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• Is it possible to do A/B testing by page rather than by individual?

  - by mojones

  Lets say I have a simple ecommerce site that sells 100 different t-shirt designs. I want to do some a/b testing to optimise my sales. Let's say I want to test two different "buy" buttons. Normally, I would use AB testing to randomly assign each visitor to see button A or button B (and try to ensure that that the user experience is consistent by storing that assignment in session, cookies etc). Would it be possible to take a different approach and instead, randomly assign each of my 100 designs to use button A or B, and measure the conversion rate as (number of sales of design n) / (pageviews of design n) This approach would seem to have some advantages; I would not have to worry about keeping the user experience consistent - a given page (e.g. www.example.com/viewdesign?id=6) would always return the same html. If I were to test different prices, it would be far less distressing to the user to see different prices for different designs than different prices for the same design on different computers. I also wonder whether it might be better for SEO - my suspicion is that Google would "prefer" that it always sees the same html when crawling a page. Obviously this approach would only be suitable for a limited number of sites; I was just wondering if anyone has tried it?

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• Find out which row caused the error

  - by Felipe Fiali

  I have a big fat query that's written dynamically to integrate some data. Basically what it does is query some tables, join some other ones, treat some data, and then insert it into a final table. The problem is that there's too much data, and we can't really trust the sources, because there could be some errored or inconsistent data. For example, I've spent almost an hour looking for an error while developing using a customer's database because somewhere in the middle of my big fat query there was an error converting some varchar to datetime. It turned out to be that they had some sales dating '2009-02-29', an out-of-range date. And yes, I know. Why was that stored as varchar? Well, the source database has 3 columns for dates, 'Month', 'Day' and 'Year'. I have no idea why it's like that, but still, it is. But how the hell would I treat that, if the source is not trustable? I can't HANDLE exceptions, I really need that it comes up to another level with the original message, but I wanted to provide some more info, so that the user could at least try to solve it before calling us. So I thought about displaying to the user the row number, or some ID that would at least give him some idea of what record he'd have to correct. That's also a hard job because there will be times when the integration will run up to 80000 records. And in an 80000 records integration, a single dummy error message: 'The conversion of a varchar data type to a datetime data type resulted in an out-of-range datetime value' means nothing at all. So any idea would be appreciated. Oh I'm using SQL Server 2005 with Service Pack 3.

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• Auto-(un)boxing fail for compound assignment

  - by polygenelubricants

  Thanks to the implicit casting in compound assignments and increment/decrement operators, the following compiles: byte b = 0; ++b; b++; --b; b--; b += b -= b *= b /= b %= b; b <<= b >>= b >>>= b; b |= b &= b ^= b; And thanks to auto-boxing and auto-unboxing, the following also compiles: Integer ii = 0; ++ii; ii++; --ii; ii--; ii += ii -= ii *= ii /= ii %= ii; ii <<= ii >>= ii >>>= ii; ii |= ii &= ii ^= ii; And yet, the last line in the following snippet gives compile-time error: Byte bb = 0; ++bb; bb++; --bb; bb--; // ... okay so far! bb += bb; // DOESN'T COMPILE!!! // "The operator += is undefined for the argument type(s) Byte, byte" Can anyone help me figure out what's going on here? The byte b version compiles just fine, so shouldn't Byte bb just follow suit and do the appropriate boxing and unboxing as necessary to accommodate?

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• OpenOffice in Java

  - by user156073

  I need a Java interface to the OpenOffice document conversion which would equal to a manual (Open... and then Save As...) as well as access to the PDF generation. The following are some example of what I want to achieve. 1) Open one type of document (fx. OpenOffice Writer document or Microsoft Office document) onto memory and save it in another supported format. 2) Open one type of document into memory and export it as PDF. I have gone through http://api.openoffice.org but didn't get any material which can help me to get started. I also tried JODConverter but it requires me to run OpenOffice as a service. I wold prefer to include all the core functionality of OpenOffice in one JAR file so that that the user can use my application without installing or running openoffice on their PC. What would be a URL/code snippet from where I can get tutorials to get started? Also do I have to add some JAR files? Will the application work even if I don't have OpenOffice installed on my PC?

