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• What is the difference between "a is b" and "id(a) == id(b)" in Python?

  - by bp

  The id() inbuilt function gives... an integer (or long integer) which is guaranteed to be unique and constant for this object during its lifetime. The is operator, instead, gives... object identity So why is it possible to have two objects that have the same id but return False to an is check? Here is an example: >>> class Test(): ... def test(): ... pass >>> a = Test() >>> b = Test() >>> id(a.test) == id(b.test) True >>> a.test is b.test False A more troubling example: (continuing the above) >>> b = a >>> b is a True >>> b.test is a.test False >>> a.test is a.test False

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• Clarification on ZVals

  - by Beachhouse

  I was reading this: http://www.dereleased.com/2011/04/27/the-importance-of-zvals-and-circular-references/ And there's an example that lost me a bit. $foo = &$bar; $bar = &$foo; $baz = 'baz'; $foo = &$baz; var_dump($foo, $bar); /* string(3) "baz" NULL */ If you’ve been following along, this should make perfect sense. $foo is created, and pointed at a ZVal location identified by $bar; when $bar is created, it points at the same place $foo was pointed. That location, of course, is null. When $foo is reassigned, the only thing that changes is to which ZVal $foo points; if we had assigned a different value to $foo first, then $bar would still retain that value. I learned to program in C. I understand that PHP is different and it uses ZVals instead of memory locations as references. But when you run this code: $foo = &$bar; $bar = &$foo; It seems to me that there would be two ZVals. In C there would be two memory locations (and the values would be of the opposite memory location). Can someone explain?

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• Timer C#. Start, stop, and get the amount of time between the calls

  - by user1886060

  I'm writing UDP chat with reliable data transfer. I need to start a timer when a packet is sent, and stop it as soon it receives an answer from the server(ACK- acknowledgment). Here is my code: private void sendButton_Click(object sender, EventArgs e) { Packet snd = new Packet(ack, textBox1.Text.Trim()); textBox1.Text = string.Empty; Smsg = snd.GetDataStream();//convert message into array of bytes to send. while (true) { try { // Here I need to Start a timer! clientSock.SendTo(Smsg, servEP); clientSock.ReceiveFrom(Rmsg, ref servEP); //Here I need to stop a timer and get elapsed amount of time. Packet rcv = new Packet(Rmsg); if (Rmsg != null && rcv.ACK01 != ack) continue; if (Rmsg != null && rcv.ACK01 == ack) { this.displayMessageDelegate("ack is received :"+ack); ChangeAck(ack); break; } Thank you.

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• JQuery 1.3.1 doesn't find dynamically generated rows

  - by Bamelis Steve

  I have just installed in the ASP.NET MVC RC2 and with that also using the JQuery 1.3.1 library. Before I was using the 1.2.6 library. Our application works fine under that library. But now I have strange problem. We have a grid view that we build up with the result of an AJAX call. With the result returned we add new rows to a table through cloning a hidden row. The generated HTML from the JQuery is placing extra parameters to the tags. These are in the form of JQuery12345678="null". They all have the same name. In the head of the table there is a checkbox that selects/unselects all the rows of the table. This by iterating through the rows of the table. $("#selectAllCheckbox").click(function() { var checked = this.checked; $("#dgNewTasks tbody tr").find(':input[type="checkbox"]').each(function() { this.checked = checked; }); }); Now by using the new library the check box are no longer set. I have used IE Developer Tools to check the HTML. If I remove the JQuery12345678="null" parameter from my rows. It works fine. Could someone tell me what I have to do?

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• How should a multi-threaded C application handle a failed malloc()?

  - by user294463

  A part of an application I'm working on is a simple pthread-based server that communicates over a TCP/IP socket. I am writing it in C because it's going to be running in a memory constrained environment. My question is: what should the program do if one of the threads encounters a malloc() that returns NULL? Possibilities I've come up with so far: No special handling. Let malloc() return NULL and let it be dereferenced so that the whole thing segfaults. Exit immediately on a failed malloc(), by calling abort() or exit(-1). Assume that the environment will clean everything up. Jump out of the main event loop and attempt to pthread_join() all the threads, then shut down. The first option is obviously the easiest, but seems very wrong. The second one also seems wrong since I don't know exactly what will happen. The third option seems tempting except for two issues: first, all of the threads need not be joined back to the main thread under normal circumstances and second, in order to complete the thread execution, most of the remaining threads will have to call malloc() again anyway. What shall I do?

