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  • How to assign a value to an pointer-pointer passed in call by reference?

    - by mystify
    I want to achieve something similar to what these guys do here: - (NSUInteger)countForFetchRequest:(NSFetchRequest *)request error:(NSError **)error like you can see, you pass an NSError pointer and that nice method will assign a real NSError object to your pointer in case there is an error. So the cool thing about this is, that the method returns an NSUInteger but can ALSO return an NSError, without having to mess around with ugly and fat arrays or dictionaries. So how could I assign an object to the passed-in error pointer?

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  • What is the ISO C++ way to directly define a conversion function to reference to array?

    - by ben
    According to the standard, a conversion function has a function-id operator conversion-type-id, which would look like, say, operator char(&)[4] I believe. But I cannot figure out where to put the function parameter list. gcc does not accept either of operator char(&())[4] or operator char(&)[4]() or anything I can think of. Now, gcc seems to accept (&operator char ())[4] but clang does not, and I am inclined to not either, since it does not seem to fit the grammar as I understand it. I do not want to use a typedef because I want to avoid polluting the namespace with it.

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  • How cast in c#/.net 3.5 works? for types with '?'

    - by Inez
    This is my code which works public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : (decimal?) null; } and this one doesn't work public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : null; } giving the compilator error: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'decimal' and '' I wonder why? any ideas?

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  • Function templates for arbitrary STL containers containing arbitrary types.

    - by Chad Brewbaker
    I have an arbitrary STL container C, which contains elements of an arbitrary type T. I want to create an std::vector that has a copy of all the elements. What is the cleanest way to do this? template <typename C> void myfunction(C container){ /*Derive the type T of elements within the container*/ std::vector<T> mystack; /* Iterate over container and push_back() the elements into mystack*/ }

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  • How can variadic char template arguments from user defined literals be converted back into numeric types?

    - by Pubby
    This question is being asked because of this one. C++11 allows you to define literals like this for numeric literals: template<char...> OutputType operator "" _suffix(); Which means that 503_suffix would become <'5','0','3'> This is nice, although it isn't very useful in the form it's in. How can I transform this back into a numeric type? This would turn <'5','0','3'> into a constexpr 503. Additionally, it must also work on floating point literals. <'5','.','3> would turn into int 5 or float 5.3 A partial solution was found in the previous question, but it doesn't work on non-integers: template <typename t> constexpr t pow(t base, int exp) { return (exp > 0) ? base * pow(base, exp-1) : 1; }; template <char...> struct literal; template <> struct literal<> { static const unsigned int to_int = 0; }; template <char c, char ...cv> struct literal<c, cv...> { static const unsigned int to_int = (c - '0') * pow(10, sizeof...(cv)) + literal<cv...>::to_int; }; // use: literal<...>::to_int // literal<'1','.','5'>::to_int doesn't work // literal<'1','.','5'>::to_float not implemented

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  • How to discovering types exported by OSGi bundle without installing/activating ?

    - by mP
    Basically i want to discover if a jar implements any number of interfaces wihtout activating or starting the bundle. Is it possible to read the meta data from the meta-inf from an API just like the container does but without activating a bundle ? I want to use OSGi to support plugins of which numerous interfaces will be published and i would like to know which interfaces are implemented by a bundle when the user uploads without activating the bundle etc.

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  • How does cast in C#/.NET 3.5 work for types with '?'

    - by Inez
    This is my code which works public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : (decimal?) null; } and this one doesn't work public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : null; } giving the compiler error: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'decimal' and '<null>' I wonder why? any ideas?

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  • Is it possible to reference a file stored in Isolated Storage by its URI?

    - by Joel
    Using this previous question as motivation, I would like to temporarily store images and videos in Isolated Storage. My application (written in WPF/C#) will allow a user to review these temporarily stored items by viewing their contents in a MediaElement. I was hoping to set the MediaElement's Source Property to a video or image's URI stored in IsolatedStorage but I cannot figure out how to dynamically create a URI since it doesn't appear to be naively supported by IsolatedStorage. Any help would be greatly appreciated - thank you in advance! Update - 1/21/09 After battling the issue for a day, I concluded that the Isolated Storage approach is not practical for storing large video files that need to be referenced by a Uri.

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  • Any problems with this C++ const reference accessor interface idiom?

    - by mskfisher
    I was converting a struct to a class so I could enforce a setter interface for my variables. I did not want to change all of the instances where the variable was read, though. So I converted this: struct foo_t { int x; float y; }; to this: class foo_t { int _x; float _y; public: foot_t() : x(_x), y(_y) { set(0, 0.0); } const int &x; const float &y; set(int x, float y) { _x = x; _y = y; } }; I'm interested in this because it seems to model C#'s idea of public read-only properties. Compiles fine, and I haven't seen any problems yet. Besides the boilerplate of associating the const references in the constructor, what are the downsides to this method? Any strange aliasing issues? Why haven't I seen this idiom before?

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  • How do you override operator == when using interfaces instead of actual types?

