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• What happens when we say "listen to a port" ?

  - by smwikipedia

  Hi, When we start a server application, we always need to speicify the port number it listens to. But how is this "listening mechanism" implemented under the hood? My current imagination is like this: The operating system associate the port number with some buffer. The server application's responsibiligy is to monitor this buffer. If there's no data in this buffer, the server application's listen operation will just block the application. When some data arrives from the wire, the operating system will know that check the data and see if it is targed at this port number. And then it will fill the buffer. And then OS will notify the blocked server application and the server application will get the data and continue to run. Question is: If the above scenario is correct, how could the opearting system know there's data arriving from wire? It cannot be a busy pooling. Is it some kind of interrupt-based mechanism? If there's too much data arriving and the buffer is not big enough, will there be data loss? Is the "listen to a port" operation really a blocking operation? Many thanks.

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• Serializing persistent/functional data structures

  - by Rob

  Persistent data structures depend on the sharing of structure for efficiency. For an example, see here. How can I preserve the structure sharing when I serialize the data structures and write them to a file or database? If I just naively traverse the datastructures, I'll store the correct values, but I'll lose the structure sharing. I'd like to be able to save data-structures with shared components to a file, restore them, and still have most of the structure shared in the restored data.

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• heeeeeeeeeeeeeeelp

  - by Yassin

  plz help me i need to make asimple calculator using c for example (1+2-44)/7 but it requiers reverse polish notation which i cant under stand if any one could help me giving me the code i'll be greatfull cause i have an exam after 2 days

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• tutorials/books to create a plugin/module/library?

  - by fayer

  i wonder if there are tutorials/books explaining how you create a library/plugin/module for other to implement? libraries/frameworks like solr, doctrine, codeigniter etc. cause it seems that they follow the same pattern. having one "bootstrap" file to load configurations, other classes and so on. i aim to understand the basics, so i can create a such library. cause at the moment i want to code an address book that other can use. just include a bootstrap file and they are ready to use my classes (like Doctrine). recommendations of sources to learn these things of stuff? you experienced guys, how did you learn it? thanks.

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• Haskell's TypeClasses and Go's Interfaces

  - by Jeremy Jose

  What are the similarities and the differences between Haskell's TypeClasses and Go's Interfaces? What are the relative merits / demerits of the two approaches?

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• Where can find examples and tutorials for Perl's Net::Pcap module?

  - by dan

  Could someone provide a good documentation / tutorial/ PDFs/ reference to book link about Net::Pcap in addtion to the module documentation and this Perl and Net::Pcap article on PerlMonks?

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• Passing a hostname of over 255 characters to getaddrinfo causes a getaddrinfo failed: memory allocat

  - by darrickc

  I am currently upgrading our software to support ipv6 and in the meantime I'm expanding hostname/ip fields to the max hostname size. In sun documentation it seems like this can be up to 1025 (netdb.h:#define NI_MAXHOST 1025 - this is the recommended hostname allocation define), but when I pass a hostname of over 255 to getaddrinfo I get "getaddrinfo failed: memory allocation failure". I am testing on a Sol10 box. Ideas?

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• Applying a function to a custom type in F#

  - by Frederik Wordenskjold

  On my journey to learning F#, I've run into a problem I cant solve. I have defined a custom type: type BinTree = | Node of int * BinTree * BinTree | Empty I have made a function which takes a tree, traverses it, and adds the elements it visits to a list, and returns it: let rec inOrder tree = seq{ match tree with | Node (data, left, right) -> yield! inOrder left yield data; yield! inOrder right | Empty -> () } |> Seq.to_list; Now I want to create a function, similar to this, which takes a tree and a function, traverses it and applies a function to each node, then returns the tree: mapInOrder : ('a -> 'b) -> 'a BinTree -> 'b BinTree This seems easy, and it probably is! But I'm not sure how to return the tree. I've tried this: let rec mapInOrder f tree = match tree with | Node(data, left, right) -> mapInOrder f left Node(f(data), left, right) mapInOrder f right | Empty -> () but this returns a unit. I havent worked with custom types before, so I'm probably missing something there!

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• "Directly accessing" return values without referencing

  - by undocumented feature

  Look at this ruby example: puts ["Dog","Cat","Gates"].1 This will output Cat as ruby allows me to directly access the "anonymous" array created. If I try this in PHP, however: echo array("Dog","Cat,"Gates")[1] This won't work. What is this called, not only concerning arrays but all functions? Where else is it possible? Feel free to change the question title when you know how this "feature" is called.

