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  • Why has to be size of dynamically-allocated array a static field?

    - by Ondrej Slinták
    I have a dummy class where I am testing arrays. I've noticed that when I want to dynamically allocate size of array at runtime, fields that indicate this size have to be static. I know I should probably use collections for this kind of code, but I'm more interested why do these fields have to be static? Is there any particular reason behind this? class Foo { private static int x; private static int y; private int[,] bar = new int[ x, y ]; public Foo( int a, int b ) { x = a; y = b; } }

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  • Why does Cache.Add return an object that represents the cached item?

    - by Pure.Krome
    From MSDN about the differences between Adding or Inserting an item the ASP.NET Cache: Note: The Add and Insert methods have the same signature, but there are subtle differences between them. First, calling the Add method returns an object that represents the cached item, while calling Insert does not. Second, their behavior is different if you call these methods and add an item to the Cache that is already stored there. The Insert method replaces the item, while the Add method fails. [emphasis mine] The second part is easy. No question about that. But with the first part, why would it want to return an object that represents the cached item? If I'm trying to Add an item to the cache, I already have/know what that item is? I don't get it. What is the reasoning behind this?

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  • Why do debug symbols so adversely affect the performance of threaded applications on Linux?

    - by fluffels
    Hi. I'm writing a ray tracer. Recently, I added threading to the program to exploit the additional cores on my i5 Quad Core. In a weird turn of events the debug version of the application is now running slower, but the optimized build is running faster than before I added threading. I'm passing the "-g -pg" flags to gcc for the debug build and the "-O3" flag for the optimized build. Host system: Ubuntu Linux 10.4 AMD64. I know that debug symbols add significant overhead to the program, but the relative performance has always been maintained. I.e. a faster algorithm will always run faster in both debug and optimization builds. Any idea why I'm seeing this behavior?

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  • Why is C++ fwrite() producing larger output in release?

    - by waffleShirt
    I recently wrote an implementation of the Canonical Huffman compression algorithm. I have a 500kb test file that can be compressed to about 250kb when running the debug and release builds from within Visual Studio 2008. However when I run the release build straight from the executeable the test file only compresses to about 330kb. I am assuming that something is going wrong when the file is written using fwrite(). I have tested the program and confirmed that uncompressing the files always produces the correct uncompressed file. Does anyone know why this could possibly be? How could the same executeable file be producing different sized outputs based on where it is launched from?

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  • Python subprocess.Popen hangs in 'for l in p.stdout' until p terminates, why?

    - by Albert
    I have that code: #!/usr/bin/python -u localport = 9876 import sys, re, os from subprocess import * tun = Popen(["./newtunnel", "22", str(localport)], stdout=PIPE, stderr=STDOUT) print "** Started tunnel, waiting to be ready ..." for l in tun.stdout: sys.stdout.write(l) if re.search("Waiting for connection", l): print "** Ready for SSH !" break The "./newtunnel" will not exit, it will constantly output more and more data to stdout. However, that code will not give any output and just keeps waiting in the tun.stdout. When I kill the newtunnel process externally, it flushes all the data to tun.stdout. So it seems that I can't get any data from the tun.stdout while it is still running. Why is that? How can I get the information? Note that the default bufsize for Popen is 0 (unbuffered). I can also specify bufsize=0 but that doesn't change anything.

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  • Why does PHP 5.2 disallow abstract static class methods?

    - by Artem Russakovskii
    After enabling strict warnings in PHP 5.2, I saw a load of strict standards warnings from a project that was originally written without strict warnings: Strict Standards: Static function Program::getSelectSQL() should not be abstract in Program.class.inc The function in question belongs to an abstract parent class Program and is declared abstract static because it should be implemented in its child classes, such as TVProgram. I did find references to this change here: Dropped abstract static class functions. Due to an oversight, PHP 5.0.x and 5.1.x allowed abstract static functions in classes. As of PHP 5.2.x, only interfaces can have them. My question is: can someone explain in a clear way why there shouldn't be an abstract static function in PHP?

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  • Why do i get a 403 error when viewing a Drupal custom menu item via clean url?