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• How do I draw the points in an ESRI Polyline, given the bounding box as lat/long and the "points" as

  - by Aaron

  I'm using OpenMap and I'm reading a ShapeFile using com.bbn.openmap.layer.shape.ShapeFile. The bounding box is read in as lat/long points, for example 39.583642,-104.895486. The bounding box is a lower-left point and an upper-right point which represents where the points are contained. The "points," which are named "radians" in OpenMap, are in a different format, which looks like this: [0.69086486, -1.8307719, 0.6908546, -1.8307716, 0.6908518, -1.8307717, 0.69085056, -1.8307722, 0.69084936, -1.8307728, 0.6908477, -1.8307738, 0.69084626, -1.8307749, 0.69084185, -1.8307792]. How do I convert the points like "0.69086486, -1.8307719" into x,y coordinates that are usable in normal graphics? I believe all that's needed here is some kind of conversion, because bringing the points into Excel and graphing them creates a line whose curve matches the curve of the road at the given location (lat/long). However, the axises need to be adjusted manually and I have no reference as how to adjust the axises, since the given bounding box appears to be in a different format than the given points. The ESRI Shapefile technical description doesn't seem to mention this (http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf).

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• non-copyable objects and value initialization: g++ vs msvc

  - by R Samuel Klatchko

  I'm seeing some different behavior between g++ and msvc around value initializing non-copyable objects. Consider a class that is non-copyable: class noncopyable_base { public: noncopyable_base() {} private: noncopyable_base(const noncopyable_base &); noncopyable_base &operator=(const noncopyable_base &); }; class noncopyable : private noncopyable_base { public: noncopyable() : x_(0) {} noncopyable(int x) : x_(x) {} private: int x_; }; and a template that uses value initialization so that the value will get a known value even when the type is POD: template <class T> void doit() { T t = T(); ... } and trying to use those together: doit<noncopyable>(); This works fine on msvc as of VC++ 9.0 but fails on every version of g++ I tested this with (including version 4.5.0) because the copy constructor is private. Two questions: Which behavior is standards compliant? Any suggestion of how to work around this in gcc (and to be clear, changing that to T t; is not an acceptable solution as this breaks POD types). P.S. I see the same problem with boost::noncopyable.

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• How to std::find using a Compare object?

  - by dehmann

  I am confused about the interface of std::find. Why doesn't it take a Compare object that tells it how to compare two objects? If I could pass a Compare object I could make the following code work, where I would like to compare by value, instead of just comparing the pointer values directly: typedef std::vector<std::string*> Vec; Vec vec; std::string* s1 = new std::string("foo"); std::string* s2 = new std::string("foo"); vec.push_back(s1); Vec::const_iterator found = std::find(vec.begin(), vec.end(), s2); // not found, obviously, because I can't tell it to compare by value delete s1; delete s2; Is the following the recommended way to do it? template<class T> struct MyEqualsByVal { const T& x_; MyEqualsByVal(const T& x) : x_(x) {} bool operator()(const T& y) const { return *x_ == *y; } }; // ... vec.push_back(s1); Vec::const_iterator found = std::find_if(vec.begin(), vec.end(), MyEqualsByVal<std::string*>(s2)); // OK, will find "foo"

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• Value get changed even though I'm not using reference

  - by atch

  In code: struct Rep { const char* my_data_; Rep* my_left_; Rep* my_right_; Rep(const char*); }; typedef Rep& list; ostream& operator<<(ostream& out, const list& a_list) { int count = 0; list tmp = a_list;//----->HERE I'M CREATING A LOCAL COPY for (;tmp.my_right_;tmp = *tmp.my_right_) { out << "Object no: " << ++count << " has name: " << tmp.my_data_; //tmp = *tmp.my_right_; } return out;//------>HERE a_list is changed } I've thought that if I'll create local copy to a_list object I'll be operating on completely separate object. Why isn't so? Thanks.

