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  • Is c++ explicit conversion really that bad?

    - by LoudNPossiblyRight
    My knowledge in c++ at this point is more academic than anything else and in all my reading thus far, the use of explicit conversion with named casts (const_cast, static_cast, reinterpret_cast, dynamic_cast) has come with a big warning label (and it's easy to see why) that pretty much implies explicit conversion is symptomatic of bad design and should only be used as a last resort in desperate circumstances. So i have to ask: Is explicit conversion with named casts really just jury rigging code or is there a more graceful and positive application to this feature? Is there a good example of the latter? Thanks in advance.

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  • Why does this cast to Base class in virtual function give a segmentation fault?

    - by dehmann
    I want to print out a derived class using the operator<<. When I print the derived class, I want to first print its base and then its own content. But I ran into some trouble (see segfault below): class Base { public: friend std::ostream& operator<<(std::ostream&, const Base&); virtual void Print(std::ostream& out) const { out << "BASE!"; } }; std::ostream& operator<<(std::ostream& out, const Base& b) { b.Print(out); return out; } class Derived : public Base { public: virtual void Print(std::ostream& out) const { out << "My base: "; //((const Base*)this)->Print(out); // infinite, calls this fct recursively //((Base*)this)->Print(out); // segfault (from infinite loop?) ((Base)*this).Print(out); // OK out << " ... and myself."; } }; int main(int argc, char** argv){ Derived d; std::cout << d; return 0; } Why can't I cast in one of these ways? ((const Base*)this)->Print(out); // infinite, calls this fct recursively ((Base*)this)->Print(out); // segfault (from infinite loop?)

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  • Is it ok to dynamic cast "this" as a return value?

    - by Panayiotis Karabassis
    This is more of a design question. I have a template class, and I want to add extra methods to it depending on the template type. To practice the DRY principle, I have come up with this pattern (definitions intentionally omitted): template <class T> class BaseVector: public boost::array<T, 3> { protected: BaseVector<T>(const T x, const T y, const T z); public: bool operator == (const Vector<T> &other) const; Vector<T> operator + (const Vector<T> &other) const; Vector<T> operator - (const Vector<T> &other) const; Vector<T> &operator += (const Vector<T> &other) { (*this)[0] += other[0]; (*this)[1] += other[1]; (*this)[2] += other[2]; return *dynamic_cast<Vector<T> * const>(this); } } template <class T> class Vector : public BaseVector<T> { public: Vector<T>(const T x, const T y, const T z) : BaseVector<T>(x, y, z) { } }; template <> class Vector<double> : public BaseVector<double> { public: Vector<double>(const double x, const double y, const double z); Vector<double>(const Vector<int> &other); double norm() const; }; I intend BaseVector to be nothing more than an implementation detail. This works, but I am concerned about operator+=. My question is: is the dynamic cast of the this pointer a code smell? Is there a better way to achieve what I am trying to do (avoid code duplication, and unnecessary casts in the user code)? Or am I safe since, the BaseVector constructor is private?

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  • NHibernate query with Projections.Cast to DateTime

    - by stiank81
    I'm experimenting with using a string for storing different kind of data types in a database. When I do queries I need to cast the strings to the right type in the query itself. I'm using .Net with NHibernate, and was glad to learn that there exists functionality for this. Consider the simple class: public class Foo { public string Text { get; set; } } I successfully use Projections.Cast to cast to numeric values, e.g. the following query correctly returns all Foos with an interger stored as int - between 1-10. var result = Session.CreateCriteria<Foo>() .Add(Restrictions.Between(Projections.Cast(NHibernateUtil.Int32, Projections.Property("Text")), 1, 10)) .List<Foo>(); Now if I try using this for DateTime I'm not able to make it work no matter what I try. Why?! var date = new DateTime(2010, 5, 21, 11, 30, 00); AddFooToDb(new Foo { Text = date.ToString() } ); // Will add it to the database... var result = Session .CreateCriteria<Foo>() .Add(Restrictions.Eq(Projections.Cast(NHibernateUtil.DateTime, Projections.Property("Text")), date)) .List<Foo>();

