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  • Performing time consuming operation on STL container within a lock

    - by Ashley
    I have an unordered_map of an unordered_map which stores a pointer of objects. The unordered map is being shared by multiple threads. I need to iterate through each object and perform some time consuming operation (like sending it through network etc) . How could I lock the multiple unordered_map so that it won't blocked for too long? typedef std::unordered_map<string, classA*>MAP1; typedef std::unordered_map<int, MAP1*>MAP2; MAP2 map2; pthread_mutex_lock(&mutexA) //how could I lock the maps? Could I reduce the lock granularity? for(MAP2::iterator it2 = map2.begin; it2 != map2.end; it2++) { for(MAP1::iterator it1 = *(it2->second).begin(); it1 != *(it2->second).end(); it1++) { //perform some time consuming operation on it1->second eg sendToNetwork(*(it1->second)); } } pthread_mutex_unlock(&mutexA)

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  • C++ memory management of reference types

    - by Russel
    Hello, I'm still a fairly novice programmer and I have a question about c++ memory management with refence types. First of all, my understanding of reference types: A pointer is put on the stack and the actual data that the pointer points to is created and placed on the heap. Standard arrays and user defined classes are refence types. Is this correct? Second, my main question is do c and c++'s memory management mechanisms (malloc, free and new, delete) always handle this properly and free the memory that a class or array is pointing to? Does everything still work if those pointers get reassigned somehow to other objects of the same size/type on the heap? What if a class has a pointer member that points to another object? I am assuming that delete/freeing the class object doesn't free what it's member pointer points to, is that correct? Thanks all! -R

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  • Copying pointers in C++

    - by tunnuz
    Hello, I have a class A containing two pointers to objects of another class B. I want to initialize one pointer or the other depending on which one is passed to init(), which also takes other parameters. My situation is thus the following: class A { public: A(); init(int parameter, int otherParameter, B* toBeInitialized); protected: B* myB; B* myOtherB; }; Now my point is that I want to call init() as: init(640, 480, this->myB); or init(640, 480, this->myOtherB); Now, my init is implemented as: void init( int parameter, int otherParameter, B* toBeInitialized ) { toBeInitialized = someConstructorFunction(parameter, otherParameter); } The problem is that the two pointers are not initialized, I suspect that toBeInitialized is overwritten, but the original parameter is not modified. I am doing something wrong? Should I use references to pointers? Thank you Tommaso

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  • Accessing subclass members from a superclass pointer C++

    - by Dr. Monkey
    I have an array of custom class Student objects. CourseStudent and ResearchStudent both inherit from Student, and all the instances of Student are one or the other of these. I have a function to go through the array, determine the subtype of each Student, then call subtype-specific member functions on them. The problem is, because these functions are not overloaded, they are not found in Student, so the compiler kicks up a fuss. If I have a pointer to Student, is there a way to get a pointer to the subtype of that Student? Would I need to make some sort of fake cast here to get around the compile-time error?

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  • Unexpected key-value behavior in a Core Data Context

    - by ????
    If I create an array of strings (via key-value coding) containing the names of a Managed Object entity's attributes which are stored in the App Delegate the first time, I get an array of NSStrings without any problems. If I subsequently make the same call later from the same entry point in code, that same collection becomes an array of NULL objects- even though nothing in the Core Data Context has changed. One unappealing work-around involves re-creating the string array every time, but I'm wondering if anyone has a guess as to what's happening behind the scenes. // Return an array of strings with the names of attributes the Activity entity - (NSArray *)activityAttributeNames { #pragma mark ALWAYS REFRESH THE ENTITY NAMES? //if (activityAttributeNames == nil) { // Create an entity pointer for Activity NSEntityDescription *entity = [NSEntityDescription entityForName:@"Activity" inManagedObjectContext:managedObjectContext]; NSArray *entityAttributeArray = [[NSArray alloc] initWithArray:[[entity attributesByName] allValues]]; // Extract the names of the attributes with Key-Value Coding activityAttributeNames = [entityAttributeArray valueForKeyPath:@"name"]; [entityAttributeArray release]; //} return activityAttributeNames; }

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  • How do I use a Lambda expression to sort INTEGERS inside a object?

    - by punkouter
    I have a collection of objects and I know that I can sort by NAME (string type) by saying collEquipment.Sort((x, y) = string.Compare(x.ItemName, y.ItemName)); that WORKS. But I want to sort by a ID (integer type) and there is no such thing as Int32.Compare So how do I do this? This doesnt work collEquipment.Sort((x, y) = (x.ID < y.ID); //error I know the answer is going to be really simple. Lambda expressions confuse me.

