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  • Can I use the [] operator in C++ to create virtual arrays

    - by Shane MacLaughlin
    I have a large code base, originally C ported to C++ many years ago, that is operating on a number of large arrays of spatial data. These arrays contain structs representing point and triangle entities that represent surface models. I need to refactor the code such that the specific way these entities are stored internally varies for specific scenarios. For example if the points lie on a regular flat grid, I don't need to store the X and Y coordinates, as they can be calculated on the fly, as can the triangles. Similarly, I want to take advantage of out of core tools such as STXXL for storage. The simplest way of doing this is replacing array access with put and get type functions, e.g. point[i].x = XV; becomes Point p = GetPoint(i); p.x = XV; PutPoint(i,p); As you can imagine, this is a very tedious refactor on a large code base, prone to all sorts of errors en route. What I'd like to do is write a class that mimics the array by overloading the [] operator. As the arrays already live on the heap, and move around with reallocs, the code already assumes that references into the array such as point *p = point + i; may not be used. Is this class feasible to write? For example writing the methods below in terms of the [] operator; void MyClass::PutPoint(int Index, Point p) { if (m_StorageStrategy == RegularGrid) { int xoffs,yoffs; ComputeGridFromIndex(Index,xoffs,yoffs); StoreGridPoint(xoffs,yoffs,p.z); } else m_PointArray[Index] = p; } } Point MyClass::GetPoint(int Index) { if (m_StorageStrategy == RegularGrid) { int xoffs,yoffs; ComputeGridFromIndex(Index,xoffs,yoffs); return GetGridPoint(xoffs,yoffs); // GetGridPoint returns Point } else return m_PointArray[Index]; } } My concern is that all the array classes I've seen tend to pass by reference, whereas I think I'll have to pass structs by value. I think it should work put other than performance, can anyone see any major pitfalls with this approach. n.b. the reason I have to pass by value is to get point[a].z = point[b].z + point[c].z to work correctly where the underlying storage type varies.

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  • Behavior of virtual function in C++

    - by Summer_More_More_Tea
    Hi everyone: I have a question, here are two class below: class Base{ public: virtual void toString(); // generic implementation } class Derive : public Base{ public: ( virtual ) void toString(); // specific implementation } The question is: If I wanna subclass of class Derive perform polymophism using a pointer of type Base, is keyword virtual in the bracket necessary? If the answer is no, what's the difference between member function toString of class Derive with and without virtual?

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  • Bash Script (Cygwin) to grep a logfile for multiple phrases and output a new file for each phrase.

    - by Chris
    Each logfile is titled based on the date it was created in the format YYYY-MM-DD.txt. I need to search each file for five different keywords and output five files prepended with the specific keyword and then the original logfile name. Example: Test-YYYY-MM-DD.txt grep -i -w 'keyword1' YYYY-MM-DD.txt Keyword1-YYYY-MM-DD.txt If it's also possible to email each new file to a different person, that would be helpful as well.

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  • Python: if key in dict vs. try/except

    - by LeeMobile
    I have a question about idioms and readability, and there seems to be a clash of Python philosophies for this particular case: I want to build dictionary A from dictionary B. If a specific key does not exist in B, then do nothing and continue on. Which way is better? try: A["blah"] = B["blah"] except KeyError: pass or if "blah" in B: A["blah"] = B["blah"] "Do and ask for forgiveness" vs. "simplicity and explicitness". Which is better and why?

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  • What is the best way to create a shortcut hook mechanism for Office

    - by rak3sh
    I am looking to create shortcut handler for MS Office. I am creating an addin with VS2010 for Office 2010. The handler needs to listen to all keyboard events when Word/PowerPoint is active. Although there is a lot of material for creating application level shortcut handlers, I couldn't find one that was specific to Office. It would be great if somebody could suggest techniques with sample c# code. Thanks

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  • DISTINCT clause in SQLite

    - by Eye of Hell
    Hello. Recently i found that SQLite don't support DISTINCT ON() clause that seems postgresql-specific. For exeample, if i have table t with columns a and b. And i want to select all items with distinct b. Is the following query the only one and correct way to do so in SQLite? select * from t where b in (select distinct b from t)

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  • Which user account to assign as owner when attaching an SQL Server database?

