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• SQL Compact performance on device

  - by Ben M

  My SQL Compact database is very simple, with just three tables and a single index on one of the tables (the table with 200k rows; the other two have less than a hundred each). The first time the .sdf file is used by my Compact Framework application on the target Windows Mobile device, the system hangs for well over a minute while "something" is done to the database: when deployed, the DB is 17 megabytes, and after this first usage, it balloons to 24 megs. All subsequent usage is pretty fast, so I'm assuming there's some sort of initialization / index building going on during this first usage. I'd rather not subject the user to this delay, so I'm wondering what this initialization process is and whether it can be performed before deployment. For now, I've copied the "initialized" database back to my desktop for use in the setup project, but I'd really like to have a better answer / solution. I've tried "full compact / repair" in the VS Database Properties dialog, but this made no difference. Any ideas? For the record, I should add that the database is only read from by the device application -- no modifications are made by that code.

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• algorithm to find longest non-overlapping sequences

  - by msalvadores

  I am trying to find the best way to solve the following problem. By best way I mean less complex. As an input a list of tuples (start,length) such: [(0,5),(0,1),(1,9),(5,5),(5,7),(10,1)] Each element represets a sequence by its start and length, for example (5,7) is equivalent to the sequence (5,6,7,8,9,10,11) - a list of 7 elements starting with 5. One can assume that the tuples are sorted by the start element. The output should return a non-overlapping combination of tuples that represent the longest continuos sequences(s). This means that, a solution is a subset of ranges with no overlaps and no gaps and is the longest possible - there could be more than one though. For example for the given input the solution is: [(0,5),(5,7)] equivalent to (0,1,2,3,4,5,6,7,8,9,10,11) is it backtracking the best approach to solve this problem ? I'm interested in any different approaches that people could suggest. Also if anyone knows a formal reference of this problem or another one that is similar I'd like to get references. BTW - this is not homework. Edit Just to avoid some mistakes this is another example of expected behaviour for an input like [(0,1),(1,7),(3,20),(8,5)] the right answer is [(3,20)] equivalent to (3,4,5,..,22) with length 20. Some of the answers received would give [(0,1),(1,7),(8,5)] equivalent to (0,1,2,...,11,12) as right answer. But this last answer is not correct because is shorter than [(3,20)].

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• Javascript inheritance: call super-constructor or use prototype chain?

  - by Jeremy S.

  Hi folks, quite recently I read about javascript call usage in MDC https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/call one linke of the example shown below, I still don't understand. Why are they using inheritance here like this Prod_dept.prototype = new Product(); is this necessary? Because there is a call to the super-constructor in Prod_dept() anyway, like this Product.call is this just out of common behaviour? When is it better to use call for the super-constructor or use the prototype chain? function Product(name, value){ this.name = name; if(value >= 1000) this.value = 999; else this.value = value; } function Prod_dept(name, value, dept){ this.dept = dept; Product.call(this, name, value); } Prod_dept.prototype = new Product(); // since 5 is less than 1000, value is set cheese = new Prod_dept("feta", 5, "food"); // since 5000 is above 1000, value will be 999 car = new Prod_dept("honda", 5000, "auto"); Thanks for making things clearer

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• "end()" iterator for back inserters?

  - by Thanatos

  For iterators such as those returned from std::back_inserter(), is there something that can be used as an "end" iterator? This seems a little nonsensical at first, but I have an API which is: template<typename InputIterator, typename OutputIterator> void foo( InputIterator input_begin, InputIterator input_end, OutputIterator output_begin, OutputIterator output_end ); foo performs some operation on the input sequence, generating an output sequence. (Who's length is known to foo but may or may not be equal to the input sequence's length.) The taking of the output_end parameter is the odd part: std::copy doesn't do this, for example, and assumes you're not going to pass it garbage. foo does it to provide range checking: if you pass a range too small, it throws an exception, in the name of defensive programming. (Instead of potentially overwriting random bits in memory.) Now, say I want to pass foo a back inserter, specifically one from a std::vector which has no limit outside of memory constraints. I still need a "end" iterator - in this case, something that will never compare equal. (Or, if I had a std::vector but with a restriction on length, perhaps it might sometimes compare equal?) How do I go about doing this? I do have the ability to change foo's API - is it better to not check the range, and instead provide an alternate means to get the required output range? (Which would be needed anyways for raw arrays, but not required for back inserters into a vector.) This would seem less robust, but I'm struggling to make the "robust" (above) work.

