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  • Pros and Cons of Different macro function / inline methods in C

    - by Robert S. Barnes
    According to the C FAQ, there are basically 3 practical methods for "inlining" code in C: #define MACRO(arg1, arg2) do { \ /* declarations */ \ stmt1; \ stmt2; \ /* ... */ \ } while(0) /* (no trailing ; ) */ or #define FUNC(arg1, arg2) (expr1, expr2, expr3) To clarify this one, the arguments are used in the expressions, and the comma operator returns the value of the last expression. or using the inline declaration which is supported as an extension to gcc and in the c99 standard. The do { ... } while (0) method is widely used in the Linux kernel, but I haven't encountered the other two methods very often if at all. I'm referring specifically to multi-statement "functions", not single statement ones like MAX or MIN. What are the pros and cons of each method, and why would you choose one over the other in various situations?

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  • How does the socket API accept() function work?

    - by Eli Bendersky
    The socket API is the de-facto standard for TCP/IP and UDP/IP communications (that is, networking code as we know it). However, one of its core functions, accept() is a bit magical. To borrow a semi-formal definition: accept() is used on the server side. It accepts a received incoming attempt to create a new TCP connection from the remote client, and creates a new socket associated with the socket address pair of this connection. In other words, accept returns a new socket through which the server can communicate with the newly connected client. The old socket (on which accept was called) stays open, on the same port, listening for new connections. How does accept work? How is it implemented? There's a lot of confusion on this topic. Many people claim accept opens a new port and you communicate with the client through it. But this obviously isn't true, as no new port is opened. You actually can communicate through the same port with different clients, but how? When several threads call recv on the same port, how does the data know where to go? I guess it's something along the lines of the client's address being associated with a socket descriptor, and whenever data comes through recv it's routed to the correct socket, but I'm not sure. It'd be great to get a thorough explanation of the inner-workings of this mechanism.

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  • prohibiting instantiation as a temporary object (C++)

    - by SuperElectric
    I like using sentry classes in c++, but I seem to have a mental affliction that results in repeatedly writing bugs like the following: { MySentryClass(arg); // ... other code } Needless to say, this fails because the sentry dies immediately after creation, rather than at the end of the scope, as intended. Is there some way to prevent MySentryClass from being instantiated as a temporary, so that the above code either fails to compile, or at least aborts with an error message at runtime?

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  • How can you query for an object using one of its properties' id

    - by James Smith
    I have two entities, say, House and People, where multiple people can live in one house. It's a unidirectional link where each Person has a field for which House they belong to, so the Person table has a column named house_id. I need to be able to return all the Person objects who belong to a certain House, but I only have the id of the house. This can be done like this: House house = houseDAO.findById(houseId); List people = session.createCriteria(Person.class).add(Restrictions.eq("house", house)).list(); But since I don't need the house, that's adding an unnecessary query. I've tried to do: session.createCriteria(Person.class).add(Restrictions.eq("house_id", houseId)).list(); But that doesn't work because house_id is not a property, it's a database column. I could just add an sql restriction, but is there a hibernate way of doing this?

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  • close other HTML window by javascript function

    - by lusey
    hello i need a popup window to appear to the user but without parent widow ! but this is impossible so i think that I may have to make the popup close the parent apter it appear, but how ? i tried this in the popup: <BODY align="center" valign="center" onload="javascript:window.opener='x';window.close();"> but it closed the popup window itself ! any idea to make the popup close its parent ?

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  • Arithmetic operators and function calling in C

    - by Robert Dalton
    I'm not quite sure why I can't do double a = (float) my_Function(45) / 2048 / 2340 / 90; printf("%.4",a); // prints out 0.00 But instead I have to use one more variable as: double a = (float) my_Function(45); double b = (float) a / 2048 / 2340 / 90; printf("%.4",b); // prints out the correct value

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  • Function call within XAML code?

    - by Matt H.
    I'd like to set a style on all my TextBox controls that does the following when it receives keyboard focus: 1) Change the background color 2) Call .SelectAll() to highlight all text I have this so far: <Style TargetType="TextBox"> <Style.Triggers> <Trigger Property="IsKeyboardFocusWithin" Value="True"> <Setter Property="Background"> <Setter.Value> <SolidColorBrush Color="#FFFFD1D9"/> </Setter.Value> </Setter> </Trigger> </Style.Triggers> </Style> Is there a way to also call .SelectAll() ? Thanks.