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• Testing for optional node - Delphi XE

  - by Seti Net

  What is the proper way to test for the existance of an optional node? A snipped of my XML is: <Antenna > <Mount Model="text" Manufacture="text"> <BirdBathMount/> </Mount> </Antenna> But it could also be: <Antenna > <Mount Model="text" Manufacture="text"> <AzEl/> </Mount> </Antenna> The child of Antenna could either be BirdBath or AzEl but not both... In Delphi XE I have tried: if (MountNode.ChildNodes.Nodes['AzEl'] <> unassigned then //Does not work if (MountNode.ChildNodes['BirdBathMount'].NodeValue <> null) then // Does not work if (MountNode.BirdBathMount.NodeValue <> null) then // Does not work I use XMLSpy to create the schema and the example XML and they parse correctly. I use Delphi XE to create the bindings and it works on most other combinations fine. This must have a simple answer that I have just overlooked - but what? Thanks...... Jim

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• Android Java error handling XML file

  - by Paul

  I'm using SAX and XML reader to read XML weather info from the web and it works fine if the page exists. But if for instance the user inputs an invalid city, zip etc the XML page that gets read from is empty and the app force closes with nullpointerexception. The area that generates the error is here right at open inputstream. Any suggestions?: SAXParserFactory spf = SAXParserFactory.newInstance(); SAXParser sp = null; try { sp = spf.newSAXParser(); } catch (ParserConfigurationException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SAXException e) { // TODO Auto-generated catch block e.printStackTrace(); } /* Get the XMLReader of the SAXParser we created. */ XMLReader xr = null; try { xr = sp.getXMLReader(); } catch (SAXException e) { // TODO Auto-generated catch block e.printStackTrace(); } /* Create a new ContentHandler and apply it to the XML-Reader*/ WeatherHandler myExampleHandler = new WeatherHandler(); xr.setContentHandler(myExampleHandler); /* Parse the xml-data from our URL. */ try { xr.parse(new InputSource(url.openStream())); parsedWeatherDataSet = myExampleHandler.getParsedData(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SAXException e) { // TODO Auto-generated catch block e.printStackTrace(); } return parsedWeatherDataSet.toString();

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• Switching from php to python

  - by ts

  Hello I am trying to make a list of things which can be difficult/surprising to someone who is changing language from PHP to Python. so far i have rather short list: forget require / include, learn import (this was most difficult to me - to understand package - module - class - object hierarchy and its mapping to filesystem) you can't just upload file on server to have webpage (-mod_python, wsgi etc) learn the python way for use variable class names (new $class() vs import + getattr) / operator in python 2.x and all float-related horrors those were difficult to me, it takes few days before mind adapts a new paradigm after i found that there is few other areas which could be challenging for someone with (too) many years of php: everything is an object you have to live with exceptions array vs list, set, dictionary, tuple ... learn (effective) list comprehensions learn generators any other ideas / personal experiences ?

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• binary number comparison

  - by EquinoX

  If I have a 32 bit two's complement number and I want to know what is the easiest way to know of two numbers are equal... what would be the fastest bitwise operator to know this? I know xor'ing both numbers and check if the results are zero works well... any other one's? how about if a number is greater than 0?? I can check the 31'st bit to see if it's greater or equal to 0..but how about bgtz?

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• How do you deal with breaking changes in a Rails migration?

  - by Adam Lassek

  Let's say I'm starting out with this model: class Location < ActiveRecord::Base attr_accessible :company_name, :location_name end Now I want to refactor one of the values into an associated model. class CreateCompanies < ActiveRecord::Migration def self.up create_table :companies do |t| t.string :name, :null => false t.timestamps end add_column :locations, :company_id, :integer, :null => false end def self.down drop_table :companies remove_column :locations, :company_id end end class Location < ActiveRecord::Base attr_accessible :location_name belongs_to :company end class Company < ActiveRecord::Base has_many :locations end This all works fine during development, since I'm doing everything a step at a time; but if I try deploying this to my staging environment, I run into trouble. The problem is that since my code has already changed to reflect the migration, it causes the environment to crash when it attempts to run the migration. Has anyone else dealt with this problem? Am I resigned to splitting my deployment up into multiple steps?

