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• What is the general feeling about reflection extensions in std::type_info?

  - by Evan Teran

  I've noticed that reflection is one feature that developers from other languages find very lacking in c++. For certain applications I can really see why! It is so much easier to write things like an IDE's auto-complete if you had reflection. And certainly serialization APIs would be a world easier if we had it. On the other side, one of the main tenets of c++ is don't pay for what you don't use. Which makes complete sense. That's something I love about c++. But it occurred to me there could be a compromise. Why don't compilers add extensions to the std::type_info structure? There would be no runtime overhead. The binary could end up being larger, but this could be a simple compiler switch to enable/disable and to be honest, if you are really concerned about the space savings, you'll likely disable exceptions and RTTI anyway. Some people cite issues with templates, but the compiler happily generates std::type_info structures for template types already. I can imagine a g++ switch like -fenable-typeinfo-reflection which could become very popular (and mainstream libs like boost/Qt/etc could easily have a check to generate code which uses it if there, in which case the end user would benefit with no more cost than flipping a switch). I don't find this unreasonable since large portable libraries like this already depend on compiler extensions. So why isn't this more common? I imagine that I'm missing something, what are the technical issues with this?

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• How do I randomly fill an array in Java?

  - by Kat

  I'm writing a program that creates a 2D array from a integer n. I then have to fill the array with values from 1 to the n*n array size and check to see if it is a magic square. The way I am doing it now fills the array in order from 1 to n*n array size. How can I make that random? My code: System.out.print("Enter an whole number: "); int n = scan.nextInt(); int [][] magic = new int [n][n]; for (int row = 0; row < magic.length; row++) { for(int col = 0; col < magic[row].length; col++) magic[row][col] = ((row * n) + 1) + col; }

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• PHP profiling with microtime(): Negative time?

  - by Boldewyn

  For a very simple profiling I use microtime() like this: $now = microtime(); for (...) { // do something echo microtime() - $now; $now = microtime(); } Now, the output of the echo line seems completely random, that is, I expected fluctuations, but I don't expected negative numbers showing up. However, a typical result contains ~ 1/3 negative numbers. I confirmed this on Solaris (PHP 5.0.x) and WinVista (PHP 5.2.3). What the heck is going on here? Have I invented accidently a time machine?

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• SQL with Regular Expressions vs Indexes with Logical Merging Functions

  - by geeko

  Hello Lads, I am trying to develop a complex textual search engine. I have thousands of textual pages from many books. I need to search pages that contain specified complex logical criterias. These criterias can contain virtually any compination of the following: A: Full words. B: Word roots (semilar to stems; i.e. all words with certain key letters). C: Word templates (in some languages are filled in certain templates to form various part of speech such as adjactives, past/present verbs...). D: Logical connectives: AND/OR/XOR/NOT/IF/IFF and parentheses to state priorities. Now, would it be faster to have the pages' full text in database (not indexed) and search though them all using SQL and Regular Expressions ? Or would it be better to construct indexes of word/root/template-page-location tuples. Hence, we can boost searching for individual words/roots/templates. However, it gets tricky as we interdouce logical connectives into our query. I thought of doing the following steps in such cases: 1: Seperately search for each individual words/roots/templates in the specified query. 2: On priority bases, we merge two result lists (from step 1) at a time depedning on the logical connective For example, if we are searching for "he AND (is OR was)": 1: We shall search for "he", "is" and "was" seperately and get result lists for each word. 2: Merge the result lists of "is" and "was" using the merging function OR-MERGE 3: Merge the merged result list from the OR-MERGE function with the one of "he" using the merging function AND-MERGE The result of step 3 is then returned as the result of the specified query. What do you think gurues ? Which is faster ? Any better ideas ? Thank you all in advance.

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• Prim's MST algorithm implementation with Java

