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  • small string optimization for vector?

    - by BuschnicK
    I know several (all?) STL implementations implement a "small string" optimization where instead of storing the usual 3 pointers for begin, end and capacity a string will store the actual character data in the memory used for the pointers if sizeof(characters) <= sizeof(pointers). I am in a situation where I have lots of small vectors with an element size <= sizeof(pointer). I cannot use fixed size arrays, since the vectors need to be able to resize dynamically and may potentially grow quite large. However, the median (not mean) size of the vectors will only be 4-12 bytes. So a "small string" optimization adapted to vectors would be quite useful to me. Does such a thing exist? I'm thinking about rolling my own by simply brute force converting a vector to a string, i.e. providing a vector interface to a string. Good idea?

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  • What's the best way to return something like a collection of `std::auto_ptr`s in C++03?

    - by Billy ONeal
    std::auto_ptr is not allowed to be stored in an STL container, such as std::vector. However, occasionally there are cases where I need to return a collection of polymorphic objects, and therefore I can't return a vector of objects (due to the slicing problem). I can use std::tr1::shared_ptr and stick those in the vector, but then I have to pay a high price of maintaining separate reference counts, and object that owns the actual memory (the container) no longer logically "owns" the objects because they can be copied out of it without regard to ownership. C++0x offers a perfect solution to this problem in the form of std::vector<std::unique_ptr<t>>, but I don't have access to C++0x. Some other notes: I don't have access to C++0x, but I do have TR1 available. I would like to avoid use of Boost (though it is available if there is no other option) I am aware of boost::ptr_container containers (i.e. boost::ptr_vector), but I would like to avoid this because it breaks the debugger (innards are stored in void *s which means it's difficult to view the object actually stored inside the container in the debugger)

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  • Why only random-access-iterator implements operator+ in C++?

    - by xopht
    I'd like get far next value for STL list iterator but it doesn't implement operator+, vector has it though. Why and how can I get the value where I want? I think I can do that if I call operator++ several times, but isn't that a little bit dirty? What I want to do is the following: list<int> l; ...omitted... list<int>::iterator itr = l.begin() + 3; // but, list iterator does not have // operator+ What is the best solution for what I want?

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  • C++ vector that *doesn't* initialize its members?

    - by Mehrdad
    I'm making a C++ wrapper for a piece of C code that returns a large array, and so I've tried to return the data in a vector<unsigned char>. Now the problem is, the data is on the order of megabytes, and vector unnecessarily initializes its storage, which essentially turns out to cut down my speed by half. How do I prevent this? Or, if it's not possible -- is there some other STL container that would avoid such needless work? Or must I end up making my own container? (Pre-C++11) Note: I'm passing the vector as my output buffer. I'm not copying the data from elsewhere.

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  • Is there a non-unique-key sorted list generic collection in C#?

    - by kdt
    I'm a bit surprised by System.Collections.Generic.SortedList, in that It requires me to use <key, value> instead of <value>(comparer) It only allows on entry per value These seem quirky in the way I want to use it (although I'm sure they're just right for other situations). Is there another collection that doesn't have these two characteristics?

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  • Generic tree implementation in Java

    - by Ivan
    Is anyone aware of a generic tree (nodes may have multiple children) implementation for Java? It should come from a well trusted source and must be fully tested. It just doesn't seem right implementing it myself. Almost reminds me of my university years when we were supposed to write all our collections ourselves. EDIT: Found this project on java.net, might be worth looking into.

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  • Date Sorting - Latest to Oldest

    - by Erika Szabo
    Collections.sort(someList, new Comparator<SomeObject>() { public int compare(final SomeObject object1, final SomeObject object2) { return (object1.getSomeDate()).compareTo(object2.getSomeDate()); }} ); Would it give me the objects with latest dates meaning the list will contain the set of objects with latest date to oldest date?

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  • Java: omitting a data member from the equals method.

