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  • How to set the width of a cell in a UITableView in grouped style

    - by Tomen
    I have been working on this for about 2 days, so i thought i share my learnings with you. The question is: Is it possible to make the width of a cell in a grouped UITableView smaller? The answer is: No. But there are two ways you can get around this problem. Solution #1: A thinner table It is possible to change the frame of the tableView, so that the table will be smaller. This will result in UITableView rendering the cell inside with the reduced width. A solution for this can look like this: -(void)viewWillAppear:(BOOL)animated { CGFloat tableBorderLeft = 20; CGFloat tableBorderRight = 20; CGRect tableRect = self.view.frame; tableRect.origin.x += tableBorderLeft; // make the table begin a few pixels right from its origin tableRect.size.width -= tableBorderLeft + tableBorderRight // reduce the width of the table tableView.frame = tableRect; } Solution #2: Having cells rendered by images This solution is described here: http://cocoawithlove.com/2009/04/easy-custom-uitableview-drawing.html I hope this information is helpful to you. It took me about 2 days to try a lot of possibilities. This is what was left.

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  • License key pattern detection?

    - by Ricket
    This is not a real situation; please ignore legal issues that you might think apply, because they don't. Let's say I have a set of 200 known valid license keys for a hypothetical piece of software's licensing algorithm, and a license key consists of 5 sets of 5 alphanumeric case-insensitive (all uppercase) characters. Example: HXDY6-R3DD7-Y8FRT-UNPVT-JSKON Is it possible (or likely) to extrapolate other possible keys for the system? What if the set was known to be consecutive; how do the methods change for this situation, and what kind of advantage does this give? I have heard of "keygens" before, but I believe they are probably made by decompiling the licensing software rather than examining known valid keys. In this case, I am only given the set of keys and I must determine the algorithm. I'm also told it is an industry standard algorithm, so it's probably not something basic, though the chance is always there I suppose. If you think this doesn't belong in Stack Overflow, please at least suggest an alternate place for me to look or ask the question. I honestly don't know where to begin with a problem like this. I don't even know the terminology for this kind of problem.

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  • Generating all unique crossword puzzle grids

    - by heydenberk
    I want to generate all unique crossword puzzle grids of a certain grid size (4x4 is a good size). All possible puzzles, including non-unique puzzles, are represented by a binary string with the length of the grid area (16 in the case of 4x4), so all possible 4x4 puzzles are represented by the binary forms of all numbers in the range 0 to 2^16. Generating these is easy, but I'm curious if anyone has a good solution for how to programmatically eliminate invalid and duplicate cases. For example, all puzzles with a single column or single row are functionally identical, hence eliminating 7 of those 8 cases. Also, according to crossword puzzle conventions, all squares must be contiguous. I've had success removing all duplicate structures, but my solution took several minutes to execute and probably was not ideal. I'm at something of a loss for how to detect contiguity so if anyone has ideas on this it'd be much appreciated. I'd prefer solutions in python but write in whichever language you prefer. If anyone wants, I can post my python code for generating all grids and removing duplicates, slow as it may be.

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  • Action on each method's return value

    - by RobGlynn
    What I'd like to do is take some action using the value returned by every method in a class. So for instance, if I have a class Order which has a method public Customer GetCustomer() { Customer CustomerInstance = // get customer return CustomerInstance; } Let's say I want to log the creation of these - Log(CustomerInstance); My options (AFAIK) are: Call Log() in each of these methods before returning the object. I'm not a fan of this because it gets unwieldy if used on a lot of classes with a lot of methods. It also is not an intrinsic part of the method's purpose. Use composition or inheritance to layer the log callon the Order class similar to: public Customer GetCustomer() { Customer CustomerInstance = this.originalCustomer.GetCustomer(); Log(CustomerInstance); return CustomerInstance; } I don't think this buys me anything over #1. Create extension methods on each of the returned types: Customer CustomerInstance = Order.GetCustomer().Log(); which has just as many downsides. I'm looking to do this for every (or almost every) object returned, automatically if possible, without having to write double the amount of code. I feel like I'm either trying to bend the language into doing something it's not supposed to, or failing to recognize some language feature that would enable this. Possible solutions would be greatly appreciated.

