opinions (so please express those as comments rather than answers). I'm asking if anyone knows if there is a best practice that one should stick to when it comes to handling this distinction. References to external sources are very welcome!

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• Using function arguments as local variables

  - by Rubys

  Something like this (yes, this doesn't deal with some edge cases - that's not the point): int CountDigits(int num) { int count = 1; while (num >= 10) { count++; num /= 10; } return count; } What's your opinion about this? That is, using function arguments as local variables. Both are placed on the stack, and pretty much identical performance wise, I'm wondering about the best-practices aspects of this. I feel like an idiot when I add an additional and quite redundant line to that function consisting of int numCopy = num, however it does bug me. What do you think? Should this be avoided?

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• Use currently logged-in user in query

  - by Degan

  I am using VisualWebDeveloperExpress2008 with Access as the membership provider. I have some cases where I want users to edit their own data. This would involve a query where the UserId should equal the UserID of the user who is using the site. I am expecting to use WHERE UserId = ?, but I have not found out where to direct "?". The IDE gives several choices, but I am uncertain which to choose. This, while it looks promising does not work: <SelectParameters> <asp:ProfileParameter Name="UserID" PropertyName="UserId" Type="Int32" /> </SelectParameters> What is best to use for the Select Parameter?

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• Improving the performance of an nHibernate Data Access Layer.

  - by Amitabh

  I am working on improving the performance of DataAccess Layer of an existing Asp.Net Web Application. The scenerios are. Its a web based application in Asp.Net. DataAccess layer is built using NHibernate 1.2 and exposed as WCF Service. The Entity class is marked with DataContract. Lazy loading is not used and because of the eager-fetching of the relations there is huge no of database objects are loaded in the memory. No of hits to the database is also high. For example I profiled the application using NHProfiler and there were about 50+ sql calls to load one of the Entity object using the primary key. I also can not change code much as its an existing live application with no NUnit test cases at all. Please can I get some suggestions here?

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• Why is super.super.method(); not allowed in Java?

  - by Tim Büthe

  I read this question and thought that would easily be solved (not that it isn't solvable without) if one could write: @Override public String toString() { return super.super.toString(); } I'm not sure if it is useful in many cases, but I wonder why it isn't and if something like this exists in other languages. What do you guys think? EDIT: To clarify: yes I know, that's impossible to at to Java and I don't really miss it. This is nothing I expected to work and was surprised getting a compiler error. I just had the idea and like to discuss it.

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• Unboxing object containing a value which is known to be assignable to an integer variable

  - by Wim Coenen

  If I have an object instance and I know it is actually a boxed integer, then I can simply cast it back to int like this: object o = GetSomethingByName("foo"); int i = (int)o; However, I don't actually know that the value is an integer. I only know that it can be assigned to an integer. For example, it could be a byte, and the above code would throw InvalidCastException in that case. Instead I would have to do this: object o = GetSomethingByName("foo"); int i = (int)(byte)o; The value could also be a short, or something else which can be assigned to an int. How do I generalize my code to handle all those cases (without handling each possibility separately)?

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• Start SharePoint workflow only with new file versions

  - by NeiOliver

  I am trying to create a workflow to send an e-mail whenever a new version of a file is uploaded to a Document Library. The Document Library has lots of fields that, if updated, will create a new version of the ListItem, but I don't want to start the workflow for this cases. Only when a new version of the document is uploaded (including the first version) I want the workflow started. My document library does not need approval, only major versions are enabled and it does not need to checkout files before editing. Is there a way of doing this, even programmatically?

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• Any valid use of goto in PHP?

  - by nikic

  I know, there are other questions about the goto statement introduced in PHP 5.3. But I couldn't find any decent answer in there, all were of the type "last resort", "xkcd", "evil", "bad", "EVIL!!!". But no valid example. Only statements that there aren't any uses. Or statements that there are some rare use cases (again, without examples). So, the question is: "Which are the valid uses of goto in PHP". Answers for "Is goto evil" are not welcome and will get downvoted. Thanks :) Or does somebody have a link to an RFC where the decision is explained - I couldn't find one.

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• how can an application use port 80/HTTP without conflicting with browsers?

  - by John

  If I understand right, applications sometimes use HTTP to send messages, since using other ports is liable to cause firewall problems. But how does that work without conflicting with other applications such as web-browsers? In fact how do multiple browsers running at once not conflict? Do they all monitor the port and get notified... can you share a port in this way? I have a feeling this is a dumb question, but not something I ever thought of before, and in other cases I've seen problems when 2 apps are configured to use the same port.

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• How to print size_t variable portably?

  - by ArunSaha

  I have a variable of type size_t, and I want to print it using printf(). What format specifier do I use to print it portably? In 32-bit machine, %u seems right. I compiled with g++ -g -W -Wall -Werror -ansi -pedantic, and there was no warning. But when I compile that code in 64-bit machine, it produces warning. size_t x = <something>; printf( "size = %u\n", x ); warning: format '%u' expects type 'unsigned int', but argument 2 has type 'long unsigned int' The warning goes away, as expected, if I change that to %lu. The question is, how can I write the code, so that it compiles warning free on both 32- and 64- bit machines? Edit: I guess one answer might be to "cast" the variable into an unsigned long, and print using %lu. That would work in both cases. I am looking if there is any other idea. (C, C++)

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• How to Audit Database Activity without Performance and Scalability Issues?

  - by GotoError

  I have a need to do auditing all database activity regardless of whether it came from application or someone issuing some sql via other means. So the auditing must be done at the database level. The database in question is Oracle. I looked at doing it via Triggers and also via something called Fine Grained Auditing that Oracle provides. In both cases, we turned on auditing on specific tables and specific columns. However, we found that Performance really sucks when we use either of these methods. Since auditing is an absolute must due to regulations placed around data privacy, I am wondering what is best way to do this without significant performance degradations. If someone has Oracle specific experience with this, it will be helpful but if not just general practices around database activity auditing will be okay as well.

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