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  • Convert to list after Cast<T>

    - by Timmie Sarjanen
    Hi, I need to convert an IQueryable to List(is it possible to convert to IList?). There had not been an problem if it was not that i need to Cast because I have interfaces to my objects. I've tried most things but for some reason I must run Cast first and then ToList() which generates System.NullReferenceException. How do I solve this? public IQueryable GetPhrases() { return (from r in _repository.All<Phrase>() select r).Cast<IPhrase() }

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  • Why are exceptions considered better than explicit error testing?

    - by Richard Keller
    I often come across heated blog posts where the author uses the argument of "exceptions vs explicit error checking" to advocate their preferred language over some other language. The general consensus seems to be that languages which make use of exceptions are inherently better / cleaner than languages which rely heavily on error checking through explicit function calls. Is the use of exceptions considered better programming practice than explicit error checking, and if so, why?

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  • How to prevent CAST errors on SSIS ?

    - by manitra
    Hello, The question Is it possible to ask SSIS to cast a value and return NULL in case the cast is not allowed instead of throwing an error ? My environment I'm using Visual Studio 2005 and Sql Server 2005 on Windows Server 2003. The general context Just in case you're curious, here is my use case. I have to store data coming from somewhere in a generic table (key/value structure with history) witch contains some sort of value that can be strings, numbers or dates. The structure is something like this : table Values { Id int, Date datetime, -- for history Key nvarchar(50) not null, Value nvarchar(50), DateValue datetime, NumberValue numeric(19,9) } I want to put the raw value in the Value column and try to put the same value in the DateValue column when i'm able to cast it to Datetime in the NumberValue column when i'm able to cast it to a number Those two typed columns would make all sort of aggregation and manipulation much easier and faster later. That's it, now you know why i'm asking this strange question. ============ Thanks in advance for your help.

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  • Have set Expiration time: Still getting "Query string present but no explicit expiration time"

    - by oligofren
    I have one local Apache instance running with mod_cache (+ disk & mem) enabled, and it seems to cache content from my appserver fine. My app server sets Expiration headers and Last-modified. Yet, when deploying on a production server with the same modules enabled, I am getting the following error in my logs: blablabla not cached. Reason: Query string present but no explicit expiration time Any clues on why Apache is not caching content? The only difference is the Apache version. Locally I am running 2.2. This is from my config CacheRoot "/var/cache/apache2/" CacheEnable disk / This is example output < HTTP/1.1 200 OK < Date: Mon, 19 Nov 2012 16:09:13 GMT < Server: Sun GlassFish Enterprise Server v2.1.1 < X-Powered-By: Servlet/2.5 < Expires: Tue Nov 20 05:00:00 CET 2012 < Last-Modified: Mon Nov 19 17:09:13 CET 2012 < Cache-Control: no-transform < Content-Type: application/x-javascript < Transfer-Encoding: chunked

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  • Make conversion to a native type explicit in C++

    - by Tal Pressman
    I'm trying to write a class that implements 64-bit ints for a compiler that doesn't support long long, to be used in existing code. Basically, I should be able to have a typedef somewhere that selects whether I want to use long long or my class, and everything else should compile and work. So, I obviously need conversion constructors from int, long, etc., and the respective conversion operators (casts) to those types. This seems to cause errors with arithmetic operators. With native types, the compiler "knows" that when operator*(int, char) is called, it should promote the char to int and call operator*(int, int) (rather than casting the int to char, for example). In my case it gets confused between the various built-in operators and the ones I created. It seems to me like if I could flag the conversion operators as explicit somehow, that it would solve the issue, but as far as I can tell the explicit keyword is only for constructors (and I can't make constructors for built-in types). So is there any way of marking the casts as explicit? Or am I barking up the wrong tree here and there's another way of solving this? Or maybe I'm just doing something else wrong...