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• When is a bool not a bool (compiler warning C4800)

  - by omatai

  Consider this being compiled in MS Visual Studio 2005 (and probably others): CPoint point1( 1, 2 ); CPoint point2( 3, 4 ); const bool point1And2Identical( point1 == point2 ); // C4800 warning const bool point1And2TheSame( ( point1 == point2 ) == TRUE ); // no warning What the...? Is the MSVC compiler brain-dead? As far as I can tell, TRUE is #defined as 1, without any type information. So by what magic is there any difference between these two lines? Surely the type of the expression inside the brackets is the same in both cases? [This part of the question now satisfactorily answered in the comments just below] Personally, I think that avoiding the warning by using the == TRUE option is ugly (though less ugly than the != 0 alternative, despite being more strictly correct), and it is better to use #pragma warning( disable:4800 ) to imply "my code is good, the compiler is an ass". Agree? Note - I have seen all manner of discussion on C4800 talking about assigning ints to bools, or casting a burger combo with large fries (hold the onions) to a bool, and wondering why there are strange results. I can't find a clear answer on what seems like a much simpler question... that might just shine line on C4800 in general.

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• Python vs all the major professional languages [closed]

  - by Matt

  I've been reading up a lot lately on comparisons between Python and a bunch of the more traditional professional languages - C, C++, Java, etc, mainly trying to find out if its as good as those would be for my own purposes. I can't get this thought out of my head that it isn't good for 'real' programming tasks beyond automation and macros. Anyway, the general idea I got from about two hundred forum threads and blog posts is that for general, non-professional-level progs, scripts, and apps, and as long as it's a single programmer (you) writing it, a given program can be written quicker and more efficiently with Python than it could be with pretty much any other language. But once its big enough to require multiple programmers or more complex than a regular person (read: non-professional) would have any business making, it pretty much becomes instantly inferior to a million other languages. Is this idea more or less accurate? (I'm learning Python for my first language and want to be able to make any small app that I want, but I plan on learning C eventually too, because I want to get into driver writing eventually. So I've been trying to research each ones strengths and weaknesses as much as I can.) Anyway, thanks for any input

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• In Java, is there a performance gain in using interfaces for complex models?

  - by Gnoupi

  The title is hardly understandable, but I'm not sure how to summarize that another way. Any edit to clarify is welcome. I have been told, and recommended to use interfaces to improve performances, even in a case which doesn't especially call for the regular "interface" role. In this case, the objects are big models (in a MVC meaning), with many methods and fields. The "good use" that has been recommended to me is to create an interface, with its unique implementation. There won't be any other class implementing this interface, for sure. I have been told that this is better to do so, because it "exposes less" (or something close) to the other classes which will use methods from this class, as these objects are referring to the object from its interface (all public methods from the implementation being reproduced in the interface). This seems quite strange to me, as it seems like a C++ use to me (with header files). There I see the point, but in Java? Is there really a point in making an interface for such unique implementation? I would really appreciate some clarifications on the topic, so I could justify not following such kind of behavior, and the hassle it creates from duplicating all declarations. Edit: Plenty of valid points in most answers, I'm wondering if I won't switch this question for a community wiki, so we can regroup these points in more structured answers.

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• Small Open source and free java applications

  - by user1089770

  I am a Perl Developer who has just stepped into the Java world and I want to be very proficient in Java EE development. However, I have found that, being a Perl guy, I have very high MTI(Mother Tongue Influence). Indians will know what MTI is. For others, it can be defined as an influence of your "main" language whenever you "speak" your new language. In other words, our mind converts/translates what we want to "say" in the new language based on the "main" language, which can be quite absurd or meaning less in the "new" language. Coming back to the point, as a result of this MTI, many lines of my code has this Perl influence and it is absurd and useless for production. Hence, I'd like to see or better do some research on existing small to medium open source java applications, so that I will know how I can "speak" in the native way of the "new" language. Some examples in PHP will be : WordPress, Zend etc. So I'd really appreciate if you guys could suggest any such apps. Apps that have a great commercial value are highly preferred

