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• std::map default value for build-in type

  - by Qifa Zhao

  Recently, I was confused by the std::map operator[] function. In the MSDN library, it says: "If the argument key value is not found, then it is inserted along with the default value of the data type." I tryed to search much more exactly explanation for this issue. For example here: std::map default value In this page, Michael Anderson said that "the default value is constructed by the default constructor(zero parameter constructor)". Now my quest comes to this:"what the default value for the build-in type?". Was it compiler related? Or is there a standard for this issue by the c++ stardard committee? I did a test on visual studio 2008 for the "int" type, and found the "int" type is construted with the value 0.

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• Hot to get generic type from object type

  - by Murat

  My Classes are; class BaseClass { } class DerivedClass1 : BaseClass { } class GenericClass<T> { } class DerivedClass2 : BaseClass { GenericClass<DerivedClass1> subItem; } I want to access all fields of DerivedClass2 class. I use System.Reflection and FieldInfo.GetValue() method; Bu I cant get subItem field. FieldInfo.GetValue() method return type is "object". And I cant cast to GenericClass<DerivedClass1> or I cant get DerivedClass1 type. I try this with BaseClass BaseClass instance = FieldInfo.Getvalue(this) as GenericClass<BaseClass>; but instance is null. How to get instance with type or how to get only type?

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• how to get the size of a C global array into an assembly program written for the avr architecture co

  - by johannes

  I have a .c file with the following uint8_t buffer[32] I have a .S file where I want to do the following cpi r29, buffer+sizeof(buffer) The second argument for cpi muste be an imidiate value not a location. But unfortunetly sizeof() is a c operator. Both files, are getting compiled to seperate object files and linked afterwards. If I do avr-objdump -x file.c. Amongst other things, I get the size of the buffer. So it is already available in the object file. How do I access the size of the buffer in my assembly file at compile time?

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• g++ How to get warning on ignoring function return value

  - by ArunSaha

  lint produces some warning like: foo.c XXX Warning 534: Ignoring return value of function bar() From the lint manual 534 Ignoring return value of function 'Symbol' (compare with Location) A function that returns a value is called just for side effects as, for example, in a statement by itself or the left-hand side of a comma operator. Try: (void) function(); to call a function and ignore its return value. See also the fvr, fvo and fdr flags in §5.5 "Flag Options". I want to get this warning, if there exists any, during compilation. Is there any option in gcc/g++ to achieve this? I had turned on -Wall but that apparently did not detect this.

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• Is there alternative way to write this query?

  - by Kugel

  I have tables A, B, C, where A represents items which can have zero or more sub-items stored in C. B table only has 2 foreign keys to connect A and C. I have this sql query: select * from A where not exists (select * from B natural join C where B.id = A.id and C.value > 10); Which says: "Give me every item from table A where all sub-items have value less than 10. Is there a way to optimize this? And is there a way to write this not using exists operator?

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• C# implicit conversions

  - by Chris Boden

  Hello, I'm currently working on an application where I need to load data from an SQL database and then assign the retrieved values into the properties of an object. I'm doing this by using reflection since the property names and column names are the same. However, many of the properties are using a custom struct type that is basically a currency wrapper for the decimal type. I have defined an implicit conversion in my struct: public static implicit operator Currency(decimal d) { return new Currency(d); } This works fine when I use it in code. However, when I have this: foreach (PropertyInfo p in props) { p.SetValue(this, table.Rows[0][p.Name], null); } It throws an ArgumentException stating that it cannot convert from System.Decimal to Currency. I'm confused since it works fine in any other circumstance.

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• Placement new in gcc

  - by Roman Prikhodchenko

  I need to find a workaround for a bug with placement new in g++. I now it was fixed in gcc-4.3 but I have to support versions 4.2 and 4.1. For example, following code compiles with an error "error: no matching function for call to 'operator new(long unsigned int, void*&)" template<class T, template<typename> class Alloc> inline void* type_ctor() { Alloc<T> a; void* p = a.allocate(1); new(p) T; return p; } ..... type_ctor<A, NewAllocator >();

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• What adapter to use for ExpandableListView with non-TextView views?