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  • C++ -- How can we call "delete this; " in a const-member function?

    - by q0987
    Hello all, I saw the code snippet as follows: class UPNumber { public: UPNumber(); UPNumber(int initValue); ... // pseudo-destructor (a const member function, because // even const objects may be destroyed) void destroy() const { delete this; } // why this line is correct??? ... private: ~UPNumber(); }; First, I am sure that above class definition is correct. Here is my question, why we can define the function 'destroy' as above? The reason being asking is that why we can modify 'this' in a const-member function? Thank you

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  • Help with porting thread functionality: Win32 --> .Net

    - by JimDaniel
    Hi, I am responsible for porting a class from legacy Win32 code to .Net and I have come across a threading model that I'm not sure how best to implement in .Net. Basically the Win32 has one worker thread, which calls WaitForMultipleObjects() and executes the particular piece of code when a particular object has been triggered. This has a sort of first-come-first-serve effect that I need to emulate in my own code. But I'm not sure how best to do this in .Net. Does anyone have any idea? I see that there is no equivalent of WaitForMultipleObjects() in .Net, only the ThreadPool class, which seems to provide most of what I need, but I'm not sure if it's the best, since I only have four objects total to wait and execute code for. Thanks, Daniel

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  • Prevent ASP.NET from encoding strings on output

    - by Darkwater23
    How can I stop ASP.Net from encoding anchor tags in List Items when the page renders? I have a collection of objects. Each object has a link property. I did a foreach and tried to output the links in a BulletedList, but ASP encoded all the links. Any idea? Thanks! Here's the offending snippet of code. When the user picks a specialty, I use the SelectedIndexChange event to clear and add links to the BulletedList: if (SpecialtyList.SelectedIndex > 0) { PhysicianLinks.Items.Clear(); foreach (Physician doc in docs) { if (doc.Specialties.Contains(SpecialtyList.SelectedValue)) { PhysicianLinks.Items.Add(new ListItem("<a href=\"" + doc.Link + "\">" + doc.FullName + "</a>")); } } }

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  • Best way to remove from NSMutableArray while iterating?

    - by Andrew Grant
    In Cocoa, if I want to loop through an NSMutableArray and remove multiple objects that fit a certain criteria, what's the best way to do this without restarting the loop each time I remove an object? Thanks, Edit: Just to clarify - I was looking for the best way, e.g. something more elegant than manually updating the index I'm at. For example in C++ I can do; iterator it = someList.begin(); while (it != someList.end()) { if (shouldRemove(it)) it = someList.erase(it); }

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  • Eclipse + AppEngine =? autocomplete

    - by Brandon Watson
    I was doing some beginner AppEngine dev on a Windows box and installed Eclipse for that. I liked the autocompletion I got with the objects and functions. I moved my dev environment over to my Macbook, and installed Eclipse Ganymede. I installed the AppEngine SDK and Eclipse plug in. However, when I am typing out code now, the autocomplete isn't functioning. Did I miss a step? UPDATE Just to add to this: the line: import cgi appears to give me what I need. When I type "cgi." I get all of the auto complete. However, the lines: from google.appengine.api import users from google.appengine.ext import webapp from google.appengine.ext.webapp.util import run_wsgi_app from google.appengine.ext import db don't give me any auto complete. If I type "users." there is no auto complete.

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  • Selecting item from set given distribution

    - by JH
    I have a set of X items such as {blower, mower, stove} and each item has a certain percentage of times it should be selected from the overall set {blower=25%,mower=25%,stove=75%} along with a certain distribution that these items should follow (blower should be selected more at the beginning of selection and stove more at the end). We are given a number of objects to be overall selected (ie 100) and a overall time to do this in (say 100 seconds). I was thinking of using a roulette wheel algorithm where the weights on the wheel are affected by the current distribution as a function of the elapsed time (and the allowed duration) so that simple functions could be used to determine the weight. Are there any common approaches to problems like this that anyone is aware of? Currently i have programmed something similar to this in java using functions such as x^2 (with correct normalization for the weights) to ensure that a good distribution occurs. Other suggestions or common practices would be welcome :-)

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  • .NET Ascertaining mouse is on line drawn between two arbitrary points

    - by johnc
    I have an arrow drawn between two objects on a Winform. What would be the simplest way to determine that my mouse is currently hovering over, or near, this line. I have considered testing whether the mouse point intersects a square defined and extrapolated by the two points, however this would only be feasible if the two points had very similar x or y values. I am thinking, also, this problem is probably more in the realms of linear algebra rather than simple trigonometry, and whilst I do remember the simpler aspects of matrices, this problem is beyond my knowledge of linear algebra. On the other hand, if a .NET library can cope with the function, even better.

