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  • returning reference to a vector from a method and using its public members

    - by memC
    dear experts, I have a vector t_vec that stores references to instances of class Too. The code is shown below. In the main , I have a vector t_vec_2 which has the same memory address as B::t_vec. But when I try to access t_vec_2[0].val1 it gives error val1 not declared. Could you please point out what is wrong? Also, if you know of a better way to return a vector from a method, please let me know! Thanks in advance. class Too { public: Too(); ~Too(){}; int val1; }; Too::Too(){ val1 = 10; }; class B { public: vector<Too*> t_vec; Too* t1; vector<Too*>& get_tvec(); B(){t1 = new Too();}; ~B(){delete t1;}; }; vector<Too*>& B::get_tvec(){ t_vec.push_back(t1); return t_vec; } int main(){ B b; b = B(); vector<Too*>& t_vec_2 = b.get_tvec(); // Getting error std::cout << "\n val1 = " << t_vec_2[0].val1; return 0; }

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  • Haskell type classes and type families (cont'd)

    - by Giuseppe Maggiore
    I need some help in figuring a compiler error which is really driving me nuts... I have the following type class: infixl 7 --> class Selectable a s b where type Res a s b :: * (-->) :: (CNum n) => (Reference s a) -> (n,(a->b),(a->b->a)) -> Res a s b which I instance twice. First time goes like a charm: instance Selectable a s b where type Res a s b = Reference s b (-->) (Reference get set) (_,read,write) = (Reference (\s -> let (v,s') = get s in (read v,s')) (\s -> \x -> let (v,s') = get s v' = write v x (_,s'') = set s' v' in (x,s''))) since the type checker infers (-->) :: Reference s a -> (n,a->b,a->b->a) -> Reference s b and this signature matches with the class signature for (--) since Res a s b = Reference s b Now I add a second instance and everything breaks: instance (Recursive a, Rec a ~ reca) => Selectable a s (Method reca b c) where type Res a s (Method reca b c) = b -> Reference s c (-->) (Reference get set) (_,read,write) = \(x :: b) -> from_constant( Constant(\(s :: s)-> let (v,s') = get s :: (a,s) m = read v ry = m x :: Reference (reca) c (y,v') = getter ry (cons v) :: (c,reca) v'' = elim v' (_,s'') = set s' v'' in (y,s''))) :: Reference s c the compiler complains that Couldn't match expected type `Res a s (Method reca b c)' against inferred type `b -> Reference s c' The lambda expression `\ (x :: b) -> ...' has one argument, which does not match its type In the expression: \ (x :: b) -> from_constant (Constant (\ (s :: s) -> let ... in ...)) :: Reference s c In the definition of `-->': --> (Reference get set) (_, read, write) = \ (x :: b) -> from_constant (Constant (\ (s :: s) -> ...)) :: Reference s c reading carefully the compiler is telling me that it has inferred the type of (--) thusly: (-->) :: Reference s a -> (n,a->(Method reca b c),a->(Method reca b c)->a) -> (b -> Reference s c) which is correct since Res a s (Method reca b c) = b -> Reference s c but why can't it match the two definitions? Sorry for not offering a more succint and standalone example, but in this case I cannot figure how to do it...

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  • Iterating over member typed collection fails when using untyped reference to generic object

    - by Alexander Pavlov
    Could someone clarify why iterate1() is not accepted by compiler (Java 1.6)? I do not see why iterate2() and iterate3() are much better. This paragraph is added to avoid silly "Your post does not have much context to explain the code sections; please explain your scenario more clearly." protection. import java.util.Collection; import java.util.HashSet; public class Test<T> { public Collection<String> getCollection() { return new HashSet<String>(); } public void iterate1(Test test) { for (String s : test.getCollection()) { // ... } } public void iterate2(Test test) { Collection<String> c = test.getCollection(); for (String s : c) { // ... } } public void iterate3(Test<?> test) { for (String s : test.getCollection()) { // ... } } } Compiler output: $ javac Test.java Test.java:11: incompatible types found : java.lang.Object required: java.lang.String for (String s : test.getCollection()) { ^ Note: Test.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. 1 error

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  • Looking for substantial open source GWT/App-Engine project to use as reference

    - by tempy
    I'm working on GAE-J/GWT app, wherein a desktop app connects to the GAE-J component, and there is also a web-app component whose front-end is written in GWT, and the GAE-J backend supports both the desktop app and the web app. I have a good amount of experience with writing pure server code and desktop code, but not so much on the web-app side of things. So I'm looking to study some good sophisticated open source code to see how other's have done things, but I can't find much open source GWT and/or GAE-J stuff, other than frameworks. Does anyone know of any good projects out there?

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  • A simple group-by (no count) in Django

    - by Daniel Quinn
    If this were raw-SQL, it'd be a no-brainer, but in Django, this is proving to be quite difficult to find. What I want is this really: SELECT user_id FROM django_comments WHERE content_type_id = ? AND object_pk = ? GROUP BY user_id It's those last two lines that're the problem. I'd like to do this the "Django-way" but the only thing I've found is mention of aggregates and annotations, which I don't think solve this issue... do they? If someone could explain this to me, I'd really appreciate it.