    - by Chaulky
    Hi all, I've created a custom menu item in my Drupal 6 website by defining it in a custom module. This is an extremely simple MENU_NORMAL_ITEM menu item. The menu item is defined as /** * Implementation of hook_menu(). */ function menu_test_menu() { $items['menu_test'] = array( 'title' => 'Menu Test', 'page callback' => 'menu_test_hello', 'access callback' => TRUE, 'type' => MENU_NORMAL_ITEM, ); return $items; } Since I have clean URLs on, the path should be www.example.com/menu_test. That URL gives me a 403 error. But, if I enter www.example.com/?q=menu_test, everything works fine. Why am I getting the 403 error? The menu item is useless because it's always trying to go to the clean URL path, which should work but doesn't for some reason. Thanks for the help!

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  • Why exactly is calling the destructor for the second time undefined behavior in C++?

    - by sharptooth
    As mentioned in this answer simply calling the destructor for the second time is already undefined behavior 12.4/14(3.8). For example: class Class { public: ~Class() {} }; // somewhere in code: { Class* object = new Class(); object->~Class(); delete object; // UB because at this point the destructor call is attempted again } In this example the class is designed in such a way that the destructor could be called multiple times - no things like double-deletion can happen. The memory is still allocated at the point where delete is called - the first destructor call doesn't call the ::operator delete() to release memory. For example, in Visual C++ 9 the above code looks working. Even C++ definition of UB doesn't directly prohibit things qualified as UB from working. So for the code above to break some implementation and/or platform specifics are required. Why exactly would the above code break and under what conditions?

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  • Why await is not taken in consideration after deploy?

    - by Cristian Boariu
    I have a method which does some sync calls to a specific REST api, something like: WSRequestHolder url = WS.url("rest_api_url"); Promise<WS.Response> promisePerPage = url.get(); promisePerPage.getWrappedPromise().await(3000, TimeUnit.MILLISECONDS); WS.Response responsePerPage = promisePerPage.get(); ProductsWrapper productsWrapper = new Gson().fromJson(responsePerPage.getBody(), ProductsWrapper.class); As you notice, I put 3 seconds between calls so each request can be parsed in time and inserted in DB. All works great locally but after I deploy to cloud, all goes continuously, without any more waiting (3 seconds) between requests... Do you know why?

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  • Why does cisco IOS require domain-name to be set before SSH keys can be generated?

    - by Daniel Papasian
    Is there a technical reason why IOS requires the device's domain-name to be set (via ip domain-name) before an SSH key can be generated? Is the domain-name used in any way in the generation of the key? Is there any way to force the generation of a key before the domain name is set? UPDATE: Myself (before I posted this question) and others in your answer seem to think it may be used as either a salt or a source of entropy for the key. Wouldn't the domain-name be very predictable? This doesn't seem like a suitable source of entropy.

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  • Why do values in the row I insert not match the values in the insert query?

    - by user202411
    I just can't understand why is my database (mysql) behaving like this! My console shows that the record is created properly (please, notice the "remote_id" value): Tweet Create (0.3ms) INSERT INTO `tweets` (`remote_id`, `text`, `user_id`, `twitter_account_id`) VALUES (12325438258, 'jamaica', 1, 1) But when I check the record, it shows that the remote_id is 2147483647 intead of the provided value (12325438258 in the example above)... This table has many entries, but this field is always written with 2147483647... It was supposed to fill this space with an unique id (which I guarantee you is being generated properly).

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  • C++: Why does space always terminate a string when read?

    - by Nullw0rm
    Using type std::string to accept a sentence, for practise (I haven't worked with strings in C++ much) I'm checking if a character is a vowel or not. I got this: for(i = 0; i <= analyse.length(); i++) { if(analyse[i] == 'a' || analyse[i] == 'e' [..etc..]) { ...vowels++; } else { ... ...consenents++; } This works fine if the string is all one word, but the second I add a space (IE: aeio aatest) it will only count the first block and count the space as a consenent, and quit reading the sentence (exiting the for loop or something). Does a space count as no character == null? Or some oddity with std::string?, It would be helpful to know why that is happening!

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  • F#: Can't hide a type abbreviation in a signature? Why not?