    - by FreshCode
    This is a simple database security & performance question, but I've always used either a special user (eg. mydbuser), or Windows' built-in NETWORK SECURITY account as the owner when attaching databases to my SQL Server instances. When deploying my database to a production server, is there a specific user I should stick to or avoid? I would think that using an account with a set password could open the database up to a potential security issue.

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  • Creating new folders if they don't exist for fopen

    - by Gbps
    I have a C++ program that takes user input for fopen in order to initiate a file write. Could someone help me find a function which will return a FILE* and use the Windows specific version of mkdir in order to create the folder structure for fopen to never fail to open a new file in the specified location because one of the folders does not exist. Thanks a bunch!

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  • state server session - cross appDomain?

    - by newone1
    When using a State server for session, are sessions still appDomain specific? So for example, I have two different IIS applications(virtual directories) on a web server, and they both point to one state server for session. The session guid from the cookie will be the same across requests from both applications, so will the same session be accessible across both of these applications? Thanks.

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  • Getting a date value in a postgres table column and check if it's bigger than todays date

    - by Roland
    I have a Postgres table called clients. The name column contains certain values eg. test23233 [987665432,2014-02-18] At the end of the value is a date, I need to compare this date, and return all records where this specific date is younger than today I tried select id,name FROM clients where name ~ '(\d{4}\-\d{1,2}\-\d{1,2})'; but this isn't returning any values. How would I go about to achieve the results I want?

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  • What alternatives to __attribute__ exist on 64-bit kernels?

    - by Saifi Khan
    Hi: Is there any alternative to non-ISO gcc specific extension __attribute__ on 64-bit kernels ? Three types that i've noticed are: function attributes, type attributes and variable attributes. eg. i'd like to avoid using __attribute__((__packed__)) for structures passed over the network, even though some gcc based code do use it. Any suggestions or pointers on how to entirely avoid __attribute__ usage in C systems/kernel code ? thanks Saifi.

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  • Generating text file from database

    - by Goldmember
    I have a requirement to hand-code an text file from data residing in a SQL table. Just wondering if there are any best practices here. Should I write it as an XMLDocument first and transform using XSL or just use Streamwriter and skip transformation altogether? The generated text file will be in EDIFACT format, so layout is very specific.

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  • Professional way to write project documentation

    - by EugeneP
    What tools and standards do you use to describe your project, database, modules, classes, their interaction for programmers, let's say after the project is finished. Do you use UML? Are there enterprise standards for Java developers, how to write such a documentation let's say from SUN? Are there specific tools that simplify this documentation process & compilation of neccessary docs. If there are good books on project documenting process, please give me links to Amazon.

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  • How to benchmark functions in clojure

    - by Peter Tillemans
    I know I can get the time take to evaluate a function can be printed out on the screen/stdout using the time function/macro. The time macro returns the value of the evaluated function, which makes it great to use it inline. However I want to automatically measure the runtime under specific circumstances. is there a function which returns the elapsed time in some library to hep with this benchmarking?

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  • How to configure DB connection in a Servlet based JPA application

    - by deamon
    By default DB connections of JPA applications are configured in the META-INF/persistence.xml, when the application is not deployed to a full Java EE application server. In my opinion it is not very elegant to place such environment specific configuration into a file that is inside a .war file. How could a DB connection of a Servlet based JPA application be configured more flexible (=outside of the .war file)?

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  • Is ASP.NET MVC 2 Bin-deployable?

    - by Nevada
    I know that ASP.NET MVC 1.0 is bin-deployable as explained in Phil Haack's article. Is ASP.NET MVC 2.0 also bin-deployable? Has anyone done this already that can point out potential pitfalls specific to version 2.0 if there are any? I would like to deploy a relatively simple ASP.NET MVC 2.0 onto a Windows 2008 Web server that does not have ASP.NET MVC 2.0 installed. It is running .NET Framework 3.5 Service Pack 1. Thanks!

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