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• DDD Model Design and Repository Persistence Performance Considerations

  - by agarhy

  So I have been reading about DDD for some time and trying to figure out the best approach on several issues. I tend to agree that I should design my model in a persistent agnostic manner. And that repositories should load and persist my models in valid states. But are these approaches realistic practically? I mean its normal for a model to hold a reference to a collection of another type. Persisting that model should mean persist the entire collection. Fine. But do I really need to load the entire collection every time I load the model? Probably not. So I can have specialized repositories. Some that load maybe a subset of the object graph via DTOs and others that load the entire object graph. But when do I use which? If I have DTOs, what's stopping client code from directly calling them and completely bypassing the model? I can have mappers and factories to create my models from DTOs maybe? But depending on the design of my models that might not always work. Or it might not allow my models to be created in a valid state. What's the correct approach here?

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• CodeGolf : Find the Unique Paths

  - by st0le

  Here's a pretty simple idea, in this pastebin I've posted some pair of numbers. These represent Nodes of a unidirected connected graph. The input to stdin will be of the form, (they'll be numbers, i'll be using an example here) c d q r a b d e p q so x y means x is connected to y (not viceversa) There are 2 paths in that example. a->b->c->d->e and p->q->r. You need to print all the unique paths from that graph The output should be of the format a->b->c->d->e p->q->r Notes You can assume the numbers are chosen such that one path doesn't intersect the other (one node belongs to one path) The pairs are in random order. They are more than 1 paths, they can be of different lengths. All numbers are less than 1000. If you need more details, please leave a comment. I'll amend as required. Shameless-Plug For those who enjoy Codegolf, please Commit at Area51 for its very own site:) (for those who don't enjoy it, please support it as well, so we'll stay out of your way...)

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• How to properly diagram lambda expressions or traversals through them in Architecture Explorer?

  - by MainMa

  I'm exploring a piece of code in Architecture Explorer in Visual Studio 2010 to study the relations between methods. I noticed a strange behavior. Take the following source code. It generates a hello message based on a template and a template engine, the template engine being a method (a sort of strategy pattern simplified at a maximum for demo purposes). public string GenerateHelloMessage(string personName) { return this.ApplyTemplate( this.DefaultTemplateEngine, this.GenerateLocalizedHelloTemplate(), personName); } private string GenerateLocalizedHelloTemplate() { return "Hello {0}!"; } public string ApplyTemplate( Func<string, string, string> templateEngine, string template, string personName) { return templateEngine(template, personName); } public string DefaultTemplateEngine(string template, string personName) { return string.Format(template, personName); } The graph generated from this code is this one: Change the first method from this: public string GenerateHelloMessage(string personName) { return this.ApplyTemplate( this.DefaultTemplateEngine, this.GenerateLocalizedHelloTemplate(), personName); } to this: public string GenerateHelloMessage(string personName) { return this.ApplyTemplate( (a, b) => this.DefaultTemplateEngine(a, b), this.GenerateLocalizedHelloTemplate(), personName); } and the graph becomes: While semantically identical, those two versions of code produce different dependency graphs, and Architecture Explorer shows no trace of the lambda expression (while Visual Studio's code coverage, for example, shows them, as well as Code analysis seems to be able to understand that the link exists). How would it be possible, without changing the source code, to: Either force Architecture Explorer to display everything, including lambda expressions, Or make it traverse lambda expressions while drawing a dependency through them (so in this case, drawing the dependency from GenerateHelloMessage to DefaultTemplateEngine in the second example)?

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• Lessons From OpenId, Cardspace and Facebook Connect

  - by mark.wilcox

  (c) denise carbonell I think Johannes Ernst summarized pretty well what happened in a broad sense in regards to OpenId, Cardspace and Facebook Connect. However, I'm more interested in the lessons we can take away from this. First  - "Apple Lesson" - If user-centric identity is going to happen it's going to require not only technology but also a strong marketing campaign. I'm calling this the "Apple Lesson" because it's very similar to how Apple iPad saw success vs the tablet market. The iPad is not only a very good technology product but it was backed by a very good marketing plan. I know most people do not want to think about marketing here - but the fact is that nobody could really articulate why user-centric identity mattered in a way that the average person cared about. Second - "Facebook Lesson" - Facebook Connect solves a number of interesting problems that is easy for both consumer and service providers. For a consumer it's simple to log-in without any redirects. And while Facebook isn't perfect on privacy - no other major consumer-focused service on the Internet provides as much control about sharing identity information. From a developer perspective it is very easy to implement the SSO and fetch other identity information (if the user has given permission). This could only happen because a major company just decided to make a singular focus to make it happen. Third - "Developers Lesson" -  Facebook Social Graph API is by far the simplest API for accessing identity information which also is another reason why you're seeing such rapid growth in Facebook enabled Websites. By using a combination of URL and Javascript - the power a single HTML page now gives a developer writing Web applications is simply amazing. For example It doesn't get much simpler than this "http://api.facebook.com/mewilcox" for accessing identity. And while I can't yet share too much publicly about the specifics - the social graph API had a profound impact on me in designing our next generation APIs.  Posted via email from Virtual Identity Dialogue