    - by cchampion
    public class GamePiece { public GamePiece(char cLetter, int nPointValue) { m_cLetter=cLetter; m_nPointValue=nPointValue; m_nTurnPlaced=0; //has not been placed on game board yet. } public char GetLetter() {return m_cLetter;} public int GetPointValue() {return m_nPointValue;} public int GetTurnPlaced() {return m_nTurnPlaced;} public void SetTurnPlaced(int nTurnPlaced) { m_nTurnPlaced=nTurnPlaced; } @Override public boolean equals(Object obj) { /*NOTE to keep this shorter I omitted some of the null checking and instanceof stuff. */ GamePiece other = (GamePiece) obj; //not case sensitive, and I don`t think we want it to be here. if(m_cLetter != other.m_cLetter) { return false; } if(m_nPointValue != other.m_nPointValue) { return false; } /* NOTICE! m_nPointValue purposely omitted. It does not affect hashcode or equals */ return true; } @Override public int hashCode() { /* NOTICE! m_nPointValue purposely omitted. It should not affect hashcode or equals */ final int prime = 41; return prime * (prime + m_nPointValue + m_cLetter); } private char m_cLetter; private int m_nPointValue; private int m_nTurnPlaced;//turn which the game piece was placed on the game board. Does not affect equals or has code! } Consider the given piece of code. This object has been immutable until the introduction of the m_nTurnPlaced member (which can be modified by the SetTurnPlaced method, so now GamePiece becomes mutable). GamePiece is used in an ArrayList, I call contains and remove methods which both rely on the equals method to be implemented. My question is this, is it ok or common practice in Java for some members to not affect equals and hashcode? How will this affect its use in my ArrayList? What type of java Collections would it NOT be safe to use this object now that it is mutable? I've been told that you're not supposed to override equals on mutable objects because it causes some collections to behave "strangely" (I read that somewhere in the java documentation).

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  • What is the minimum interface that has the Count property in .Net

    - by SoMoS
    Hello, I need to change a method that has one parameter that takes a serie of objects. I need to find the lowest Interface (in inheritance tree) that has the Count property. Until now I was using the IEnumerable but as this has not Count I need to change it to the wider interface possible so the method can work with the biggest number of types of series (collections, lists, arrays, etc). Thanks in advance.

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  • Concurrent Linked HashMap java

    - by Nilesh
    Please help me use/create Concurrent LinkedHashMap. As per my belief, if I use Collections.synchronizedMap(), I would have to use synchronized blocks for getter/setter. If I use ConcurrentSkipListMap, is there any way to implement a Comparator to store sequentially. I would like to use java's built in instead of third party packages. Thanks

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  • Why does sorted list have to have a key value pair?

    - by clawson
    If I just want a sorted list of just dates, integers, or doubles is it really necessary to have to define a SortedList(of Integer, Integer)? Seems intriguing to me, but may just be trival. I'd prefer just to use a SortedList(of Integer). (This question is in relation to the .Net generic collections)

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  • Java equivalent of C++ std::map?

    - by Rudiger
    I'm looking for a Java class with the characteristics of C++ std::map's usual implementation (as I understand it, a self-balancing binary search tree): O(log n) performance for insertion/removal/search Each element is composed of a unique key and a mapped value Keys follow a strict weak ordering I'm looking for implementations with open source or design documents; I'll probably end up rolling my own support for primitive keys/values. This question's style is similar to: Java equivalent of std::deque, whose answer was "ArrayDeque from Primitive Collections for Java".

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  • What's the right Java generic for a collection of elements with unique addressable indices?

    - by Rocreex
    I'm on my way to programming a database application and in our course we are told to implement a library of elements using one of the Java Collections. Each of the elements has a unique ID with which it's supposed to be addressed. Now I am wondering how this can be done. I though about using a ListArray but this won't work because the only way of addressing List elements is through the index which you can't control. Do you have some advice for me?

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  • Model binding nested collections in ASP.NET MVC