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• How to render all records from a nested set into a real html tree

  - by Christoph Schiessl

  I'm using the awesome_nested_set plugin in my Rails project. I have two models that look like this (simplified): class Customer < ActiveRecord::Base has_many :categories end class Category < ActiveRecord::Base belongs_to :customer # Columns in the categories table: lft, rgt and parent_id acts_as_nested_set :scope => :customer_id validates_presence_of :name # Further validations... end The tree in the database is constructed as expected. All the values of parent_id, lft and rgt are correct. The tree has multiple root nodes (which is of course allowed in awesome_nested_set). Now, I want to render all categories of a given customer in a correctly sorted tree like structure: for example nested <ul> tags. This wouldn't be too difficult but I need it to be efficient (the less sql queries the better). Update: Figured out that it is possible to calculate the number of children for any given Node in the tree without further SQL queries: number_of_children = (node.rgt - node.lft - 1)/2. This doesn't solve the problem but it may prove to be helpful.

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• gcc compilations (sometimes) result in cpu underload

  - by confusedCoder

  I have a larger C++ program which starts out by reading thousands of small text files into memory and storing data in stl containers. This takes about a minute. Periodically, a compilation will exhibit behavior where that initial part of the program will run at about 22-23% CPU load. Once that step is over, it goes back to ~100% CPU. It is more likely to happen with O2 flag turned on but not consistently. It happens even less often with the -p flag which makes it almost impossible to profile. I did capture it once but the gprof output wasn't helpful - everything runs with the same relative speed just at low cpu usage. I am quite certain that this has nothing to do with multiple cores. I do have a quad-core cpu, and most of the code is multi-threaded, but I tested this issue running a single thread. Also, when I run the problematic step in multiple threads, each thread only runs at ~20% CPU. I apologize ahead of time for the vagueness of the question but I have run out of ideas as to how to troubleshoot it further, so any hints might be helpful. UPDATE: Just to make sure it's clear, the problematic part of the code does sometimes (~30-40% of the compilations) run at 100% CPU, so it's hard to buy the (otherwise reasonable) argument that I/O is the bottleneck

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• 32-bit JVM on 64-bit Windows crashes on launch with -Xmx1300m and plenty of free memory

  - by Konrad Garus

  I'm struggling with Java heap space settings. The default Java on Windows is the 32-bit client regardless of OS version (that's what Oracle recommends to all users). It appears to set max heap size to 256 MB by default, and that is too little for me. I use a custom launcher to start the application. I would like it to use more memory on computers with plenty RAM, and default to -Xmx512m on those with less RAM. As far as I'm aware, the only way is the static -Xmx setting (that has to be set on launch). I have a user who has 8 GB RAM, 64-bit Windows and 32-bit Java 7. Maximum memory visible to the JVM is 4G (as returned by querying OperatingSystemMXBean). I understand why, no issue. For some reason my application is unable to start for this user with -Xmx1300m, even though he has 2.3G free memory. He closed some applications (having 5G free memory), and still it would not launch. The error reported to me was: error occured during init of vm could not reserve enough space for object heap What's going on? Could it be that the 32-bit JVM is only able to address the "first" 4G of memory and has to have a 1300M block available within those first 4 gigabytes? How can I solve this problem, except for asking everyone to install 64-bit Java (what is unlikely to be acceptable)?

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• Storing an encrypted cookie with Rails

  - by J. Pablo Fernández

  I need to store a small piece of data (less than 10 characters) in a cookie in Rails and I need it to be secure. I don't want anybody being able to read that piece of data or injecting their own piece of data (as that would open up the app to many kinds of attacks). I think encrypting the contents of the cookie is the way to go (should I also sign it?). What is the best way to do it? Right now I'm doing this, which looks secure, but many things looked secure to people that knew much more than I about security and then it was discovered it wasn't really secure. I'm saving the secret in this way: encryptor = ActiveSupport::MessageEncryptor.new(Example::Application.config.secret_token) cookies[:secret] = { :value => encryptor.encrypt(secret), :domain => "example.com", :secure => !(Rails.env.test? || Rails.env.development?) } and then I'm reading it like this: encryptor = ActiveSupport::MessageEncryptor.new(Example::Application.config.secret_token) secret = encryptor.decrypt(cookies[:secret]) Is that secure? Any better ways of doing it? Update: I know about Rails' session and how it is secure, both by signing the cookie and by optionally storing the contents of the session server side and I do use the session for what it is for. But my question here is about storing a cookie, a piece of information I do not want in the session but I still need it to be secure.