    - by Nels Beckman
    In F#, I'd like to have what I see as a fairly standard Abstract Datatype: // in ADT.fsi module ADT type my_Type // in ADT.fs module ADT type my_Type = int In other words, code inside the module knows that my_Type is an int, but code outside does not. However, F# seems to have a restriction where type abbreviations specifically cannot be hidden by a signature. This code gives a compiler error, and the restriction is described here. If my_Type were instead a discriminated union, then there is no compiler error. My question is, why the restriction? I seem to remember being able to do this in SML and Ocaml, and furthermore, isn't this a pretty standard thing to do when creating an abstract datatype? Thanks

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  • Why Is It That Generics Constraint Can't Be Casted to Its Derived Type?

    - by Ngu Soon Hui
    It is quite puzzling to find out that Generics Constraint Can't Be Casted to Its Derived Type. Let's say I have the following code: public abstract class BaseClass { public int Version { get { return 1; } } public string FixString { get; set; } public BaseClass() { FixString = "hello"; } public virtual int GetBaseVersion() { return Version; } } public class DeriveClass: BaseClass { public new int Version { get { return 2; } } } And guess what, this method will return a compilation error: public void FreeConversion<T>(T baseClass) { var derivedMe = (DeriveClass)baseClass; } I would have to cast the baseClass to object first before I can cast it to DerivedClass. Seems to me pretty ugly. Why this is so?

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  • File.Copy with opened stream not crashing. Know why?

    - by Carlo
    I have this code, I open a stream (without closing or disposing it), then I copy the file used by the stream, I thought I should get a "Process can't access file somefile.xml because it's being used by another process" exception, but I don't. Any idea why? Thanks! The code: StreamWriter writer = new StreamWriter("C:\\somefile.xml"); writer.Write(string.Empty); // I thought this should crash since a stream is using "C:\somefile.xml" File.Copy("C:\\somefile.xml", "C:\\copy of somefile.xml", true);

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  • Hibernate - why use many-to-one to represent a one-to-one?

    - by aberrant80
    I've seen people use many-to-one mappings to represent one-to-one relationships. I've also read this in a book by Gavin King and on articles. For example, if a customer can have exactly one shipping address, and a shipping address can belong to only one customer, the mapping is given as: <class name="Customer" table="CUSTOMERS"> ... <many-to-one name="shippingAddress" class="Address" column="SHIPPING_ADDRESS_ID" cascade="save-update" unique="true"/> ... </class> The book reasons as (quoting it): "You don't care what's on the target side of the association, so you can treat it like a to-one association without the many part." My question is, why use many-to-one and not one-to-one? What is it about a one-to-one that makes it a less desirable option to many-to-one? Thanks.

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  • Why does Google Page-Speed say that elements need compressing, when they already are compressed?

    - by Peter Snow
    My page is compressed using the following in .htaccess <ifModule mod_gzip.c> mod_gzip_on Yes mod_gzip_dechunk Yes mod_gzip_item_include file \.(html?|txt|css|js|php|pl)$ mod_gzip_item_include handler ^cgi-script$ mod_gzip_item_include mime ^text/.* mod_gzip_item_include mime ^application/x-javascript.* mod_gzip_item_exclude mime ^image/.* mod_gzip_item_exclude rspheader ^Content-Encoding:.*gzip.* </ifModule> Yslow says that the page and specifically the elements which Page-Speed is complaining about, are compressed and it gives the page an overall score of 90/100. Why then, does Page-Speed say that Compressing the following resources with gzip could reduce their transfer size by 118.8KiB (70% reduction). and it gives the page an overall score of 33/100?

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  • why does the array doesn't get initialized by global variable , even though it should not?

    - by ashish yadav
    why does the array a does not get initialized by global variable 'size'. include int size=5; int main() { int a[size]={1,2,3,4,5}; printf("%d",a[0]); return 0; } the compilation error is shown as "variable-sized object may not be initialized". according to me the array should get initialized by 'size'. i apologize if i am not clear but i feel i have expressed myself well enough. thank you!!!!!!!!!!!

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  • Why are C, C++, and LISP so prevalent in embedded devices and robots?

    - by David
    It seems that the software language skills most sought for embedded devices and robots are C, C++, and LISP. Why haven't more recent languages made inroads into these applications? For example, Erlang would seem particularly well-suited to robotic applications, since it makes concurrent programming easier and allows hot swapping of code. Python would seem to be useful, if for no other reason than its support of multiple programming paradigms. I'm even surprised that Java hasn't made a foray into general robotic programming. I'm sure one argument would be, "Some newer languages are interpreted, not compiled" - implying that compiled languages are quicker and use fewer computational resources. Is this still the case, in a time when we can put a Java Virtual Machine on a cell phone or a SunSpot? (and isn't LISP interpreted anyway?)