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• Linux - Programmatically write to a proc file

  - by Zach

  I have found several examples online where we can create a proc file, assign read and write methods that are called every time the proc file is opened for read or written to. However, I can't seem to find any documentation on how to programatically write to a proc file. Ideally, I would like to add a timestamp with other user details every time the proc file is opened for read or for write. Again, I've found where I can add the read and write functions that are triggered when the proc file is opened, but I can't find documentation on how to actually write to a proc file programatically. This would be different from a regular IO read/write, correct?

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• Differneces between static class and instance class with private constructor

  - by dotnetdev

  Hi, Although a static class has only one instance and can't be instantiated, a class with a private constructor can't be instantiated (as the constructor can't be seen), so every time you call this class, this is the same one instance? Factory classes always follow the last convention (instance class with private constructor). Why is this? Thanks

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• What are the general factors, that a developer should keep when he start to develop?

  - by Oden

  Hey, I'm new in the developer business, and I'm interested in the way, how other programmers start to develop, design an application. What are the factors, I should keep when I sit down and start thinking about the app? How do you do it? I'm really interested, because I think the design, and the main thoughts of an application affect the future of it.

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• Stop NSXMLParser Instance from Causing _NSAutoreleaseNoPool

  - by PF1

  Hi Everyone: In my iPhone application, I have an instance of NSXMLParser that is set to a custom delegate to read the XML. This is then moved into its own thread so it can update the data in the background. However, ever since I have done this, it has been giving me a lot of _NSAutoreleaseNoPool warnings in the console. I have tried to add a NSAutoreleasePool to each of my delegate classes, however, this hasn't seemed to solve the problem. I have included my method of creating the NSXMLParser in case that is at fault. NSURL *url = [[NSURL alloc] initWithString:@"http://www.mywebsite.com/xmlsource.xml"]; NSXMLParser *xmlParser = [[NSXMLParser alloc] initWithContentsOfURL:url]; CustomXMLParser *parser = [[CustomXMLParser alloc] init]; parser.managedObjectContext = self.managedObjectContext; parser = [parser initXMLParser]; [xmlParser setDelegate:parser]; [NSThread detachNewThreadSelector:@selector(parse) toTarget:xmlParser withObject:nil]; If anyone has any ideas to get rid of this problem, I would really appreciate it. Thanks.

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• How do I use Declarations (type, inline, optimize) in Scheme?

  - by kunjaan

  How do I declare the types of the parameters in order to circumvent type checking? How do I optimize the speed to tell the compiler to run the function as fast as possible like (optimize speed (safety 0))? How do I make an inline function in Scheme? How do I use an unboxed representation of a data object? And finally are any of these important or necessary? Can I depend on my compiler to make these optimizations? thanks, kunjaan.

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• Multiple-File Template Implementation

  - by Maxpm

  With normal functions, the declaration and definition are often separated across multiple files like so: // Foo.h namespace Foo { void Bar(); } . // Foo.cpp #include "Foo.h" void Foo::Bar() { cout << "Inside function." << endl; } It is my understanding that this cannot be done with templates. The declaration and definition must not be separate because the appropriate form of the template is created "on-demand" when needed. So, how and where are templates typically defined in a multiple-file project like this? My intuition is that it would be in Foo.cpp because that's where the "meat" of functions normally is, but on the other hand it's the header file that's going to be included.

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• Question on Simple Look Up Tables [closed]

  - by CVS26

  Hi everyone... I'm doing some research on Simple Look Up Tables. I have : been thru wikipedia. Googled Look-up tables Browsed thedailywtf.com Been thru several websites illustrating/documenting look-up table code. Currently i am looking for any insight anyone can throw on the topic (LuTs). Also, I am specifically looking for any anecdotes one would like to share (again on LuTs). All content will be adequately acknowledge (or anonymised, if requested) in the article. Thank You

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• What factors could determine whether Clojure, Scala or Haskell will gain traction?

  - by i_like_monkeys

  Given that it's impossible to see into the future, what factors related to Clojure, Scala or Haskell are likely to determine whether one of them catches on? Are there cultural or economic issues that could give one of these languages an advantage over the others? Or are none of these languages likely to gain traction because of their conceptual complexity?

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• Which is the best pick?

