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• Why open source it? And how to get real involvement?

  - by donpal

  For me the main goal of open sourcing something is collaboration. If the most that other developers are going to do is take it and use it and report bugs to me, then I might as well close source it. Closed source provides me with all that. I was recently looking at a small javascript library (or more like a plugin, 1000 lines of code) that's actually quite popular. There were some bugs in it because new browsers and browser versions get released everyday and these bugs just pop up as a result. What bothered me is that these bugs would actually be quite easy to fix by even intermediate javascript developers, but for an entire month no one stepped up to fix the bug and submit the fixed version. The original author was apparently busy for that month, but that's the point of open sourcing your code: so that others can use it and help themselves AND the project if they can. So this makes me doubt the promise of open source. If people aren't working on it too, I might as well close source my new projects. And how do you get people involved so that open sourcing is worth it?

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• Why does a sub-class class of a class have to be static in order to initialize the sub-class in the

  - by Alex

  So, the question is more or less as I wrote. I understand that it's probably not clear at all so I'll give an example. I have class Tree and in it there is the class Node, and the empty constructor of Tree is written: public class RBTree { private RBNode head; public RBTree(RBNode head,RBTree leftT,RBTree rightT){ this.head=head; this.head.leftT.head.father = head; this.head.rightT.head.father = head; } public RBTree(RBNode head){ this(head,new RBTree(),new RBTree()); } public RBTree(){ this(new RBNode(),null,null); } public class RBNode{ private int value; private boolean isBlack; private RBNode father; private RBTree leftT; private RBTree rightT; } } Eclipse gives me the error: "No enclosing instance of type RBTree is available due to some intermediate constructor invocation" for the "new RBTree()" in the empty constructor. However, if I change the RBNode to be a static class, there is no problem. So why is it working when the class is static. BTW, I found an easy solution for the cunstructor: public RBTree(){ this.head = new RBNode(); } So, I have no idea what is the problem in the first piece of code.

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• .NET Regex - Replace multiple characters at once without overwriting?

  - by Everaldo Aguiar

  I'm implementing a c# program that should automatize a Mono-alphabetic substitution cipher. The functionality i'm working on at the moment is the simplest one: The user will provide a plain text and a cipher alphabet, for example: Plain text(input): THIS IS A TEST Cipher alphabet: A - Y, H - Z, I - K, S - L, E - J, T - Q Cipher Text(output): QZKL KL QJLQ I thought of using regular expressions since I've been programming in perl for a while, but I'm encountering some problems on c#. First I would like to know if someone would have a suggestion for a regular expression that would replace all occurrence of each letter by its corresponding cipher letter (provided by user) at once and without overwriting anything. Example: In this case, user provides plaintext "TEST", and on his cipher alphabet, he wishes to have all his T's replaced with E's, E's replaced with Y and S replaced with J. My first thought was to substitute each occurrence of a letter with an individual character and then replace that character by the cipherletter corresponding to the plaintext letter provided. Using the same example word "TEST", the steps taken by the program to provide an answer would be: 1 - replace T's with (lets say) @ 2 - replace E's with # 3 - replace S's with & 4 - Replace @ with E, # with Y, & with j 5 - Output = EYJE This solution doesn't seem to work for large texts. I would like to know if anyone can think of a single regular expression that would allow me to replace each letter in a given text by its corresponding letter in a 26-letter cipher alphabet without the need of splitting the task in an intermediate step as I mentioned. If it helps visualize the process, this is a print screen of my GUI for the program:

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• Multiple UIWebViewNavigationTypeBackForward not only false but make inferring the actual url impossi

  - by SG1

  I have a UIWebView and a UITextField for the url. Naturally, I want the textField to always show the current document url. This works fine for urls directly input in the field, but I also have some buttons attached to the view for reload, back, and forward. So I've added all the UIWebViewDelegate methods to my controller, so it can listen to whenever the webView navigates and change the url in the textField as needed. Here's how I'm using the shouldStartLoadWithRequest: method: - (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType { NSLog(@"navigated via %d", navigationType); //loads the user cares about if ( navigationType == UIWebViewNavigationTypeLinkClicked || navigationType == UIWebViewNavigationTypeBackForward ) { //URL setting [self setUrlQuietly:request.URL]; } return YES; } Now, my problem here is that an actual click will generate a single navigation of type "LinkClicked" followed by a dozen type "Other" (redirects and ad loads I assume), which gets handled correctly by the code, but a back/forward action will generate all its requests as back/forward requests. In other words, a click calls setUrlQuietly: once, but a back/forward calls it multiple times. I am trying to use this method to determine if the user actually initiated the action (and I'd like to catch page redirects too). But if the method has no way of distinguishing between an actual "back" and a "load initiated as a result of a back", how can I make this assessment? Without this, I am completely stumped as to how I can only show the actual url and not intermediate urls. Thank you!