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• Do ORMs enable the creation of rich domain models?

  - by Augusto

  After using Hibernate on most of my projects for about 8 years, I've landed on a company that discourages its use and wants applications to only interact with the DB through stored procedures. After doing this for a couple of weeks, I haven't been able to create a rich domain model of the application I'm starting to build, and the application just looks like a (horrible) transactional script. Some of the issues I've found are: Cannot navigate object graph as the stored procedures just load the minimum amount of data, which means that sometimes we have similar objects with different fields. One example is: we have a stored procedure to retrieve all the data from a customer, and another to retrieve account information plus a few fields from the customer. Lots of the logic ends up in helper classes, so the code becomes more structured (with entities used as old C structs). More boring scaffolding code, as there's no framework that extracts result sets from a stored procedure and puts it in an entity. My questions are: has anyone been in a similar situation and didn't agree with the store procedure approch? what did you do? Is there an actual benefit of using stored procedures? appart from the silly point of "no one can issue a drop table". Is there a way to create a rich domain using stored procedures? I know that there's the posibility of using AOP to inject DAOs/Repositories into entities to be able to navigate the object graph. I don't like this option as it's very close to voodoo.

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• How to visualize the design of a program in order to communicate it to others

  - by Joris Meys

  I am (re-)designing some packages for R, and I am currently working out the necessary functions, objects, both internal and for the interface with the user. I have documented the individual functions and objects. So I have the description of all the little parts. Now I need to give an overview of how the parts fit together. The scheme of the motor so to say. I've started with making some flowchart-like graphs in Visio, but that quickly became a clumsy and useless collection of boxes, arrrows and-what-not. So hence the question: Is there specific software you can use for vizualizing the design of your program If so, care to share some tips on how to do this most efficiently If not, how do other designers create the scheme of their programs and communicate that to others? Edit: I am NOT asking how to explain complex processes to somebody, nor asking how to illustrate programming logic. I am asking how to communicate the design of a program/package, i.e.: the objects (with key features and representation if possible) the related functions (with arguments and function if possible) the interrelation between the functions at the interface and the internal functions (I'm talking about an extension package for a scripting language, keep that in mind) So something like this : But better. This is (part of) the interrelations between functions in the old package that I'm now redesigning for obvious reasons :-) PS : I made that graph myself, using code extraction tools on the source and feeding the interrelation matrix to yEd Graph Editor.

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• How to prevent duplicate data access methods that retrieve similar data?

  - by Ronald Wildenberg

  In almost every project I work on with a team, the same problem seems to creep in. Someone writes UI code that needs data and writes a data access method: AssetDto GetAssetById(int assetId) A week later someone else is working on another part of the application and also needs an AssetDto but now including 'approvers' and writes the following: AssetDto GetAssetWithApproversById(int assetId) A month later someone needs an asset but now including the 'questions' (or the 'owners' or the 'running requests', etc): AssetDto GetAssetWithQuestionsById(int assetId) AssetDto GetAssetWithOwnersById(int assetId) AssetDto GetAssetWithRunningRequestsById(int assetId) And it gets even worse when methods like GetAssetWithOwnerAndQuestionsById start to appear. You see the pattern that emerges: an object is attached to a large object graph and you need different parts of this graph in different locations. Of course, I'd like to prevent having a large number of methods that do almost the same. Is it simply a matter of team discipline or is there some pattern I can use to prevent this? In some cases it might make sense to have separate methods, i.e. getting an asset with running requests may be expensive so I do not want to include these all the time. How to handle such cases?

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• would it be bad to put <span> tags within the <head>, for grouping meta data in schema.org format?

