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  • Type-safe generic data structures in plain-old C?

    - by Bradford Larsen
    I have done far more C++ programming than "plain old C" programming. One thing I sorely miss when programming in plain C is type-safe generic data structures, which are provided in C++ via templates. For sake of concreteness, consider a generic singly linked list. In C++, it is a simple matter to define your own template class, and then instantiate it for the types you need. In C, I can think of a few ways of implementing a generic singly linked list: Write the linked list type(s) and supporting procedures once, using void pointers to go around the type system. Write preprocessor macros taking the necessary type names, etc, to generate a type-specific version of the data structure and supporting procedures. Use a more sophisticated, stand-alone tool to generate the code for the types you need. I don't like option 1, as it is subverts the type system, and would likely have worse performance than a specialized type-specific implementation. Using a uniform representation of the data structure for all types, and casting to/from void pointers, so far as I can see, necessitates an indirection that would be avoided by an implementation specialized for the element type. Option 2 doesn't require any extra tools, but it feels somewhat clunky, and could give bad compiler errors when used improperly. Option 3 could give better compiler error messages than option 2, as the specialized data structure code would reside in expanded form that could be opened in an editor and inspected by the programmer (as opposed to code generated by preprocessor macros). However, this option is the most heavyweight, a sort of "poor-man's templates". I have used this approach before, using a simple sed script to specialize a "templated" version of some C code. I would like to program my future "low-level" projects in C rather than C++, but have been frightened by the thought of rewriting common data structures for each specific type. What experience do people have with this issue? Are there good libraries of generic data structures and algorithms in C that do not go with Option 1 (i.e. casting to and from void pointers, which sacrifices type safety and adds a level of indirection)?

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  • Make conversion to a native type explicit in C++

    - by Tal Pressman
    I'm trying to write a class that implements 64-bit ints for a compiler that doesn't support long long, to be used in existing code. Basically, I should be able to have a typedef somewhere that selects whether I want to use long long or my class, and everything else should compile and work. So, I obviously need conversion constructors from int, long, etc., and the respective conversion operators (casts) to those types. This seems to cause errors with arithmetic operators. With native types, the compiler "knows" that when operator*(int, char) is called, it should promote the char to int and call operator*(int, int) (rather than casting the int to char, for example). In my case it gets confused between the various built-in operators and the ones I created. It seems to me like if I could flag the conversion operators as explicit somehow, that it would solve the issue, but as far as I can tell the explicit keyword is only for constructors (and I can't make constructors for built-in types). So is there any way of marking the casts as explicit? Or am I barking up the wrong tree here and there's another way of solving this? Or maybe I'm just doing something else wrong...

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  • Behaviour of System.Timer when Interval property changed

    - by lowlyintern
    I have a System.Timer setup to trigger an event every day at 2AM. If the process the timer starts fails then I want the timer to be reset to run every 15 minutes until the process completes succesfully. // this is how the timer is set up. // this is working correctly. double startTime = milliseconds_of_hour_to_start. Timer = new System.Timers.Timer( startTime); Here is the code to reset the timer on success or failure of the event handler. NOTE the timer is not being stopped, just the Interval property is being reset. if (ProcessSuccess) { Timer.Interval = TimeSpan.FromHours(24).TotalMilliseconds; } else { Timer.Interval = TimeSpan.FromMinutes(15).TotalMilliseconds; } My question is this, if the process fails say 4 times, then succeeds will the Timer now be running at around 3AM? i.e. after failing will the original start time of 2AM be advanced by 15 minutes?

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  • Mac OS X - detect file system read

    - by quano
    I want to know what files a specific application is trying to access on my disk. I know that you can use fs_usage, but this outputs events from all applications. I know that you can target a single application, but only one that is already running. I want to detect all readfile-events an application is trying to do, ever since it is started. I don't want to miss out on any event. How do you achieve this?

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  • Recommended laptops for system admins?