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  • Giving another object a NSManagedObject

    - by Wayfarer
    Alright, so I'm running into an issue with my code. What I have done is subclassed UIButton so I can give it some more infomormation that pertain to my code. I have been able to create the buttons and they work great. Capiche. However, one of the things I want my subclass to hold is a reference to a NSMangedObject. I have this code in my header file: @interface ButtonSubclass : UIButton { NSManagedObjectContext *context; NSManagedObject *player; } @property (nonatomic, retain) NSManagedObject *player; @property (nonatomic, retain) NSManagedObjectContext *context; - (id)initWithFrame:(CGRect)frame andTitle:(NSString*)title; //- (void)setPlayer:(NSManagedObject *)aPlayer; @end As you can see, it has a instance variable to the NSMangedobject I want it to hold (as well as the Context). But for the life of me, I can't get it to hold that NSManagedObject. I run both the @synthesize methods in the Implementation file. @synthesize context; @synthesize player; So I'm not sure what I'm doing wrong. This is how I create my button: ButtonSubclass *playerButton = [[ButtonSubclass alloc] initWithFrame:frame andTitle:@"20"]; //works playerButton.context = self.context; //works playerButton.player = [players objectAtIndex:i]; //FAILS And I have initilaized the players array earlier, where I get the objects. Another weird thing is that when it gets to this spot in the code, the app crashes (woot) and the the console output stops. It doesn't give me any error, and notification at all that the app has crashed. It just... stops. So I don't even know what the error is that is crashing the code, besides it has to do with that line up there setting the "player" variable. Thoughts and ideas? I'd love your wisdom!

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  • Looping through an array to remove a touched object (iPhone/Cocos2d)

    - by Michael Lowe
    I am using cocos2d to build a game. I have an array of CCSprites and I want to be able to touch them and delete the one that was touched. Right now I have this... -(void) spawn { mySprite = [CCSprite spriteWithFile:@"image.png"]; mySprite.position = ccp(positionX,positionY); [myArray addObject:mySprite]; [self addChild:mySprite]; } - (void) ccTouchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { UITouch* touch = [touches anyObject]; CGPoint location = [touch locationInView: [touch view]]; NSUInteger i, count = [myArray count]; for (i = 0; i < count; i++) { mySprite = (CCSprite *)[myArray objectAtIndex:i]; if (CGRectContainsPoint([mySprite boundingBox], location)) { [self removeChild:mySprite cleanup:YES]; } } I have never done this before. Does anyone have a solution? Thanks, Michael

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  • Parsing plain text to some structured object

    - by Jeriho
    I am working on parsing plain text and converting it to key-value pairs. For example, plain text: some_uninteresting_thing key1 valueA, valueB, valueC key2 valueD key3 valueE valueF key4 valueG(valueH, valueI) key5 some_uninteresting_thing valueJ some_uninteresting_thing key6 some_uninteresting_thing (key6 shouldn't be mapped because has no appropriate values) As you can see plain text is lenient. What java library can handle this? If no such library exist, any suggestions on algorithm to do this.

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  • .Remove(object) on a List<T> returned from LINQ to SQL compiled query won't delete the Object right

    - by soldieraman
    I am returning two lists from the database using LINQ to SQL compiled query. While looping the first list I remove duplicates from the second list as I dont want to process already existing objects again. eg. //oldCustomers is a List returned by my Compiled Linq to SQL Statmenet that I have added a .ToList() at the end to //Same goes for newCustomers for (Customer oC in oldCustomers) { //Do some processing newCustomers.Remove(newCusomters.Find(nC=> nC.CustomerID == oC.CusomterID)); } for (Cusomter nC in newCustomers) { //Do some processing } DataContext.SubmitChanges() I expect this to only save the changes that have been made to the customers in my processing and not Remove or Delete any of my customers from the database. Correct? I have tried it and it works fine - but I am trying to know if there is any rare case it might actually get removed

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  • Noob boost::bind member function callback question

    - by shaz
    #include <boost/bind.hpp> #include <iostream> using namespace std; using boost::bind; class A { public: void print(string &s) { cout << s.c_str() << endl; } }; typedef void (*callback)(); class B { public: void set_callback(callback cb) { m_cb = cb; } void do_callback() { m_cb(); } private: callback m_cb; }; void main() { A a; B b; string s("message"); b.set_callback(bind(A::print, &a, s)); b.do_callback(); } So what I'm trying to do is to have the print method of A stream "message" to cout when b's callback is activated. I'm getting an unexpected number of arguments error from msvc10. I'm sure this is super noob basic and I'm sorry in advance.

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  • C# Object Declarations

    - by pm_2
    Are there any overheads to using the following sytax: Form1 myForm = new Form1(); myForm.Show(); As opposed to: Form1 myForm; myForm = new Form1(); myForm.Show(); When I was learning VB6, I was told doing the quivelent in VB had an overhead - is the same true in .NET?