  - by user1290164

  I'm trying to write a program that'll find the MST of a given undirected weighted graph with Kruskal's and Prim's algorithms. I've successfully implemented Kruskal's algorithm in the program, but I'm having trouble with Prim's. To be more precise, I can't figure out how to actually build the Prim function so that it'll iterate through all the vertices in the graph. I'm getting some IndexOutOfBoundsException errors during program execution. I'm not sure how much information is needed for others to get the idea of what I have done so far, but hopefully there won't be too much useless information. This is what I have so far: I have a Graph, Edge and a Vertex class. Vertex class mostly just an information storage that contains the name (number) of the vertex. Edge class can create a new Edge that has gets parameters (Vertex start, Vertex end, int edgeWeight). The class has methods to return the usual info like start vertex, end vertex and the weight. Graph class reads data from a text file and adds new Edges to an ArrayList. The text file also tells us how many vertecis the graph has, and that gets stored too. In the Graph class, I have a Prim() -method that's supposed to calculate the MST: public ArrayList<Edge> Prim(Graph G) { ArrayList<Edge> edges = G.graph; // Copies the ArrayList with all edges in it. ArrayList<Edge> MST = new ArrayList<Edge>(); Random rnd = new Random(); Vertex startingVertex = edges.get(rnd.nextInt(G.returnVertexCount())).returnStartingVertex(); // This is just to randomize the starting vertex. // This is supposed to be the main loop to find the MST, but this is probably horribly wrong.. while (MST.size() < returnVertexCount()) { Edge e = findClosestNeighbour(startingVertex); MST.add(e); visited.add(e.returnStartingVertex()); visited.add(e.returnEndingVertex()); edges.remove(e); } return MST; } The method findClosesNeighbour() looks like this: public Edge findClosestNeighbour(Vertex v) { ArrayList<Edge> neighbours = new ArrayList<Edge>(); ArrayList<Edge> edges = graph; for (int i = 0; i < edges.size() -1; ++i) { if (edges.get(i).endPoint() == s.returnVertexID() && !visited(edges.get(i).returnEndingVertex())) { neighbours.add(edges.get(i)); } } return neighbours.get(0); // This is the minimum weight edge in the list. } ArrayList<Vertex> visited and ArrayList<Edges> graph get constructed when creating a new graph. Visited() -method is simply a boolean check to see if ArrayList visited contains the Vertex we're thinking about moving to. I tested the findClosestNeighbour() independantly and it seemed to be working but if someone finds something wrong with it then that feedback is welcome also. Mainly though as I mentioned my problem is with actually building the main loop in the Prim() -method, and if there's any additional info needed I'm happy to provide it. Thank you. Edit: To clarify what my train of thought with the Prim() method is. What I want to do is first randomize the starting point in the graph. After that, I will find the closest neighbor to that starting point. Then we'll add the edge connecting those two points to the MST, and also add the vertices to the visited list for checking later, so that we won't form any loops in the graph. Here's the error that gets thrown: Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0 at java.util.ArrayList.rangeCheck(Unknown Source) at java.util.ArrayList.get(Unknown Source) at Graph.findClosestNeighbour(graph.java:203) at Graph.Prim(graph.java:179) at MST.main(MST.java:49) Line 203: return neighbour.get(0); in findClosestNeighbour() Line 179: Edge e = findClosestNeighbour(startingVertex); in Prim()

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• How do I compute the approximate entropy of a bit string?

  - by dreeves

  Is there a standard way to do this? Googling -- "approximate entropy" bits -- uncovers multiple academic papers but I'd like to just find a chunk of pseudocode defining the approximate entropy for a given bit string of arbitrary length. (In case this is easier said than done and it depends on the application, my application involves 16,320 bits of encrypted data (cyphertext). But encrypted as a puzzle and not meant to be impossible to crack. I thought I'd first check the entropy but couldn't easily find a good definition of such. So it seemed like a question that ought to be on StackOverflow! Ideas for where to begin with de-cyphering 16k random-seeming bits are also welcome...) See also this related question: http://stackoverflow.com/questions/510412/what-is-the-computer-science-definition-of-entropy

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• Why is this the output of this python program?

  - by Andrew Moffat

  Someone from #python suggested that it's searching for module "herpaderp" and finding all the ones listed as its searching. If this is the case, why doesn't it list every module on my system before raising ImportError? Can someone shed some light on what's happening here? import sys class TempLoader(object): def __init__(self, path_entry): if path_entry == 'test': return raise ImportError def find_module(self, fullname, path=None): print fullname, path return None sys.path.insert(0, 'test') sys.path_hooks.append(TempLoader) import herpaderp output: 16:00:55 $> python wtf.py herpaderp None apport None subprocess None traceback None pickle None struct None re None sre_compile None sre_parse None sre_constants None org None tempfile None random None __future__ None urllib None string None socket None _ssl None urlparse None collections None keyword None ssl None textwrap None base64 None fnmatch None glob None atexit None xml None _xmlplus None copy None org None pyexpat None problem_report None gzip None email None quopri None uu None unittest None ConfigParser None shutil None apt None apt_pkg None gettext None locale None functools None httplib None mimetools None rfc822 None urllib2 None hashlib None _hashlib None bisect None Traceback (most recent call last): File "wtf.py", line 14, in <module> import herpaderp ImportError: No module named herpaderp

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• Embedding a YouTube Video Based on a PHP Variable

  - by jeffpm

  I have a website that I am creating for a class project. The website shows information about bands (which is stored in a mysql database). I am trying to spruce up the site a bit, and I would like to embed a YouTube video based on the band's name. Say, for instance, I have "Led Zeppelin" stored in my database. How can I take a PHP variable containing "Led Zeppelin", search YouTube using that variable, find a random video, and then embed that in the website? From the research I've done, it seems you can only embed YouTube videos if you know the exact address of the video. Thanks!