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  • how can I make a "downstream only" copy of a file in TFS

    - by jcollum
    I've got this SQL script that needs to exist in two places in source control. I want to have only one real copy of this file and keep a virtual copy of the file in the other solution. One is needed for a unit test and the other for a development tool. The files, should, by definition, always be the same. If they have differences then there's a problem with our process. In Sourcegear I could make a virtual copy of a specific version of a file and keep it somewhere else in the source tree. That doesn't seem to be possible in TFS. Is it possible in SVN? So what are my options here? Branching/merging -- which is what the TFS team says I should be doing here -- means just another step that I have to remember to do. Plus it isn't automatic and I would prefer that this be automated. Is there some way to run an exe on checkin of a specific file? I'm thinking if I could do that then I could do a checkout-edit-checkin of the downstream copy of the file.

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  • how to delete the pluginassembly after AppDomain.Unload(domain)

    - by Ase
    hello, i have a weird problem. i would like to delete an assembly(plugin.dll on harddisk) which is already loaded, but the assembly is locked by the operating system (vista), even if i have unloaded it. f.e. AppDomainSetup setup = new AppDomainSetup(); setup.ShadowCopyFiles = "true"; AppDomain appDomain = AppDomain.CreateDomain(assemblyName + "_AppDomain", AppDomain.CurrentDomain.Evidence, setup); IPlugin plugin = (IPlugin)appDomain.CreateInstanceFromAndUnwrap(assemblyName, "Plugin.MyPlugins"); I also need the assemblyinfos, because I don't know which classes in the pluginassembly implements the IPlugin Interface. It should be possible to have more than one Plugin in one Pluginassembly. Assembly assembly = appDomain.Load(assemblyName); if (assembly != null) { Type[] assemblyTypes = assembly.GetTypes(); foreach (Type assemblyTyp in assemblyTypes) { if (typeof(IPlugin).IsAssignableFrom(assemblyTyp)) { IPlugin plugin = (IPlugin)Activator.CreateInstance(assemblyTyp); plugin.AssemblyName = assemblyNameWithEx; plugin.Host = this; } } } AppDomain.Unload(appDomain); How is it possible to get the assemblyinfos from the appDomain without locking the assembly? best regards

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  • Displaying Query Results Horizontally

    - by AndyD273
    I am wondering if it is possible to take the results of a query and return them as a CSV string instead of as a column of cells. Basically, we have a table called Customers, and we have a table called CustomerTypeLines, and each Customer can have multiple CustomerTypeLines. When I run a query against it, I run into problems when I want to check multiple types, for instance: Select * from Customers a Inner Join CustomerTypeLines b on a.CustomerID = b.CustomerID where b.CustomerTypeID = 14 and b.CustomerTypeID = 66 ...returns nothing because a customer can't have both on the same line, obviously. In order to make it work, I had to add a field to Customers called CustomerTypes that looks like ,14,66,67, so I can do a Where a.CustomerTypes like '%,14,%' and a.CustomerTypes like '%,66,%' which returns 85 rows. Of course this is a pain because I have to make my program rebuild this field for that Customer each time the CustomerTypeLines table is changed. It would be nice if I could do a sub query in my where that would do the work for me, so instead of returning the results like: 14 66 67 it would return them like ,14,66,67, Is this possible?

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  • Implementing search functionality with multiple optional parameters against database table.