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• Run multiple MySQL queries based on a series of ifs

  - by OldWest

  I am just getting started on this complex query I need to write and was hoping for any suggestions or feedback regarding table structure and the actual query itself.. I've already created my tables and populated test data, and now just trying to sort out how and what is possible within MySQL. Here is an outline of the problem: End result: Listing of rates based on specific queried criteria (see below): Age: [ 27 ] Spouse Age: [ 25 ] Num of Children: [ 3 ] Zip Code: [ 97128 ] The problem I am running into is each company that provides rates has a unique way of dealing with the rate. And I am looking for the best approach for multiple queries based on the company (one query with results for each company more or less all combined into one result set). Here are some facts: - Each company deals with zip code ranges which assist in the query result. - Each company has a different method of calculating the rate based on the Applicant, Spouse, Num of Children: Example, a) Company A determines rate by: Applicant + Spouse + Child(ren) = rate (age is pertinent to the applicant within a range). b) Company B determines the rate by total number of applicants like: 1, 2, 3, 4, 5, 6+ = rate (and age is ignored). First off, what would I call this type of query? Multiple nested query? And should I intertwine php within it to determine the If()s ... I apologize if this thread lacks sufficient data, so please tell me anything you would like to see.

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• Why do I need to give my options a value attribute in my dropdown? JQuery related.

  - by Alex

  So far in my web developing experiences, I've noticed that almost all web developers/designers choose to give their options in a select a value like so: <select name="foo"> <option value="bar">BarCheese</option> // etc. // etc. </select> Is this because it is best practice to do so? I ask this because I have done a lot of work with jQuery and dropdown's lately, and sometimes I get really annoyed when I have to check something like: $('select[name=foo]').val() == "bar"); To me, many times that seems less clear than just being able to check the val() against BarCheese. So why is it that most web developers/designers specify a value paramater instead of just letting the options actual value be its value? And yes, if the option has a value attribute I know I can do something like this: $('select[name=foo] option:contains("BarCheese")').attr('selected', 'selected'); But I would still really like to know why this is done. Thanks!!

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• Is there unresizable space in latex? Pictures in good looking grid.

  - by drasto

  I've created latex macro to typeset guitar chords diagrams(using picture environment). Now I want to make diagrams of different appear in good looking grid when typeset one next to each other as the picture shows: The picture. (on the picture: Labeled "First" bad layout of diagrams, labeled "Second" correct layout when equal number of diagrams in line) I'm using \hspace to make some skips between diagrams, otherwise they would be too near to each other. As you can see in second case when latex arrange pictures in so that there is same number of them in each line it works. However if there is less pictures in the last line they become "shifted" to the right. I don't want this. I guess is because latex makes the space between diagrams in first line a little longer for the line to exactly fit the page width. How do I tell latex not to resize spaces created by \hspace ? Or is there any other way ? I guess I cannot use tables because I don't know how many diagrams will fit in one line... This is current state of code: \newcommand{\spaceForChord}{1.7cm} \newcommnad{\chordChart}[1]{% %calculate dimensions xdim and ydim according to setings \begin{picture}(xdim, ydim){% %draw the diagram inside defined area }% \hspace*{\spaceForChord}% \hspace*{-\xdim}% }% %end preambule and begin document \begin{document} First:\\* \\* \chordChart{...some arguments for to change diagram look...} \chordChart{...some arguments for to change diagram look...} \chordChart{...some arguments for to change diagram look...} \chordChart{...some arguments for to change diagram look...} \chordChart{...some arguments for to change diagram look...} %...above line is repeated 12 more times to produce result shown at the picture \end{document} Thanks for any help.