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• Essential skills of a Data Scientist

  - by harshsinghal

  I would like to know more about the relevant skills in the arsenal of a Data Scientist, and with new technologies coming in every day, how one picks and chooses the essentials. A few ideas germane to this discussion: Knowing SQL and the use of a DB such as MySQL, PostgreSQL was great till the advent of NoSql and non-relational databases. MongoDB, CouchDB etc. are becoming popular to work with web-scale data. Knowing a stats tool like R is enough for analysis, but to create applications one may need to add Java, Python, and such others to the list. Data now comes in the form of text, urls, multi-media to name a few, and there are different paradigms associated with their manipulation. What about cluster computing, parallel computing, the cloud, Amazon EC2, Hadoop ? OLS Regression now has Artificial Neural Networks, Random Forests and other relatively exotic machine learning/data mining algos. for company Thoughts?

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• How do quickly search through a .csv file in Python

  - by Baldur

  I'm reading a 6 million entry .csv file with Python, and I want to be able to search through this file for a particular entry. Are there any tricks to search the entire file? Should you read the whole thing into a dictionary or should you perform a search every time? I tried loading it into a dictionary but that took ages so I'm currently searching through the whole file every time which seems wasteful. Could I possibly utilize that the list is alphabetically ordered? (e.g. if the search word starts with "b" I only search from the line that includes the first word beginning with "b" to the line that includes the last word beginning with "b") I'm using import csv. (a side question: it is possible to make csv go to a specific line in the file? I want to make the program start at a random line) Edit: I already have a copy of the list as an .sql file as well, how could I implement that into Python?

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• Setting a VCProject property to default

  - by Ofek Shilon

  I'm trying some VS2005 IDE macros to modify a large amount of projects (~80) within a solution. Some of the properties I wish to set do expose a programmatic interface to 'default', but many others do not. Is there a generic way to set such properties to their default? (eventually meaning erasing them from the .vcproj file) Simplified example, setting some random properties: Sub SetSomeProps() Dim prj As VCProject Dim cfg As VCConfiguration Dim toolCompiler As VCCLCompilerTool Dim toolLinker As VCLinkerTool Dim EnvPrj As EnvDTE.Project For Each EnvPrj In DTE.Solution.Projects prj = EnvPrj.Object cfg = prj.Configurations.Item(1) toolLinker = cfg.Tools("VCLinkerTool") If toolLinker IsNot Nothing Then ' Some tool props that expose a *default* interface' toolLinker.EnableCOMDATFolding = optFoldingType.optFoldingDefault toolLinker.OptimizeReferences = optRefType.optReferencesDefault toolLinker.OptimizeForWindows98 = optWin98Type.optWin98Default End If toolCompiler = cfg.Tools("VCCLCompilerTool") If toolCompiler IsNot Nothing Then ' How to set it to default? (*erase* the property from the .vcproj)' toolCompiler.CallingConvention = callingConventionOption.callConventionCDecl toolCompiler.WholeProgramOptimization = False toolCompiler.Detect64BitPortabilityProblems = False End If Next End Sub Any advice would be appreciated.

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• Where to find great proxy servers for testing GeoIP services?

  - by Andreas

  We would like to test a GeoIP-Service. Therefore we need to go to the site with an IP from another country. There are a lot of free proxy lists like http://nntime.com/proxy-country/ The problem with them is, that only the CoDeen-Proxies are working. But with CoDeen you can't select your country of origin (the same as with TOR). You get redirected to a random proxy in the network. Where to find good proxy server for testing the GeoIP Services? Free proxy servers would be great, but if they cost something small that doesn't matter.

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• How do you diagnose a 500 error on Heroku when there is no error message in the logs?