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  • Making GridView Respond to 2 Drop Down Lists

    - by raziiq
    Hi there. I have got 2 Drop Down Lists on my Form and 1 GridView. I want GridView to display the data according to selection from the Drop Down Lists. For Example, One Drop Down List contains Names and other contains Dates. Both the Drop Down Lists can post back. So if i select a name from 1st Drop Down list, the Grid View should show all the results according to that Name. Similarly if i select the Date from the other Drop Down List , the Grid View should show the results according to the dates. But i cant figure out as how to bind Grid View to respond to 2 Drop Down List. BTW i am binding both the Drop Down Lists and the Grid View to the DataSource Objects, which is getting data from the database. Any Suggestions??

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  • Trick to getting initWithNibFile to be invoked?

    - by PhazeZero
    I've implemented a View Controller, and I'm trying to do some very basic initialization in initWithNibFile...which I understand to be the designated initializer for View Controller objects. I've tried to put breakpoints on the code, and have put very simple NSLog statements into it as well. Regardless...I'm not seeing it be executed (and the object i'm attempting to alloc/init inside the function is also not being allocated - so I'm about 99% sure I'm not hitting the code. Is there something I need to do elsewhere to cause this method to be invoked? I'm getting a clean build, no warnings or errors. And the app successfully loads up the View, and I can invoke a ButtonClick method I've coded and connected to this same View Controller. Any suggestions would be appreciated. TC

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  • How to remove a single event in a recuring event

    - by albertos
    hi all. I' m having an issue with fullCalendar. I created a script that, adds an event to fullCalendar, along a day range, and set a unique id in order to have this event recur. let say for example that i have a recuring event from 1/1/10 till 10/1/10. i create 10 single event Objects with the same id, and place then on fullCalendar. my question is, that i want to exclude a single day over this recuring event. (for example 3/1/10). i found out, that if i remove that particural event from the sources table and then update the event its fine. but how can i get on runtime the actucal index of this eventObj on sources table? Note that, i add the events on the fullCalendar using the .fullCalendar("renderEvent") method. Thanks.

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  • Java and Different Types of Stacks

    - by Rarge
    Currently the only stack I know anything about is Vector, I normally use this in place of an array but I understand that there is other types of stacks and they all suit different jobs. The project I am currently working on requires me to be inserting objects in a certain position inside a stack, not always the front of the stack and I am under the impression that a Vector may not be the best class for this job. Could somebody please give me a brief description of the other types of stacks available to me with the Java language and their advantages and disadvantages? Are these names homogeneous? E.g. Are they only used in the Java language or are they used as general terms in Computer Science? Thank you

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  • Many-to-many relationship on same table with association object

    - by Nicholas Knight
    Related (for the no-association-object use case): http://stackoverflow.com/questions/1889251/sqlalchemy-many-to-many-relationship-on-a-single-table Building a many-to-many relationship is easy. Building a many-to-many relationship on the same table is almost as easy, as documented in the above question. Building a many-to-many relationship with an association object is also easy. What I can't seem to find is the right way to combine association objects and many-to-many relationships with the left and right sides being the same table. So, starting from the simple, naïve, and clearly wrong version that I've spent forever trying to massage into the right version: t_groups = Table('groups', metadata, Column('id', Integer, primary_key=True), ) t_group_groups = Table('group_groups', metadata, Column('parent_group_id', Integer, ForeignKey('groups.id'), primary_key=True, nullable=False), Column('child_group_id', Integer, ForeignKey('groups.id'), primary_key=True, nullable=False), Column('expires', DateTime), ) mapper(Group_To_Group, t_group_groups, properties={ 'parent_group':relationship(Group), 'child_group':relationship(Group), }) What's the right way to map this relationship?

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  • WPF combo box, adding an all options item, when binding to an Observable Collection

    - by Joel Barsotti
    So I've got an object that has an observable collection. Most places I bind to this collection I only want the user to select a single item. But in one place I want the combobox to include an all items option. Is the way to do this simply with xaml converter? It seems like doing it in the view model would be a good idea, but it's really a lot dependency object goop to basically wire up an collection that is two objects deep for an on change event, where as the xaml converter just works. But I always feel like xaml converters should be generic and reusable, where in this instance, the xaml converter would be more of a one off. Of course the third option would be to create one off list for UI in the object that contains the standard observable collection. But this seems to be mixing the logic and presentation in a way that makes me uncomfortable.