    - by quarkX
    Hello, I would like to check if there is a preferred design pattern for implementing search functionality with multiple optional parameters against database table where the access to the database should be only via stored procedures. The targeted platform is .Net with SQL 2005, 2008 backend, but I think this is pretty generic problem. For example, we have customer table and we want to provide search functionality to the UI for different parameters, like customer Type, customer State, customer Zip, etc., and all of them are optional and can be selected in any combinations. In other words, the user can search by customerType only or by customerType, customerZIp or any other possible combinations. There are several available design approaches, but all of them have some disadvantages and I would like to ask if there is a preferred design among them or if there is another approach. Generate sql where clause sql statement dynamically in the business tier, based on the search request from the UI, and pass it to a stored procedure as parameter. Something like @Where = ‘where CustomerZip = 111111’ Inside the stored procedure generate dynamic sql statement and execute it with sp_executesql. Disadvantage: dynamic sql, sql injection Implement a stored procedure with multiple input parameters, representing the search fields from the UI, and use the following construction for selecting the records only for the requested fields in the where statement. WHERE (CustomerType = @CustomerType OR @CustomerType is null ) AND (CustomerZip = @CustomerZip OR @CustomerZip is null ) AND ………………………………………… Disadvantage: possible performance issue for the sql. 3.Implement separate stored procedure for each search parameter combinations. Disadvantage: The number of stored procedures will increase rapidly with the increase of the search parameters, repeated code.

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  • Which Android hardware devices should I test on? [closed]

    - by Tchami
    Possible Duplicate: What hardware devices do you test your Android apps on? I'm trying to compile a list of Android hardware devices that it would make sense to buy and test against if you want to target an as broad audience as possible, while still not buying every single Android device out there. I know there's a lot of information regarding screen sizes and Android versions available elsewhere, but: when developing for Android it's not terribly useful to know if the screen size of a device is 480x800 or 320x240, unless you feel like doing the math to convert that into Android "units" (i.e. small, normal, large or xlarge screens, and ldpi, mdpi, hdpi or xhdpi densities). Even knowing the dimensions of a device, you cannot be sure of the actual Android units as there's some overlap, see Range of screens supported in the Android documentation Taking into account the distribution of Platform versions and Screen Sizes and Densities, below is my current list based on information from the Wikipedia article on Comparison of Android devices. I'm fairly sure the information in this list is correct, but I'd welcome any suggestions/changes. Phones | Model | Android Version | Screen Size | Density | | HTC Wildfire | 2.1/2.2 | Normal | mdpi | | HTC Tattoo | 1.6 | Normal | mdpi | | HTC Hero | 2.1 | Normal | mdpi | | HTC Legend | 2.1 | Normal | mdpi | | Sony Ericsson Xperia X8 | 1.6/2.1 | Normal | mdpi | | Motorola Droid | 2.0-2.2 | Normal | hdpi | | Samsung Galaxy S II | 2.3 | Normal | hdpi | | Samsung Galaxy Nexus | 4.0 | Normal | xhdpi | | Samsung Galaxy S III | 4.0 | Normal | xhdpi | **Tablets** | Model | Android Version | Screen Size | Density | | Samsung Galaxy Tab 7" | 2.2 | Large | hdpi | | Samsung Galaxy Tab 10" | 3.0 | X-Large | mdpi | | Asus Transformer Prime | 4.0 | X-Large | mdpi | | Motorola Xoom | 3.1/4.0 | X-Large | mdpi | N.B.: I have seen (and read) other posts on SO on this subject, e.g. Which Android devices should I test against? and What hardware devices do you test your Android apps on? but they don't seem very canonical. Maybe this should be marked community wiki?

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  • Calling member functions dynamically

    - by user652511
    I'm pretty sure it's possible to call a class and its member function dynamically in Delphi, but I can't quite seem to make it work. What am I missing? // Here's a list of classes (some code removed for clarity) moClassList : TList; moClassList.Add( TClassA ); moClassList.Add( TClassB ); // Here is where I want to call an object's member function if the // object's class is in the list: for i := 0 to moClassList.Count - 1 do if oObject is TClass(moClassList[i]) then with oObject as TClass(moClassList[i]) do Foo(); I get an undeclared identifier for Foo() at compile. Clarification/Additional Information: What I'm trying to accomplish is to create a Change Notification system between business classes. Class A registers to be notified of changes in Class B, and the system stores a mapping of Class A - Class B. Then, when a Class B object changes, the system will call a A.Foo() to process the change. I'd like the notification system to not require any hard-coded classes if possible. There will always be a Foo() for any class that registers for notification. Maybe this can't be done or there's a completely different and better approach to my problem. By the way, this is not exactly an "Observer" design pattern because it's not dealing with objects in memory. Managing changes between related persistent data seems like a standard problem to be solved, but I've not found very much discussion about it. Again, any assistance would be greatly appreciated. Jeff

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  • How can I create dynamically updated views in a tab bar view, based on settings selection?