  - by lala

  I have a Rails app on Heroku that is serving 500 errors at random intervals. Web pages will display "Internal server error" in plain text, instead of the usual "We're sorry. Something went wrong." page. When I refresh the page, it works fine. The logs don't show me an error message, just » 14:20:34.107 2013-10-11 12:20:33.763690+00:00 heroku router - - at=info method=HEAD path=/ host=www.mydomain.com fwd="184.73.237.85/ec2-184-73-237-85.compute-1.amazonaws.com" dyno=web.1 connect=1ms service=63ms status=200 bytes=0 » 14:21:03.957 2013-10-11 12:21:03.561867+00:00 heroku router - - at=info method=GET path=/ host=www.mydomain.com fwd="50.112.95.211/ec2-50-112-95-211.us-west-2.compute.amazonaws.com" dyno=web.1 connect=0ms service=1ms status=500 bytes=21 Support has told me to look at request queuing in New Relic, but New Relic only shows a big red mark saying the server is down (even though the site works fine when refreshed). With no error messages, I'm at a loss for how to diagnose this issue.

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• prevent multiple login with same login credentials in php

  - by shinod

  My website has premium videos, for which users have to pay to watch it. I am sending a random user name and password to the user's email id when the payment is completed. Then I want to assure no more than one user use that login credentials simultaneously. For that I use a login_status column in database table with login credentials and change it to 1 when one user login and change to 0 when user log out. But the problem is, if the user close browser or network connection loss may happened will not update database. Then login_will be 1 undefinitely and no one can use that login credentials again. Is there any idea to accomplish my task?

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• WPF ListView.CurrentChanged too fast for binding

  - by matt

  My case: MVVM ListView+Details(custom UserControl) List bound to MV.Items (IsSynchronizedWithCurrent=true) Details bound to MV.Items.Current MV.Items.Count == 100 about 0.2sec to read details (lazy mode) When I hold the down arrow on the list, very strange things happen: list items order change current changes in the random order CPU usage drastically increments and eventually all hangs. I've read some post that one should start the timer or run handler in the background, but I am not able to do that, since all the binding WPF does for me. Is there some way to instruct the binding in my DetailsControl, to wait a while before accepting CurrentItem? Or should I just resign from the clean solution and write custom code in my MV to handle that?

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• Cross-platform and language (de)serialization

  - by fwgx

  I'm looking for a way to serialize a bunch of C++ structs in the most convenient way so that the serialization is portable across C++ and Java (at a minimum) and across 32bit/64bit, big/little endian platforms. The structures to be serialized just contain data, i.e. they're pure data objects with no state or behavior. The idea being that we serialize the structs into an octet blob that we can store in a database "generically" and be read out later on. Thus avoiding changing the database whenever a struct changes and also avoiding assigning each data member to a field - i.e. we only want one table to hold everything "generically" as a binary blob. This should make less work for developers and require less changes when structures change. I've looked at boost.serialize but don't think there's a way to enable compatibility with Java. And likewise for inheriting Serializable in Java. If there is a way to do it by starting with an IDL file that would be best as we already have IDL files that describe the structures. Cheers in advance!

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• Compact a given array problem

  - by Bragaadeesh

  Dont know whether this is a duplicate, but this was an interview question asked to me. Given an array of random numbers and -1 placed inbetween, I have to compact the array meaning all the -1s are to be replaced and the final output should be the last valid index with the fresh array. For example. Input: 3 4 -1 -1 -1 5 8 -1 8 Output: 3 4 5 8 8 5 8 -1 8 and last valid index is 4 Input: -1 -1 -1 -1 -1 2 Output: 2 -1 -1 -1 -1 2 and last valid index is 0 Input: -1 -1 -1 3 3 3 Output: 3 3 3 3 3 3 and last valid index is 2 You should not swap the values just the last valid index along with the array is enough to decipher the non negative values.

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• How do I get the name of the newest file via the Terminal?

  - by Alec

  I'm trying to create a macro for Keyboard Maestro for OS X doing the following: Get name of newest file in a directory on my disk based on date created; Paste the text "newest file: " plus the name of the newest file. One of its options is to "Execute a shell script", so I thought that would do it for 1. After Googling around a bit I came up with this: cd /path/to/directory/ ls -t | head -n1 This sorts it right, and returns the first filename. However, it also seems to includes a line break, which I do not want. As for 2: I can output the text "newest file: " with a different action in the app, and paste the filename behind that. But I'm wondering if you can't return "random text" + the outcome of the ls command. So my question is: can I do this only using the ls command? And how do I get just the name of the latest file without any linebreaks or returns?