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• C# Application process hangs after some time

  - by Chris

  Hi, I implemented a simple C# application which inserts about 350000 records into the database. This used to work well and the process took approximately 20 minutes. I created a progress bar which lets you know approximately the progress of the records insertion. When the progress bar reaches about 75% it stops progressing. I have to manually terminate the program as the process doesn't seem to complete. If I use less data (like 10000), the progress bar finishes and the process is completed. However when I try to insert all the records, this won't happen any more. Note that if I wait longer to terminate the program manually, more records would have been inserted. For example, if I terminate the program after 15 minutes, 200000 records are inserted, whereas if I terminate the program after 20 minutes, 250000 records are inserted. This program is using a single thread. In face I can't do anything else until the process is complete. Does this have anything to do with threading or processes? Any feedback will be greatly appreciated. Thanks.

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• Retain numerical precision in an R data frame?

  - by David

  When I create a dataframe from numeric vectors, R seems to truncate the value below the precision that I require in my analysis: data.frame(x=0.99999996) returns 1 (see update 1) I am stuck when fitting spline(x,y) and two of the x values are set to 1 due to rounding while y changes. I could hack around this but I would prefer to use a standard solution if available. example Here is an example data set d <- data.frame(x = c(0.668732936336141, 0.95351462456867, 0.994620622127435, 0.999602102672081, 0.999987126195509, 0.999999955814133, 0.999999999999966), y = c(38.3026509783688, 11.5895099585560, 10.0443344234229, 9.86152339768516, 9.84461434575695, 9.81648333804257, 9.83306725758297)) The following solution works, but I would prefer something that is less subjective: plot(d$x, d$y, ylim=c(0,50)) lines(spline(d$x, d$y),col='grey') #bad fit lines(spline(d[-c(4:6),]$x, d[-c(4:6),]$y),col='red') #reasonable fit Update 1 Since posting this question, I realize that this will return 1 even though the data frame still contains the original value, e.g. > dput(data.frame(x=0.99999999996)) returns structure(list(x = 0.99999999996), .Names = "x", row.names = c(NA, -1L), class = "data.frame") Update 2 After using dput to post this example data set, and some pointers from Dirk, I can see that the problem is not in the truncation of the x values but the limits of the numerical errors in the model that I have used to calculate y. This justifies dropping a few of the equivalent data points (as in the example red line).

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• C# : How to round-off hours based on Minutes(hours+0 if min<30, hours+1 otherwise) ?

  - by infant programmer

  I need to round-off the hours based on the minutes in a dateTime variable. The condition is : if minutes are less than 30, then minutes must be set to zero and no changes to hours, Else if minutes =30, then hours must be set to hours+1 and minutes are again set to zero. Seconds are ignored. example: 11/08/2008 04:30:49 should become 11/08/2008 05:00:00 and 11/08/2008 04:29:49 should become 11/08/2008 04:00:00 I have written a Code which works perfectly fine, but just wanted to know a better method if could be written and also would appreciate alternative method(s). string date1 = "11/08/2008 04:30:49"; DateTime startTime; DateTime.TryParseExact(date1, "MM/dd/yyyy HH:mm:ss", null, System.Globalization.DateTimeStyles.None, out startTime); if (Convert.ToInt32((startTime.Minute.ToString())) > 29) { startTime = DateTime.Parse(string.Format("{0}/{1}/{2} {3}:{4}:{5}", startTime.Month.ToString(), startTime.Day.ToString(), startTime.Year.ToString(), startTime.Hour.ToString(), "00", "00")); startTime = startTime.Add(TimeSpan.Parse("01:00:00")); Console.WriteLine("startTime is :: {0}", startTime.ToString("MM/dd/yyyy HH:mm:ss")); } else { startTime = DateTime.Parse(string.Format("{0}/{1}/{2} {3}:{4}:{5}", startTime.Month.ToString(), startTime.Day.ToString(), startTime.Year.ToString(), startTime.Hour.ToString(), "00", "00")); Console.WriteLine("startTime is :: {0}", startTime.ToString("MM/dd/yyyy HH:mm:ss")); }

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• Timing issues with playback of the HTML5 Audio API