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• Closures in Ruby

  - by Isaac Cambron

  I'm kind of new to Ruby and some of the closure logic has me a confused. Consider this code: array = [] for i in (1..5) array << lambda {j} end array.map{|f| f.call} => [5, 5, 5, 5, 5] This makes sense to me because i is bound outside the loop, so the same variable is captured by each trip through the loop. It also makes sense to me that using an each block can fix this: array = [] (1..5).each{|i| array << lambda {i}} array.map{|f| f.call} => [1, 2, 3, 4, 5] ...because i is now being declared separately for each time through. But now I get lost: why can't I also fix it by introducing an intermediate variable? array = [] for i in 1..5 j = i array << lambda {j} end array.map{|f| f.call} => [5, 5, 5, 5, 5] Because j is new each time through the loop, I'd think a different variable would be captured on each pass. For example, this is definitely how C# works, and how -- I think-- Lisp behaves with a let. But in Ruby not so much. It almost looks like = is aliasing the variable instead of copying the reference, but that's just speculation on my part. What's really happening?

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• Vehicle License Plate Detection

  - by Ash

  Hey all Basically for my final project at university, I'm developing a vehicle license plate detection application. Now I consider myself an intermediate programmer, however my mathematics knowledge lacks anything above secondary school, therefore producing detection formulae is basically impossible. I've spend a good amount of time looking up academic papers such as: http://www.scribd.com/doc/266575/Detecting-Vehicle-License-Plates-in-Images http://www.cic.unb.br/~mylene/PI_2010_2/ICIP10/pdfs/0003945.pdf http://www.eurasip.org/Proceedings/Eusipco/Eusipco2007/Papers/d3l-b05.pdf When it comes to the maths, I'm lost. Due to this testing various graphic images proved productive, for example: to However this approach is only catered to that particular image, and if the techniques were applied to different images, I'm sure a different, most likely poorer conversion would occur. I've read about a formula called the bottom hat morphology transform, which according to the first does the following: "Basically, the trans- formation keeps all the dark details of the picture, and eliminates everything else (including bigger dark regions and light regions)." Sadly I can't find much information on this, however the image within the documentation near the end of the report shows it's effectiveness. I'm aware this is complicated and vast, I'd just appreciate a little advice, even in terms of what transformation techniques I should focus on developing, or algorithm regarding edge detection or pixel detection. Few things I need to add Developing in C Sharp Confining the project to UK registration plates only I can basically choose the images to convert as a demonstration Thanks

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• linear combinations in python/numpy

  - by nmaxwell

  greetings, I'm not sure if this is a dumb question or not. Lets say I have 3 numpy arrays, A1,A2,A3, and 3 floats, c1,c2,c3 and I'd like to evaluate B = A1*c1+ A2*c2+ A3*c3 will numpy compute this as for example, E1 = A1*c1 E2 = A2*c2 E3 = A3*c3 D1 = E1+E2 B = D1+E3 or is it more clever than that? In c++ I had a neat way to abstract this kind of operation. I defined series of general 'LC' template functions, LC for linear combination like: template<class T,class D> void LC( T & R, T & L0,D C0, T & L1,D C1, T & L2,D C2) { R = L0*C0 +L1*C1 +L2*C2; } and then specialized this for various types, so for instance, for an array the code looked like for (int i=0; i<L0.length; i++) R.array[i] = L0.array[i]*C0 + L1.array[i]*C1 + L2.array[i]*C2; thus avoiding having to create new intermediate arrays. This may look messy but it worked really well. I could do something similar in python, but I'm not sure if its nescesary. Thanks in advance for any insight. -nick

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• Static Vs Non-Static Method Performance C#