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  • How to delete from table if count is greater than 20

    - by joseph
    Hi, I have a mysql table that I need to only contain 20 newest records before adding additional records. New rows are added daily so I would like it first delete any records that are greater than the 20 allowed starting with the earliest. The table contains an auto increment "id" column so I can easily determine which is the earliest records. Thanks for any help.

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  • Redeclaration of parameters

    - by Scott
    While looking through the Selenium source code I noticed the following in the PageFactory: public static <T> T initElements(WebDriver driver, Class<T> pageClassToProxy) { T page = instantiatePage(driver, pageClassToProxy); initElements(driver, page); return page; } public static void initElements(WebDriver driver, Object page) { final WebDriver driverRef = driver; initElements(new DefaultElementLocatorFactory(driverRef), page); } What is the benefit of having the following line? final WebDriver driverRef = driver; Wouldn't it have made sense to just make the parameter final, and then passing that along to the next method without declaring the new reference?

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  • Translating 3-dimensional array reference onto 1-dimensional array

    - by user146780
    If there is an array of ar[5000] then how could I find where element [5][5][4] would be if this was a 3 dimensional array? Thanks I'm mapping pixels: imagine a bimap of [768 * 1024 * 4] where would pixel [5][5][4] be? I want to make this: static GLubyte checkImage[checkImageHeight][checkImageWidth][4]; static GLuint texName; bool itt; void makeCheckImage(void) { Bitmap *b = new Bitmap(L"c:/boo.png"); int i, j, c; Color cul; for (i = 0; i < checkImageHeight; i++) { for (j = 0; j < checkImageWidth; j++) { b->GetPixel(j,i,&cul); checkImage[i][j][0] = (GLubyte) cul.GetR(); checkImage[i][j][1] = (GLubyte) cul.GetG(); checkImage[i][j][2] = (GLubyte) cul.GetB(); checkImage[i][j][3] = (GLubyte) cul.GetA(); } } delete(b); } work without making a multidimensional array. width = 512, height = 1024....

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  • Doing a SetLength on an array passed into a proc by reference

    - by csharpdefector
    Hi All, Sure, even I can do this... var testarray : array of string; setlength(testarray, 5); but if I want to get clever and have a procedure into which I pass the array by referance like this I cant do it! procedure DoStuffWithArray(var passedarray : array of string); begin setlength(passedarray, 5); end; compiler says 'incompatible types' on the single line of code in my proc. I can do other stuff on the array like set set element values if i do a setlength before i call the proc, but I cannot do the setlength in my proc, which is what I want to do. Any help much appreciated, thanks all.

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  • Backbone: Easiest way to maintain reference to 'this' for a Model inside callbacks

    - by Garrett
    var JavascriptHelper = Backbone.Model.extend("JavascriptHelper", {}, // never initialized as an instance { myFn: function() { $('.selector').live('click', function() { this.anotherFn(); // FAIL! }); }, anotherFn: function() { alert('This is never called from myFn()'); } } ); The usual _.bindAll(this, ...) approach won't work here because I am never initializing this model as an instance. Any ideas? Thanks.

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  • How can I add a function reference to an object literal

    - by rob
    I need to add binders to DOM elements after rendering is done. Therefore I want to pass a list with (ID, callback) tuples to the rendering function so it can bind it after the rendering is done. So i would like to create a list of such objects and pass it to the rendering function: {id:'#someDOMelement', callback: someObject.someFunction} and bind it after the rendering like this: $(binders[i].id).bind('click', binders[i].callback);

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  • Approximate Number of CPU Cycles for Various Operations

    - by colordot
    I am trying to find a reference for approximately how many CPU cycles various operations require. I don't need exact numbers (as this is going to vary between CPUs) but I'd like something relatively credible that gives ballpark figures that I could cite in discussion with friends. As an example, we all know that floating point division takes more CPU cycles than say doing a bitshift. I'd guess that the difference is that the division is around 100 cycles, where as a shift is 1 but I'm looking for something to cite to back that up. Can anyone recommend such a resource?

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  • c++: Reference array of maps

    - by donalmg
    I have a function which creates an array of Maps: map<string, int> *pMap And a function which writes maps to the array: int iAddMap(map<string, int> mapToAdd, map<string, int> *m, int i) { m = &(pMap[i]); memcpy(m, mapToAdd, sizeof(map<string, int>)); } And a function to get maps from the array map<string, int>& getMap(int i) { return pMap[i]; } I can write maps to the array without any issue, but every get call results in a seg fault: int val; // val defined after this map<string, int> * pGetMap = &(getMap(val)); Any suggestions on why this is happening?

