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  • Why is this code invalid in C#?

    - by mmattax
    The following code will not compile: string foo = "bar"; Object o = foo == null ? DBNull.Value : foo; I get: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'System.DBNull' and 'string' To fix this, I must do something like this: string foo = "bar"; Object o = foo == null ? DBNull.Value : (Object)foo; This cast seems pointless as this is certainly legal: string foo = "bar"; Object o = foo == null ? "gork" : foo; It seems to me that when the ternary branches are of different types, the compiler will not autobox the values to the type object...but when they are of the same type then the autoboxing is automatic. In my mind the first statement should be legal... Can anyone describe why the compiler does not allow this and why the designers of C# chose to do this? I believe this is legal in Java...Though I have not verified this. Thanks. EDIT: I am asking for an understanding of why Java and C# handle this differently, what is going on underneath the scenes in C# that make this invalid. I know how to use ternary, and am not looking for a "better way" to code the examples. I understand the rules of ternary in C#, but I want to know WHY... EDIT (Jon Skeet): Removed "autoboxing" tag as no boxing is involved in this question.

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  • in haskell, why do I need to specify type constraints, why can't the compiler figure them out?

    - by Steve
    Consider the function, add a b = a + b This works: *Main> add 1 2 3 However, if I add a type signature specifying that I want to add things of the same type: add :: a -> a -> a add a b = a + b I get an error: test.hs:3:10: Could not deduce (Num a) from the context () arising from a use of `+' at test.hs:3:10-14 Possible fix: add (Num a) to the context of the type signature for `add' In the expression: a + b In the definition of `add': add a b = a + b So GHC clearly can deduce that I need the Num type constraint, since it just told me: add :: Num a => a -> a -> a add a b = a + b Works. Why does GHC require me to add the type constraint? If I'm doing generic programming, why can't it just work for anything that knows how to use the + operator? In C++ template programming, you can do this easily: #include <string> #include <cstdio> using namespace std; template<typename T> T add(T a, T b) { return a + b; } int main() { printf("%d, %f, %s\n", add(1, 2), add(1.0, 3.4), add(string("foo"), string("bar")).c_str()); return 0; } The compiler figures out the types of the arguments to add and generates a version of the function for that type. There seems to be a fundamental difference in Haskell's approach, can you describe it, and discuss the trade-offs? It seems to me like it would be resolved if GHC simply filled in the type constraint for me, since it obviously decided it was needed. Still, why the type constraint at all? Why not just compile successfully as long as the function is only used in a valid context where the arguments are in Num? Thank you.

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  • What does the Spring framework do? Should I use it? Why or why not?

    - by sangfroid
    So, I'm starting a brand-new project in Java, and am considering using Spring. Why am I considering Spring? Because lots of people tell me I should use Spring! Seriously, any time I've tried to get people to explain what exactly Spring is or what it does, they can never give me a straight answer. I've checked the intros on the SpringSource site, and they're either really complicated or really tutorial-focused, and none of them give me a good idea of why I should be using it, or how it will make my life easier. Sometimes people throw around the term "dependency injection", which just confuses me even more, because I think I have a different understanding of what that term means. Anyway, here's a little about my background and my app : Been developing in Java for a while, doing back-end web development. Yes, I do a ton of unit testing. To facilitate this, I typically make (at least) two versions of a method : one that uses instance variables, and one that only uses variables that are passed in to the method. The one that uses instance variables calls the other one, supplying the instance variables. When it comes time to unit test, I use Mockito to mock up the objects and then make calls to the method that doesn't use instance variables. This is what I've always understood "dependency injection" to be. My app is pretty simple, from a CS perspective. Small project, 1-2 developers to start with. Mostly CRUD-type operations with a a bunch of search thrown in. Basically a bunch of RESTful web services, plus a web front-end and then eventually some mobile clients. I'm thinking of doing the front-end in straight HTML/CSS/JS/JQuery, so no real plans to use JSP. Using Hibernate as an ORM, and Jersey to implement the webservices. I've already started coding, and am really eager to get a demo out there that I can shop around and see if anyone wants to invest. So obviously time is of the essence. I understand Spring has quite the learning curve, plus it looks like it necessitates a whole bunch of XML configuration, which I typically try to avoid like the plague. But if it can make my life easier and (especially) if make it can make development and testing faster, I'm willing to bite the bullet and learn Spring. So please. Educate me. Should I use Spring? Why or why not?