    - by RickL
    I have some code like this: How should I implement the operator == so that it will be called when the variables are of interface IMyClass? public class MyClass : IMyClass { public static bool operator ==(MyClass a, MyClass b) { if (ReferenceEquals(a, b)) return true; if ((Object)a == null || (Object)b == null) return false; return false; } public static bool operator !=(MyClass a, MyClass b) { return !(a == b); } } class Program { static void Main(string[] args) { IMyClass m1 = new MyClass(); IMyClass m2 = new MyClass(); MyClass m3 = new MyClass(); MyClass m4 = new MyClass(); Console.WriteLine(m1 == m2); // does not go into custom == function. why not? Console.WriteLine(m3 == m4); // DOES go into custom == function } }

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  • Nonstatic conversion functions; Casting different types, e.g. DirectX vector to OpenGL vector

    - by Markus
    I am currently working on a game "engine" that needs to move values between a 3D engine, a physics engine and a scripting language. Since I need to apply vectors from the physics engine to 3D objects very often and want to be able to control both the 3D, as well as the physics objects through the scripting system, I need a mechanism to convert a vector of one type (e.g. vector3d<float>) to a vector of the other type (e.g. btVector3). Unfortunately I can make no assumptions on how the classes/structs are laid out, so a simple reinterpret_cast probably won't do. So the question is: Is there some sort of 'static'/non-member casting method to achieve basically this: vector3d<float> operator vector3d<float>(btVector3 vector) { // convert and return } btVector3 operator btVector3(vector3d<float> vector) { // convert and return } Right now this won't compile since casting operators need to be member methods. (error C2801: 'operator foo' must be a non-static member)

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  • Can I get a reference to an object created in a jQuery plugin?

    - by gargantaun
    Perhaps my brain is fried, but I'm writing a plugin that created an tweaks an element, but also creates an object that i'd like access to. So the plugin looks like this (function ($) { $.fn.myPlugin = function () { return this.each(function () { // do some stuff to the element... this.objectInstance = new usefulObject(); }); }; })(jQuery); function usefulObject(){ // useful object properties and methods.... this.doSomething = function(){ alert("Don't google Google. You'll break the internet."); } } so when I call the plugin, I also want to be able to get access to that usefulObject that I created. I thought something like this might work.... tweakedElement = $("#someDiv").myPlugin(); tweakedElement.objectInstance.doSomething(); ... but that's not working. How can I achieve this? Can I achieve this? Answers on a postcard, or down below, whichever suits you.

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  • Where can I find "reference barcodes" to verify barcode library output?

    - by mjustin
    This question is not about 'best' barcode library recommendation, we use various products on different platforms, and need a simple way to verify if a given barcode is correct (according to its specification). There are some free online bar code generators in the Internet, and I found many differences between their output and our library output regarding graphics and text field below the code. Now I am not sure which one is wrong, and before filing bug report I want to make sure how the correct barcode should look like. We mainly need Code128 and UCC/EAN-128 with A/B/C subcodes. Which resource would you suggest?

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  • How can I build a voting system to support multiple types of objects to vote on?

    - by Kyle Hayes
    I'm really looking for something very similar to the way SO is setup where a few different kinds of things can be voted on (questions AND answers). What kind of DB schema, generally, could I use to support voting on many different kinds of objects? Would I have a single Vote table that would have references to other objects in the database? Or do I have to have or should have a separate vote table for each of the objects I would like to vote on.

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  • How to reference a string from another package in a library using XML in Android?

    - by Garret Wilson
    The Android documentation tells me that I can access a string from another package by using the "package name", whatever that means: @[<package_name>:]<resource_type>/<resource_name> So in my manifest I want to access a string that I've placed in a separate library project, in the com.globalmentor.android package---that's where my R class is, after all: <activity android:label="@com.globalmentor.android:string/app_applicationlistactivity_label" android:name="com.globalmentor.android.app.ApplicationListActivity" > </activity> That doesn't even compile. But this does: <activity android:label="@string/app_applicationlistactivity_label" android:name="com.globalmentor.android.app.ApplicationListActivity" > </activity> Why? What does the Android documentation mean which it talks about the "package_name"? Why doesn't the first example work, and why does the second example work? I don't want all my resource names merged into the same R file---I want them partitioned into packages, like I wrote them.

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  • How to do a back-reference on Google Webapp?

    - by jCuga
    I'm trying to access an object that is linked to by a db.ReferenceProperty in Google app engine. here's the model's code: class InquiryQuestion(db.Model): inquiry_ref = db.ReferenceProperty(reference_class=GiftInquiry, required=True, collection_name="inquiry_ref") And I am trying to access it in the following way: linkedObject = question.inquiry_ref and then linkedKey = linkedObject.key but it's not working. Can anyone please help?

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  • Is foreign key reference from two different primary key from two different tables valid?

    - by arundex
    I have a foreign key that has to refer primary keys of two different tables. Table 1: animal animal_ id (primary key) Table 2: bird bird_ id (primary key) Table 3: Pet_info pet_id, type ENUM ('bird', 'animal') foreign key (pet_ id) references animal(animal_id), bird(bird_id) So, I need to check for pet_id either from animal or bird table depending on the need. Is this valid? Or should I go for some restructuring . . . NOTE: I referred this . . but I'm not sure whether I have to change my existing design

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