  - by dotnetguts

  Hello All, I have few global methods declared in public class in my asp.net web application. I have habbit of declaring all global methods in public class in following format public static string MethodName(parameters) { } I want to know how it would impact on performance point of view? 1) Which one is Better? Static Method or Non-Static Method? 2) Reason why it is better? Following link shows Non-Static methods are good because, static methods are using locks to be Thread-safe. The always do internally a Monitor.Enter() and Monitor.exit() to ensure Thread-safety. http://bytes.com/topic/c-sharp/answers/231701-static-vs-non-static-function-performance And Following link shows Static Methods are good static methods are normally faster to invoke on the call stack than instance methods. There are several reasons for this in the C# programming language. Instance methods actually use the 'this' instance pointer as the first parameter, so an instance method will always have that overhead. Instance methods are also implemented with the callvirt instruction in the intermediate language, which imposes a slight overhead. Please note that changing your methods to static methods is unlikely to help much on ambitious performance goals, but it can help a tiny bit and possibly lead to further reductions. http://dotnetperls.com/static-method I am little confuse which one to use? Thanks

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• $HTTP_RAW_POST_DATA and Wordpress media_handle_upload

  - by BaronVonKaneHoffen

  Hi there! So I'm making something for which users need to upload images from a canvas element (on the front end) using Wordpress's in-built Media Upload API. I've successfully uploaded images with the API from a file input in a form: <input type="file" name="async-upload" id="async-upload" size="40" /> ... <?php $new_attach_id = media_handle_upload( 'async-upload', $new_id ); ?> and I've saved images from the canvas using my own script: <script type="text/javascript"> ... var img = canvas.toDataURL("image/png"); ... ajax.send(img ); </script> ... <?php $imageData=$GLOBALS['HTTP_RAW_POST_DATA']; $filteredData=substr($imageData, strpos($imageData, ",")+1); $unencodedData=base64_decode($filteredData); $fp = fopen( 'saved_images/canv_save_test.png', 'wb' ); fwrite( $fp, $unencodedData); ... ?> Problem is, Wordpress's media_handle_upload() only accepts an index to the $_FILES array for the upload. So the question is: How can I pass the image data from HTTP_RAW_POST_DATA to it? Could I make the $_FILES['tmp-name'] point to it somehow? Could I use another script as an intermediate step somehow? Could I unleash the monkeys on the typewriter until they come up with the answer? Any help very very much appreciated! Thanks, Kane

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• Delphi: How to avoid EIntOverflow underflow when subtracting?

  - by Ian Boyd

  Microsoft already says, in the documentation for GetTickCount, that you could never compare tick counts to check if an interval has passed. e.g.: Incorrect (pseudo-code): DWORD endTime = GetTickCount + 10000; //10 s from now ... if (GetTickCount > endTime) break; The above code is bad because it is suceptable to rollover of the tick counter. For example, assume that the clock is near the end of it's range: endTime = 0xfffffe00 + 10000 = 0x00002510; //9,488 decimal Then you perform your check: if (GetTickCount > endTime) Which is satisfied immediatly, since GetTickCount is larger than endTime: if (0xfffffe01 > 0x00002510) The solution Instead you should always subtract the two time intervals: DWORD startTime = GetTickCount; ... if (GetTickCount - startTime) > 10000 //if it's been 10 seconds break; Looking at the same math: if (GetTickCount - startTime) > 10000 if (0xfffffe01 - 0xfffffe00) > 10000 if (1 > 10000) Which is all well and good in C/C++, where the compiler behaves a certain way. But what about Delphi? But when i perform the same math in Delphi, with overflow checking on ({Q+}, {$OVERFLOWCHECKS ON}), the subtraction of the two tick counts generates an EIntOverflow exception when the TickCount rolls over: if (0x00000100 - 0xffffff00) > 10000 0x00000100 - 0xffffff00 = 0x00000200 What is the intended solution for this problem? Edit: i've tried to temporarily turn off OVERFLOWCHECKS: {$OVERFLOWCHECKS OFF}] delta = GetTickCount - startTime; {$OVERFLOWCHECKS ON} But the subtraction still throws an EIntOverflow exception. Is there a better solution, involving casts and larger intermediate variable types?