  - by hdavis84

  Alright, I'm currently practicing schema.org microdata, and trying to find the best route for every site I build. I have found that i can piggyback itemprops on open graph meta tags. I would like to piggyback more itemprops on opengraph meta tags. However, schema.org requires you to change itemtypes to define all aspects of a "thing". Say I'm defining a LocalBusiness. Open graph has street address, locality, and region i'd like to piggyback on. I'd have to do something like: <html lang="en" itemscope itemtype="http://schema.org/LocalBusiness"> <head> ... <meta itemprop="name" content="Business Name" /> <meta property="og:url" itemprop="url" content="http://example.com" /> <meta property="og:image" itemprop="image" content="http://example.com/logo.png" /> <span itemprop="address" itemscope itemtype="http://schema.org/PostalAddress"> <meta property="og:street-address" itemprop="streetAddress" content="1234 Amazing Rd." /> <meta property="og:locality" itemprop="addressLocality" content="Greenfield" /> <meta property="og:region" itemprop="addressRegion" content="IN" /> </span> </head> Although there's more that can be added in, this is enough of an example to show what I'm trying to achieve. I've searched the web to see if it is an issue to use spans in the head or not, because I don't want invalid markup. I know I can mark up the address information in the body of the pages, but the route above would be more efficient. Does anyone have an answer for this?

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• implementing dynamic query handler on historical data

  - by user2390183

  EDIT : Refined question to focus on the core issue Context: I have historical data about property (house) sales collected from various sources in a centralized/cloud data source (assume info collection is handled by a third party) Planning to develop an application to query and retrieve data from this centralized data source Example Queries: Simple : for given XYZ post code, what is average house price for 3 bed room house? Complex: What is estimated price for an house at "DD,Some Street,XYZ Post Code" (worked out from average values of historic data filtered by various characteristics of the house: house post code, no of bed rooms, total area, and other deeper insights like house building type, year of built, features)? In addition to average price, the application should support other property info ** maximum, or minimum price..etc and trend (graph) on a selected property attribute over a period of time**. Hence, the queries should not enforce the search based on a primary key or few fixed fields In other words, queries can be What is the change in 3 Bed Room house price (irrespective of location) over last 30 days? What kind of properties we can get for X price (irrespective of location or house type) The challenge I have is identifying the domain (BI/ Data Analytical or DB Design or DB Query Interface or DW related or something else) this problem (dynamic query on historic data) belong to, so that I can do further exploration My findings so far I could be wrong on the following, so please correct me if you think so I briefly read about BI/Data Analytics - I think it is heavy weight solution for my problem and has scalability issues. DB Design - As I understand RDBMS works well if you know Data model at design time. I am expecting attributes about property or other entity (user) that am going to bring in, would evolve quickly. hence maintenance would be an issue. As I am going to have multiple users executing query at same time, performance would be a bottleneck Other options like Graph DB (http://www.tinkerpop.com/) seems to be bit complex (they are good. but using those tools meant for generic purpose, make me think like assembly programming to solve my problem ) BigData related solution are to analyse data from multiple unrelated domains So, Any suggestion on the space this problem fit in ? (Especially if you have design/implementation experience of back-end for property listing or similar portals)

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• maxItemsInObjectGraph limit required to be changed for server and client

  - by Michael Freidgeim

  We have a wcf service, that expects to return a huge XML data. It worked ok in testing, but in production it failed with error  "Maximum number of items that can be serialized or deserialized in an object graph is '65536'. Change the object graph or increase the MaxItemsInObjectGraph quota."The MSDN article about   dataContractSerializer xml configuration  element  correctly  describes maxItemsInObjectGraph attribute default as 65536, but documentation for of the DataContractSerializer.MaxItemsInObjectGraph property and DataContractJsonSerializer.MaxItemsInObjectGraph Property are talking about Int32.MaxValue, which causes confusion, in particular because Google shows properties articles before configuration articles.When we changed the value in WCF service configuration, it didn't help, because the similar change must be ALSO done on client.There are similar posts:http://stackoverflow.com/questions/6298209/how-to-fix-maxitemsinobjectgraph-error/6298356#6298356You need to set the MaxItemsInObjectGraph on the dataContractSerializer using a behavior on both the client and service. See  for an example.http://devlicio.us/blogs/derik_whittaker/archive/2010/05/04/setting-maxitemsinobjectgraph-for-wcf-there-has-to-be-a-better-way.aspxhttp://stackoverflow.com/questions/2325321/maxitemsinobjectgraph-ignored/4455209#4455209 I had forgot to place this setting in my client app.config file.http://stackoverflow.com/questions/9191167/maximum-number-of-items-that-can-be-serialized-or-deserialized-in-an-object-graphttp://stackoverflow.com/questions/5867304/datacontractjsonserializer-and-maxitemsinobjectgraph?rq=1 -It seems that DataContractJsonSerializer.MaxItemsInObjectGraph has actual default 65536, because there is no configuration for JSON serializer, but  it complains about the limit.I believe that MS should clarify the properties documentation re default limit and make more specific error messages to distinguish server side and client side errors.Note, that as a workaround it's possible to use commonBehaviors section which can be defined only in machine.config:<commonBehaviors> <behaviors> <endpointBehaviors> <dataContractSerializer maxItemsInObjectGraph="..." /> </endpointBehaviors> </behaviors></commonBehaviors>v