    - by 80skeys
    Hey all - I'm in the market for a new laptop and wanted to get some recommendations. I'm a Linux sysadmin and this laptop is primarily for work related use, working from home, after hours, occasional trips to the data center, etc. We all know the drill. My typical setup includes various utilities and tools plus multiple partitions for booting different OS's including VMware. Need serial port of course, DVD-RW, and all the usual stuff we use in our daily routine. I'm kinda thinking a Thinkpad T510 but open to other suggestions! Brief explanation of why you suggest some particular brand and configuration is appreciated.

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  • ASP.NET - How to edit 'bit' data type?

    - by Peter
    I am coding in Visual Basic. I am using a checkbox control. Now depending on its checked property I need to set/unset a bit column in a SQL Server database. Here's the code: Try conSQL.Open() Dim cmd As New SqlCommand("update Student set send_mail = " + _ sendemailCheckBox.Checked.ToString + " where student_id = '" _ + sidnolabel.Text + "'", conSQL) cmd.ExecuteNonQuery() Finally conSQL.Close() End Try The send_mail attribute is of bit datatype. This code is not working. How do I go about it?

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  • How to pass parameters with spaces via cstdlib system

    - by buchtak
    Hi, I have this windows console app which takes a file, do some calculations, and then writes the output to a specified file. The input is specified in "app.exe -input fullfilename" format. I need to call this application from my C++ program, but I have a problem with spaces in paths to files. When I call the app directly from cmd.exe by typing (without specifying output file for clarity) "c:\first path\app.exe" -input "c:\second path\input.file" everything works as expected. But, when I try using cstdlib std::system() function, i.e. std::system(" \"c:\\first path\\app.exe\" -input \"c:\\second path\\input.file\" "); the console prints out that c:\first is not any valid command. It's probably common mistake and has simple solution, but I have been unable to find any. Thx for any help.

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  • Hibernate saveOrUpdate problem on char data type

    - by Yashwant Chavan
    Hi I am using Hibernate 3.0 , facing issue related to the char datatype field. I am trying to save Client pojo in the database, using following method. Problem is my client_id field is char(10) in the database. when client_id is 10 characters it works fine. but when client_id is less than ten characters it gives problem at the time of update. Rather than updating data it try to insert cleint record again and gives the unquie key exeception. i drill down the problem because of char(10) client_id field. it keeps space after client_id value upto 10 characters. Is there is any confuguration to overcome this problem. rather than modifying client_id to varchar2. public boolean saveClient(Clnt client) { boolean lReturnValue = false; SessionFactory sessionFactory = null; Session session = null; Transaction transaction = null; try { HibernateTemplate hibernateTemplate = getHibernateTemplate(); sessionFactory = hibernateTemplate.getSessionFactory(); session = sessionFactory.getCurrentSession(); transaction = session.beginTransaction(); session.saveOrUpdate(client); transaction.commit(); lReturnValue = true; } catch (HibernateException e) { lReturnValue = false; // TODO Auto-generated catch block if (transaction != null) { transaction.rollback(); } e.printStackTrace(); } return lReturnValue; }

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  • Measuring execution time of a call to system() in C++

    - by jm1234567890
    I have found some code on measuring execution time here http://www.dreamincode.net/forums/index.php?showtopic=24685 However, it does not seem to work for calls to system(). I imagine this is because the execution jumps out of the current process. clock_t begin=clock(); system(something); clock_t end=clock(); cout<<"Execution time: "<<diffclock(end,begin)<<" s."<<endl; Then double diffclock(clock_t clock1,clock_t clock2) { double diffticks=clock1-clock2; double diffms=(diffticks)/(CLOCKS_PER_SEC); return diffms; } However this always returns 0 seconds... Is there another method that will work? Also, this is in Linux. Thanks!