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• Calculating a consecutive streak in data

  - by Jura25

  I’m trying to calculate the maximum winning and losing streak in a dataset (i.e. the highest number of consecutive positive or negative values). I’ve found a somewhat related question here on StackOverflow and even though that gave me some good suggestions, the angle of that question is different, and I’m not (yet) experienced enough to translate and apply that information to this problem. So I was hoping you could help me out, even an suggestion would be great. My data set look like this: > subRes Instrument TradeResult.Currency. 1 JPM -3 2 JPM 264 3 JPM 284 4 JPM 69 5 JPM 283 6 JPM -219 7 JPM -91 8 JPM 165 9 JPM -35 10 JPM -294 11 KFT -8 12 KFT -48 13 KFT 125 14 KFT -150 15 KFT -206 16 KFT 107 17 KFT 107 18 KFT 56 19 KFT -26 20 KFT 189 > split(subRes[,2],subRes[,1]) $JPM [1] -3 264 284 69 283 -219 -91 165 -35 -294 $KFT [1] -8 -48 125 -150 -206 107 107 56 -26 189 In this case, the maximum (winning) streak for JPM is four (namely the 264, 284, 69 and 283 consecutive positive results) and for KFT this value is 3 (107, 107, 56). My goal is to create a function which gives the maximum winning streaks per instrument (i.e. JPM: 4, KFT: 3). To achieve that: R needs to compare the current result with the previous result, and if it is higher then there is a streak of at least 2 consecutive positive results. Then R needs to look at the next value, and if this is also higher: add 1 to the already found value of 2. If this value isn’t higher, R needs to move on to the next value, while remembering 2 as the intermediate maximum. I’ve tried cumsum and cummax in accordance with conditional summing (like cumsum(c(TRUE, diff(subRes[,2]) > 0))), which didn’t work out. Also rle in accordance with lapply (like lapply(rle(subRes$TradeResult.Currency.), function(x) diff(x) > 0)) didn’t work. How can I make this work?

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• What algorithms compute directions from point A to point B on a map?

  - by A. Rex

  How do map providers (such as Google or Yahoo! Maps) suggest directions? I mean, they probably have real-world data in some form, certainly including distances but also perhaps things like driving speeds, presence of sidewalks, train schedules, etc. But suppose the data were in a simpler format, say a very large directed graph with edge weights reflecting distances. I want to be able to quickly compute directions from one arbitrary point to another. Sometimes these points will be close together (within one city) while sometimes they will be far apart (cross-country). Graph algorithms like Dijkstra's algorithm will not work because the graph is enormous. Luckily, heuristic algorithms like A* will probably work. However, our data is very structured, and perhaps some kind of tiered approach might work? (For example, store precomputed directions between certain "key" points far apart, as well as some local directions. Then directions for two far-away points will involve local directions to a key points, global directions to another key point, and then local directions again.) What algorithms are actually used in practice? PS. This question was motivated by finding quirks in online mapping directions. Contrary to the triangle inequality, sometimes Google Maps thinks that X-Z takes longer and is farther than using an intermediate point as in X-Y-Z. But maybe their walking directions optimize for another parameter, too? PPS. Here's another violation of the triangle inequality that suggests (to me) that they use some kind of tiered approach: X-Z versus X-Y-Z. The former seems to use prominent Boulevard de Sebastopol even though it's slightly out of the way. (Edit: this example doesn't work anymore, but did at the time of the original post. The one above still works as of early November 2009.)

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• Using Mercurial (hg), can you just "hg backout" all the commits you did for the files you don't want

  - by Jian Lin

  Using Mercurial (hg), can you just "hg backout" all the commits you did for the files you don't want to push, and then do a push? Because Mercurial (or Git) won't let us push a single file or a single folder to another repository, so I am thinking: 1) How about, we just look at the commit we did, and hg backout the ones we don't want to push. 2) hg out -v to see the list of files that will be pushed 3) now do the push by hg push Is this a good way? This is because I got the following advice: 1) Don't commit that file if you don't want it to be pushed (but sometimes even just for experimentation, I do want to keep the intermediate revisions) (-- maybe I can hg commit and hg backout right away to prevent it from being pushed.) 2) Some people told me just to hg clone tmp from that repository i want to push to, and then copy the local file over to this tmp working directory, hg commit to this tmp repository, and then do a push. But I found that the hg clone tmp will take up 400MB of new data and files, and make the hard drive work very hard, just to push 1 file? So I would rather not use this method.