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• new[n] and delete every location with delete instead the whole chunk with delete[]

  - by pmr

  Is this valid C++ (e.g. not invoking UB) and does it achieve what I want without leaking memory? valgrinds complains about mismatching free and delete but says "no leaks are possible" in the end. int main() { int* a = new int[5]; for(int i = 0; i < 5; ++i) a[i] = i; for(int i = 0; i < 5; ++i) delete &a[i]; } The reason I'm asking: I have a class that uses boost::intrusive::list and I new every object that is added to that list. Sometimes I know how many objects I want to add to the list and was thinking about using new[] to allocate a chunk and still be able to delete every object on its own with the Disposer-style of boost::intrusive.

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• How to read verbose VC++ linker output

  - by Assaf Lavie

  Trying to debug some linker errors, I turned on /VERBOSE and I'm trying to make sense of the output. It occurs to me that I really don't know how to read it. For example: 1>Compiling version info 1>Linking... 1>Starting pass 1 1>Processed /DEFAULTLIB:mfc80.lib 1>Processed /DEFAULTLIB:mfcs80.lib 1>Processed /DEFAULTLIB:msvcrt.lib 1>Processed /DEFAULTLIB:kernel32.lib 1>Processed /DEFAULTLIB:user32.lib .... 1>Processed /DEFAULTLIB:libgslcblasMD.lib 1>Searching libraries 1> Searching V:\Src\Solutions\\..\..\\Common\Win32\Lib\PlxApi.lib: 1> Searching ..\..\..\..\out\win32\release\lib\camerageometry.lib: 1> Searching ..\..\..\..\out\win32\release\lib\geometry.lib: 1> Found "public: __thiscall VisionMap::Geometry::Box2d::operator class VisionMap::Geometry::Box2DInt(void)const " (??BBox2d@Geometry@VisionMap@@QBE?AVBox2DInt@12@XZ) 1> Referenced in FocusDlg.obj 1> Loaded geometry.lib(Box2d.obj) 1>Processed /DEFAULTLIB:CGAL-vc80-mt.lib 1>Processed /DEFAULTLIB:boost_thread-vc80-mt-1_33_1.lib What's going on here? I think I understand this bit: 1>Processed /DEFAULTLIB:libgslcblasMD.lib 1>Searching libraries 1> Searching V:\Src\Solutions\\..\..\\Common\Win32\Lib\PlxApi.lib: 1> Searching ..\..\..\..\out\win32\release\lib\camerageometry.lib: 1> Searching ..\..\..\..\out\win32\release\lib\geometry.lib: 1> Found "public: __thiscall VisionMap::Geometry::Box2d::operator class VisionMap::Geometry::Box2DInt(void)const " (??BBox2d@Geometry@VisionMap@@QBE?AVBox2DInt@12@XZ) 1> Referenced in FocusDlg.obj 1> Loaded geometry.lib(Box2d.obj) It's trying to find the implementation of the above operator, which is used somewhere in FocusDlg.cpp, and it finds it in geometry.lib. But what does 1>Processed /DEFAULTLIB:libgslcblasMD.lib mean? What determines the order of symbol resolution? Why is it loading this particular symbol while processing libgslcblasMD.lib which is a 3rd party library? Or am I reading it wrong? It seems that the linker is going through the symbols referenced in the project's various object files, but I have no idea in what order. It then searches the static libraries the project uses - by project reference, explicit import and automatic default library imports; but it does so in an order that, again, seems arbitrary to me. When it finds a symbol, for example in geometry.lib, it then continues to find a bunch of other symbols from the same lib: 1> Searching V:\Src\Solutions\\..\..\\Common\Win32\Lib\PlxApi.lib: 1> Searching ..\..\..\..\out\win32\release\lib\camerageometry.lib: 1> Searching ..\..\..\..