  - by David

  I have an ExpandableListView in which I'd like to have controls other than TextView. Apparently, SimpleExandableListViewAdapter assumes all the controls are TextViews. A cast exception is generated if they are not. What is the recommended solution? Options I can think of include: - Use some other included adapter. But I can't tell if they all have the same assumption. - Create my own adapter. Is there a doc which describes the contract, ie the sequence of method calls an adapter will encounter? I expected the existing adapters to require the views to conform to some interface to allow any conforming view to be used, rather than hardcode to textview and limit where they can be used.

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• How does sizeof calculate the size of structures

  - by Gearoid Murphy

  I know that a char and an int are calculated as being 8 bytes on 32 bit architectures due to alignment, but I recently came across a situation where a structure with 3 shorts was reported as being 6 bytes by the sizeof operator. Code is as follows: #include <iostream> using namespace std ; struct IntAndChar { int a ; unsigned char b ; }; struct ThreeShorts { unsigned short a ; unsigned short b ; unsigned short c ; }; int main() { cout<<sizeof(IntAndChar)<<endl; // outputs '8' cout<<sizeof(ThreeShorts)<<endl; // outputs '6', I expected this to be '8' return 0 ; } Compiler : g++ (Debian 4.3.2-1.1) 4.3.2. This really puzzles me, why isn't alignment enforced for the structure containing 3 shorts?

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• Does std::multiset guarntee insertion order?

  - by Naveen

  I have a std::multiset which stores elements of class A. I have provided my own implementation of operator< for this class. My question is if I insert two equivalent objects into this multiset is their order guaranteed? For example, first I insert a object a1 into the set and then I insert an equivalent object a2 into this set. Can I expect the a1 to come before a2 when I iterate through the set? If no, is there any way to achieve this using multiset?

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• How to read from a method that returns a filehandle in perl?

  - by Ryan Thompson

  I have an object with a method that returns a filehandle, and I want to read from that handle. The following doesn't work, because the right angle bracket of the method call is interpreted as the closing angle bracket of the input reader: my $input = <$object->get_handle()>; That gets parsed as: my $input = ( < $object- > ) get_handle() >; which is obviously a syntax error. Is there any way I can perform a method call within an angle operator, or do I need to break it into two steps like this? my $handle = $object->get_handle(); my $input = <$handle>;

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• matlab noninteger step indexing

  - by rlbond

  So, I have a vector: k = 1:100; And I want to take 19 elements from it, which are roughly equally-spaced. So I write this: m = k(1:(99/18):end); This works great, except for a tiny problem: Warning: Integer operands are required for colon operator when used as index m = 1 7 12 18 23 29 34 40 45 51 56 62 67 73 78 84 89 95 100 Now, I understand why this comes up, but I'd like to get rid of that warning. Is there a "right" way to do this without a warning?

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• Why will this code compile using ifort compiler and not when using gfortran compiler? Help!

  - by CuriousCompiler

  I'm rewriting some code to make a program compile with the gfortran compiler as opposed to ifort compiler I usually use. The code follows: _Subroutine SlideBits (WORD, BITS, ADDR) Implicit None Integer(4) WORD Integer(4) BITS Integer(4) ADDR Integer(4) ADDR1 ADDR1 = 32 - ADDR WORD = (WORD .And. (.Not.ISHFT(1,ADDR1))) .Or. ISHFT(BITS,ADDR1) End_ When I compile the above code using the gfortran compiler, I recieve this error: WORD = (WORD .And. (.Not.ISHFT(1,ADDR1))) .Or. ISHFT(BITS,ADDR1) Error: Operand of .NOT. operator at (1) is INTEGER(4) All three of the variables coming into the subroutine are integers. I've looked around a bit and the gfortran wiki states that the gfortran compiler should be able to handle logical statments being applied to integer values. Several other sites I've visited either quote from the gnu wiki or agree with it. This is the first time I've seen this error as the Intel Fortran compiler (ifort) I normally use compiles cleanly.