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• Distributed Cache with Serialized File as DataStore in Oracle Coherence

  - by user226295

  Weired but I am investigating the Oracle Coherence as a substitue for distribute cache. My primarr problem is that we dont have distribituted cache as such as of now in our app. Thats my major concern. And thats what I want to implement. So, lets say if I take up a machine and start a new (3rd) reading process, it will be able to connect to the cache and listen to the cache and will have a full set of cache triplicated (as of now its duplicated) Now thats waste from a common person stanpoint too. The size of the cache is 2 GB and without going distibuted its limiting us. Thats bring me to Coheremce. But now, we dont have database as persistent store too. we have the archival processes as our persistent store. (90 days worth of data) Ok now multiply that with soem where around 2 GB * 90 (thats the bare minimum we want to keep). Preliminary/Intermediate analysis of Coherence as a solution. And a (supposedly) brilliant thought crossed my mind. Why not have this as persistant storage with my distributed cache. Does Oracle Coherence support that. I will get rid of archiving infrastructure too (i hate daemon archiving processes). For some starnge reasons, I dont wanna go to the DB to replace those flat files. What say?, can Coherence be my savior? Any other stable alternate too. (Coherence is imposed on me by big guys, FYI)

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• Begin game programming basics

  - by AJ

  My 14 year old kid brother wants to learn to program games. He has never programmed but would like to learn programming. His interest lies with games and game programming and he understands that it can be difficult but he wants to do that. So, obviously, I turned to SO folks to know what you feel on how he should go about it. Remember, please suggest on Areas that beginners can choose, how to begin in that area, what to read in the beginning, initial languages in the beginning etc. Once the beginning part is taken care of, you may also suggest the intermediate and advanced stuff but this question is about very beginning level. If there are areas like Web games Vs. console games Vs generic computer games, then please advice on the areas. As I said he has never programmed, he might want to try all the areas and choose the one he likes the best. I hope this is not too much to ask for someone who is in this field but if this question is huge, please advice on how to break it into multiple questions. ~Thanks.

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• byte + byte = int... why?

  - by Robert C. Cartaino

  Looking at this C# code... byte x = 1; byte y = 2; byte z = x + y; // ERROR: Cannot implicitly convert type 'int' to 'byte' The result of any math performed on byte (or short) types is implicitly cast back to an integer. The solution is to explicitly cast the result back to a byte, so... byte z = (byte)(x + y); // works What I am wondering is why? Is it architectural? Philosophical? We have: int + int = int long + long = long float + float = float double + double = double So why not: byte + byte = byte short + short = short ? A bit of background: I am performing a long list of calculations on "small numbers" (i.e. < 8) and storing the intermediate results in a large array. Using a byte array (instead of an int array) is faster (because of cache hits). But the extensive byte-casts spread through the code make it that much more unreadable.

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• Why does DeviceIoControl throw error 21 (Device Not Ready) from C# when the equivalent in C works fine?

  - by Ragesh

  I'm trying to send an IOCTL_SERVICE_REFRESH command to the GPS Intermediate Driver service using C# like this: handle = CreateFile("GPD0:", GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, IntPtr.Zero, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, IntPtr.Zero); if (handle.ToInt32() == INVALID_HANDLE_VALUE) { rc = Marshal.GetLastWin32Error(); return rc; } int numBytesReturned = 0; rc = DeviceIoControl( handle, IOCTL_SERVICE_REFRESH, null, 0, null, 0, ref numBytesReturned, IntPtr.Zero); int error = Marshal.GetLastWin32Error(); GetLastWin32Error always gives me error 21 (device not ready). However, the equivalent call when made from C++ works fine: HANDLE hGPS = CreateFile(L"GPD0:", GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0); if (hGPS != INVALID_HANDLE_VALUE) { BOOL ret = DeviceIoControl(hGPS,IOCTL_SERVICE_REFRESH,0,0,0,0,0,0); DWORD err = GetLastError(); } I suspected a problem with the PInvoke signatures, but I can't seem to find anything wrong here: [DllImport("coredll.dll", EntryPoint = "DeviceIoControl", SetLastError = true)] public static extern int DeviceIoControl( IntPtr hDevice, uint dwIoControlCode, byte[] lpInBuffer, int nInBufferSize, byte[] lpOutBuffer, int nOutBufferSize, ref int lpBytesReturned, IntPtr lpOverlapped); [DllImport("coredll.dll", SetLastError = true)] public static extern IntPtr CreateFile( String lpFileName, uint dwDesiredAccess, uint dwShareMode, IntPtr attr, uint dwCreationDisposition, uint dwFlagsAndAttributes, IntPtr hTemplateFile); What am I missing here?

