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  • Showplan Operator of the Week – BookMark/Key Lookup

    Fabiano continues in his mission to describe the major Showplan Operators used by SQL Server's Query Optimiser. This week he meets a star, the Key Lookup, a stalwart performer, but most famous for its role in ill-performing queries where an index does not 'cover' the data required to execute the query. If you understand why, and in what circumstances, key lookups are slow, it helps greatly with optimising query performance.

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  • How do I overload an operator for an enumeration in C#?

    - by ChrisHDog
    I have an enumerated type that I would like to define the , <, =, and <= operators for. I know that these operators are implictly created on the basis of the enumerated type (as per the documentation) but I would like to explictly define these operators (for clarity, for control, to know how to do it, etc...) I was hoping I could do something like: public enum SizeType { Small = 0, Medium = 1, Large = 2, ExtraLarge = 3 } public SizeType operator >(SizeType x, SizeType y) { } But this doesn't seem to work ("unexpected toke") ... is this possible? It seems like it should be since there are implictly defined operators. Any suggestions?

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  • How does delete deal with pointer constness?

    - by aJ
    I was reading this question Deleting a const pointer and wanted to know more about delete behavior. Now, as per my understanding: delete expression works in two steps: invoke destructor then releases the memory (often with a call to free()) by calling operator delete. operator delete accepts a void*. As part of a test program I overloaded operator delete and found that operator delete doesn't accept const pointer. Since operator delete does not accept const pointer and delete internally calls operator delete, how does Deleting a const pointer work ? Does delete uses const_cast internally?

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  • html.checkbox - explicit value to hidden field value

    - by Tassadaque
    Hi I am creating list of checkboxes in partial view by follwoing http://blog.stevensanderson.com/2010/01/28/editing-a-variable-length-list-aspnet-mvc-2-style/ code and Rendered HTML for checkboxes is as follows <%=Html.CheckBox("EmployeeID", new { value = user.EmployeeID, @class = "ccboxes", title = user.Designation + "(" + user.EmployeeName + ")" })%> <INPUT id=MemoUsers_a29f82e4-ebbc-47b0-8cdd-7d54f94143be__EmployeeID class=boxes title=Programmer(Zia) value=6 type=checkbox name=MemoUsers[a29f82e4-ebbc-47b0-8cdd-7d54f94143be].EmployeeID jQuery1276681299292="27"> <INPUT value=false type=hidden name=MemoUsers[a29f82e4-ebbc-47b0-8cdd-7d54f94143be].EmployeeID> In rendered html it can be seen that value attribute of hidden field is false. i want to assign explicit value(same as checkbox value) to this value. Is this possible using html.checkbox or html.checkboxfor. one way is recommended in http://stackoverflow.com/questions/626901/asp-net-mvc-rc2-checkboxes-with-explicit-values. Is there any other better way i want to do this as ModelState.IsValid is returning false because of hidden field value attribute Regards

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  • Constructor or Explicit cast

    - by Felan
    In working with Linq to Sql I create a seperate class to ferry data to a web page. To simplify creating these ferry objects I either use a specialized constructor or an explicit conversion operator. I have two questions. First which approach is better from a readibility perspective? Second while the clr code that is generated appeared to be the same to me, are there situations where one would be treated different than the other by the compiler (in lambda's or such). Example code (DatabaseFoo uses specialized constructor and BusinessFoo uses explicit operator): public class DatabaseFoo { private static int idCounter; // just to help with generating data public int Id { get; set; } public string Name { get; set; } public DatabaseFoo() { Id = idCounter++; Name = string.Format("Test{0}", Id); } public DatabaseFoo(BusinessFoo foo) { this.Id = foo.Id; this.Name = foo.Name; } } public class BusinessFoo { public int Id { get; set; } public string Name { get; set; } public static explicit operator BusinessFoo(DatabaseFoo foo) { return FromDatabaseFoo(foo); } public static BusinessFoo FromDatabaseFoo(DatabaseFoo foo) { return new BusinessFoo {Id = foo.Id, Name = foo.Name}; } } public class Program { static void Main(string[] args) { Console.WriteLine("Creating the initial list of DatabaseFoo"); IEnumerable<DatabaseFoo> dafoos = new List<DatabaseFoo>() { new DatabaseFoo(), new DatabaseFoo(), new DatabaseFoo(), new DatabaseFoo(), new DatabaseFoo(), new DatabaseFoo()}; foreach(DatabaseFoo dafoo in dafoos) Console.WriteLine(string.Format("{0}\t{1}", dafoo.Id, dafoo.Name)); Console.WriteLine("Casting the list of DatabaseFoo to a list of BusinessFoo"); IEnumerable<BusinessFoo> bufoos = from x in dafoos select (BusinessFoo) x; foreach (BusinessFoo bufoo in bufoos) Console.WriteLine(string.Format("{0}\t{1}", bufoo.Id, bufoo.Name)); Console.WriteLine("Creating a new list of DatabaseFoo by calling the constructor taking BusinessFoo"); IEnumerable<DatabaseFoo> fufoos = from x in bufoos select new DatabaseFoo(x); foreach(DatabaseFoo fufoo in fufoos) Console.WriteLine(string.Format("{0}\t{1}", fufoo.Id, fufoo.Name)); } }