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  • I don't know C. And why should I learn it?

    - by Stephen
    My first programming language was PHP (gasp). After that I started working with JavaScript. I've recently done work in C#. I've never once looked at low or mid level languages like C. The general consensus in the programming-community-at-large is that "a programmer who hasn't learned something like C, frankly, just can't handle programming concepts like pointers, data types, passing values by reference, etc." I do not agree. I argue that: Because high level languages are easily accessible, more "non-programmers" dive in and make a mess, and In order to really get anything done in a high level language, one needs to understand the same similar concepts that most proponents of "learn-low-level-first" evangelize about. Some people need to know C. Those people have jobs that require them to write low to mid-level code. I'm sure C is awesome. I'm sure there are a few bad programmers who know C. My question is, why the bias? As a good, honest, hungry programmer, if I had to learn C (for some unforeseen reason), I would learn C. Considering the multitude of languages out there, shouldn't good programmers focus on learning what advances us? Shouldn't we learn what interests us? Should we not utilize our finite time moving forward? Why do some programmers disagree with this? I believe that striving for excellence in what you do is the fundamental deterministic trait between good programmers and bad ones. Does anyone have any real world examples of how something written in a high level language--say Java, Pascal, PHP, or Javascript--truely benefitted from a prior knowledge of C? Examples would be most appreciated. (revised to better coincide with the six guidelines.)

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  • I don't know C. And why should I learn it?

    - by Stephen
    My first programming language was PHP (gasp). After that I started working with JavaScript. I've recently done work in C#. I've never once looked at low or mid level languages like C. The general consensus in the programming-community-at-large is that "a programmer who hasn't learned something like C, frankly, just can't handle programming concepts like pointers, data types, passing values by reference, etc." I do not agree. I argue that: Because high level languages are easily accessible, more "non-programmers" dive in and make a mess In order to really get anything done in a high level language, one needs to understand the same similar concepts that most proponents of "learn-low-level-first" evangelize about. Some people need to know C; those people have jobs that require them to write low to mid-level code. I'm sure C is awesome, and I'm sure there are a few bad programmers who know C. Why the bias? As a good, honest, hungry programmer, if I had to learn C (for some unforeseen reason), I would learn C. Considering the multitude of languages out there, shouldn't good programmers focus on learning what advances us? Shouldn't we learn what interests us? Should we not utilize our finite time moving forward? Why do some programmers disagree with this? I believe that striving for excellence in what you do is the fundamental deterministic trait between good programmers and bad ones. Does anyone have any real world examples of how something written in a high level language—say Java, Pascal, PHP, or Javascript—truely benefitted from a prior knowledge of C? Examples would be most appreciated.

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  • Why Is Web Sharing Broken on My Mac?