    - by Diggers
    Hi all, Noob question.... I've created a Tab Bar application. It has four tabs and works fine. Each view is created with a XIB and is effectively static. Each view takes user input and responds on screen. What I need to be able to do is change the input options the user have - in effect remove some UITextFields dependant upon which option the user selects in settings. I've created root.plist and created settings no problem i've also created additional XIBS for the altered UI, but what I don't know how to do, is call these into the tab view controller on demand. Effectively tab one has 3 possible views, tab two 3 possible views etc. But I only want the one that's relevant for the users settings selction to be displayed? Make sense? For reference, if we call the different views - UIInputViewA1, ...A2,....A3 UIInputViewB1,....B2....B3 etc. Hope someone can help, been trawling the net for nights trying to get my head round this. Beggining iPhone Development Bible doesn't help either. If you need any more info, please shout. Cheers Paul.

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  • Bind WPF control with property of custom type

    - by TheBlueSky
    Hello everyone, I'm trying to bind a Label's 'Content' property to a property from some custom type I have; unfortunately, I didn't figure out how to do it, and that's why I'm here :) Let's assume that I have the following type (can be in the same namespace as my WPF Window that contains the Label or different namespace): namespace MyNS { pubic class Person { private int age = 0; public int Age { get { return age; } } public void GetOlder { age++; } } } 1) How to I bind my Label to 'Age' property? 2) At runtime I will create an instance of 'Person'; I want to make sure that my Label is bound to the right instance; i.e. if I called: Person SomePerson = new Person(); SomePerson.GetOlder(); I want my Lable to have the new value of 'Age' property for 'SomePerson'. 3) If #2 was possible (I hope so), what if I called 'GetOlder' in different thread? Will I still get the latest value of 'Age'? Or do I have to take care of some other things as well to make this scenario possible? Thanks in advance, TheBlueSky

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  • Is there such a thing as a MemberExpression that handles a many-to-many relationship?

    - by Jaxidian
    We're trying to make it easy to write strongly-typed code in all areas of our system, so rather than setting var sortColumn = "FirstName" we'd like to say sortOption = (p => p.FirstName). This works great if the sortOption is of type Expression<Func<Person, object>> (we actually use generics in our code but that doesn't matter). However, we run into problems for many-to-many relationships because this notation breaks down. Consider this simple code: internal class Business { public IQueryable<Address> Addresses { get; set; } public string Name { get; set; } } internal class Address { public State MyState { get; set; } } internal class State { public string Abbreviation { get; set; } public int StateID { get; set; } } Is it possible to have this sort of MemberExpression to identify the StateID column off of a business? Again, the purpose of using this is not to return a StateID object, it's to just identify that property off of that entity (for sorting, filtering, and other purposes). It SEEMS to me that there should be some way to do this, even if it's not quite as pretty as foo = business.Addresses.SomeExtension(a => a.State.StateID);. Is this really possible? If more background is needed, take a look at this old question of mine. We've since updated the code significantly, but this should give you the general detailed idea of the context behind this question.

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  • Writing all the html of a document with jquery instead of in the page body?

    - by Robert
    I'm a UI person currently working on a web application, where most of the people I work with are back end developers. I'm currently at a disagreement with them about whether or not the above is a prudent thing to do. This application doe use quite a bit of JavaScript, and wouldn't even work without it unfortunately. This being the case, One of the back end developers that I'm working with is claiming that pages could and even SHOULD be build completely with JavaScript or jquery. This caught me completely off guard. We're talking about div tags, lists, background images and text here. I'm trying to explain to him that this isn't the right way to do things at all, and from a best practices perspective: content(html) should be separate from presentation(css), and behavior(script etc.). I know that it's possible to write html in jquery, although I haven't done it, but am I wrong in my thinking that this isn't the way things should be done. Is it even possible to write ALL the code with jquery? would love to hear any thoughts either way, as I will be discussing this with him again tomorrow.