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• Quickly retrieve the subset of properties used in a huge collection in C#

  - by ccornet

  I have a huge Collection (which I can cast as an enumerable using OfType<()) of objects. Each of these objects has a Category property, which is drawn from a list somewhere else in the application. This Collection can reach sizes of hundreds of items, but it is possible that only, say, 6/30 of the possible Categories are actually used. What is the fastest method to find these 6 Categories? The size of the huge Collection discourages me from just iterating across the entire thing and returning all unique values, so is there a faster method of accomplishing this? Ideally I'd collect the categories into a List.

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• try catch finally

  - by gligom

  Maby this is simple for you, but for me is not. I have this code: Private int InsertData() { int rezultat = 0; try { if (sqlconn.State != ConnectionState.Open) { sqlconn.Open(); } rezultat = (int)cmd.ExecuteScalar(); } catch (Exception ex) { lblMesaje.Text = "Eroare: " + ex.Message.ToString(); } finally { if (sqlconn.State != ConnectionState.Closed) { sqlconn.Close(); } } return rezultat; } Is just for inserting a new record in a table. Even if this throw an error "Specified cast is not valid." "rezultat=(int)cmd.ExecuteScalar();" - the code is executed and the row is inserted in the database, and the execution continues. Why it continues? Maby i don't understand the try catch finally yet Smile | :) Thank you!

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• Selecting an element based on class and id in jquery - similar to an SQL query

  - by Ankur

  I want to select an element based on it's class and id, I have seen many similar questions on SO. Most of the users ask why would you ever want to do this - which is not very helpful, trust me, this is the simplest way of solving my UI problem, and it's a very unique and intereting UI related to making generic triple stores easily browsable. At the moment the jQUery looks like this: $(document).ready( function() { $(".predicates").hide(); $(".objects").hide(); $("#subject").click( function() { $("#predId, .predicates").toggle(); // this line } ); $("#predId").click( function() { $("#objId, .objects").toggle(); } ); }); The line I am really interested in is this $("#predId, .predicates").toggle(); how do I get the select to ensure that both #predId and .predicates are true, at the moment it seems that only one or the other has to be true. Is there something like an && operator?

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• Alternative to c++ static virtual methods

  - by Jaime Pardos

  In C++ is not possible to declare a static virtual function, neither cast a non-static function to a C style function pointer. Now, I have a plain ol' C SDK that uses function pointers heavily. I have to fill a structure with several function pointers. I was planning to use an abstract class with a bunch of static pure virtual methods, and redefine them in derived classes and fill the structure with them. It wasn't until then that I realized that static virtual are not allowed in C++. Is there any good alternative? The best I can think of is defining some pure virtual methods GetFuncA(), GetFuncB(),... and some static members FuncA()/FuncB() in each derived class, which would be returned by the GetFuncX(). Then a function in the abstract class would call those functions to get the pointers and fill the structure.

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• How can I match at the beginning of any line, including the first, with a Perl regex?

  - by JoelFan

  According the the Perl documentation on regexes: By default, the "^" character is guaranteed to match only the beginning of the string ... Embedded newlines will not be matched by "^" ... You may, however, wish to treat a string as a multi-line buffer, such that the "^" will match after any newline within the string ... you can do this by using the /m modifier on the pattern match operator. The "after any newline" part means that it will only match at the beginning of the 2nd and subsequent lines. What if I want to match at the beginning of any line (1st, 2nd, etc.)? EDIT: OK, it seems that the file has BOM information (3 chars) at the beginning and that's what's messing me up. Any way to get ^ to match anyway? EDIT: So in the end it works (as long as there's no BOM), but now it seems that the Perl documentation is wrong, since it says "after any newline"

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• Weird behaviour with vector::erase and std::remove_if with end range different from vector.end()

  - by Edison Gustavo Muenz

  Hi, I need to remove elements from the middle of a std::vector. So I tried: struct IsEven { bool operator()(int ele) { return ele % 2 == 0; } }; int elements[] = {1, 2, 3, 4, 5, 6}; std::vector<int> ints(elements, elements+6); std::vector<int>::iterator it = std::remove_if(ints.begin() + 2, ints.begin() + 4, IsEven()); ints.erase(it, ints.end()); After this I would expect that the ints vector have: [1, 2, 3, 5, 6]. In the debugger of Visual studio 2008, after the std::remove_if line, the elements of ints are modified, I'm guessing I'm into some sort of undefined behaviour here. So, how do I remove elements from a Range of a vector?