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• File Storage for Web Applications: Filesystem vs DB vs NoSQL engines

  - by El Yobo

  I have a web application that stores a lot of user generated files. Currently these are all stored on the server filesystem, which has several downsides for me. When we move "folders" (as defined by our application) we also have to move the files on disk (although this is more due to strange design decisions on the part of the original developers than a requirement of storing things on the filesystem). It's hard to write tests for file system actions; I have a mock filesystem class that logs actions like move, delete etc, without performing them, which more or less does the job, but I don't have 100% confidence in the tests. I will be adding some other jobs which need to access the files from other service to perform additional tasks (e.g. indexing in Solr, generating thumbnails, movie format conversion), so I need to get at the files remotely. Doing this over network shares seems dodgy... Dealing with permissions on the filesystem as sometimes given us problems in the past, although now that we've moved to a pure Linux environment this should be less of an issue. What are the downsides of storing files as BLOBs in MySQL? I guess that it would massively increase the database size and reduce the effectiveness of caches, but are there other problems? Do the same problems exist with NoSQL systems like Cassandra? Does anyone have any other suggestions that might be appropriate?

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• How to iterate over modifed std::map values?

  - by Frank

  I have an std::map, and I would like to define an iterator that returns modified values. Typically, a std::map<int,double>::iterator iterates over std::pair<int,double>, and I would like the same behavior, just the double value is multiplied by a constant. I tried it with boost::transform_iterator, but it doesn't compile: #include <map> #include <boost/iterator/transform_iterator.hpp> #include <boost/functional.hpp> typedef std::map<int,double> Map; Map m; m[100] = 2.24; typedef boost::binder2nd< std::multiplies<double> > Function; typedef boost::transform_iterator<Function, Map::value_type*> MultiplyIter; MultiplyIter begin = boost::make_transform_iterator(m.begin(), Function(std::multiplies<double>(), 4)); // now want to similarly create an end iterator // and then iterate over the modified map The error is: error: conversion from 'boost ::transform_iterator< boost::binder2nd<multiplies<double> >, gen_map<int, double>::iterator , boost::use_default, boost::use_default >' to non-scalar type 'boost::transform_iterator< boost::binder2nd<multiplies<double> >, pair<const int, double> * , boost::use_default, boost::use_default >' requested What is gen_map and do I really need it? I adapted the transform_iterator tutorial code from here to write this code ...

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• Null Safe dereferencing in Java like ?. in Groovy using Maybe monad

  - by Sathish

  I'm working on a codebase ported from Objective C to Java. There are several usages of method chaining without nullchecks dog.collar().tag().name() I was looking for something similar to safe-dereferencing operator ?. in Groovy instead of having nullchecks dog.collar?.tag?.name This led to Maybe monad to have the notion of Nothing instead of Null. But all the implementations of Nothing i came across throw exception when value is accessed which still doesn't solve the chaining problem. I made Nothing return a mock, which behaves like NullObject pattern. But it solves the chaining problem. Is there anything wrong with this implementation of Nothing? [http://github.com/sathish316/jsafederef/blob/master/src/s2k/util/safederef/Nothing.java] As far as i can see 1. It feels odd to use mocking library in code 2. It doesn't stop at the first null. 3. How do i distinguish between null result because of null reference or name actually being null? How is it distinguished in Groovy code?