    - by MartinHN
    Hi I'm using Steve Sanderson's BeginCollectionItem helper with ASP.NET MVC 2 to model bind a collection if items. That works fine, as long as the Model of the collection items does not contain another collection. I have a model like this: -Product --Variants ---IncludedAttributes Whenever I render and model bind the Variants collection, it works jusst fine. But with the IncludedAttributes collection, I cannot use the BeginCollectionItem helper because the id and names value won't honor the id and names value that was produced for it's parent Variant: <div class="variant"> <input type="hidden" value="bbd4fdd4-fa22-49f9-8a5e-3ff7e2942126" autocomplete="off" name="Variants.index"> <input type="hidden" value="0" name="Variants[bbd4fdd4-fa22-49f9-8a5e-3ff7e2942126].SlotAmount" id="Variants_bbd4fdd4-fa22-49f9-8a5e-3ff7e2942126__SlotAmount"> <table class="included-attributes"> <input type="hidden" value="0" name="Variants.IncludedAttributes[c5989db5-b1e1-485b-b09d-a9e50dd1d2cb].Id" id="Variants_IncludedAttributes_c5989db5-b1e1-485b-b09d-a9e50dd1d2cb__Id" class="attribute-id"> <tr> <td> <input type="hidden" value="0" name="Variants.IncludedAttributes[c5989db5-b1e1-485b-b09d-a9e50dd1d2cb].Id" id="Variants_IncludedAttributes_c5989db5-b1e1-485b-b09d-a9e50dd1d2cb__Id" class="attribute-id"> </td> </tr> </table> </div> If you look at the name of the first hidden field inside the table, it is Variants.IncludedAttributes - where it should have been Variants[bbd4fdd4-fa22-49f9-8a5e-3ff7e2942126].IncludedAttributes[...]... That is because when I call BeginCollectionItem the second time (On the IncludedAttributes collection) there's given no information about the item index value of it's parent Variant. My code for rendering a Variant looks like this: <div class="product-variant round-content-box grid_6" data-id="<%: Model.AttributeType.Id %>"> <h2><%: Model.AttributeType.AttributeTypeName %></h2> <div class="box-content"> <% using (Html.BeginCollectionItem("Variants")) { %> <div class="slot-amount"> <label class="inline" for="slotAmountSelectList"><%: Text.amountOfThisVariant %>:</label> <select id="slotAmountSelectList"><option value="1">1</option><option value="2">2</option></select> </div> <div class="add-values"> <label class="inline" for="txtProductAttributeSearch"><%: Text.addVariantItems %>:</label> <input type="text" id="txtProductAttributeSearch" class="product-attribute-search" /><span><%: Text.or %> <a class="select-from-list-link" href="#select-from-list" data-id="<%: Model.AttributeType.Id %>"><%: Text.selectFromList.ToLowerInvariant() %></a></span> <div class="clear"></div> </div> <%: Html.HiddenFor(m=>m.SlotAmount) %> <div class="included-attributes"> <table> <thead> <tr> <th><%: Text.name %></th> <th style="width: 80px;"><%: Text.price %></th> <th><%: Text.shipping %></th> <th style="width: 90px;"><%: Text.image %></th> </tr> </thead> <tbody> <% for (int i = 0; i < Model.IncludedAttributes.Count; i++) { %> <tr><%: Html.EditorFor(m => m.IncludedAttributes[i]) %></tr> <% } %> </tbody> </table> </div> <% } %> </div> </div> And the code for rendering an IncludedAttribute: <% using (Html.BeginCollectionItem("Variants.IncludedAttributes")) { %> <td> <%: Model.AttributeName %> <%: Html.HiddenFor(m => m.Id, new { @class = "attribute-id" })%> <%: Html.HiddenFor(m => m.ProductAttributeTypeId) %> </td> <td><%: Model.Price.ToCurrencyString() %></td> <td><%: Html.DropDownListFor(m => m.RequiredShippingTypeId, AppData.GetShippingTypesSelectListItems(Model.RequiredShippingTypeId)) %></td> <td><%: Model.ImageId %></td> <% } %>

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  • Write-only collections in MongoDB

    - by rcoder
    I'm currently using MongoDB to record application logs, and while I'm quite happy with both the performance and with being able to dump arbitrary structured data into log records, I'm troubled by the mutability of log records once stored. In a traditional database, I would structure the grants for my log tables such that the application user had INSERT and SELECT privileges, but not UPDATE or DELETE. Similarly, in CouchDB, I could write a update validator function that rejected all attempts to modify an existing document. However, I've been unable to find a way to restrict operations on a MongoDB database or collection beyond the three access levels (no access, read-only, "god mode") documented in the security topic on the MongoDB wiki. Has anyone else deployed MongoDB as a document store in a setting where immutability (or at least change tracking) for documents was a requirement? What tricks or techniques did you use to ensure that poorly-written or malicious application code could not modify or destroy existing log records? Do I need to wrap my MongoDB logging in a service layer that enforces the write-only policy, or can I use some combination of configuration, query hacking, and replication to ensure a consistent, audit-able record is maintained?