  - by pat

  I'm using the following code to try to play a sound clip with the HTML5 Audio API: HTMLAudioElement.prototype.playClip = function(startTime, stopTime) { this.stopTime = stopTime; this.currentTime = startTime; this.play(); $(this).bind('timeupdate', function(){ if (this.ended || this.currentTime >= stopTime) { this.pause(); $(this).unbind('timeupdate'); } }); } I utilize this new playClip method as follows. First I have a link with some data attributes: <a href=# data-stop=1.051 data-start=0.000>And then I was thinking,</a> And finally this bit of jQuery which runs on $(document).ready to hook up a click on the link with the playback: $('a').click(function(ev){ $('a').click(function(ev){ var start = $(this).data('start'), stop = $(this).data('stop'), audio = $('audio').get(0), $audio = $(audio); ev.preventDefault(); audio.playClip(start,stop); }) This approach seems to work, but there's a frustrating bug: sometimes, the playback of a given clip plays beyond the correct data-stop time. I suspect it could have something to do with the timing of the timeupdate event, but I'm no JS guru and I don't know how to begin debugging the problem. Here are a few clues I've gathered: The same behavior appears to come up in both FF and Chrome. The playback of a given clip actually seems to vary a bit -- if I play the same clip a couple times in a row, it may over-play a different amount of time on each playing. Is the problem here the inherent accuracy of the Audio API? My app needs milliseconds. Is there a problem with the way I'm using jQuery to bind and unbind the timeupdate event? I tried using the jQuery-less approach with addEventListener but I couldn't get it to work. Thanks in advance, I would really love to know what's going wrong.

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• Regular Expressions .NET

  - by Fosa

  I need a regular expression for some arguments that must match on a string. here it is... The string exists out of minimum 8 en maximum 20 characters. These characters of this string may be characters of the alfabet or special chars --With other words..all charachters except from the whitespaces In the complete string there must be atleast 1 number. The string cannot start with a number or an underscore The last 2 characters of the string must be identical, But it doenst matter if those last --identical characters are capital or non-capital (case insensitive) Must match all : +234567899 a_1de*Gg xy1Me*__ !41deF_hij2lMnopq3ss C234567890123$^67800 *5555555 sDF564zer"" !!!!!!!!!4!!!!!!!!!! abcdefghijklmnopq9ss May not match : Cannot be less then 8 or more then 20 chars: a_1+Eff B41def_hIJ2lmnopq3stt Cannot contain a whitespace: A_4 e*gg b41def_Hij2l nopq3ss Cannot start with a number or an underscore: __1+Eff 841DEf_hij2lmnopq3stt cannot end on 2 diffrent characters: a_1+eFg b41DEf_hij2lmnopq3st Cannot be without a number in the string: abCDefghijklmnopqrss abcdef+++dF !!!!!!!!!!!!!!!!!!!! ------------------------------------------------------ This is what I have so far...But I'm really breaking my head on this... If you Don't know the answer completely it's not a problem... I just want to get in the right direction ([^0-9_])(?=.*\d)(\S{8,20})(?i:[\S])\1

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• Error in bisection method code in Matlab

  - by Amanda Collins

  I need to write a proper implementation of the bisection method, which means I must address all possible user input errors. Here is my code: function [x_sol, f_at_x_sol, N_iterations] = bisection(f, xn, xp, eps_f, eps_x) % solving f(x)=0 with bisection method % f is the function handle to the desired function, % xn and xp are borders of search, % f(xn)<0 and f(xp)>0 required, % eps_f defines how close f(x) should be to zero, % eps_x defines uncertainty of solution x if(f(xp) < 0) error('xp must be positive') end; if(f(xn)>0) error('xn must be negative') end; if (xn >= xp) error ('xn must be less than xp') end; xg=(xp+xn)/2; %initial guess fg=f(xg); % initial function evaluation N_iterations=1; while ( (abs(fg) > eps_f) & (abs(xg-xp) > eps_x) ) if (fg>0) xp=xg; else xn=xg; end xg=(xp+xn)/2; %update guess fg=f(xg); %update function evaluation N_iterations=N_iterations+1; end x_sol=xg; %solution is ready f_at_x_sol=fg; if (f_at_x_sol > eps_f) error('No convergence') end and here is the error message I receive when I try to test this in Matlab: >> bisection(x.^2, 2, -1, 1e-8, 1e-10) Attempted to access f(-1); index must be a positive integer or logical. Error in bisection (line 9) if(f(xp)<0) I was attempting to see if my error codes worked, but it doesn't look like they do. I get the same error when I try to test it on a function that should work.