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  • Why would the assignment operator ever do something different than its matching constructor?

    - by Neil G
    I was reading some boost code, and came across this: inline sparse_vector &assign_temporary(sparse_vector &v) { swap(v); return *this; } template<class AE> inline sparse_vector &operator=(const sparse_vector<AE> &ae) { self_type temporary(ae); return assign_temporary(temporary); } It seems to be mapping all of the constructors to assignment operators. Great. But why did C++ ever opt to make them do different things? All I can think of is scoped_ptr?

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  • Why does javascript's "in" operator return true when testing if 0 exists in an array that doesn't co

    - by Mariano Peterson
    For example, this returns true, and makes sense: var x = [1,2]; 1 in x; // true This returns false, and makes sense: var x = [1,2]; 3 in x; // false However this returns true, and I don't understand why: var x = [1,2]; 0 in x; You can quickly test it by putting this in your browser's address bar: javascript:var x=[1,2]; alert(0 in x); Why does the "in" operator in Javascript return true when testing if "0" exists in array, even when the array doesn't appear to contain "0"?

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  • C++: Overload != When == Overloaded

    - by Mark W
    Say I have a class where I overloaded the operator == as such: Class A { ... public: bool operator== (const A &rhs) const; ... }; ... bool A::operator== (const A &rhs) const { .. return isEqual; } I already have the operator == return the proper Boolean value. Now I want to extend this to the simple opposite (!=). I would like to call the overloaded == operator and return the opposite, i.e. something of the nature bool A::operator!= (const A &rhs) const { return !( this == A ); } Is this possible? I know this will not work, but it exemplifies what I would like to have. I would like to keep only one parameter for the call: rhs. Any help would be appreciated, because I could not come up with an answer after several search attempts.

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  • Moq: Unable to cast to interface

    - by Pickels
    Hello, earlier today I asked this question. So since moq creates it's own class from an interface I wasn't able to cast it to a different class. So it got me wondering what if I created a ICustomPrincipal and tried to cast to that. This is how my mocks look: var MockHttpContext = new Mock<HttpContextBase>(); var MockPrincipal = new Mock<ICustomPrincipal>(); MockHttpContext.SetupGet(h => h.User).Returns(MockPrincipal.Object); In the method I am trying to test the follow code gives the error(again): var user = (ICustomPrincipal)httpContext.User; The error is the following: Unable to cast object of type 'IPrincipalProxy4081807111564298854aabfc890edcc8' to type 'MyProject.Web.ICustomPrincipal'. I guess I still need some practice with interfaces and moq but shouldn't I be able to cast the class that moq created back to ICustomPrincipal? I know httpContext.User returns an IPrincipal so maybe something gets lost there? Well if anybody can help me I would appreciate that. Pickels Edit: As requested the full code of the method I am testing. It's still not finished but this is what I have so far: public bool AuthorizeCore(HttpContextBase httpContext) { if (httpContext == null) { throw new ArgumentNullException("httpContext"); } var user = (ICustomPrincipal)httpContext.User; if (!user.Identity.IsAuthenticated) { return false; } return true; }

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  • Performance: float to int cast and clipping result to range