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• Configuring an offscreen framebuffer fails the completeness test

  - by randallmeadows

  I'm trying to create an offscreen framebuffer into which I can do some OpenGL drawing, and then pull the bits out manually. I'm following the instructions here, but in step 4, status is 0 instead of GL_FRAMEBUFFER_COMPLETE_OES. If I insert a call go glGetError() after every gl call, it returns 0 (GL_NO_ERROR) every time. But, the values of variables do not change during the call. E.g., GLuint framebuffer; glGenFramebuffersOES(1, &framebuffer); glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer); the value of framebuffer does not get altered at all (even when I change it to some arbitrary value and re-execute). It's almost like the gl calls are not actually being made. I'm linking against OpenGLES framework, and get no compile, link, or run-time errors (or warnings). I'm at a loss as to what to do to fix this. I've tried continuing on with my drawing, but do not see the results I expect, but at this point I can't tell whether it's because of the above error, or the conversion to a UIImage.

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• Oracle output: cursor, file, or very long string?

  - by Klay

  First, the setup: I have a table in an Oracle10g database with spatial columns. I need to be able to pass in a spatial reference so that I can reproject the geometry into an arbitrary coordinate system. Ultimately, I need to compress the results of this projection to a zip file and make it available for download through a Silverlight project. I would really appreciate ideas as to the best way to accomplish this. In the examples below, the SRID is the Spatial reference ID integer used to convert the geometric points into a new coordinate system. In particular, I can see a couple of possibilities. There are many more, but this is an idea of how I'm thinking: a) Pass SRID to a dynamic view -- perform projection, output a cursor -- send cursor to UTL_COMPRESS -- write output to a file (somehow) -- send URL to Silverlight app b) Use SRID to call Oracle function from Silverlight app -- perform projection, output a string -- build strings into a file -- compress file using SharpZipLib library in .NET -- send bytestream back to Silverlight app I've done the first two steps of b), and the conversion of 100 points took about 7 seconds, which is unacceptably slow. I'm hoping it would be faster doing the processing totally in Oracle. If anyone can see potential problems with either way of doing this, or can suggest a better way, it would be very helpful. Thanks!

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• Your favourite C++ Standard Library wrapper functions?

  - by Neil Butterworth

  This question, asked this morning, made me wonder which features you think are missing from the C++ Standard Library, and how you have gone about filling the gaps with wrapper functions. For example, my own utility library has this function for vector append: template <class T> std::vector<T> & operator += ( std::vector<T> & v1, const std::vector <T> v2 ) { v1.insert( v1.end(), v2.begin(), v2.end() ); return v1; } and this one for clearing (more or less) any type - particularly useful for things like std::stack: template <class C> void Clear( C & c ) { c = C(); } I have a few more, but I'm interested in which ones you use? Please limit answers to wrapper functions - i.e. no more than a couple of lines of code.

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• How to use a class's type as the type argument for an inherited collection property in C#

  - by Edelweiss Peimann

  I am trying to create a representation of various types of card that inherit from a generic card class and which all contain references to their owning decks. I tried re-declaring them, as suggested here, but it still won't convert to the specific card type. The code I currently have is as such: public class Deck<T> : List<T> where T : Card { void Shuffle() { throw new NotImplementedException("Shuffle not yet implemented."); } } public class Card { public Deck<Card> OwningDeck { get; set; } } public class FooCard : Card { public Deck<FooCard> OwningDeck { get { return (Deck<FooCard>)base.OwningDeck; } set { OwningDeck = value; } } } The compile-time error I am getting: Error 2 Cannot convert type 'Game.Cards.Deck' to 'Game.Cards.Deck' And a warning suggesting I use a new operator to specify that the hiding is intentional. Would doing so be a violation of convention? Is there a better way? My question to stackoverflow is this: Can what I am trying to do be done elegantly in the .NET type system? If so, can some examples be provided?