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  • XSLT Type Checking

    - by mo
    Hi Folks Is it possible to check an elements ComplexType? i have this (simplified): complexType Record complexType Customer extension of Record complexType Person extension of Record <xsl:template match="/"> <records> <xsl:apply-templates /> </records> </xsl:template> <xsl:template match="!!! TYPECHECK FOR RECORD !!!" name="Record"> <record><xsl:value-of select="." /></record> </xsl:template> is it possible to check elementstype incl. inheritence? i dont know the elements name only that they are a subtype of Record. schema 1: complexType name="Customer" extension base="Record" element name="customers" element name="customer" type="Customer" schema 2: complexType name="Person" extension base="Record" element name="persons" element name="person" type="Person" schema ?: complexType name="UnknownType" extension base="Record" element name="unknowns" element name="unknown" type="UnknownType" xml 1: <customers> <customer /> <customer /> </customers> xml 2: <persons> <person /> <person /> </persons> xml ?: <?s> <? /> <? /> </?s> the xml input ist custom so i have to match by the type (i think)

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  • Passing huge amounts of data as an hexadecimal (0x123AB...) parameter of a clr stored procedure in s

    - by user193655
    I post this question has followup of This question, since the thread is not recieving more answers. I'm trying to understand if it is possible to pass as a parameter of a CLR stored procedure a large amount of data as "0x5352532F...". This is to avoid to send the data directly to the CLR stored procedure, instead of sending ti to a temporary DB field and from there passing it as varbinary(max) parmeter to the CLR stored procedure. I have a triple question: 1) is it possible, if yes how? Let's say i want to pass a pdf file to the CLR stored procedure (not the path, the full bits that make up the file). Something like: exec MyCLRStoredProcs.dbo.insertfile @file_remote_path ='c:\temp\test_file.txt' , @file_contents=0x4D5A90000300000004000.... --(this long list is the file content) where insertfile is a stored proc that writes to the server path (at file_remote_path) the binary data I pass as (file_contents). 2) is it there corruption risk of adopting this approach (or it is the same approach that sql server uses behind the scenes)? 3) how to convert the content of a file into the "0x23423..." hexadecimal representation

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  • Need help INSERT record(s) MySQL DB

    - by JM4
    I have an online form which collects member(s) information and stores it into a very long MySQL database. We allow up to 16 members to enroll at a single time and originally structured the DB to allow such. For example: If 1 Member enrolls, his personal information (first name, last name, address, phone, email) are stored on a single row. If 15 Members enroll (all at once), their personal information are stored in the same single row. The row has information housing columns for all 'possible' inputs. I am trying to consolidate this code and having every nth member that enrolls put onto a new record within the database. I have seen sugestions before for inserting multiple records as such: INSERT INTO tablename VALUES (('$f1name', '$f1address', '$f1phone'), ('$f2name', '$f2address', '$f2phone')... The issue with this is two fold: I do not know how many records are being enrolled from person to person so the only way to make the statement above is to use a loop The information collected from the forms is NOT a single array so I can't loop through one array and have it parse out. My information is collected as individual input fields like such: Member1FirstName, Member1LastName, Member1Phone, Member2Firstname, Member2LastName, Member2Phone... and so on Is it possible to store information in separate rows WITHOUT using a loop (and therefore having to go back and completely restructure my form field names and such (which can't happen due to the way the validation rules are built.)

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  • How can I get a default value in some instances but not others?