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• Using an embedded DB (SQLite / SQL Compact) for Message Passing within an app?

  - by wk1989

  Hello, Just out of curiosity, for applications that have a fairly complicated module tree, would something like sqlite/sql compact edition work well for message passing? So if I have modules containing data such as: \SubsystemA\SubSubSysB\ModuleB\ModuleDataC, \SubSystemB\SubSubSystemC\ModuleA\ModuleDataX Using traditional message passing/routing, you have to go through intermediate modules in order to pass a message to ModuleB to request say ModuleDataC. Instead of doing that, if we we simply store "\SubsystemA\SubSubSysB\ModuleB\ModuleDataC" in a sqlite database, getting that data is as simple as a sql query and needs no routing and passing stuff around. Has anyone done this before? Even if you haven't, do you foresee any issues & performance impact? The only concern I have right now would be the passing of custom types, e.g. if ModuleDataC is a custom data structure or a pointer, I'll need some way of storing the data structure into the DB or storing the pointer into the DB. Thanks, JW EDIT One usage case I haven't thought about is when you want to send a message from ModuleA to ModuleB to get ModuleB to do something rather than just getting/setting data. Is it possible to do this using an embedded DB? I believe callback from the DB would be needed, how feasible is this?

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• Most efficient way to LIMIT results in a JOIN?

  - by johnnietheblack

  I have a fairly simple one-to-many type join in a MySQL query. In this case, I'd like to LIMIT my results by the left table. For example, let's say I have an accounts table and a comments table, and I'd like to pull 100 rows from accounts and all the associated comments rows for each. Thy only way I can think to do this is with a sub-select in in the FROM clause instead of simply selecting FROM accounts. Here is my current idea: SELECT a.*, c.* FROM (SELECT * FROM accounts LIMIT 100) a LEFT JOIN `comments` c on c.account_id = a.id ORDER BY a.id However, whenever I need to do a sub-select of some sort, my intermediate level SQL knowledge feels like it's doing something wrong. Is there a more efficient, or faster, way to do this, or is this pretty good? By the way... This might be the absolute simplest way to do this, which I'm okay with as an answer. I'm simply trying to figure out if there IS another way to do this that could potentially compete with the above statement in terms of speed.

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• C Typecast: How to

  - by Jean

  #include<stdio.h> int main(void) { unsigned short a,e,f ; // 2 bytes data type unsigned int temp1,temp2,temp4; // 4 bytes data type unsigned long temp3; // 8 bytes data type a=0xFFFF; e=((a*a)+(a*a))/(2*a); // Line 8 //e=(((unsigned long)(a*a)+(unsigned long)(a*a)))/(unsigned int)(2*a); temp1=a*a; temp2=a*a; temp3=(unsigned long)temp1+(unsigned long)temp2; // Line 14 temp4=2*a; f=temp3/temp4; printf("%u,%u,%lu,%u,%u,%u,%u\n",temp1,temp2,temp3,temp4,e,f,a); return(1); } How do I fix the arithmetic (At Line 8 by appropriate typecasting of intermediate results) so that overflows are taken care of ? Currently it prints 65534 instead of expected 65535. Why is the typecast necessary for Line 14 ?

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• C++ Iterator Pipelining Designs

  - by Kirakun

  Suppose we want to apply a series of transformations, int f1(int), int f2(int), int f3(int), to a list of objects. A naive way would be SourceContainer source; TempContainer1 temp1; transform(source.begin(), source.end(), back_inserter(temp1), f1); TempContainer2 temp2; transform(temp1.begin(), temp1.end(), back_inserter(temp2), f2); TargetContainer target; transform(temp2.begin(), temp2.end(), back_inserter(target), f3); This first solution is not optimal because of the extra space requirement with temp1 and temp2. So, let's get smarter with this: int f123(int n) { return f3(f2(f1(n))); } ... SourceContainer source; TargetContainer target; transform(source.begin(), source.end(), back_inserter(target), f123); This second solution is much better because not only the code is simpler but more importantly there is less space requirement without the intermediate calculations. However, the composition f123 must be determined at compile time and thus is fixed at run time. How would I try to do this efficiently if the composition is to be determined at run time? For example, if this code was in a RPC service and the actual composition--which can be any permutation of f1, f2, and f3--is based on arguments from the RPC call.