    - by Sam Murray-Sutton
    Background: I use my Mac for web development, running copies of web sites locally. I recently installed the Snow Leopard update, which to all intents and purposes seems to have gone fine, except... What's not working? Web-sharing; more specifically I can't turn it on via preferences. The preference pane just hangs when I try to. So Apache doesn't start on reboot. I can start Apache by hand, but I don't know enough to either setup apache to start with the computer, or to properly fix web sharing. Further details My Apache error log shows nothing on when the system boots up (as I would expect). This is the error message when I try to start web sharing from the sharing preference pane. 28/09/2009 10:58:05 System Preferences[834] setInetDServiceEnabled failed with 1 for org.apache.httpd Here's the messages given when I start apache from the command line. [Mon Sep 28 10:35:53 2009] [warn] Init: Session Cache is not configured [hint: SSLSessionCache] [Mon Sep 28 10:35:54 2009] [warn] mod_bonjour: Skipping user 'sams' - index file /Users/sams/Sites/index.html has zero length. [Mon Sep 28 10:35:54 2009] [notice] Digest: generating secret for digest authentication ... [Mon Sep 28 10:35:54 2009] [notice] Digest: done [Mon Sep 28 10:35:54 2009] [notice] Apache/2.2.11 (Unix) mod_ssl/2.2.11 OpenSSL/0.9.8k DAV/2 PHP/5.3.0 Phusion_Passenger/2.2.5 configured -- resuming normal operations Please let me know if you need any further details on this. Any help would be greatly appreciated. UPDATE I have added an answer of my own below - I was able to solve it thanks to being pointed in the right direction by the comments below, so thanks very much. But I'm still not totally clear as to what caused the problem or how my solution addressed it, so I'm leaving the question open for now.

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  • How To Find Reasons of Why Site Goes Online/Offline

    - by HollerTrain
    Seems today a website I manage has been going online and offline throughout the entire day. I have no idea what is causing the issue so I am seeking guidance on where to start. It is a Wordpress based site. So here is what I DO know: I use a program that pings the server every minute and when the server is not responding me it emails me, so I can know exactly when the site is online and offline. The site between 8pm to 12pm 12.28, and around the 1a hour early morning 12.29 (New York City timezone, and all times below are in same timezone). At the time of the ups/downs I see a lot of strain on the memory usage. Look at the load average when the site is going online/offline (http://screencast.com/t/BRlfXkqrbJII). Then I ran this command to restart http (http://screencast.com/t/usVtYWZ2Qi) and the memory usage then goes down to this (http://screencast.com/t/VdTIy3bgZiQB). An hour after I restarted http, the site then went offline/online so restarting the http didn't do much help. When the site is going offline/online, I ran the top command and get this (http://screencast.com/t/zEwr7YQj3). Here is a top command when the site is at it's lowest (http://screencast.com/t/eaMfha9lbT - so this would be dubbged "normal"). Here is a bandwidth report (http://screencast.com/t/AS0h2CH1Gypq). The traffic doesn't seem to be that much (http://screencast.com/t/s7hrWNNic1K), but looking at my times the site is going up/down this may be one of the reasons? I have the dvp Nitro package at Media Temple (http://mediatemple.net/webhosting/nitro/). So at this point I would request some help in trying to figure out what the cause of this is, and how I can go about pinpointing this issue. ANY HELP is greatly appreciated.

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  • Disk (EXT4) suddenly empty without any sign of why

    - by Ohnomydisk
    I have a Ubuntu 10.04 server with several disks in it. The disks are setup with a union filesystem, which presents them all as one logical /home. A few days ago, one of the disks appears to have suddenly 'become empty', for lack of better explanation. The amount of data on the /home mount almost halved within minutes - the disk appears to have had just over 400 GB of data prior to 'becoming empty'. I have absolutely no idea what happened. I was not using the server at the other time, but there are half a dozen other users who may have been (without root access and without the ability to hose a whole disk). I've ran SMART tests on the disk and it comes back clean. The filesystem checks fine (it has 12 GB used now, as some user software continued downloading after the incident). All I know is that around around midnight on October 19, the disk usage changed dramatically: The data points are every 15 minutes, and the full loss occured between captures: 2012-10-18 23:58:03.399647 - has 953.97/2059.07 GB [46.33 percent] 2012-10-19 00:13:15.909010 - has 515.18/2059.07 GB [25.02 percent] Other than that, I have not much to go off :-( I know that: There's nothing interesting in log files at that time Nobody appeared to be logged in via SSH at the time it occured (most users do not even use SSH) The server was online through whatever occured (3 months uptime) None of the other disks were affected and everything else on the server looks completely normal I have tried using "extundelete" on the disk and it didn't really find anything (some temporary files, but they looked new anyway) I am completely at a loss to what could have caused this. I was initially thinking maybe root escalation exploit, but even if someone did maliciously "rm" the disk contents, it would take more than 15 minutes for 400 GB?