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  • function not working in production mode

    - by maps
    I am using the rvideo gem to transcode files to a .flv format. class Video < ActiveRecord::Base include AASM aasm_column :status aasm_initial_state :initial aasm_state :initial aasm_state :converting, :exit => :transcode aasm_state :transfering , :exit => :send_s3 aasm_state :completed aasm_state :failed aasm_event :convert do transitions :from => [:initial], :to => :converting end aasm_event :transfer do transitions :from => [:converting], :to => :transfering end aasm_event :complete do transitions :from => [:transfering], :to => :completed end aasm_event :error do transitions :from => [:initial, :converting, :transfering, :completed] end has_attached_file :asset, :path => "uploads/:attachment/:id.:basename.:extension" def flash_path return self.asset.path + '.flv' end def flash_name return File::basename(self.asset.path)# + '.flv' end def flash_url return "#{AWS_HOST}/#{AWS_BUCKET}/#{self.flash_name}" end # transcode file def transcode begin RVideo::Transcoder.logger = logger file = RVideo::Inspector.new(:file => self.asset.path) command = "ffmpeg -i $input_file$ -y -s $resolution$ -ar 44100 -b 64k -r 15 -sameq $output_file$" options = { :input_file => "#{RAILS_ROOT}/#{self.asset.path}", :output_file => "#{RAILS_ROOT}/#{self.flash_path}", :resolution => "320x200" } transcoder = RVideo::Transcoder.new transcoder.execute(command, options) rescue RVideo::TranscoderError => e logger.error "Encountered error transcoding #{self.asset.path}" logger.error e.message end end The input file is added to the asset directory, but I never get an outputted file. On the view page aasm hangs on "converting".

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  • tidy/efficient function writing in R

    - by romunov
    Excuse my ignorance, as I'm not a computer engineer but with roots in biology. I have become a great fan of pre-allocating objects (kudos to SO and R inferno by Patrick Burns) and would like to improve my coding habits. In lieu of this fact, I've been thinking about writing more efficient functions and have the following question. Is there any benefits in removing variables that will be overwritten at the start of the next loop, or is this just a waste of time? For the sake of argument, let's assume that the size of old and new variables is very similar or identical.

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  • Value object or not for 3d points ?

    - by Stefano Borini
    I need to develop a geometry library in python, describing points, lines and planes in 3d space, and various geometry operations. Related to my previous question. The main issue in the design is if these entities should have identity or not. I was wondering if there's a similar library out there (developed in another language) to take inspiration from, what is the chosen design, and in particular the reason for one choice vs. the other.

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  • Call method immediately after object construction in LINQ query

    - by Steffen
    I've got some objects which implement this interface: public interface IRow { void Fill(DataRow dr); } Usually when I select something out of db, I go: public IEnumerable<IRow> SelectSomeRows { DataTable table = GetTableFromDatabase(); foreach (DataRow dr in table.Rows) { IRow row = new MySQLRow(); // Disregard the MySQLRow type, it's not important row.Fill(dr); yield return row; } } Now with .Net 4, I'd like to use AsParallel, and thus LINQ. I've done some testing on it, and it speeds up things alot (IRow.Fill uses Reflection, so it's hard on the CPU) Anyway my problem is, how do I go about creating a LINQ query, which calls Fills as part of the query, so it's properly parallelized? For testing performance I created a constructor which took the DataRow as argument, however I'd really love to avoid this if somehow possible. With the constructor in place, it's obviously simple enough: public IEnumerable<IRow> SelectSomeRowsParallel { DataTable table = GetTableFromDatabase(); return from DataRow dr in table.Rows.AsParallel() select new MySQLRow(dr); } However like I said, I'd really love to be able to just stuff my Fill method into the LINQ query, and thus not need the constructor overload.

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  • st-ordering library function?

    - by chang
    I'm in the search for an implementation of an ear-decomposition algorithm (http://www.ics.uci.edu/~eppstein/junkyard/euler/ear.html). I examined networkx and didn't find one. Although the algorithm layout is vaguely in my mind, I'd like to see some reference implementation, too. Side problem: First step could be an st-ordering of a graph. Are there any implementations for st-ordering algorithms you know? Thanks for your input. I'd really like to contribute e.g. to networkx by implementing the ear-decomposition algorithm in python.

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  • Modifying existing object attributes in Core Data after the fact

    - by glorifiedHacker
    In a previous question, I was looking for an alternative to modifying how "no date" was being stored in the date attribute of my NSManagedObject subclass. Previously, I had assigned nil to that attribute when a user didn't assign a date. In order to address sorting issues when using NSFetchedResultsController, I have decided to assign [NSDate distantFuture] to the date attribute when a user doesn't assign a date. However, given that this app is already in the wild, I need to update the Core Data store such that any existing nil date values are changed to [NSDate distantFuture]. What is the best way to make this change? The first thing that comes to mind is to iterate through all of the objects in the store in an array and change any nil values that are found. This could be limited to a one-time event by checking against a user defaults key that indicates whether this upgrade has been performed. Is there a way that I can do this with Core Data versioning instead? Or another method that doesn't involve me writing throw-away code?

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  • Javascript function, on web page close

    - by AXheladini
    Hello there, I have an problem that i can not solve. The problem is this way: When i close my page on some browser i want an message box to appear and to ask me if I really want to close the page or not. logically: click on x (close tab on web browser) and than the box appears with two buttons yes and now, if i click yes the page will be closed if i click no the page will not close. I know there must be some javascript or ajax code but i can not configure it by my self.

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