\out\win32\release\lib\geometry.lib: 1> Found "public: __thiscall VisionMap::Geometry::Box2d::operator class VisionMap::Geometry::Box2DInt(void)const " (??BBox2d@Geometry@VisionMap@@QBE?AVBox2DInt@12@XZ) 1> Referenced in FocusDlg.obj 1> Loaded geometry.lib(Box2d.obj) 1>Processed /DEFAULTLIB:CGAL-vc80-mt.lib 1>Processed /DEFAULTLIB:boost_thread-vc80-mt-1_33_1.lib 1> Found "public: __thiscall VisionMap::Geometry::Box2DInt::Box2DInt(int,int,int,int)" (??0Box2DInt@Geometry@VisionMap@@QAE@HHHH@Z) 1> Referenced in FocusDlg.obj 1> Referenced in ImageView.obj 1> Referenced in geometry.lib(Box2d.obj) 1> Loaded geometry.lib(Box2DInt.obj) 1> Found "public: virtual __thiscall VisionMap::Geometry::Point3d::~Point3d(void)" (??1Point3d@Geometry@VisionMap@@UAE@XZ) 1> Referenced in GPSFrm.obj 1> Referenced in MainFrm.obj 1> Loaded geometry.lib(Point3d.obj) 1> Found "void __cdecl VisionMap::Geometry::serialize<class boost::archive::binary_oarchive>(class boost::archive::binary_oarchive &,class VisionMap::Geometry::Point3d &,unsigned int)" (??$serialize@Vbinary_oarchive@archive@boost@@@Geometry@VisionMap@@YAXAAVbinary_oarchive@archive@boost@@AAVPoint3d@01@I@Z) 1> Referenced in GPSFrm.obj 1> Referenced in MainFrm.obj 1> Loaded geometry.lib(GeometrySerializationImpl.obj) But then, for some reason, it goes on to find symbols that are defined in other libs, and returns to geometry later on (a bunch of times). So clearly it's not doing "look in geometry and load every symbol that's references in the project, and then continue to other libraries". But it's not clear to me what is the order of symbol lookup. And what's the deal with all those libraries being processed at the beginning of the linker's work, but not finding any symbols to load from them? Does this project really not use anything from msvcrt.lib, kernel32.lib? Seems unlikely. So basically I'm looking to decipher the underlying order in the linker's operation.

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• How do I set scons system include path

  - by Michael Anderson

  Using scons I can easily set my include paths: env.Append( CPPPATH=['foo'] ) This passes the flag -Ifoo to gcc However I'm trying to compile with a lot of warnings enabled. In particular with env.Append( CPPFLAGS=['-Werror', '-Wall', '-Wextra'] ) which dies horribly on certain boost includes ... I can fix this by adding the boost includes to the system include path rather than the include path as gcc treats system includes differently. So what I need to get passed to gcc instead of -Ifoo is -isystem foo I guess I could do this with the CPPFLAGS variable, but was wondering if there was a better solution built into scons.

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• Compiling and installing pyactivemq on osx

  - by muanis

  I'm having a hardtime trying to install pyactivemq (link) on my osx leopard. Following a tutorial (in portuguese) on compiling it ends up ok, but when I run the tests i receive only a crypt message: "Fatal Python error: Interpreter not initialized (version mismatch?)" There is not much information on the web about using pyactivemq on osx, but what I could find is that is something related to wrong linking when boost compiles. I'm running: Mac OS 10.5.8 MacPorts 1.8.2 APR 1.3.9 Xcode 3.1.4 Boost 1.41.0 (installing for python 2.5) Activemq-cpp 2.2.6 pyactivemq 0.1.0 If someone has any info on this it would be helpful

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• Links to official style guides

  - by User1

  C++ has several types of styles: MFC, Boost, Google, etc. I would like to examine these styles and determine which one is best for my projects, but I want to read from the official style guidebook. Does anyone have an official guide that they typically use? Here are two that I found. I bet there are more: http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml http://www.boost.org/development/requirements.html Note: This is NOT a discussion about which styleis best..only a call for official style guides that people currently use. Please refrain from bashing other style guides that you don't like. Side question: Is there a good tool that can examine source code and tell if it matches a given style guide?