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• [Scala] Using overloaded, typed methods on a collection

  - by stephanos

  I'm quite new to Scala and struggling with the following: I have database objects (type of BaseDoc) and value objects (type of BaseVO). Now there are multiple convert methods (all called 'convert') that take an instance of an object and convert it to the other type accordingly. For example: def convert(doc: ClickDoc): ClickVO = doc match { case null => null case _ => val result = new ClickVO result.x = doc.x result.y = doc.y result } Now I sometimes need to convert a list of objects. How would I do this - I tried: def convert[D <: MyBaseDoc, V <: BaseVO](docs: List[D]):List[V] = docs match { case List() => List() case xs => xs.map(doc => convert(doc)) } Which results in 'overloaded method value convert with alternatives ...'. I tried to add manifest information to it, but couldn't make it work. I couldn't even create one method for each because it'd say that they have the same parameter type after type erasure (List). Ideas welcome!

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• EMSA_PSS_ENCODE with libssl

  - by luiss

  Hi I'm trying to use libssl to get some EMSA_PSS_ENCRODING through the function RSA_padding_add_PKCS1_type1 in libssl, but I can't find nor docs nor solutions, so this is the example code I've written: #include <stdio.h> #include <stdlib.h> #include <string.h> #include <openssl/rsa.h> #include <openssl/err.h> FILE *error_file; int main() { int lSize; const unsigned char *string1= (unsigned char *)"The pen is on the table"; unsigned char *stringa=NULL; int num = 64; if ((stringa = (unsigned char *)OPENSSL_malloc(num)) == NULL) fprintf(stderr,"OPENSSL_malloc error\n"); fprintf(stdout,"string1 len is %u\n",lSize); if(RSA_padding_add_PKCS1_type_1(stringa,num,string1,lSize) != 1) fprintf(stderr,"Error: RSA_PADDING error\n"); error_file = fopen("libssl.log", "w"); ERR_print_errors_fp(error_file); fclose(error_file); fprintf(stdout,(char *)stringa); fprintf(stdout,"\n"); } The problem is that I get no output in stringa, I think the function RSA_padding_add.. should be initialized, but I can't find how to do it in the few doc at the openssl site. Thanks

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• Can't compile std::map sorting, why?

  - by Vincenzo

  This is my code: map<string, int> errs; struct Compare { bool operator() (map<string, int>::const_iterator l, map<string, int>::const_iterator r) { return ((*l).second < (*r).second); } } comp; sort(errs.begin(), errs.end(), comp); Can't compile. This is what I'm getting: no matching function for call to ‘sort(..’ Why so? Can anyone help? Thanks!

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• MySQL Table Loop using PHP

  - by JM4

  I have an online form which collects consumer data and stores in a dedicated MySQL database. In some instances, data is passed in the URL under the "RefID" variable which is also stored in the database and attached to each registration. I use the 'mysql_num_rows ($result)' to fetch all agent details on another page but this only returns ALL available details. My goal is as follows: GOAL I want to create an HTML table in which rows are automatically generated based on the list of all registrations on my site. A new row is created IF and ONLY IF a unique RefID is present on that particular record. In the event the field is NULL, it is reported on a single line. In short, the HTML table could look something like this: RefID - Number of Enrollments abc123 - 10 baseball - 11 twonk - 7 NULL - 33 Where abc123 is a particular RefID and 10 is the number of times that RefID appears in the DB. If a new registration comes in with RefID = "horses", a new row is created, showing "horses - 1". The HTML table will be viewable by account administrators needing to see the number of enrollments for a particular RefID (which they won't know ahead of time). Anybody have any suggestions?