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• Storing multiple checkbox values in database

  - by Madjokr

  Hi, I want to store multiple column values in table.Lets take a example .. What are your favourite colors? the choices can be red,blue,green, orange. So lets assume, the user selects atleast 2 values. Is there any way to store the multiple values in table. I have implemented by concatinating choices of users in a column in the table. I later found that it is a bad practise. Currently i can think of using Bitwise operator and habtm. What are the different ways for storing multiple choices values in table? If I am implementing in rails, What is the best way to implement this with OOP concepts? Is there any builtin options in rails?

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• Worst side effects from chars signedness. (Explanation of signedness effects on chars and casts)

  - by JustSmith

  I frequently work with libraries that use char when working with bytes in C++. The alternative is to define a "Byte" as unsigned char but that not the standard they decided to use. I frequently pass bytes from C# into the C++ dlls and cast them to char to work with the library. When casting ints to chars or chars to other simple types what are some of the side effects that can occur. Specifically, when has this broken code that you have worked on and how did you find out it was because of the char signedness? Lucky i haven't run into this in my code, used a char signed casting trick back in an embedded systems class in school. I'm looking to better understand the issue since I feel it is relevant to the work I am doing.

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• Does all SPWeb or SPSite instances automatically disposed when console app process has ended?

  - by Janis Veinbergs

  We have Best practices on using disposable object in SharePoint. But i`m thinking - can I skip these when using Console Application? That's some code I want to execute once and after that process has finished. Do or don't SPSite and SPWeb's remain opened somwhere? Why i`m asking this? I just don't want to stress when using something like var lists = from web in site.AllWebs.Cast<SPWeb>() where web is meeting workspace && list is task list select list then do some stuff on lists etc. Some serious resource leak there because webs get opened, filtered and NOT closed. So should I worry in console app?

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• Postgres column casting...

  - by Simon

  I have a query SELECT assetid, type_code, version, name, short_name, status, languages, charset, force_secure, created, created_userid, updated, updated_userid, published, published_userid, status_changed, status_changed_userid FROM sq_ast WHERE assetid = 7 which doesn't work and throws ERROR: operator does not exist: character varying = integer LINE 4: FROM sq_ast WHERE assetid = 7 I can get it to work by doing SELECT assetid, type_code, version, name, short_name, status, languages, charset, force_secure, created, created_userid, updated, updated_userid, published, published_userid, status_changed, status_changed_userid FROM sq_ast WHERE assetid = '7' Please note the quoting of the 7 in the WHERE clause... I am deploying an huge application and I cannot rewrite the core... similarly I don't want to risk changing the type of the column... I'm no Postgres expert... please help... Is there an option for strict casting of columns???

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• Google Datastore low-level api query by key property

  - by Keyur

  I'm using the low-level google datastore api and I want to query by the key property and another property (let's call it category). I need to query based on a list of keys for which I'll use the IN operator. I know that the max. number of values you can provide for the IN clause is 30. I have 2 questions: Does the limit of 30 IN values apply to the key property as well? Do I need to create a composite index on {_key_ + category} or just on {category} for this query? Thanks, Keyur

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• Getting error in MVC Proj while writing Lambda Expression

  - by Shrewd Demon

  hi, i am creating a sample movie (MVC) application. I was getting fine with Viewing and Creating a new record, but when i wrote the code to get the details of a particular record i met with the following error: Unable to cast objec`t of type 'System.Data.Objects.ObjectQuery`1[MovieApp.Models.Movie]' to type 'MovieApp.Model`s.Movie'. here is the code i wrote for getting the details public ActionResult Details(int id) { var moviedetail = (Movie)_entities.MovieSet.Where(mvid => mvid.Id == id); return View(moviedetail); } can any body tell me whats going wrong and where ?? thank you.

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