    - by durandai
    I'm doing some audio processing with float. The result needs to be converted back to PCM samples, and I noticed that the cast from float to int is surprisingly expensive. Whats furthermore frustrating that I need to clip the result to the range of a short (-32768 to 32767). While I would normally instictively assume that this could be assured by simply casting float to short, this fails miserably in Java, since on the bytecode level it results in F2I followed by I2S. So instead of a simple: int sample = (short) flotVal; I needed to resort to this ugly sequence: int sample = (int) floatVal; if (sample > 32767) { sample = 32767; } else if (sample < -32768) { sample = -32768; } Is there a faster way to do this? (about ~6% of the total runtime seems to be spent on casting, while 6% seem to be not that much at first glance, its astounding when I consider that the processing part involves a good chunk of matrix multiplications and IDCT) EDIT The cast/clipping code above is (not surprisingly) in the body of a loop that reads float values from a float[] and puts them into a byte[]. I have a test suite that measures total runtime on several test cases (processing about 200MB of raw audio data). The 6% were concluded from the runtime difference when the cast assignment "int sample = (int) floatVal" was replaced by assigning the loop index to sample. EDIT @leopoldkot: I'm aware of the truncation in Java, as stated in the original question (F2I, I2S bytecode sequence). I only tried the cast to short because I assumed that Java had an F2S bytecode, which it unfortunately does not (comming originally from an 68K assembly background, where a simple "fmove.w FP0, D0" would have done exactly what I wanted).

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  • Warning: cast increases required alignment

    - by dash-tom-bang
    I'm recently working on this platform for which a legacy codebase issues a large number of "cast increases required alignment to N" warnings, where N is the size of the target of the cast. struct Message { int32_t id; int32_t type; int8_t data[16]; }; int32_t GetMessageInt(const Message& m) { return *reinterpret_cast<int32_t*>(&data[0]); } Hopefully it's obvious that a "real" implementation would be a bit more complex, but the basic point is that I've got data coming from somewhere, I know that it's aligned (because I need the id and type to be aligned), and yet I get the message that the cast is increasing the alignment, in the example case, to 4. Now I know that I can suppress the warning with an argument to the compiler, and I know that I can cast the bit inside the parentheses to void* first, but I don't really want to go through every bit of code that needs this sort of manipulation (there's a lot because we load a lot of data off of disk, and that data comes in as char buffers so that we can easily pointer-advance), but can anyone give me any other thoughts on this problem? I mean, to me it seems like such an important and common option that you wouldn't want to warn, and if there is actually the possibility of doing it wrong then suppressing the warning isn't going to help. Finally, can't the compiler know as I do how the object in question is actually aligned in the structure, so it should be able to not worry about the alignment on that particular object unless it got bumped a byte or two?

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  • How to save transferred MP3 on Centova cast?

    - by cHAKE
    We have uploaded and transferred the mp3 files on centova cast successfully with Filezilla. We know how to update the media library We know how to create playlists We know how to drag the songs into different playlists We know how to save the media or the playlists BUT, we are losing all the media library saved files (songs) the moment we get new files in media library. However we want to keep the media library and playlist saved.

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  • How do I overload the square-bracket operator in C#?

    - by Coderer
    DataGridView, for example, lets you do this: DataGridView dgv = ...; DataGridViewCell cell = dgv[1,5]; but for the life of me I can't find the documentation on the index/square-bracket operator. What do they call it? Where is it implemented? Can it throw? How can I do the same thing in my own classes? ETA: Thanks for all the quick answers. Briefly: the relevant documentation is under the "Item" property; the way to overload is by declaring a property like public object this[int x, int y]{ get{...}; set{...} }; the indexer for DataGridView does not throw, at least according to the documentation. It doesn't mention what happens if you supply invalid coordinates. ETA Again: OK, even though the documentation makes no mention of it (naughty Microsoft!), it turns out that the indexer for DataGridView will in fact throw an ArgumentOutOfRangeException if you supply it with invalid coordinates. Fair warning.

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  • How do I overload () operator with two parameters; like (3,5)?

    - by hkBattousai
    I have a mathematical matrix class. It contains a member function which is used to access any element of the class. template >class T> class Matrix { public: // ... void SetElement(T dbElement, uint64_t unRow, uint64_t unCol); // ... }; template <class T> void Matrix<T>::SetElement(T Element, uint64_t unRow, uint64_t unCol) { try { // "TheMatrix" is define as "std::vector<T> TheMatrix" TheMatrix.at(m_unColSize * unRow + unCol) = Element; } catch(std::out_of_range & e) { // Do error handling here } } I'm using this method in my code like this: // create a matrix with 2 rows and 3 columns whose elements are double Matrix<double> matrix(2, 3); // change the value of the element at 1st row and 2nd column to 6.78 matrix.SetElement(6.78, 1, 2); This works well, but I want to use operator overloading to simplify things, like below: Matrix<double> matrix(2, 3); matrix(1, 2) = 6.78; // HOW DO I DO THIS?