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• NSSortDescriptor for NSFetchRequest sorting unexpectedly

  - by E-Madd

  My entity has a property (sortOrder) that is of the type Decimal(NSDecimalNumber) but when I execute a fetch request using that property as a key, I get back results in a seemingly random order. If I output the value of the property I get really strange values until I get it's intValue. Example: The first run produces this result. The first value is the raw value of the property. The second is the intValue, the actual value of the property when I created the object - or at least I thought. 85438160 10 74691424 20 Second run... 85333744 10 85339168 20 Third... 85263696 20 85269568 10 What the hell?

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• A database of questions with unambiguous numeric answers.

  - by dreeves

  I (and co-hackers) are building a sort of trivia game inspired by this blog post: http://messymatters.com/calibration. The idea is to give confidence intervals and learn how to be calibrated (when you're "90% sure" you should be right 90% of the time). We're thus looking for, ideally, thousands of questions with unambiguous numerical answers. Also, they shouldn't be too boring. There are a lot of random statistics out there -- eg, enclosed water area in different countries -- that would make the game mind-numbing. Things like release dates of classic movies are more interesting (to most people). Other interesting ones we've found include Olympic records, median incomes for different professions, dates of famous inventions, and celebrity ages. Scraping things like above, by the way, was my reason for asking this question: http://stackoverflow.com/questions/2611418/scrape-html-tables So, if you know of other sources of interesting numerical facts (in a parsable form) I'm eager for pointers to them. Thanks!

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• complex mysql query problem

  - by Scarface

  Hey guys I have a query that selects data and organizes but not in the correct order. What I want to do is select all the comments for a user in that week and sort it by each topic, then sort the cluster by the latest timestamp of each comment in their respective cluster. My current query selects the right data, but in seemingly random order. Does anyone have any ideas? select * from ( SELECT topic.topic_title, topic.topic_id FROM comments JOIN topic ON topic.topic_id=comments.topic_id WHERE comments.user='$user' AND comments.timestamp>$week order by comments.timestamp desc) derived_table group by topic_id

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• Truncate a HTML formatted text.

  - by marharépa

  Hi there! I've got a variable which is formatted with random HTML code. I call it to {$text} and i truncate it. The value is for example: <div>Lorem <i>ipsum <b>dolor <span>sit </span>amet</b>, con</i> elit.</div> If i truncate the text's first ~30 letters, I'll get this: <div>Lorem <i>ipsum <b>dolor <span>sit The problem is, I can't close the elements. So, I need a script, which check the <*> elements in the code (where * could be anything), and if it dont have a close tag, close 'em. Please help me in this. Thanks.

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• Thread safe lazy contruction of a singleton in C++

  - by pauldoo

  Is there a way to implement a singleton object in C++ that is: Lazily constructed in a thread safe manner (two threads might simultaneously be the first user of the singleton - it should still only be constructed once). Doesn't rely on static variables being constructed beforehand (so the singleton object is itself safe to use during the construction of static variables). (I don't know my C++ well enough, but is it the case that integral and constant static variables are initialized before any code is executed (ie, even before static constructors are executed - their values may already be "initialized" in the program image)? If so - perhaps this can be exploited to implement a singleton mutex - which can in turn be used to guard the creation of the real singleton..) Excellent, it seems that I have a couple of good answers now (shame I can't mark 2 or 3 as being the answer). There appears to be two broad solutions: Use static initialisation (as opposed to dynamic initialisation) of a POD static varible, and implementing my own mutex with that using the builtin atomic instructions. This was the type of solution I was hinting at in my question, and I believe I knew already. Use some other library function like pthread_once or boost::call_once. These I certainly didn't know about - and am very grateful for the answers posted.

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• What is the right approach when using STL container for median calculation?

  - by sharkin

  Let's say I need to retrieve the median from a sequence of 1000000 random numeric values. If using anything but STL::list, I have no (built-in) way to sort sequence for median calculation. If using STL::list, I can't randomly access values to retrieve middle (median) of sorted sequence. Is it better to implement sorting myself and go with e.g. STL::vector, or is it better to use STL::list and use STL::list::iterator to for-loop-walk to the median value? The latter seems less overheadish, but also feels more ugly.. Or are there more and better alternatives for me?

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• Throw of a dice in Java

  - by Arkapravo

  The throw of a dice is a popular program in Java, public class Dice { /* This program simulates rolling a dice */ public static void main(String[] args) { int dice; // The number on the dice. dice = (int) (Math.random() * 6 + 1); System.out.println (dice); } } What I wish to do is make it repeat, 500 times. I have not been able to put this program into a loop of 500. I usually program in Python, thus I guess my Java has rusted ! Any help is most welcome !

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