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• A quick design question about C++ container classes in shared memory

  - by recipriversexclusion

  I am writing a simple wrapper around boost::interprocess's vector container to implement a ring buffer in shared memory (shm) for IPC. Assume that buf is an instance of RingBuffer created in shm. Now, in its ctor, buf itself allocates a private boost::interprocess::vector data member to store values, e.g. m_data. My question is: I think m_data should also be created in shared memory. But it this a necessity? What happens if buf that was created in shm itself, allocates standard memory, i.e. using new. Does this get allocated on the calling process's heap? I don't think buf is allocated there so how come a data member that is private to an object not on a process's heap gets allocated there. I'm confused.

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• C++: what regex library should I use?

  - by Stéphane

  I'm working on a commercial (not open source) C++ project that runs on a linux-based system. I need to do some regex within the C++ code. (I know: I now have 2 problems.) QUESTION: What libraries do people who regularly do regex from C/C++ recommend I look into? A quick search has brought the following to my attention: 1) Boost.Regex (I need to go read the Boost Software License, but this question is not about software licenses) 2) C (not C++) POSIX regex (#include <regex.h>, regcomp, regexec, etc.) 3) http://freshmeat.net/projects/cpp_regex/ (I know nothing about this one; seems to be GPL, therefore not usable on this project) Thanks.

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• Link error (LNK2019) when including other projects in Visual Studio 2005

  - by jules

  I am trying to work with several projects on visual studio 2005. I have one project that depends on two others. I have included those two project in the first project solution, and set the dependencies correctly. I get this error when linking the project: 1>server_controller.obj : error LNK2019: unresolved external symbol "public: __thiscall server_communication::TcpServer::TcpServer(class boost::asio::io_service &,struct server_communication::ServerParameters &)" (??0TcpServer@server_communication@@QAE@AAVio_service@asio@boost@@AAUServerParameters@1@@Z) referenced in function "public: __thiscall server_controller::ServerController::ServerController(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >)" (??0ServerController@server_controller@@QAE@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@0@Z) I seems that the symbols can not be found in the other projects, even though there are defined in those projects.

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• How to initialize a static const map in c++?

  - by Meloun

  Hi, I need just dictionary or asociative array string = int. There is type map C++ for this case. But I need make one map in my class make for all instances(- static) and this map cannot be changed(- const); I have found this way with boost library std::map<int, char> example = boost::assign::map_list_of(1, 'a') (2, 'b') (3, 'c'); Is there other solution without this lib? I have tried something like this, but there are always some issues with map initialization. class myClass{ private: static map<int,int> create_map() { map<int,int> m; m[1] = 2; m[3] = 4; m[5] = 6; return m; } static map<int,int> myMap = create_map(); } thanks

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• C++ -- typedef "inside" template arguments?

  - by redmoskito

  Imagine I have a template function like this: template<Iterator> void myfunc(Iterator a, Iterator::value_type b) { ... } Is there a way to declare a typedef for Iterator::valuetype that I can use in the function signature? For example: template< typename Iterator, typedef Iterator::value_type type> void myfunc(Iterator a, type b) { ... } Thus far, I've resorted to using default template arguments and Boost concept checking to ensure the default is always used: template< typename Iterator, typename type = Iterator::value_type > void myfunc(Iterator a, type b) { BOOST_STATIC_ASSERT(( boost::type_traits::is_same< typename Iterator::value_type, type >::value )); ... } ...but it would be nice if there was support in the language for this type of thing.

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• Detect template presence at compilation time

  - by doublep

  GCC up to 4.5 doesn't have standard C++0x type trait template has_nothrow_move_constructor. I could use it in my package for optimization, but I don't want to rule out one of the common compilers and don't want to overload configuration with symbols like HAVE_STD_HAS_NOTHROW_MOVE_CONSTRUCTOR. Is it somehow possible to use that template if present and just fall back to copying if not present without using any predefined configuration symbols? I also don't want to depend on Boost, since my library is small and doesn't need Boost for any other reasons. In pseudocode, I need something like: template <typename type> struct has_nothrow_move_constructor_robust : public integral_constant <bool, /* if possible */ has_nothrow_move_constructor <type>::value /* otherwise */ false> { }; Since move constructors are only for C++0x anyway, I don't mind using other C++0x features for the above definition, if at all possible.