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  • why use branches in svn?

    - by ajsie
    i know that you could organize your files according to this structure in svn: trunk branches tags that you copy the trunk to a folder in branches if you want to have a seperate development line. later on you merge this branch back to trunk. but i wonder why me and my group should do this. why should one copy the trunk to a branch and work with this copy just to merge it back to the trunk, and mean while the code is frequently updated/commited to stay in sync with the trunk. why not just work with the trunk then? what is the benefits with creating a branch? would be great if someone could shed a light on this topic. thanks in advance

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  • Why Do Browsers Leak Memory?

    - by Dane Balia
    A colleague and I were speaking about browsers (using browser control in a project), and it appears as plain as day that all browsers (Firefox, Chrome, IE, Opera) display the same characteristic or side-effect from their usage and that being 'Leaking Memory'. Can someone explain why that is the case? Surely as with any form of code, there should be proper garbage collection? PS. I've read about some defensive patterns on why this can happen from a developer's perspective. I am aware of an article Crockford wrote on IE; but why is the problem symptomatic of every browser? Thanks

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  • Why not standard Android emulators?

    - by Gerry
    I'm new to Android, but have published iphone and bberry apps. I see that I have to create an emulator using the SDK, before I can write and test an app. Why are there no default emulators? Why not at least a Nexus one, or HTC hero emulator shipped with the product? Sure its supposed to be flexible, but why not make it easy to create hello world and play around with a virtual Android phone? Both blackberry and iphone come with default simulators when you download the sdk. Thanks, Gerry

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  • How to know my free disk space on web hosting server?

    - by Abu
    I have got some work from my friend for updating his website. Earlier his website was made by some other person and he used to maintain all the stuff. Now that developer has given only the ftp username and password to my friend. He asks me to update his website. But the problem is I don't know how to access the things for this particular web hosting account like knowing the available free space, accesing email account, etc. I asked him about website control panel but he says that he doesn't know about. Is there any other site/client program/control panel that I can use to manage that website. So can any one help me out?

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  • Why is VB so popular? [closed]

    - by aaaidan
    To me, Visual Basic seems clumsy, ugly, error-prone, and difficult to read. I'll let others explain why. While VB.net has clearly been a huge leap forward for the language in terms of features, I still don't understand why anyone would choose to code in VB over, say, C#. However, I still see (what seems to be) the vast majority of commercial web apps from "MS shops" are built in VB. I could stand corrected on this, but VB still seems more popular than it deserves. Can anyone help answer any (or all) of these questions: Am I missing something with VB? Is it easier to learn, or "friendlier" than C#? Are there features I don't know about? Why is VB/VB.net so frequently used today, especially in web projects?

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  • I would like to know what kind of tools I should be looking for web development.

    - by user646636
    I would like to know what kind of tools I should be looking for web development. I have learned the basics of HTML/CSS/PHP/JS/phpmyadmin Now, I was looking to a write a website for purchasing and selling products for clients and sellers. I was wondering what other languages I would need to learn and also what kinda development tools I should use. Also, what would be the best type of language to write a website like this. I have heard that I should be using python for this type of web development. Do you guys have any suggestion as to what I should be looking at? And Also I would like to know if I should be setting up my own database or should I be using something like MySQL. I'm looking for languages that would have low maintenance cost in the long run. Thanks

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  • Do I really need to "learn" C# for XNA if I know Java?

    - by CJ Sculti
    so I want to start developing in XNA. As of now, I do not know C#, but I would consider myself "good" at Java. I have looked at some C# code and it looks almost IDENTICAL to Java... After looking at this, http://www.harding.edu/fmccown/java_csharp_comparison.html it looks like they are basically the same. Obviously some function names are going to be different, but I think I can handle it. Now if I want to learn game development in XNA, do I really need to "learn" and master C#, or can I just jump right in and learn along the way? I should also mention, I also know PHP which looks very similar...