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• Initializing ExportFactory using MEF

  - by Riz

  Scenario Application has multiple parts. Each part is in separate dll and implements interface IFoo All such dlls are present in same directory (plugins) The application can instantiate multiple instances of each part Below is the code snippet for the interfaces, part(export) and the import. The problem I am running into is, the "factories" object is initialized with empty list. However, if I try container.Resolve(typeof(IEnumerable< IFoo )) I do get object with the part. But that doesn't serve my purpose (point 4). Can anyone point what I am doing wrong here? public interface IFoo { string Name { get; } } public interface IFooMeta { string CompType { get; } } Implementation of IFoo in separate Dll [ExportMetadata("CompType", "Foo1")] [Export(typeof(IFoo), RequiredCreationPolicy = CreationPolicy.NonShared))] public class Foo1 : IFoo { public string Name { get { return this.GetType().ToString(); } } } Main application that loads all the parts and instantiate them as needed class PartsManager { [ImportMany] private IEnumerable<ExportFactory<IFoo, IFooMeta>> factories; public PartsManager() { IContainer container = ConstructContainer(); factories = (IEnumerable<ExportFactory<IFoo, IFooMeta>>) container.Resolve(typeof(IEnumerable<ExportFactory<IFoo, IFooMeta>>)); } private static IContainer ConstructContainer() { var catalog = new DirectoryCatalog(@"C:\plugins\"); var builder = new ContainerBuilder(); builder.RegisterComposablePartCatalog(catalog); return builder.Build(); } public IFoo GetPart(string compType) { var matchingFactory = factories.FirstOrDefault( x => x.Metadata.CompType == compType); if (factories == null) { return null; } else { IFoo foo = matchingFactory.CreateExport().Value; return foo; } } }

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• PHP function to handle most database queries has a problem with results. I am getting the right numb

  - by asdasds

  Here is my little function. It does not handle the results correctly. I do get all the rows that I want, but all the rows of the $results array contain the exact same values. So i make 2 arrays, a temporary array to hold the values after each fetch, and another array to hold all the temporary arrays. First i take the temp array and map its keys to the column names. Then i give it to bind_result, and call fetch() and use it like I would any other result value. Could this be because I re-use the $results array? numresults is the number of values you are taking from each row. if 0, you are not getting any results back. function db_query($db, $query, $params = NULL, $numresults = 0) { if($stmt = $db -> prepare($query)) { if($params != NULL) { call_user_func_array(array($stmt, 'bind_param'), $params); } if(!$stmt -> execute()) { //echo 'exec error:',$db->error; return false; } if($numresults > 0) { $results = array(); $tmpresult = array(); $meta = $stmt->result_metadata(); while ($columnName = $meta->fetch_field()) $tmpresult[] = &$results[$columnName->name]; call_user_func_array(array($stmt, 'bind_result'), $tmpresult); $meta->close(); $results = array(); while($stmt -> fetch()) $results[] = $tmpresult; } $stmt -> close(); } else { //echo 'prepare error: ',$db->error; return false; } if($numresults == 0) return true; return $results; }

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• Javascript dynamic table memory usage

  - by Dan

  I use a dynamic table: <html> <body> <button id="button">Build table</button> <div id="container"> <script type="text/javascript"> window.onload=function(){ var table = null; var row = "<tr><td>111111111111111111111111111111111111111111111111111111</td>" + "<td>222222222222222222222222222222222222222222222222222222</td>" + "<td>333333333333333333333333333333333333333333333333333333</td></tr>"; var data = null; for (var i = 0; i < 2000; i++){ data += row; } var obj = document.getElementById("button"); obj.onclick=function buildTable(){ document.getElementById("container").innerHTML = "<div><table><tbody>" + data + "</tbody></table></div>"; }; }; </script> </body> </html> Using chromes task manager, each time new data is loaded the memory usage increases considerably and doesn't go down, so after some time the app consumes a lot of memory and requires the browser to be closed. Is there any change in the code I can use to solve this or is it a browser side problem?