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• Abstracting boxed array structures in J

  - by estanford

  I've been working on a J function for a while, that's supposed to scan a list and put consecutive copies of an element into separate, concatenated boxes. My efforts have taken me as far as the function (<;. 2) ((2&(~:/\)),1:) which tests successive list entries for inequality, returns a list of boolean values, and cuts the list into boxes that end each time the number 1 appears. Here's an example application: (<;. 2) ((2&(~:/\)),1:) 1 2 3 3 3 4 1 1 1 +-+-+-----+-+-----+ |1|1|0 0 1|1|0 0 1| +-+-+-----+-+-----+ The task would be finished if I could then replace all those booleans with their corresponding values in the input argument. I've been looking for some kind of mystery function that would let me do something like final =: mysteryfunction @ (<;. 2) ((2&(~:/\)),1:) final 1 2 3 3 3 4 1 1 1 +-+-+-----+-+-----+ |1|2|3 3 3|4|1 1 1| +-+-+-----+-+-----+ In an ideal situation, there would be some way to abstractly represent the nesting pattern generated by (<;. 2) ((2&(~:/\)),1:) to the original input list. (i.e. "This boxed array over here has the first element boxed at depth one, the second element boxed at depth one, the third, fourth, and fifth elements boxed together at depth one,..., so take that unboxed list over there and box it up the same way.") I tried fooling around with ;. , S: , L:, L. and &. to produce that behavior, but I haven't had much luck. Is there some kind of operator or principle I'm missing that could make this happen? It wouldn't surprise me if I were overthinking the whole issue, but I'm running out of ideas.

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• Creating a Function in SQL Server with a Phone Number as a parameter and returns a Random Number

  - by Emer

  Hi Guys, I am hoping someone can help me here as google is not being as forthcoming as I would have liked. I am relatively new to SQL Server and so this is the first function I have set myself to do. The outline of the function is that it has a Phone number varchar(15) as a parameter, it checks that this number is a proper number, i.e. it is 8 digits long and contains only numbers. The main character I am trying to avoid is '+'. Good Number = 12345678 Bad Number = +12345678. Once the number is checked I would like to produce a random number for each phone number that is passed in. I have looked at substrings, the like operator, Rand(), left(), Right() in order to search through the number and then produce a random number. I understand that Rand() will produce the same random number unless alterations are done to it but right now it is about actually getting some working code. Any hints on this would be great or even point me towards some more documentation. I have read books online and they haven't helped me, maybe I am not looking in the right places. Here is a snippet of code I was working on the Rand declare @Phone Varchar (15) declare @Counter Varchar (1) declare @NewNumber Varchar(15) set @Phone = '12345678' set @Counter = len(@Phone) while @Counter > 0 begin select case when @Phone like '%[0-9]%' then cast(rand()*100000000 as int) else 'Bad Number' end set @counter = @counter - 1 end return Thanks for the help in advance Emer

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• C++ Beginner Delete Question

  - by Pooch

  Hi all, This is my first year learning C++ so bear with me. I am attempting to dynamically allocate memory to the heap and then delete the allocated memory. Below is the code that is giving me a hard time: // String.cpp #include "String.h" String::String() {} String::String(char* source) { this->Size = this->GetSize(source); this->CharArray = new char[this->Size + 1]; int i = 0; for (; i < this->Size; i++) this->CharArray[i] = source[i]; this->CharArray[i] = '\0'; } int String::GetSize(const char * source) { int i = 0; for (; source[i] != '\0'; i++); return i; } String::~String() { delete[] this->CharArray; } Here is the error I get when the compiler tries to delete the CharArray: 0xC0000005: Access violation reading location 0xccccccc0. And here is the last call on the stack: msvcr100d.dll!operator delete(void * pUserData) Line 52 + 0x3 bytes C++ I am fairly certain the error exists within this piece of code but will provide you with any other information needed. Oh yeah, using VS 2010 for XP. Thanks for any and all help!

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• Is it possible to use SqlGeography with Linq to Sql?