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  • Why don't stacks grow upwards (for security)?

    - by AshleysBrain
    This is related to the question 'Why do stacks typically grow downwards?', but more from a security point of view. I'm generally referring to x86. It strikes me as odd that the stack would grow downwards, when buffers are usually written to upwards in memory. For example a typical C++ string has its end at a higher memory address than the beginning. This means that if there's a buffer overflow you're overwriting further up the call stack, which I understand is a security risk, since it opens the possibility of changing return addresses and local variable contents. If the stack grew upwards in memory, wouldn't buffer overflows simply run in to dead memory? Would this improve security? If so, why hasn't it been done? What about x64, do those stacks grow upwards and if not why not?

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  • Java: why can't iterate over an iterator?

    - by noamtm
    I read http://stackoverflow.com/questions/839178/why-is-javas-iterator-not-an-iterable and http://stackoverflow.com/questions/27240/why-arent-enumerations-iterable, but I still don't understand why this: void foo(Iterator<X> it) { for (X x : it) { bar(x); baz(x); } } was not made possible. In other words, unless I'm missing something, the above could have been nice and valid syntactic sugar for: void foo(Iterator<X> it) { for (X x; it.hasNext();) { x = it.next(); bar(x); baz(x); } }

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  • Why my laptop sends ARP request to itself ?

    - by user58859
    I have just started to learn about protocols. While studying the packets in wireshark, I came across a ARP request sent by my machine to my own IP. Here is the details of the packet : No. Time Source Destination Protocol Info 15 1.463563 IntelCor_aa:aa:aa Broadcast ARP Who has 192.168.1.34? Tell 0.0.0.0 Frame 15: 42 bytes on wire (336 bits), 42 bytes captured (336 bits) Arrival Time: Jan 7, 2011 18:51:43.886089000 India Standard Time Epoch Time: 1294406503.886089000 seconds [Time delta from previous captured frame: 0.123389000 seconds] [Time delta from previous displayed frame: 0.123389000 seconds] [Time since reference or first frame: 1.463563000 seconds] Frame Number: 15 Frame Length: 42 bytes (336 bits) Capture Length: 42 bytes (336 bits) [Frame is marked: False] [Frame is ignored: False] [Protocols in frame: eth:arp] [Coloring Rule Name: ARP] [Coloring Rule String: arp] Ethernet II, Src: IntelCor_aa:aa:aa (aa:aa:aa:aa:aa:aa), Dst: Broadcast (ff:ff:ff:ff:ff:ff) Destination: Broadcast (ff:ff:ff:ff:ff:ff) Address: Broadcast (ff:ff:ff:ff:ff:ff) .... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast) .... ..1. .... .... .... .... = LG bit: Locally administered address (this is NOT the factory default) Source: IntelCor_aa:aa:aa (aa:aa:aa:aa:aa:aa) Address: IntelCor_aa:aa:aa (aa:aa:aa:aa:aa:aa) .... ...0 .... .... .... .... = IG bit: Individual address (unicast) .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default) Type: ARP (0x0806) Address Resolution Protocol (request) Hardware type: Ethernet (0x0001) Protocol type: IP (0x0800) Hardware size: 6 Protocol size: 4 Opcode: request (0x0001) [Is gratuitous: False] Sender MAC address: IntelCor_aa:aa:aa (aa:aa:aa:aa:aa:aa) Sender IP address: 0.0.0.0 (0.0.0.0) Target MAC address: 00:00:00_00:00:00 (00:00:00:00:00:00) Target IP address: 192.168.1.34 (192.168.1.34) Here the sender's mac address is mine(Here I have hiden my mac address). target IP is mine. Why my machine is sending ARP request to itself? I found 3 packets of this type. There was no ARP reply for these packets. Can anybody explain me why it is? (My operating system is windows-7. I am directly connected to a wifi modem. I got these packets as soon as I started my connection.) I want one suggestion also. many places I read that RFC's are enough for study about protocols. I studied the RFC 826 on ARP. I personally feel that is not enough at all. Any suggestion regarding this? Is there more then 1 RFC for a protocol? I want to study about the protocols in very detail. Can anybody guide me for this? Thanks in advance.

