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  • What to Learn after C++?

    - by Stephen Whitmore
    I have been learning C++ for a while now, I find it very powerful. But, the problem is the the level of abstraction is not much and I have to do memory management myself. What are the languages that I can use which uses a higher level of abstraction.

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  • About first-,second- and third-class value

    - by forest58
    First-class value can be passed as an argument returned from a subroutine assigned into a variable. Second-class value just can be passed as an argument. Third-class value even can't be passed as an argument. Why should these things defined like that? As I understand, "can be passed as an argument" means it can be pushed into the runtime stack;"can be assigned into a variable" means it can be moved into a different location of the memory; "can be returned from a subroutine" almost has the same meaning of "can be assigned into a variable" since the returned value always be put into a known address, so first class value is totally "movable" or "dynamic",second class value is half "movable" , and third class value is just "static", such as labels in C/C++ which just can be addressed by goto statement, and you can't do nothing with that address except "goto" .Does My understanding make any sense? or what do these three kinds of values mean exactly?

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  • Haskell: How to compose `not` with a function of arbitrary arity?

    - by Hynek -Pichi- Vychodil
    When I have some function of type like f :: (Ord a) => a -> a -> Bool f a b = a > b I should like make function which wrap this function with not. e.g. make function like this g :: (Ord a) => a -> a -> Bool g a b = not $ f a b I can make combinator like n f = (\a -> \b -> not $ f a b) But I don't know how. *Main> let n f = (\a -> \b -> not $ f a b) n :: (t -> t1 -> Bool) -> t -> t1 -> Bool Main> :t n f n f :: (Ord t) => t -> t -> Bool *Main> let g = n f g :: () -> () -> Bool What am I doing wrong? And bonus question how I can do this for function with more and lest parameters e.g. t -> Bool t -> t1 -> Bool t -> t1 -> t2 -> Bool t -> t1 -> t2 -> t3 -> Bool

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  • Does using functional languages help against computing values repeatedly?

    - by sharptooth
    Consider a function f(x,y): f(x,0) = x*x; f(0,y) = y*(y + 1); f(x,y) = f(x,y-1) + f(x-1,y); If one tries to implement that recursively in some language like C++ he will encounter a problem. Suppose the function is first called with x = x0 and y = y0. Then for any pair (x,y) where 0 <= x < x0 and 0 <= y < y0 the intermediate values will be computed multiple times - recursive calls will form a huge tree in which multiple leaves will in fact contain the same pairs (x,y). For pairs (x,y) where x and y are both close to 0 values will be computed numerous times. For instance, I tested a similar function implemented in C++ - for x=20 and y=20 its computation takes about 4 hours (yes, four Earth hours!). Obviously the implementation can be rewritten in such way that repeated computation doesn't occur - either iteratively or with a cache table. The question is: will functional languages perform any better and avoid repeated computations when implementing a function like above recursively?

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  • Excelsheet query

    - by kunj
    Hi, Please tell me how can I find the last word from any particular cell in excel sheet if cell contains multiple words or instructions. For ex- The below string is in particular cell: C:\Documents and Settings\All Users\Documents\My Pictures\Sample Pictures\Blue hills.jpg My requirement is to search only last word in that cell i.e. Blue hills.jpg Your early response is highly appreciated!!!

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  • Permuting output of a tree of closures

    - by yan
    This a conceptual question on how one would implement the following in Lisp (assuming Common Lisp in my case, but any dialect would work). Assume you have a function that creates closures that sequentially iterate over an arbitrary collection (or otherwise return different values) of data and returns nil when exhausted, i.e. (defun make-counter (up-to) (let ((cnt 0)) (lambda () (if (< cnt up-to) (incf cnt) nil)))) CL-USER> (defvar gen (make-counter 3)) GEN CL-USER> (funcall gen) 1 CL-USER> (funcall gen) 2 CL-USER> (funcall gen) 3 CL-USER> (funcall gen) NIL CL-USER> (funcall gen) NIL Now, assume you are trying to permute a combinations of one or more of these closures. How would you implement a function that returns a new closure that subsequently creates a permutation of all closures contained within it? i.e.: (defun permute-closures (counters) ......) such that the following holds true: CL-USER> (defvar collection (permute-closures (list (make-counter 3) (make-counter 3)))) CL-USER> (funcall collection) (1 1) CL-USER> (funcall collection) (1 2) CL-USER> (funcall collection) (1 3) CL-USER> (funcall collection) (2 1) ... and so on. The way I had it designed originally was to add a 'pause' parameter to the initial counting lambda such that when iterating you can still call it and receive the old cached value if passed ":pause t", in hopes of making the permutation slightly cleaner. Also, while the example above is a simple list of two identical closures, the list can be an arbitrarily-complicated tree (which can be permuted in depth-first order, and the resulting permutation set would have the shape of the tree.). I had this implemented, but my solution wasn't very clean and am trying to poll how others would approach the problem. Thanks in advance.