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  • C# - Cast object to IList<T> based on Type

    - by blu
    I am trying out a little reflection and have a question on how the cast the result object to an IList. Here is the reflection: private void LoadBars(Type barType) { // foo has a method that returns bars Type foo = typeof(Foo); MethodInfo method = foo.GetMethod("GetBars") .MakeGenericMethod(bar); object obj = method.Invoke(foo, new object[] { /* arguments here */ }); // how can we cast obj to an IList<Type> - barType } How can we cast the result of method.Invoke to an IList of Type from the barType argument?

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  • Cast integer to real

    - by Dave Jarvis
    Question How do you cast an INTEGER value as a REAL value? Attempts CAST( Y.YEAR AS REAL), but that failed (the documentation indicates you cannot CAST or CONVERT values to REALs. Y.YEAR + 0.0, but that failed, too. Error Message Using udf_slope fails due to: Can't initialize function 'slope'; slope() requires a real as parameter 2 Code SELECT D.AMOUNT, Y.YEAR, slope(D.AMOUNT, Y.YEAR + 0.0) as SLOPE, intercept(D.AMOUNT, Y.YEAR + 0.0) as INTERCEPT FROM YEAR_REF Y, DAILY D Here, D.AMOUNT is a FLOAT and Y.YEAR is an INTEGER. Thank you!

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  • Logical operator AND having higher order of precedence than IN

    - by AspOnMyNet
    I’ve read that logical operator AND has higher order of precedence than logical operator IN, but that doesn’t make sense since if that was true, then wouldn’t in the following statement the AND condition got evaluated before the IN condition ( thus before IN operator would be able to check whether Released field equals to any of the values specified within parentheses ? SELECT Song, Released, Rating FROM Songs WHERE Released IN (1967, 1977, 1987) AND SongName = ’WTTJ’ thanx

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  • Why won't this SQL CAST work?

    - by Kev
    I have a nvarchar(50) column in a SQL Server 2000 table defined as follows: TaskID nvarchar(50) NULL I need to fill this column with some random SQL Unique Identifiers (I am unable to change the column type to uniqueidentifier). I tried this: UPDATE TaskData SET TaskID = CAST(NEWID() AS nvarchar) but I got the following error: Msg 8115, Level 16, State 2, Line 1 Arithmetic overflow error converting expression to data type nvarchar. I also tried: UPDATE TaskData SET TaskID = CAST(NEWID() AS nvarchar(50)) but then got this error: Msg 8152, Level 16, State 6, Line 1 String or binary data would be truncated. I don't understand why this doesn't work but this does: DECLARE @TaskID nvarchar(50) SET @TaskID = CAST(NEW() AS nvarchar(50)) I also tried CONVERT(nvarchar, NEWID()) and CONVERT(nvarchar(50), NEWID()) but got the same errors.

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  • cons operator (::) in F#

    - by Max
    The :: operator in F# always prepends elements to the list. Is there an operator that appends to the list? I'm guessing that using @ operator [1; 2; 3] @ [4] would be less efficient, than appending one element.

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  • what is this operator called and what is it used for <=>

    - by Scott
    I recently came across this magical operator when digging into Groovy: <= Groovy has really made me happy with elvis operators ?. and ?: which I use constantly now and very much wish were in Java. With this new operator, I have only found this reference. It seems to make comparators much easier. My question is how does it handle null values and how does it compare non Comparable object. Does this operator have a name, I couldn't find it Googling.

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  • How to cast/convert form Object in an byte[] array

    - by maddash
    I've got a maybe simple problem, but at the moment I am not able to solve it. I have an Object and I need to convert it into a byte[]. public byte[] GetMapiPropertyBytes(string propIdentifier) { return (byte[])this.GetMapiProperty(propIdentifier); //InvalidCastException } Exception: Unable to cast COM object of type 'System.__ComObject' to class type 'System.Byte[]'. Instances of types that represent COM components cannot be cast to types that do not represent COM components; however they can be cast to interfaces as long as the underlying COM component supports QueryInterface calls for the IID of the interface. So far so good - I've tried to serialize it, but I got another exception - NOT serializable Could someone help me? I need a method to convert it...

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