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  • postgres - group by on multiple columns - master/detail type table

    - by smpillay
    I have a table order(orderid, ordernumber, clientid, orderdesc etc.,) and a corresponding status for that order on an order_status table ( statusid, orderid, statusdesc, statusNote, statustimestamp) say I have a record in order as below orderid orderumber clientid orderdesc 1111 00980065 ABC blah..blah.. and a corresponding status entries statusid orderid statusdesc statusNote statustimestamp 11 1111 recvd status blah yyyy-mm-dd:10:00 12 1111 clientproce status blah yyyy-mm-dd:11:00 13 1111 clientnotice status blah yyyy-mm-dd:15:00 14 1111 notified status blah yyyy-mm-dd:17:00 How can I get the following result (latest timestamp along with multiple columns) 1111 14 00980065 ABC blah..blah.. notified status blah yyyy-mm-dd:17:00

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  • Response.Redirect causes System.Threading.ThreadAbortException

    - by RandomBen
    When I use Response.Redirect(...) to redirect my form to a new page I get the error: A first chance exception of type 'System.Threading.ThreadAbortException' occurred in mscorlib.dll An exception of type 'System.Threading.ThreadAbortException' occurred in mscorlib.dll but was not handled in user code My understanding of this is that the error is being caused by the webserver aborting the remainder of the page the response.redirect was called on. I know I can add a second parameter to Response.Redirect that is called endResponse. If I set endResponse to True I still get the error but if I set it to False then I do not. I am pretty sure though that that means the webserver is running the rest of the page I redirected away from. Which would seem to be inefficient to say the least. Is there a better way to do this? Something other than Response.Redirect or is there a way to force the old page to stop loading where I will not get a ThreadAbortException?

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  • Why can I derived from a templated/generic class based on that type in C# / C++

    - by stusmith
    Title probably doesn't make a lot of sense, so I'll start with some code: class Foo : public std::vector<Foo> { }; ... Foo f; f.push_back( Foo() ); Why is this allowed by the compiler? My brain is melting at this stage, so can anyone explain whether there are any reasons you would want to do this? Unfortunately I've just seen a similar pattern in some production C# code and wondered why anyone would use this pattern.

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  • System requirements for running windows 8 (basic office use) in virtualbox (ubuntu as host os)

    - by Tor Thommesen
    I want to run windows 8 as a guest os with virtualbox on some thinkpad (haven't bought one yet) running Ubuntu 12.04. Apart from virtualizing windows 8 (mostly just for use with the office suite app) my needs are very modest, I don't need much more than emacs and a browser. What I'd like to know is what kind of specs will be necessary to run windows 8 well as a vm, using the office apps. It would be a shame to waste money on overpowered hardware. Are there any official guidelines from oracle or windows on this? Would this lenovo x220, for example, be sufficiently strong? The specs below were taken from this review. Intel Core i5-2520M dual-core processor (2.5GHz, 3MB cache, 3.2GHz Turbo frequency) Windows 7 Professional (64-bit) 12.5-inch Premium HD (1366 x 768) LED Backlit Display (IPS) Intel Integrated HD Graphics 4GB DDR3 (1333MHz) 320GB Hitachi Travelstar hard drive (Z7K320) Intel Centrino Advanced-N 6205 (Taylor Peak) 2x2 AGN wireless card Intel 82579LM Gigabit Ethernet 720p High Definition webcam Fingerprint reader 6-cell battery (63Wh) and optional slice battery (65Wh) Dimensions: 12 (L) x 8.2 (W) x 0.5-1.5 (H) inches with 6-cell battery Weight: 3.5 pounds with 6-cell battery 4.875 pounds with 6-cell battery and optional external battery slice Price as configured: $1,299.00 (starting at $979.00)

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  • Would you allow this type of query?