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  • Using block around a static/singleton resource reference

    - by byte
    This is interesting (to me anyway), and I'd like to see if anyone has a good answer and explanation for this behavior. Say you have a singleton database object (or static database object), and you have it stored in a class Foo. public class Foo { public static SqlConnection DBConn = new SqlConnection(ConfigurationManager.ConnectionStrings["BAR"].ConnectionString); } Then, lets say that you are cognizant of the usefulness of calling and disposing your connection (pretend for this example that its a one-time use for purposes of illustration). So you decide to use a 'using' block to take care of the Dispose() call. using (SqlConnection conn = Foo.DBConn) { conn.Open(); using (SqlCommand cmd = new SqlCommand()) { cmd.Connection = conn; cmd.CommandType = System.Data.CommandType.StoredProcedure; cmd.CommandText = "SP_YOUR_PROC"; cmd.ExecuteNonQuery(); } conn.Close(); } This fails, with an error stating that the "ConnectionString property is not initialized". It's not an issue with pulling the connection string from the app.config/web.config. When you investigate in a debug session you see that Foo.DBConn is not null, but contains empty properties. Why is this?

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  • get id parameter and increment count for each click in jquery

    - by Jean
    Hello, I want to get the id value of c_i. And each time c_i is clicked I want to increment the value at chk_count, using jquery <div id='d<? echo $i; ?>' style='margin-bottom:8px; border:#cccccc thin solid; height:25px;'> <span style='color:#cccccc; margin-right:5px;'><? echo $i; ?></span> <span><? echo $row_dw_all['d1e']; ?></span> <span style='position:absolute;right:0px;'> <input type='checkbox' name='c_i<? echo $i; ?>' id="c_i<? echo $i; ?>" value='<? echo $row_dw_all['dle']; ?>'> </span> </div> <input type="hidden" name="chk_count" id="chk_count" value="" /> Thanks Jean

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  • Is there a definitive list of uri patterns for use in android apps made by google?

    - by The Trav
    Apart from http://developer.android.com/guide/appendix/g-app-intents.html (which is quite good but fairly limited in the number of apps/uri's it covers) I've been unable to find a decent reference source for looking up URI's to use when integrating with google apps. I'm currently working on triggering the "add new contact" UI, and have found that the tel: uri pattern seems to work, but what if I only have a name and an email? I wouldn't have expected I'd need to rely on sample code / trial and error, but I really can't see anywhere where the intent/URI interface is supposed to be documented in android apps. Does such a standard exist? Is there some quasi standard / user database that I can consult? On a platform with such a good inter-interoperability architecture it just seems like something so useful I can't believe it's not there

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  • Count in base 2, 3, 4 etc in Java and output all permutations

    - by tree-hacker
    I want to write a function in Java that takes as input an integer and outputs every possible permutation of numbers up to that integer. For example: f(1) 0 f(2) should output: 00 01 10 11 f(3) should output: 000 001 002 010 011 012 020 021 022 100 .... 220 221 222 That is it should output all 27 permutations of the digits of the numbers 0, 1, 2. f(4) should output 0000 0001 0002 0003 0010 ... 3330 3331 3332 3333 f(4) should output 00000 00001 ... 44443 44444 I have been trying to solve this problem but cannot seem to work out how to do it and keep getting confused by how many loops I need. Does anyone know how to solve this problem? Thanks in advance.

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  • Referencing text input fields in CKEditor dialogs

    - by rt-uk
    Hi, I've been playing around with this for a couple of weeks now with no success... In a CKEditor dialog, text input fields are renamed with a unique number - e.g. id: 'txtUrl' will become something like id='27_textinput'. How do I reference this? // I feel it should be something like: var myfield = CKEDITOR.instances.myElement.document.$.body.getId('txtUrl'); // or maybe: var myfield = CKEDITOR.dialog.getContentElement('info','txtUrl'); // and then: myfield.value = 'myvalue'; But these don't work. Please help! Thanks in advance, R

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  • Object pointer value as key into dictionary

    - by Ranking Stackingblocks
    I want to use the object's reference value as a key into a dictionary, as opposed to a copy of value of the object. So, I essentially want to store an object associated with a particular instance of another object in a dictionary and retrieve that value later. Is this possible? Is it completely against the idea of NSDictionary? I can tell that I am probably approaching this the wrong way because the dictionary wants me to implement NSCopying on the object itself, which doesn't really make sense in terms of what I'm doing. I can see that what I should really be doing is wrapping the pointer value, but that seems a little mad. Advice would be appreciated.

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  • C# - What is root reference ?

    - by DotNetGuy
    class GCTest { static Object r1; static void Main() { r1 = new Object(); Object r2 = new Object(); Object r3 = new Object(); System.GC.Collect(); // what can be reclaimed here ? r1 = null; r3.ToString(); System.GC.Collect(); // what can be reclaimed here ? } } // code from - DonBox's Essential .Net

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  • DB Design - Linking to a parent without circular reference issues

    - by zSysop
    Hi all, I'm having trouble coming up with a solution for the following issue. Lets say i have a db that looks something like the following: Issue Table Id | Details | CreateDate | ClosedDate Issue Notes Table Id | ObjectId | Notes | NoteDate Issue Assignment Table Id | ObjectId | AssignedToId| AssignedDate I'd like allow the linking of an issue to another issue. I thought about adding a column to the Issue table called ParentIssueId and that would allow me the ability to link issues, but i foresee circular references occurring within the issue table if i go through with this implementation. Is there a better way to go about doing this, and if so, how? Thanks

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