    - by Connor Wagner
    I am making an iPhone app and want to use an 'if' statement and a boolean to set default values in some instances but not others... is this possible? Are there alternative options if it is not possible? In the MainViewController.m I have: @interface MainViewController (){ BOOL moveOver; } [...] - (void)viewDidLoad { [super viewDidLoad]; _label.text = [NSString stringWithFormat:@"%i", computerSpeed]; } } [...] - (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller { [self dismissViewControllerAnimated:YES completion:nil]; moveOver = true; } The problem that it is redefined when the ViewDidLoad runs... I need a statement that will not redefine when the ViewDidLoad runs. I have something that I feel like is much closer to working... In the ViewDidLoad I have: if (playToInt != 10 || computerMoveSpeed != 3) { moveOver = TRUE; } which connects to my created method, gameLoop. It has if (moveOver == false) { computerMoveSpeed = 3; playToInt = 10; } I have tried putting the code in the gameLoop into the ViewDidLoad, but it had the same effect. When moveOver was false, the computerMoveSpeed and the playToInt were both seemingly 0. I have two UITextFields and typed 10 and 3 in them... does this not set it to the default? It seems to set the default to 0 for both, how do I change this? THIS IS A DIFFERENT ISSUE THAN THE THREE BOOLEAN VALUES QUESTION

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  • Flex Setting form height dynamically

    - by Daryl
    I'm not sure if this is possible, is there a way to get the <mx:Form> to set its own height based on the position of an element within it? For example something like this: <mx:Form height="{submitBtn.y + submitBtn.height}"> <mx:FormItem>... </mx:FormItem> <mx:FormItem>... </mx:FormItem> <mx:FormItem>... </mx:FormItem> <mx:FormItem> <s:Button id="submitBtn" label="Submit" /> </mx:FormItem> </mx:Form> where the form height is dynamically set based on submitBtn's y position and its height. I tried using Alert.show to show these values and turned out submitBtn.y = 0 and submitBtn.height = 21. height sounds reasonable, but I know the y of submitBtn can't be 0 since it's below several other Is it possible to set the form height dynamically?

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  • Minimizing MySQL output with Compress() and by concatening results?

    - by johnrl
    Hi all. It is crucial that I transfer the least amount of data possible between server and client. Therefore I thought of using the mysql Compress() function. To get the max compression I also want to concatenate all my results in one large string (or several of max length allowed by MySql), to allow for similar results to be compressed, and then compress these/that string. 1st problem (concatenating mysql results): SELECT name,age FROM users returns 10 results. I want to concatenate all these results in one strign on the form: name,age,name,age,name,age... and so on. Is this possible? 2nd problem (compressing the results from above) When I have comstructed the concatenated string as above I want to compress it. If I do: SELECT COMPRESS('myname'); then it just gives me as output the character '-' - sometimes it even returns unprintable characters. How do I get COMPRESS() to return a compressed printable string that I can trasnfer in ex ASCII encoding?

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  • Best way to store data in database when you don't know the type

    - by stiank81
    I have a table in my database that represents datafields in a custom form. The DataField gives some representation of what kind of control it should be represented with, and what value type it should take. Simplified you can say that I have 2 entities in this table - Textbox taking any string and Textbox only taking numbers. Now I have the different values stored in a separate table, referencing the datafield definition. What is the best way to store the data value here, when the type differs? One possible solution is to have the FieldValue table hold one field per possible value type. Now this would certainly be redundant, but at least I would get the value stored in its correct form - simplifying queries later. FieldValue ---------- Id DataFieldId IntValue DoubleValue BoolValue DataValue .. Another possibility is just storing everything as String, and casting this in the queries. I am using .Net with NHibernate, and I see that at least here there is a Projections.Cast that can be used to cast e.g. string to int in the query. Either way in these two solutions I need to know which type to use when doing the query, but I will know that from the DataField, so that won't be a problem. Anyway; I don't think any of these solutions sounds good. Are they? Or is there a better way?