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  • Minimize the sequence by putting appropriate operations ' DP'

    - by Vikas
    Given a sequence,say, 222 We have to put a '+' or '* ' between each adjacent pair. '* ' has higher precedence over '+' We have to o/p the string whose evaluation leads to minimum value. O/p must be lexicographically smallest if there are more than one. inp:222 o/p: 2*2+2 Explaination: 2+2+2=6 2+2*2=6 2*2+2=6 of this 3rd is lexicographically smallest. I was wondering how to construct a DP solution for this.

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  • What will be the OOP approach? (or YOUR approach?)

    - by hsmit
    I'm having difficulties with some general OOP & Java approach. There are various ways to let classes/objects communicate with each other. To give a simple example: I need object A to perform action X. Object A needs P, Q and R to perform this action X. Will then Object A retrieve P, Q and R by itself (within action X), or must these values be parameters for action X?

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  • tool to find out distance in terms of no. of hops in unix

    - by mawia
    Hi! all, I am writing an application for video streaming.In the application server is required to know the distance of the client from it self in terms of hop number.My question is,is there any tool/method other than traceroute available in unix environment to find it? I also need to find out the geographical location of the client.So is their any tool/method for this as well? Any help in this regard will be highly appreciated. Thanks in advance. Mawia

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  • SQL finding overlapping of times pass midnight (across 2 days)

    - by janechii
    Hi everyone, I know there are lots of these types of questions, but i didn't see one that was similar enough to my criteria. So i'd like to ask for your help please. The fields i have are just start and end which are of time types. I cannot involve any specific dates in this. If the time ranges don't go pass midnight across day, i'd just compare two tuples as such: end1 > start2 AND start1 < end2 (end points touching are not considered overlapped here.) But when I involve time range that pass (or at) midnight, this obviously doesn't work. For example, given: start | end --------+-------- 06:00PM | 01:00AM 03:00PM | 09:00PM Without involving dates, how can i achieve this, please. My assumption is, if end is less than start, then we're involving 2 days. I'm trying to do this in plain standard SQL, so just a simple and concise logic in the WHERE clause. Thank you everyone!

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  • Capture IP packets on Dialup connection - Windows 7

    - by Assaf Levy
    Our product utilizes (the wonderful) Winpcap to capture ip packets from all devices with an IP address and analyze them in real time. Unfortunately, we discovered that it does NOT capture any packets on dialup (e.g. PPP) connections on Windows 7, and that there are no near-term plans for enabling this (1). So we need something else. Microsoft Network Monitor and Windows Packet Filter are two options that surfaced during a bit of googling, but before delving into research I wanted to ask the experienced: what are out options, given the following requirements: Capture all in/outbound IP packets on the machine. Complete background processing - no UI should be involved. Support Windows Vista / 7. Performance (user should not feel the difference). Thanks in advance.

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  • When machine code is generated from a program how does it translates to hardware level operations ??

    - by user553492
    Like if say the instruction is something like 100010101 1010101 01010101 011101010101. Now how is this translating to an actual job of deleting something from memory? Memory consists of actual physical transistors the HOLD data. What causes them to lose that data is some external signal? I want to know how that signal is generated. Like how some binary numbers change the state of a physical transistor. Is there a level beyond machine code that isn't explicitly visible to a programmer? I have heard of microcode that handle code at hardware level, even below assembly language. But still I pretty much don't understand. Thanks!

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  • Python: Calling method A from class A within class B?

    - by Tommo
    There are a number of questions that are similar to this, but none of the answers hits the spot - so please bear with me. I am trying my hardest to learn OOP using Python, but i keep running into errors (like this one) which just make me think this is all pointless and it would be easier to just use methods. Here is my code: class TheGUI(wx.Frame): def __init__(self, title, size): wx.Frame.__init__(self, None, 1, title, size=size) # The GUI is made ... textbox.TextCtrl(panel1, 1, pos=(67,7), size=(150, 20)) button1.Bind(wx.EVT_BUTTON, self.button1Click) self.Show(True) def button1Click(self, event): #It needs to do the LoadThread function! class WebParser: def LoadThread(self, thread_id): #It needs to get the contents of textbox! TheGUI = TheGUI("Text RPG", (500,500)) TheParser = WebParser TheApp.MainLoop() So the problem i am having is that the GUI class needs to use a function that is in the WebParser class, and the WebParser class needs to get text from a textbox that exists in the GUI class. I know i could do this by passing the objects around as parameters, but that seems utterly pointless, there must be a more logical way to do this that doesn't using classes seem so pointless? Thanks in advance!

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  • Call/Return feature of classic C++(C with Classes), what modern languages have it?