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  • EDM -> POCO -> WCF (.NET4) But transferring Collections causes IsReadOnly set to TRUE

    - by Gary B
    Ok, this may sound a little 'unorthodox', but...using VS2010 and the new POCO t4 template for Entity Framework (http://tinyurl.com/y8wnkt2), I can generate nice POCO's. I can then use these POCO's (as DTO's) in a WCF service essentially going from EDM all the way through to the client. Kinda what this guys is doing (http://tinyurl.com/yb4bslv), except everything is generated automatically. I understand that an entity and a DTO 'should' be different, but in this case, I'm handling client and server, and there's some real advantages to having the DTO in the model and automatically generated. My problem is, that when I transfer an entity that has a relationship, the client generated collection (ICollection) has the read-only value set, so I can't manipulate that relationship. For example, retrieving an existing Order, I can't add a product to the Products collection client-side...the Products collection is read-only. I would prefer to do a bunch of client side 'order-editing' and then send the updated order back rather than making dozens of server round trips (eg AddProductToOrder(product)). I'd also prefer not to have a bunch of thunking between Entity and DTO. So all-in-all this looks good to me...except for the read-only part. Is there a solution, or is this too much against the SOA grain?

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  • NHibernate returning duplicate object in child collections when using Fetch

    - by UpTheCreek
    When doing a query like this (using Nhibernate 2.1.2): ICriteria criteria = session.CreateCriteria<MyRootType>() .SetFetchMode("ChildCollection1", FetchMode.Eager) .SetFetchMode("ChildCollection2", FetchMode.Eager) .Add(Restrictions.IdEq(id)); I am getting multiple duplicate objects in some cartesian fashion. E.g. if ChildCollection1 has 3 elements, and ChildColection2 has 2 elements then I get results with each element in ChildColection1 one duplicated, and each element in ChildColection2 triplicated! This was a bit of a WTF moment for me... So how to do this correctly? Is using SetFetchMode like this only supported when specifying one collection? Am I just using it wrong (I've seen some references to results transformers, but imagined this would be simplier). Is this something that's different in NH3? Update: As per Felice's suggestion, I tried using the DistinctRootEntity transformer, but this is still returning duplicates. Code: ICriteria criteria = session.CreateCriteria<MyRootType>() .SetFetchMode("ChildCollection1", FetchMode.Eager) .SetFetchMode("ChildCollection2", FetchMode.Eager) .Add(Restrictions.IdEq(id)); criteria.SetResultTransformer(Transformers.DistinctRootEntity); return criteria.UniqueResult<MyRootType>();

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  • Unique items in Hibernate collections

    - by Rickard Lindberg
    I have defined a collection in Hibernate like this: ... public class Item { ... @ElementCollection List<Object> relatedObjects; } It creates a mapping table with colums item_id and object_id. The problem is that object_id seems to be unique. In other words I can not have two different items being related to the same object. But that is what I want. I would like the combination of item_id and object_id to be unique. How do I do that?

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  • Equals method of System.Collections.Generic.List<T>...?

    - by Sambo
    I'm creating a class that derives from List... public class MyList : List<MyListItem> {} I've overridden Equals of MyListItem... public override bool Equals(object obj) { MyListItem li = obj as MyListItem; return (ID == li.ID); // ID is a property of MyListItem } I would like to have an Equals method in the MyList object too which will compare each item in the list, calling Equals() on each MyListItem object. It would be nice to simply call... MyList l1 = new MyList() { new MyListItem(1), new MyListItem(2) }; MyList l2 = new MyList() { new MyListItem(1), new MyListItem(2) }; if (l1 == l2) { ... } ...and have the comparisons of the list done by value. What's the best way...?

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  • Ruby types of collections in ActiveRecord

    - by kmorris511
    If I have an object with a collection of child objects in ActiveRecord, i.e. class Foo < ActiveRecord::Base has_many :bars, ... end and I attempt to run Array's find method against that collection: foo_instance.bars.find { ... } I receive: ActiveRecord::RecordNotFound: Couldn't find Bar without an ID I assume this is because ActiveRecord has hijacked the find method for its own purposes. Now, I can use detect and everything is fine. However to satisfy my own curiousity, I attempted to use metaprogramming to explicitly steal the find method back for one run: unbound_method = [].method('find').unbind unbound_method.bind(foo_instance.bars).call { ... } and I receive this error: TypeError: bind argument must be an instance of Array so clearly Ruby doesn't think foo_instance.bars is an Array and yet: foo_instance.bars.instance_of?(Array) -> true Can anybody help me with an explanation of this and of a way to get around it with metaprogramming?

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