    - by user564577
    I'm exploring using an ORM tool in our development shop, and in particular Entity Framework 4.0. Since we work with VERY large databases, I'm a bit concerned about the query's it generates. Doing something simple like getting clients with an address in a state looks like below. As a database developer or admin would you allow this? Is it as bad as it looks? Assume every join is on a clustered index. SELECT [Project2].[ClientKey] AS [ClientKey], [Project2].[FirstName] AS [FirstName], [Project2].[LastName] AS [LastName], [Project2].[IsEnabled] AS [IsEnabled], [Project2].[ChangeUser] AS [ChangeUser], [Project2].[ChangeDate] AS [ChangeDate], [Project2].[C1] AS [C1], [Project2].[AddressKey] AS [AddressKey], [Project2].[ClientKey1] AS [ClientKey1], [Project2].[AddressTypeCode] AS [AddressTypeCode], [Project2].[PrimaryAddress] AS [PrimaryAddress], [Project2].[AddressLine1] AS [AddressLine1], [Project2].[AddressLine2] AS [AddressLine2], [Project2].[City] AS [City], [Project2].[State] AS [State], [Project2].[ZIP] AS [ZIP] FROM ( SELECT [Distinct1].[ClientKey] AS [ClientKey], [Distinct1].[FirstName] AS [FirstName], [Distinct1].[LastName] AS [LastName], [Distinct1].[IsEnabled] AS [IsEnabled], [Distinct1].[ChangeUser] AS [ChangeUser], [Distinct1].[ChangeDate] AS [ChangeDate], [Extent3].[AddressKey] AS [AddressKey], [Extent3].[ClientKey] AS [ClientKey1], [Extent3].[AddressTypeCode] AS [AddressTypeCode], [Extent3].[PrimaryAddress] AS [PrimaryAddress], [Extent3].[AddressLine1] AS [AddressLine1], [Extent3].[AddressLine2] AS [AddressLine2], [Extent3].[City] AS [City], [Extent3].[State] AS [State], [Extent3].[ZIP] AS [ZIP], CASE WHEN ([Extent3].[AddressKey] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1] FROM (SELECT DISTINCT [Extent1].[ClientKey] AS [ClientKey], [Extent1].[FirstName] AS [FirstName], [Extent1].[LastName] AS [LastName], [Extent1].[IsEnabled] AS [IsEnabled], [Extent1].[ChangeUser] AS [ChangeUser], [Extent1].[ChangeDate] AS [ChangeDate] FROM [Common].[Clients] AS [Extent1] INNER JOIN [Common].[ClientAddresses] AS [Extent2] ON [Extent1].[ClientKey] = [Extent2].[ClientKey] WHERE (( CAST(CHARINDEX(UPPER('D'), UPPER([Extent1].[LastName])) AS int)) > 0) AND ([Extent1].[IsEnabled] = 1) AND ([Extent2].[City] IS NOT NULL) AND ((UPPER([Extent2].[City])) = (UPPER('Colorado Springs'))) ) AS [Distinct1] LEFT OUTER JOIN [Common].[ClientAddresses] AS [Extent3] ON [Distinct1].[ClientKey] = [Extent3].[ClientKey] ) AS [Project2] ORDER BY [Project2].[ClientKey] ASC, [Project2].[FirstName] ASC, [Project2].[LastName] ASC, [Project2].[IsEnabled] ASC, [Project2].[ChangeUser] ASC, [Project2].[ChangeDate] ASC, [Project2].[C1] ASC

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  • 9gag type of website

    - by awtasdfas
    for something like www.9gag.com , which open source mvc framework can be used? in particular the main page, with highly rated content is what i am looking for.. along with an option for users to thumbs up/heart every article/post/blog/vlog/podcast/link.

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  • File System Types in .Net

    - by Avi
    I don't get the abstractions and the terminology :-( For example, DirectoryInfo.FullName is defined as the full path of the directory or file, but it's a string! So is DirectoryInfo.Name, FileInfo.FullName, Path.GetDirectoyName and so on. This means that in .Net there is no "depth" (or "meat" - my English isn't so good) for the file system objects. There's no protection from a type system. I can't, for example, define two Path objects and ask if one of them is "above" the other - I have to manipulate the strings. I can't differentiate between a Path that identifies a directory and a path that identifies a file. I can't do anything!-( Just manipulate strings. Is this correct (or am I simply missing something). If correct, are there any alternatives?

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  • Java: Get current Date and Time from Server not System clock

    - by Insectatorious
    In my Java program, I need to create an instance of the current moment in time. I use Date date = new Date(); This gives me the current date and time as per the host machine's system clock. Is there any way I can get the current date and time from an online server? The world time server perhaps? I have seen this post and it describes what I want but I'm afraid I need more help than what's provided there. In a nutshell, I want to get a date and time that is not dependant on the host machine's system clock. Thanks!

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