  - by Daniel

  Hi, considering I have experience with Java SE: which language should I learn(and is best for that purpose) in order to build web applications some day with it? I have been contemplating PHP and Java EE. The latter does indeed seems as an obvious choice given my Java SE knowledge. But how does it fares in comparison with PHP and how good is it for the aforementioned purpose? If there is a better language for this purpose, feel free to recommend it. Thank you.

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• get file path from svn diff file with PHP and C

  - by coderex

  hi i have a file having svn diff i wish to extract the filenames form the diff. How to write the parser for that.. Index: libs/constant.php =================================================================== --- libs/constant.php (revision 1243) +++ libs/constant.php (revision 1244) @@ -26,5 +26,5 @@ // changesss - +// test 2 ?> \ No newline at end of file Index: libs/Tools.php =================================================================== --- libs/Tools.php (revision 1243) +++ libs/Tools.php (revision 1244) @@ -34,5 +34,5 @@ // another file an change - +// test ?> \ No newline at end of file Sample output. libs/constant.php libs/Tools.php How to write parser in PHP and C.

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• which ad solution is best for iPhone apps

  - by nbojja

  Hi All, i have a iPhone free app downloaded by 3000 users. mostly every one uses my app atleast once in a day. So i am planning to keep ads on my app. Which ad solution is best. and i looked in some sites. No one is giving clear details about CPMs. my direct question is "How much will i get for 1000 impressions using different ad solutions?" thanks

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• How to cast a character to int in Clojure?

  - by Learning Clojure

  How to cast a character to int in Clojure? I am trying to write a rot 13 in clojure, so I need to have something to cast my char to int. I found something called (int), so I put: (int a) Get: CompilerException java.lang.RuntimeException: Unable to resolve symbol: a in this context, compiling:(NO_SOURCE_PATH:13:1) Then I put: (int 'a) Get: ClassCastException clojure.lang.Symbol cannot be cast to java.lang.Character clojure.lang.RT.intCast (RT.java:1087) Then: (rot13 ''a') Get: ClassCastException clojure.lang.PersistentList cannot be cast to java.lang.Character clojure.lang.RT.intCast (RT.java:1087) And: (rot13 "a") Get: ClassCastException java.lang.String cannot be cast to java.lang.Character clojure.lang.RT.intCast (RT.java:1087) So what is the right way to do it? btw, I always get confused with all these clojure syntax. But I can never find any source only help me with my problem. Any suggestions? Thank you!!

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• difference between StandBy and Hibernate in windowsXp?

  - by androidbase Praveen

  what is the difference between standby and hibernate? when i put my laptop as standby when the power is plugged there is no problem to resume. when the power is unplugged my system will dumped. i want to do illegal shutdown(holding power button) and the switch it on.? why?

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• Why is glpk-java.jar not the same across all platforms?

  - by pruefsumme

  I'm using glpk-java in one of my projects. It provides a JNI to GLPK, a free LP/MIP solver. To use it under different platforms, you need different shared libraries (libglpk.so under Linux, libglpk.dylib under Mac OS X, glpk.dll under Windows) which is fully understandable. In addition, a java library is needed: glpk-java.jar. It's created as part of the build process. I was wondering why this JAR file (which only contains .class files) is different under different platforms? I.e., I cannot use the same glpk-java.jar under Linux and Mac OS X which means that I cannot put this file under revision control.

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• Why I can't called my doSomething method?

  - by Tattat

  This is my DrawSomethingCmd: #import "Command.h"; @interface DrawSomethingCmd : Command { } -(void)doSomething; -(void)execute; @end and the DrawSomethingCmd.m's doSomething method is like that: -(void)doSomething{ NSLog(@"did"); } The Command.h: #import <Foundation/Foundation.h> @interface Command : NSObject { } -(void)execute; And the Command.m: #import "Command.h" @implementation Command -(id)init{ return self; } -(void)execute{ } @end And I have the method like this: DrawSomethingCmd *tempCmd = [[DrawSomethingCmd alloc] init]; [tempCmd doSomething]; But my Console did't show any things on that, what's going on?

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• From a programmer's perspective, which is your everyday Python uses?

  - by Vimvq1987

  I've finished my thesis and now having a free time. I intend to learn another language, and Python seems to be a good choice. I'll probably have to use .NET for every day works, but I heard that Python helps programmer a lot, in mean of automation. That would be great if I can write "small" Python scripts to do something automatically. From a programmer's perspective, which is your everyday Python's uses? What did it do to have your works done?

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