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• Processing forms that generate many rows in DB

  - by Zack

  I'm wondering what the best approach to take here is. I've got a form that people use to register for a class and a lot of times the manager of a company will register multiple people for the class at the same time. Presently, they'd have to go through the registration process multiple times and resubmit the form once for every person they want to register. What I want to do is give the user a form that has a single <input/> for one person to register with, along with all the other fields they'll need to fill out (Email, phone number, etc); if they want to add more people, they'll be able to press a button and a new <input/> will be generated. This part I know how to do, but I'm including it to best describe what I'm aiming to do. The part I don't know how to approach is processing that data the form submits, I need some way of making a new row in the Registrant table for every <input/> that's added and include the same contact information (phone, email, etc) as the first row with that row. For the record, I'm using the Django framework for my back-end code. What's the best approach here? Should it just POST the form x times for x people, or is there a less "brute force" way of handling this?

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• Syntax for finding structs in multisets - C++

  - by Sarah

  I can't seem to figure out the syntax for finding structs in containers. I have a multiset of Event structs. I'm trying to find one of these structs by searching on its key. I get the compiler error commented below. struct Event { public: bool operator < ( const Event & rhs ) const { return ( time < rhs.time ); } bool operator > ( const Event & rhs ) const { return ( time > rhs.time ); } bool operator == ( const Event & rhs ) const { return ( time == rhs.time ); } double time; int eventID; int hostID; int s; }; typedef std::multiset< Event, std::less< Event > > EventPQ; EventPQ currentEvents; double oldRecTime = 20.0; EventPQ::iterator ceItr = currentEvents.find( EventPQ::key_type( oldRecTime ) ); // no matching function call I've tried a few permutations to no avail. I thought defining the conditional equality operator was going to be enough.

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• Point covering problem

  - by Sean

  I recently had this problem on a test: given a set of points m (all on the x-axis) and a set n of lines with endpoints [l, r] (again on the x-axis), find the minimum subset of n such that all points are covered by a line. Prove that your solution always finds the minimum subset. The algorithm I wrote for it was something to the effect of: (say lines are stored as arrays with the left endpoint in position 0 and the right in position 1) algorithm coverPoints(set[] m, set[][] n): chosenLines = [] while m is not empty: minX = min(m) bestLine = n[0] for i=1 to length of n: if n[i][0] <= m and n[i][1] > bestLine[1] then bestLine = n[i] add bestLine to chosenLines for i=0 to length of m: if m <= bestLine[1] then delete m[i] from m return chosenLines I'm just not sure if this always finds the minimum solution. It's a simple greedy algorithm so my gut tells me it won't, but one of my friends who is much better than me at this says that for this problem a greedy algorithm like this always finds the minimal solution. For proving mine always finds the minimal solution I did a very hand wavy proof by contradiction where I made an assumption that probably isn't true at all. I forget exactly what I did. If this isn't a minimal solution, is there a way to do it in less than something like O(n!) time? Thanks

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• C++ private inheritance and static members/types

  - by WearyMonkey

  I am trying to stop a class from being able to convert its 'this' pointer into a pointer of one of its interfaces. I do this by using private inheritance via a middle proxy class. The problem is that I find private inheritance makes all public static members and types of the base class inaccessible to all classes under the inheriting class in the hierarchy. class Base { public: enum Enum { value }; }; class Middle : private Base { }; class Child : public Middle { public: void Method() { Base::Enum e = Base::value; // doesn't compile BAD! Base* base = this; // doesn't compile GOOD! } }; I've tried this in both VS2008 (the required version) and VS2010, neither work. Can anyone think of a workaround? Or a different approach to stopping the conversion? Also I am curios of the behavior, is it just a side effect of the compiler implementation, or is it by design? If by design, then why? I always thought of private inheritance to mean that nobody knows Middle inherits from Base. However, the exhibited behavior implies private inheritance means a lot more than that, in-fact Child has less access to Base than any namespace not in the class hierarchy!

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