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  • Alert Box Methods

    - by Vecta
    I just need a little advice on what may be the best method for handling my situation. I'm in need of placing three buttons in the sidebar of the website I maintain. The website is massive and hard to handle. Currently, it's all HTML files (there are over 10,000 of them believe it or not). We're transitioning to a database website so I don't want to make any sweeping changes that are site-wide, as they may just be scrapped in our re-design process in coming months. However, these buttons are for an application process. When you click on them, an alert box will need to pop up to give you a bit of information and they either allow you to cancel the action or proceed. The buttons are currently located in the left nav which is included on every page of the website. Would it be possible to accomplish this using JS or jQuery? I'd be unable to easily add scripts into the tags on all of the applicable pages, but I'd like to avoid the browser driven "http://www...Says: blah blah" message if possible. Any insight is greatly appreciated! Thank you!

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  • for loop vs std::for_each with lambda

    - by Andrey
    Let's consider a template function written in C++11 which iterates over a container. Please exclude from consideration the range loop syntax because it is not yet supported by the compiler I'm working with. template <typename Container> void DoSomething(const Container& i_container) { // Option #1 for (auto it = std::begin(i_container); it != std::end(i_container); ++it) { // do something with *it } // Option #2 std::for_each(std::begin(i_container), std::end(i_container), [] (typename Container::const_reference element) { // do something with element }); } What are pros/cons of for loop vs std::for_each in terms of: a) performance? (I don't expect any difference) b) readability and maintainability? Here I see many disadvantages of for_each. It wouldn't accept a c-style array while the loop would. The declaration of the lambda formal parameter is so verbose, not possible to use auto there. It is not possible to break out of for_each. In pre- C++11 days arguments against for were a need of specifying the type for the iterator (doesn't hold any more) and an easy possibility of mistyping the loop condition (I've never done such mistake in 10 years). As a conclusion, my thoughts about for_each contradict the common opinion. What am I missing here?

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  • SQL Server: Why use shorter VARCHAR(n) fields?

    - by chryss
    It is frequently advised to choose database field sizes to be as narrow as possible. I am wondering to what degree this applies to SQL Server 2005 VARCHAR columns: Storing 10-letter English words in a VARCHAR(255) field will not take up more storage than in a VARCHAR(10) field. Are there other reasons to restrict the size of VARCHAR fields to stick as closely as possible to the size of the data? I'm thinking of Performance: Is there an advantage to using a smaller n when selecting, filtering and sorting on the data? Memory, including on the application side (C++)? Style/validation: How important do you consider restricting colunm size to force non-sensical data imports to fail (such as 200-character surnames)? Anything else? Background: I help data integrators with the design of data flows into a database-backed system. They have to use an API that restricts their choice of data types. For character data, only VARCHAR(n) with n <= 255 is available; CHAR, NCHAR, NVARCHAR and TEXT are not. We're trying to lay down some "good practices" rules, and the question has come up if there is a real detriment to using VARCHAR(255) even for data where real maximum sizes will never exceed 30 bytes or so. Typical data volumes for one table are 1-10 Mio records with up to 150 attributes. Query performance (SELECT, with frequently extensive WHERE clauses) and application-side retrieval performance are paramount.

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  • Checking if a function has C-linkage at compile-time [unsolvable]

    - by scjohnno
    Is there any way to check if a given function is declared with C-linkage (that is, with extern "C") at compile-time? I am developing a plugin system. Each plugin can supply factory functions to the plugin-loading code. However, this has to be done via name (and subsequent use of GetProcAddress or dlsym). This requires that the functions be declared with C-linkage so as to prevent name-mangling. It would be nice to be able to throw a compiler error if the referred-to function is declared with C++-linkage (as opposed to finding out at runtime when a function with that name does not exist). Here's a simplified example of what I mean: extern "C" void my_func() { } void my_other_func() { } // Replace this struct with one that actually works template<typename T> struct is_c_linkage { static const bool value = true; }; template<typename T> void assertCLinkage(T *func) { static_assert(is_c_linkage<T>::value, "Supplied function does not have C-linkage"); } int main() { assertCLinkage(my_func); // Should compile assertCLinkage(my_other_func); // Should NOT compile } Is there a possible implementation of is_c_linkage that would throw a compiler error for the second function, but not the first? I'm not sure that it's possible (though it may exist as a compiler extension, which I'd still like to know of). Thanks.

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