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• C++ reference variable again!!!

  - by kumar_m_kiran

  Hi All, I think most would be surprised about the topic again, However I am referring to a book "C++ Common Knowledge: Essential Intermediate Programming" written by "Stephen C. Dewhurst". In the book, he quotes a particular sentence (in section under Item 5. References Are Aliases, Not Pointers), which is as below A reference is an alias for an object that already exists prior to the initialization of the reference. Once a reference is initialized to refer to a particular object, it cannot later be made to refer to a different object; a reference is bound to its initializer for its whole lifetime Can anyone please explain the context of "cannot later be made to refer to a different object" Below code works for me, #include <iostream> using namespace std; int main(int argc, char *argv[]) { int i = 100; int& ref = i; cout<<ref<<endl; int k = 2000; ref = k; cout<<ref<<endl; return 0; } Here I am referring the variable ref to both i and j variable. And the code works perfectly fine. Am I missing something? I have used SUSE10 64bit linux for testing my sample program. Thanks for your input in advance.

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• Why does Perl lose foreign characters on Windows; can this be fixed (if so, how)?

  - by Alex R

  Note below how ã changes to a. NOTE2: Before you blame this on CMD.EXE and Windows pipe weirdness, see Experiment 2 below which gets a similar problem using File::Find. The particular problem I'm trying to fix involves working with image files stored on a local drive, and manipulating the file names which may contain foreign characters. The two experiments shown below are intermediate debugging steps. The ã character is common in latin languages. e.g. http://pt.wikipedia.org/wiki/Cão Experiment 1 Experiment 2 To get around my particular problem, I tried using File::Find instead of piped input. The issue actually gets worse: Debugging update: I tried some of the tricks listed at http://perldoc.perl.org/perlunicode.html, e.g. use utf8, use feature 'unicode_strings', etc, to no avail. Environment and Version Info The OS is Windows 7, 64-bit. The Perl is: This is perl 5, version 12, subversion 2 (v5.12.2) built for MSWin32-x64-multi-thread (with 8 registered patches, see perl -V for more detail) Copyright 1987-2010, Larry Wall Binary build 1202 [293621] provided by ActiveState http://www.ActiveState.com Built Sep 6 2010 22:53:42

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• regular expression repeating subexpression

  - by Michael Z

  I have the following text <pattern name="pattern1"/> <success>success case 1</success> <failed> failure 1</failed> <failed> failure 2</failed> <unknown> unknown </unknown> <pattern name="pattern2"/> <success>success case 2</success> <otherTag>There are many other tags.</otherTag> <failed> failure 3</failed> And the regular expression <failed>[\w|\W]*?</failed> matches all the lines contains failed tag. What do I need to to if I want to include the lines contains pattern tag as well? Basically, I want the following output: <pattern name="pattern1"/> <failed> failure 1</failed> <failed> failure 2</failed> <pattern name="pattern2"/> <failed> failure 3</failed> I am doing this in javascript, I do not mind of doing some intermediate steps.

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• Does using functional languages help against computing values repeatedly?

  - by sharptooth

  Consider a function f(x,y): f(x,0) = x*x; f(0,y) = y*(y + 1); f(x,y) = f(x,y-1) + f(x-1,y); If one tries to implement that recursively in some language like C++ he will encounter a problem. Suppose the function is first called with x = x0 and y = y0. Then for any pair (x,y) where 0 <= x < x0 and 0 <= y < y0 the intermediate values will be computed multiple times - recursive calls will form a huge tree in which multiple leaves will in fact contain the same pairs (x,y). For pairs (x,y) where x and y are both close to 0 values will be computed numerous times. For instance, I tested a similar function implemented in C++ - for x=20 and y=20 its computation takes about 4 hours (yes, four Earth hours!). Obviously the implementation can be rewritten in such way that repeated computation doesn't occur - either iteratively or with a cache table. The question is: will functional languages perform any better and avoid repeated computations when implementing a function like above recursively?

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