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  • why doesn't perl sort the hash key in numeric order ?

    - by Haiyuan Zhang
    #!/usr/bin/perl use strict; use warnings; my %hash; foreach ( 1 .. 10 ) { $hash{$_} = $_; } foreach ( sort(keys %hash) ) { print $_ . ": " . "$hash{$_}" . "\n" ; } execute the above code, the result is as below : 1: 1 10: 10 2: 2 3: 3 4: 4 5: 5 6: 6 7: 7 8: 8 9: 9 Yes, I expect "10: 10" to be the last one taht is printed . So I just need someone to explain why perl give me surprise in this case.

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  • Can anyone explain why this behaviour might be happening in Windows Forms?

    - by gizgok
    I'm developing a Windows Forms Application. See attached image for the Interface. Now I've put a close button (X) in the Panel(say Panel2) which has Application Constants as label.The first combo box is in another panel(say Panel1). Now when I click on the X button in Panel 2 I want the Panel to be invisible and the combo box text to be blank. Simple enough. So I write Panel2.visible=false; comboBox1.SelectedIndex=-1; When I click on X, the text in combo box goes blank, then I have to click again for the Panel2 to go invisible. Then I changed the sequence comboBox1.SelectedIndex=-1; Panel2.visible=fasle; and this works smooth. Not sure why this might be happening? Is there anything that I might be doing with my form design/code to have such a behaviour?

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  • How to figure out why ssh session does not exit sometimes?

    - by WilliamKF
    I have a C++ application that uses ssh to summon a connection to the server. I find that sometimes the ssh session is left lying around long after the command to summon the server has exited. Looking at the Centos4 man page for ssh I see the following: The session terminates when the command or shell on the remote machine exits and all X11 and TCP/IP connections have been closed. The exit status of the remote program is returned as the exit status of ssh. I see that the command has exited, so I imagine not all the X11 and TCP/IP connections have been closed. How can I figure out which of these ssh is waiting for so that I can fix my summon command's C++ application to clean up whatever is being left behind that keeps the ssh open. I wonder why this failure only occurs some of the time and not on every invocation? It seems to occur approximately 50% of the time. What could my C++ application be leaving around to trigger this?

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  • Why am I not getting correct result when I calculate exponent with ^ in C++?

    - by xbonez
    I am using Bode's formuala to calculate distance of nth planet from sun dist = (4 + 3*(2^(n-2)))/10 If I calculate the distance this way, I get the right values: dist[2] = ((4 + 3*1)/10.0) ; dist[3] = ((4 + 3*2)/10.0) ; dist[4] = ((4 + 3*4)/10.0) ; But doing it this way, gives me incorrect values: vector <double> dist(5); for (unsigned int i = 2; i < 5; i++) { dist[i] = ((4 + 3*(2^(3-2)))/10.0) ; } Why so?

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  • Why jquery.animate on a textarea make the blinking cursor disapears?

    - by Tom S.
    Hello everyone. I have the following code $(document).ready(function() { $("#myTextArea").focus(function() { $("#myTextArea").animate({ "height": "75px"}, "normal"); return false; }); to expand a textbox when it gets focus. The expand occurs, however the blinking cursor disapears, at least in Firefox! Edited: The textarea is still focused, and i can type on it. Why does this happen? Is there a way to show it again? Thanks in advance

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  • C# - Why can't I enforce derived classes to have parameterless constructors?

    - by FrisbeeBen
    I am trying to do the following: public class foo<T> where T : bar, new { _t = new T(); private T _t; } public abstract class bar { public abstract void someMethod(); // Some implementation } public class baz : bar { public overide someMethod(){//Implementation} } And I am attempting to use it as follows: foo<baz> fooObject = new foo<baz>(); And I get an error explaining that 'T' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method. I fully understand why this must be, and also understand that I could pass a pre-initialized object of type 'T' in as a constructor argument to avoid having to 'new' it, but is there any way around this? any way to enforce classes that derive from 'bar' to supply parameterless constructors?

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