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• Is this a correct implementation of singleton C++?

  - by Kamal

  class A{ static boost::shared_ptr<A> getInstance(){ if(pA==NULL){ pA = new A(); } return boost::shared_ptr(pA); } //destructor ~A(){ delete pA; pA=NULL; } private: A(){ //some initialization code } //private assigment and copy constructors A(A const& copy); // Not Implemented A& operator=(A const& copy); // Not Implemented static A* pA; }; A* A::pA = NULL;

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• Finding if all elements in a vector<string> are in a string

  - by devin

  I have a vector and I need to see if all the strings in that vector are substrings of another given string. eg vector<string> v; v.push_back("str1"); v.push_back("str2"); string s1 = "str1, str2, str3"; string s2 = "str1, str3"; Is there a way to get true from s1 and false from s2 without looping over the vector? Also, note that due to my environment, I can't use boost. I think if I had boost, I could do this.

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• How to interrupt a waiting C++0x thread?

  - by doublep

  I'm considering to use C++0x threads in my application instead of Boost threads. However, I'm not sure how to reimplement what I have with standard C++0x threads since they don't seem to have an interrupt() method. My current setup is: a master thread that manages work; several worker threads that carry out master's commands. Workers call wait() on at least two different condition variables. Master has a "timed out" state: in this case it tells all workers to stop and give whatever result they got by then. With Boost threads master just uses interrupt_all() on a thread group, which causes workers to stop waiting. In case they are not waiting at the moment, master also sets a bool flag which workers check periodically. However, in C++0x std::thread I don't see any replacement for interrupt(). Do I miss something? If not, how can I implement the above scheme so that workers cannot just sleep forever?

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• Multiset of shared_ptrs as a dynamic priority queue: Concept and practice

  - by Sarah

  I was using a vector-based priority queue typedef std::priority_queue< Event, vector< Event >, std::greater< Event > > EventPQ; to manage my Event objects. Now my simulation has to be able to find and delete certain Event objects not at the top of the queue. I'd like to know if my planned work-around can do what I need it to, and if I have the syntax right. I'd also like to know if dramatically better solutions exist. My plan is to make EventPQ a multiset of smart pointers to Event objects: typedef std::multi_set< boost::shared_ptr< Event > > EventPQ; I'm borrowing functions of the Event class from a related post on a multimap priority queue. // Event.h #include <cstdlib> using namespace std; #include <set> #include <boost/shared_ptr.hpp> class Event; typedef std::multi_set< boost::shared_ptr< Event > > EventPQ; class Event { public: Event( double t, int eid, int hid ); ~Event(); void add( EventPQ& q ); void remove(); 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; EventPQ* mq; EventPQ::iterator mIt; }; // Event.cpp Event::Event( double t, int eid, int hid ) { time = t; eventID = eid; hostID = hid; } Event::~Event() {} void Event::add( EventPQ& q ) { mq = &q; mIt = q.insert( boost::shared_ptr<Event>(this) ); } void Event::remove() { mq.erase( mIt ); mq = 0; mIt = EventPQ::iterator(); } I was hoping that by making EventPQ a container of pointers, I could avoid wasting time copying Events into the container and avoid accidentally editing the wrong copy. Would it be dramatically easier to store the Events themselves in EventPQ instead? Does it make more sense to remove the time keys from Event objects and use them instead as keys in a multimap? Assuming the current implementation seems okay, my questions are: Do I need to specify how to sort on the pointers, rather than the objects, or does the multiset automatically know to sort on the objects pointed to? If I have a shared_ptr ptr1 to an Event that also has a pointer in the EventPQ container, how do I find and delete the corresponding pointer in EventPQ? Is it enough to .find( ptr1 ), or do I instead have to find by the key (time)? Is the Event::remove() sufficient for removing the pointer in the EventPQ container? There's a small chance multiple events could be created with the same time (obviously implied in the use of multiset). If the find() works on event times, to avoid accidentally deleting the wrong event, I was planning to throw in a further check on eventID and hostID. Does this seem reasonable? (Dumb syntax question) In Event.h, is the declaration of dummy class Event;, then the EventPQ typedef, and then the real class Event declaration appropriate? I'm obviously an inexperienced programmer with very spotty background--this isn't for homework. Would love suggestions and explanations. Please let me know if any part of this is confusing. Thanks.

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