  - by cofiem

  I've been having quite a few problems trying to use Microsoft.SqlServer.Types.SqlGeography. I know full well that support for this in Ling to Sql is not great. I've tried numerous ways, beginning with what would the expected way (Database type of geography, CLR type of SqlGeography). This produces the NotSupportedException, which is widely discussed via blogs. I've then gone down the path of treating the geography column as a varbinary(max), as geography is a UDT stored as binary. This seems to work fine (with some binary reading and writing extension methods). However, I'm now running into a rather obscure issue, which does not seem to have happened to many other people. System.InvalidCastException: Unable to cast object of type 'Microsoft.SqlServer.Types.SqlGeography' to type 'System.Byte[]'. This error is thrown from an ObjectMaterializer when iterating through a query. It seems to only occur when the tables containing geography columns are included in a query implicitly (ie. using the EntityRef<> properties to do joins). System.Data.Linq.SqlClient.ObjectReaderCompiler.ObjectReader`2.MoveNext() My question: If I'm retrieving the geography column as varbinary(max), I might expect the reverse error: can't cast byte[] to SqlGeography. That I would understand. This I don't. I do have some properies on the partial LINQ to SQL classes that hide the binary conversion... could those be the issue? Any help appreciated, and I know there's probably not enough information.

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• Using forward declarations for build in datatypes.

  - by bdhar

  I understand that wherever possible we shall use forward declarations instead of includes to speed up the compilation. I have a class Person like this. #pragma once #include <string> class Person { public: Person(std::string name, int age); std::string GetName(void) const; int GetAge(void) const; private: std::string _name; int _age; }; and a class Student like this #pragma once #include <string> class Person; class Student { public: Student(std::string name, int age, int level = 0); Student(const Person& person); std::string GetName(void) const; int GetAge(void) const; int GetLevel(void) const; private: std::string _name; int _age; int _level; }; In Student.h, I have a forward declaration class Person; to use Person in my conversion constructor. Fine. But I have done #include <string> to avoid compilation error while using std::string in the code. How to use forward declaration here to avoid the compilation error? Is it possible? Thanks.

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• Why does using Collections.emptySet() with generics work in assignment but not as a method parameter

  - by Karl von L

  So, I have a class with a constructor like this: public FilterList(Set<Integer> labels) { ... } and I want to construct a new FilterList object with an empty set. Following Joshua Bloch's advice in his book Effective Java, I don't want to create a new object for the empty set; I'll just use Collections.emptySet() instead: FilterList emptyList = new FilterList(Collections.emptySet()); This gives me an error, complaining that java.util.Set<java.lang.Object> is not a java.util.Set<java.lang.Integer>. OK, how about this: FilterList emptyList = new FilterList((Set<Integer>)Collections.emptySet()); This also gives me an error! Ok, how about this: Set<Integer> empty = Collections.emptySet(); FilterList emptyList = new FilterList(empty); Hey, it works! But why? After all, Java doesn't have type inference, which is why you get an unchecked conversion warning if you do Set<Integer> foo = new TreeSet() instead of Set<Integer> foo = new TreeSet<Integer>(). But Set<Integer> empty = Collections.emptySet(); works without even a warning. Why is that?

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• recommended format to save time with MJD + BCD format in database

  - by pierr

  Hi, There is a time represented in MJD and BCD format with 5 bytes .I am wondering what is the recommended format to save this date-time in the sqlite database so that user can search against it ? My first attempt is to save it just as it is, that is a 5 bytes string. The user will use the same format to search and the result will be converted to unix time by the user with following code. However, later, I was suggested to save the time in the integer - the UTC time, for example. But I can not find a standard way to do the conversion. I feel this is a common issue and would like to hear your comments. time_t sidate_to_unixtime(unsigned char sidate[]) { int k = 0; struct tm tm; double mjd; /* check for the undefined value */ if ((sidate[0] == 0xff) && (sidate[1] == 0xff) && (sidate[2] == 0xff) && (sidate[3] == 0xff) && (sidate[4] == 0xff)) { return -1; } memset(&tm, 0, sizeof(tm)); mjd = (sidate[0] << 8) | sidate[1]; tm.tm_year = (int) ((mjd - 15078.2) / 365.25); tm.tm_mon = (int) (((mjd - 14956.1) - (int) (tm.tm_year * 365.25)) / 30.6001); tm.tm_mday = (int) mjd - 14956 - (int) (tm.tm_year * 365.25) - (int) (tm.tm_mon * 30.6001); if ((tm.tm_mon == 14) || (tm.tm_mon == 15)) k = 1; tm.tm_year += k; tm.tm_mon = tm.tm_mon - 2 - k * 12; tm.tm_sec = bcd_to_integer(sidate[4]); tm.tm_min = bcd_to_integer(sidate[3]); tm.tm_hour = bcd_to_integer(sidate[2]); return mktime(&tm); }