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• Ajax Code to run PHP query After Facebook Like Button is Clicked

  - by John

  I have the PHP below on a file called fblike.php. On another file, I have the Facebook Like button. The Like button functions. I would like to run the code below when the Facebook Like button is clicked. I know that FB.Event.subscribe('edge.create', function(response) {} is supposed to run whenever the Like button is clicked. I know that I am probably supposed to use Javascript and maybe Ajax to cause the PHP on fblike.php to run. But after multiple tries, I can't get it to work. What is the specific Ajax code that I could include within the Facebook Event? Do I need to do anything to the Like button code to allow the Facebook Event to work? $submissionid = $_POST['submissionid']; $uid = $_POST['uid']; mysql_connect("server", "username", "password") or die(mysql_error()); mysql_select_db("database") or die(mysql_error()); $q = "INSERT INTO fblikes VALUES (NULL, '$submissionid', '$uid', NULL)"; $r = mysql_query($q); if($r) { echo "Success!"; } elseif(!$r) { echo "Failed!"; }

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• Double "!!" in Ruby [closed]

  - by Alex Maslakov

  Possible Duplicate: What does !! mean in ruby? Ruby, !! operator (a/k/a the double-bang) Sometimes I see a Ruby code like this def sent? !!@sent_at end It seems to be not logical. Is it necessary to use here double !? As far as I'm concerned, it might be just def sent? @sent_at end UPDATE: then what is the difference between these def sent? !!@sent_at end def sent? @sent_at.nil? end def sent? @sent_at == nil end

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• How to use strtok in C properly so there is no memory leak?

  - by user246392

  I am somewhat confused by what happens when you call strtok on a char pointer in C. I know that it modifies the contents of the string, so if I call strtok on a variable named 'line', its content will change. Assume I follow the bellow approach: void function myFunc(char* line) { // get a pointer to the original memory block char* garbageLine = line; // Do some work // Call strtok on 'line' multiple times until it returns NULL // Do more work free(garbageLine); } Further assume that 'line' is malloced before it is passed to myFunc. Am I supposed to free the original string after using strtok or does it do the job for us? Also, what happens if 'line' is not malloced and I attempt to use the function above? Is it safer to do the following instead? (Assume the programmer won't call free if he knows the line is not malloced) Invocation char* garbageLine = line; myFunc(line); free(garbageLine); Function definition void function myFunc(char* line) { // Do some work // Call strtok on 'line' multiple times until it returns NULL // Do more work }

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• Implementing an iterator over binary tree using C++ 11

  - by user1459339

  I would like to create an iterator over the binary tree so as to be able to use range-based for loop. I understand I ought to implement the begin() and end() function first. Begin should probably point to the root. According to the specification, however, the end() functions returns "the element following the last valid element". Which element (node) is that? Would it not be illegal to point to some "invalid" place? The other thing is the operator++. What is the best way to return "next" element in tree? I just need some advice to begin with this programming.

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• question about copy constructor

  - by lego69

  I have this class: class A { private: int player; public: A(int initPlayer = 0); A(const A&); A& operator=(const A&); ~A(); void foo() const; }; and I have function which contains this row: A *pa1 = new A(a2); can somebody please explain what exactly is going on, when I call A(a2) compiler calls copy constructor or constructor, thanks in advance

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• can function return 0 as reference

  - by helloWorld

  I have this snippet of the code Account& Company::findAccount(int id){ for(list<Account>::const_iterator i = listOfAccounts.begin(); i != listOfAccounts.end(); ++i){ if(i->nID == id){ return *i; } } return 0; } Is this right way to return 0 if I didn't find appropriate account? cause I receive an error: no match for 'operator!' in '!((Company*)this)->Company::findAccount(id)' I use it this way: if(!(findAccount(id))){ throw "hey"; } thanks in advance

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• name of class that manipulates the entities

  - by cyberguest

  hi, i have a general question regarding naming convention. if I separate the data and operations into two separate classes. one has the data elements (entity), the other class manipulates the entity class. what do we usually call that class that manipulates the entity class? (the entity I am referring to has nothing to do with any kind of entity framework) manager? controller? operator? manipulator? thanks in advance

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• Doubt regarding usage of array as a pointer in C

  - by Som

  For eg. I have an array of structs 'a' as below: struct mystruct{ int b int num; }; struct bigger_struct { struct my_struct a[10]; } struct bigger_struct *some_var; i know that the name of an array when used as a value implicitly refers to the address of the first element of the array.(Which is how the array subscript operator works at-least) Can i know do the other way around i.e if i do: some_var->a->b, it should be equivalent to some_var->a[0]->b, am i right? I have tested this and it seems to work , but is this semantically 100% correct?

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