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  • Why has anybody ever used COBOL?

    - by sarzl
    I know: You and me hate COBOL. I took a look at a lot of code examples and it didn't take me long to know why everybody tries to avoid it. So I really have no idea: Why was COBOL ever used? I mean: Hey - there was Fortran before it, and Fortran looks like a jesus-language compared to COBOL. This isn't argumentative but historical as I'm young and didn't even know about COBOL before 4 months.

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  • Does anybody know what happens to money spent in the Ubuntu One Music Store?

    - by Dave
    I remember reading on the Canonical website around the launch of the Ubuntu One Music store that after revenue was divided between Canonical, 7 digital and the artists involved that all profit or a significant percentage would be donated to a charity. This information has either disappeared from their website or my detective skills have failed me once more. Does anybody happen to understand the break down of revenue generated by the Ubuntu One Music Store or even know where to find this information. Also it would be useful to know which charity benefits from this. (Not that that would impact upon my purchases or send me running to iTunes. ;) Promise)

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  • Why isn't Hadoop implemented using MPI?

    - by artif
    Correct me if I'm wrong, but my understanding is that Hadoop does not use MPI for communication between different nodes. What are the technical reasons for this? I could hazard a few guesses, but I do not know enough of how MPI is implemented "under the hood" to know whether or not I'm right. Come to think of it, I'm not entirely familiar with Hadoop's internals either. I understand the framework at a conceptual level (map/combine/shuffle/reduce and how that works at a high level) but I don't know the nitty gritty implementation details. I've always assumed Hadoop was transmitting serialized data structures (perhaps GPBs) over a TCP connection, eg during the shuffle phase. Let me know if that's not true.

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  • Know a little of a lot or a lot of a little? [closed]

    - by Jeff V
    Possible Duplicate: Is it better to specialize in a single field I like, or expand into other fields to broaden my horizons? My buddy and I who have been programming for 13 years or so were talking this morning and a question that came up was is it better to know a little of a lot (i.e. web, desktop, VB.Net, C#, jQuery, PHP, Java etc.) or is it better to know a lot of a little (meaning expert in something). The context of this question is what makes someone a senior programmer? Is it someone that has been around the block a few times and has been in many different situations or one that is locked in to a specific technology that is super knowledgeable in that one technology? I see pro's and con's of both scenarios.. Just wondering what others thought.

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  • Why does it work

    - by A-ha
    Guys I've asked few days ago a question and didn't have really time to check it and think about it, but now I've tried one of the solutions and I can't understand why does it work? I mean why destructor is called at the end of line like this: #include "stdafx.h" #include "coutn.h" #define coutn coutn() int _tmain(int argc, _TCHAR* argv[]) { coutn << "Line one " << 1;//WHY DTOR IS CALLED HERE coutn << "Line two " << " and some text."; return 0; } I assume that it has something to do with lifetime of an object but I'm not sure what and how. As I think of it there are two unnamed objects created but they do not go out of scope so I can't understand for what reason is dtor called. Thank you.

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  • What is "networking" for your career and how do you know if you have done it successfully?

    - by Jay Godse
    Many people suggest "networking" as a tool or technique to build your career, get better jobs, get promotions, et cetera. But what is "networking"? And more importantly, how do you know if you have "networked" or "built your network" "successfully"? (I quoted all the terms which I think may have subjective and widely varying definitions). Many folks think that networking is schmoozing at networking events. Others think it is adding "friends" to Facebook or LinkedIn. But how do measure the success of such networks or activities? But we all know people (perhaps ourselves) who have done those things and still have trouble getting jobs, promotions, and recognition.

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