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  • How do I extend a WPF application using an addin-like architeture?

    - by Thiado de Arruda
    Lets say I have a WPF application that shows a ListBox with an ArrayList -populated with objects of arbitrary types- as a source, and this application is hosted in an assembly 'A'. By default the ListBox will display the custom object 'ToString' method return value. If a data template for that object type is found, the ListBox will use it for rendering. Imagine that theres another assembly 'B' that references of 'A' and seeks to extend it by providing custom data templates for certain types, to be used in that ListBox. Is there some way to do that without 'A'being aware of B?

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  • Free object/widget in GTK?

    - by wag2639
    I've got a pack box in my GTK application and I'm replacing it every once in a while with a completely new entry (at least for now cause I'm in a hurry). Since I'm replacing it with a new instance, do I need to explicitly free from memory the old pack box contents or is there some garbage collection in GTK? If I do need to explicitly need to free the object, is there a command that will recursively go to all objects in that tree (like will it clear my button in a box container inside my main pack box)? I'm using C/GTK-2.0 (gcc v4.4.3 and GTK 2.20.0).

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  • Python implementation of avro slow?

    - by lazy1
    I'm reading some data from avro file using the avro library. It takes about a minute to load 33K objects from the file. This seem very slow to me, specially with the Java version reading the same file in about 1sec. Here is the code, am I doing something wrong? import avro.datafile import avro.io from time import time def load(filename): fo = open(filename, "rb") reader = avro.datafile.DataFileReader(fo, avro.io.DatumReader()) for i, record in enumerate(reader): pass return i + 1 def main(argv=None): import sys from argparse import ArgumentParser argv = argv or sys.argv parser = ArgumentParser(description="Read avro file") start = time() num_records = load("events.avro") end = time() print("{0} records in {1} seconds".format(num_records, end - start)) if __name__ == "__main__": main()

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  • How does Ruby's Enumerator object iterate externally over an internal iterator?

    - by Salman Paracha
    As per Ruby's documentation, the Enumerator object uses the each method (to enumerate) if no target method is provided to the to_enum or enum_for methods. Now, let's take the following monkey patch and its enumerator, as an example o = Object.new def o.each yield 1 yield 2 yield 3 end e = o.to_enum loop do puts e.next end Given that the Enumerator object uses the each method to answer when next is called, how do calls to the each method look like, every time next is called? Does the Enumeartor class pre-load all the contents of o.each and creates a local copy for enumeration? Or is there some sort of Ruby magic that hangs the operations at each yield statement until next is called on the enumeartor? If an internal copy is made, is it a deep copy? What about I/O objects that could be used for external enumeration? I'm using Ruby 1.9.2.

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  • Using a backwards relation (i.e FOO_set) for ModelChoiceField in Django

    - by Bwmat
    I have a model called Movie, which has a ManyToManyField called director to a model called Person, and I'm trying to create a form with ModelChoiceField like so: class MovieSearchForm(forms.Form): producer = forms.ModelChoiceField(label='Produced by', queryset=movies.models.Person.producer_set, required=False) but this seems to be failing to compile (I'm getting a ViewDoesNotExist exception for the view that uses the form, but it goes away if I just replace the queryset with all the person objects), I'm guessing because '.producer_set' is being evaluated too 'early'. How can I get this work? here are the relevant parts of the movie/person classes: class Person(models.Model): name = models.CharField(max_length=100) class Movie(models.Model): ... producer = models.ForeignKey(Person, related_name="producers") director = models.ForeignKey(Person, related_name="directors") What I'm trying to do is get ever Person who is used in the producer field of some Movie.

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  • why don't more programming languages have builtin interfaces to the window manager?

    - by Naveen
    Programming is at the heart about automating tasks on a computer. Presumably those tasks would normally be done manually by a human. Humans use the computer through the keyboard, mouse, and interaction with the console or the window manager. But very few languages have built in functions that provide an interface to these basic computing objects. A notable exception is autohotkey, an open source language on windows, providing builtin functions that allow the following simple tasks: * Get Pixel Information * Get mouse position * Keyboard macros * Simulate key strokes * Simulate mouse click * Window management See examples on rosettacode. There have been various attempts on linux, many of which were stopped without explanation. One is the inactive tcl library: android. Search google code for android, lang:tcl

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