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• Template compiling errors on iPhone SDK 3.2

  - by Didier Malenfant

  I'm porting over some templated code from Windows and I'm hitting some compiler differences on the iPhone 3.2 SDK. Original code inside a class template's member function is: return BinarySearch<uint32, CSimpleKey<T> >(key); where BinarySearch is a method inherited from another template. This produces the following error: csimplekeytable.h:131: error: no matching function for call to 'BinarySearch(NEngine::uint32&)' The visual studio compiler seems to walk up the template hierarchy fine but gcc needs me to fully qualify where the function comes from (I have verified this by fixing the same issues with template member variables that way). So I now need to change this into: return CSimpleTable<CSimpleKey<T> >::BinarySearch<uint32, CSimpleKey<T> >(key); Which now produces the following error: csimplekeytable.h:132: error: expected primary-expression before ',' token csimplekeytable.h:132: error: expected primary-expression before '>' token After some head scratching, I believe what's going on here is that it's trying to resolve the '<' before BinarySearch as a 'Less Than' operator for some reason. So two questions: - Am I on the right path with my interpretation of the error? - How do I fix it? -D

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• Is extending a base class with non-virtual destructor dangerous in C++

  - by Akusete

  Take the following code class A { }; class B : public A { }; class C : public A { int x; }; int main (int argc, char** argv) { A* b = new B(); A* c = new C(); //in both cases, only ~A() is called, not ~B() or ~C() delete b; //is this ok? delete c; //does this line leak memory? return 0; } when calling delete on a class with a non-virtual destructor with member functions (like class C), can the memory allocator tell what the proper size of the object is? If not, is memory leaked? Secondly, if the class has no member functions, and no explicit destructor behaviour (like class B), is everything ok? I ask this because I wanted to create a class to extend std::string, (which I know is not recommended, but for the sake of the discussion just bear with it), and overload the +=,+ operator. -Weffc++ gives me a warning because std::string has a non virtual destructor, but does it matter if the sub-class has no members and does not need to do anything in its destructor? -- FYI the += overload was to do proper file path formatting, so the path class could be used like class path : public std::string { //... overload, +=, + //... add last_path_component, remove_path_component, ext, etc... }; path foo = "/some/file/path"; foo = foo + "filename.txt"; //and so on... I just wanted to make sure someone doing this path* foo = new path(); std::string* bar = foo; delete bar; would not cause any problems with memory allocation

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• implement SIMD in C++

  - by Hristo

  I'm working on a bit of code and I'm trying to optimize it as much as possible, basically get it running under a certain time limit. The following makes the call... static affinity_partitioner ap; parallel_for(blocked_range<size_t>(0, T), LoopBody(score), ap); ... and the following is what is executed. void operator()(const blocked_range<size_t> &r) const { int temp; int i; int j; size_t k; size_t begin = r.begin(); size_t end = r.end(); for(k = begin; k != end; ++k) { // for each trainee temp = 0; for(i = 0; i < N; ++i) { // for each sample int trr = trRating[k][i]; int ei = E[i]; for(j = 0; j < ei; ++j) { // for each expert temp += delta(i, trr, exRating[j][i]); } } myscore[k] = temp; } } I'm using Intel's TBB to optimize this. But I've also been reading about SIMD and SSE2 and things along that nature. So my question is, how do I store the variables (i,j,k) in registers so that they can be accessed faster by the CPU? I think the answer has to do with implementing SSE2 or some variation of it, but I have no idea how to do that. Any ideas? Thanks, Hristo

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