    - by AraK
    Hi, On page 57 of The Design and Evolution of C++, Dr. Stroustrup talks about a feature that was initially part of C with Classes, but it isn't part of modern C++(standard C++). The feature is called call/return. This is an example: class myclass { call() { /* do something before each call to a function. */ } return() { /* do something else after each call to a function. */ } ... }; I find this feature very interesting. Does any modern language have this particular feature?

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  • How can I programmatically get the connection status of OSX network services?

    - by BigBrainz
    In the OS X System Preferences, when I click on 'Network' I see a green dot by 'Ethernet', and red dots by 'AirPort' and 'FireWire'. This is because I turned off AirPort and FireWire, as I access networks and the Internet via Ethernet. I need to programmatically determine which of these network services displayed in System Preferences have green dots and which have red dots. For Ethernet and FireWire the displayed status is 'Connected' or 'Not Connected', and for AirPort the displayed status is 'On' or 'Off'. Perhaps other network services have other status labels. I have picked through all the plist files in '/Library/Preferences/SystemConfiguration', particularly 'preferences.plist' and 'NetworkInterfaces.plist'. I can get all sorts of information there, such as the Location set, network service order, proxy information (which is also important to my task), but I cannot find how to determine whether a given network service is on or off--the equivalent of having the green dot displayed. I have also tried using System Configuration framework, specifically the SCNetworkConnectionGetStatus function, but all I get are invalid connection statuses. Does anyone know how to actually retrieve this connection status information? Thanks.

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  • Properly handling NSURLConnection errors

    - by Cal S
    Hi, I have a simple form interface set up that send username and password information to a server: (working) NSString *postData = [NSString stringWithFormat:@"user=%@&pass=%@",[self urlEncodeValue:sysUsername],[self urlEncodeValue:password]]; NSLog(@"Post data -> %@", postData); /// NSData* postVariables = [postData dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES]; NSMutableURLRequest* request = [[[NSMutableURLRequest alloc] init] autorelease]; NSString* postLength = [NSString stringWithFormat:@"%d", [postVariables length]]; NSURL* postUrl = [NSURL URLWithString:@"http://localhost/~csmith/cocoa/test.php"]; [request setURL:postUrl]; [request setHTTPMethod:@"POST"]; [request setValue:postLength forHTTPHeaderField:@"Content-Length"]; [request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"]; [request setHTTPBody: postVariables]; NSData *returnData = [NSURLConnection sendSynchronousRequest:request returningResponse:NULL error:NULL]; NSLog(@"Post data SENT & returned -> %@", returnData); How do I handle connection errors such as no internet connection, firewall, etc. Also, does this method use the system-wide proxy settings? Many of my users are behind a proxy. Thanks a lot!

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  • what is main focus for a developer when coding?

    - by ajsie
    i read a lot of books about how to code right and usually the are talking about all these techniques from a point of view i can't understand. eg. lets consider the singleton pattern. i'm restricting so the class can only be instantiated once. but since it's only me creating the application, if i know that the class only should be instantiated once, then why would i create it a second time? i feel like missing the big picture. what is my main goal when coding an application? how should i think? thanks

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  • CSS Brace Styles

    - by Nimbuz
    I'm unable to figure how the standard (or just popular) brace style names apply to CSS. Here're all the brace styles: /* one - pico? */ selector { property: value; property: value; } /* two */ selector { property: value; /* declaration starts on newline */ property: value; } /* three */ selector { property: value; property: value; } /* four - Allman or GNU?*/ selector { property: value; /* declaration starts on newline */ property: value; }? /* five */ selector { property: value; property: value; } /* six - horstmann? */ selector { property: value; /* declaration starts on newline */ property: value; } /* seven - banner?*/ selector { property: value; property: value; } /* eight */ selector { property: value; /* declaration starts on newline */ property: value; } Can someone please name each brace style for me? Many thanks!

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  • Getting started with MIT Proto

    - by Charles
    MIT Proto lacks a basic getting started guide. How do I find a shell that accepts commands like (def foo...) and proto -n 1000 -l -m ...? http://groups.csail.mit.edu/stpg/proto.html I can run in my bash shell: ./proto -n 1000 -s 0.1 -T -l "(red (gradient (= (mid) 0)))" I can't figure out how to run e.g. channel.proto: (def channel (src dst width) (let* ((d (distance src dst)) (trail (<= (+ (gradient src) (gradient dst)) (+ d 0.01))) ;; float error ;; (trail (= (+ (gradient src) (gradient dst)) d)) ) (dilate trail width))) ;; To see a channel calculated from geometric primitives, run: ;; proto -n 1000 -l -m -s 0.5 "(blue (channel (sense 1) (sense 2) 10))" ;; click on a device and hit 't' to set up the source, then click on ;; another device and hit 'y' to designate the destination. At first ;; every device will be blue, but then it should clear and you should ;; see a thick blue path connecting the two devices you selected. Thanks! P.S. Somebody please tag this mit-proto. I can't.

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