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  • Primitive type 'short' - casting in Java

    - by gemm
    Hello, I have a question about the primitive type 'short' in Java. I am using JDK 1.6. If I have the following: short a = 2; short b = 3; short c = a + b; the compiler does not want to compile - it says that it "cannot convert from int to short" and suggests that I make a cast to short, so this: short c = (short) (a + b); really works. But my question is why do I need to cast? The values of a and b are in the range of short - the range of short values is {-32,768, 32767}. I also need to cast when I want to perform the operations -, *, / (I haven't checked for others). If I do the same for primitive type int, I do not need to cast aa+bb to int. The following works fine: int aa = 2; int bb = 3; int cc = aa +bb; I discovered this while designing a class where I needed to add two variables of type short, and the compiler wanted me to make a cast. If I do this with two variables of type int, I don't need to cast. Thank you very much in advance. A small remark: the same thing also happens with the primitive type byte. So, this workes: byte a = 2; byte b = 3; byte c = (byte) (a + b); but this not: byte a = 2; byte b = 3; byte c = a + b; For long, float, double, and int, there is no need to cast. Only for short and byte values.

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  • How to cast C struct just another struct type if their memory size are equal?

    - by Eonil
    I have 2 matrix structs means equal data but have different form like these: // Matrix type 1. typedef float Scalar; typedef struct { Scalar e[4]; } Vector; typedef struct { Vector e[4]; } Matrix; // Matrix type 2 (you may know this if you're iPhone developer) struct CATransform3D { CGFloat m11, m12, m13, m14; CGFloat m21, m22, m23, m24; CGFloat m31, m32, m33, m34; CGFloat m41, m42, m43, m44; }; typedef struct CATransform3D CATransform3D; Their memory size are equal. So I believe there is a way to convert these types without any pointer operations or copy like this: // Implemented from external lib. CATransform3D CATransform3DMakeScale (CGFloat sx, CGFloat sy, CGFloat sz); Matrix m = (Matrix)CATransform3DMakeScale ( 1, 2, 3 ); Is this possible? Currently compiler prints an "error: conversion to non-scalar type requested" message.

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  • NTFS Permissions - Access Denied even though Explicit Allow and no Deny

    - by chris613
    I'm hoping someone can help me with this NTFS permissions problem. The short version is that I can't write a new file in F:\SomeDir even though I seem to be granted full permissions via both the "Domain Admins" group and a second unprivileged group. The "Effective Permissions" tab in the explorer permissions UI shows that I have full control, and there are no "Deny"s anywhere in the ACL or anything else that looks unusual. I am logged into the machine over RDP and accessing the disk directly, not through a share. F:\SomeDir>set U USERDNSDOMAIN=THEOFFICE.LOCAL USERDOMAIN=THEOFFICE USERNAME=thisisme USERPROFILE=C:\Users\thisisme F:\SomeDir>icacls . . BUILTIN\Administrators:(I)(F) CREATOR OWNER:(I)(OI)(CI)(IO)(F) THEOFFICE\Domain Admins:(I)(OI)(CI)(F) NT AUTHORITY\SYSTEM:(I)(OI)(CI)(F) BUILTIN\Administrators:(I)(OI)(CI)(IO)(F) BUILTIN\Users:(I)(OI)(CI)(RX) Successfully processed 1 files; Failed processing 0 files F:\SomeDir>net group /domain "Domain Admins" The request will be processed at a domain controller for domain THEOFFICE.local. Group name Domain Admins Comment Designated administrators of the domain Members ------------------------------------------------------------------------------- Administrator thatguy thisisme The command completed successfully. F:\SomeDir>echo "whyUNoCreateFile?" > whyUNoCreateFile.txt Access is denied. I searched for answers and came across similar problems that lead to UAC (ex. Why does removing the EVERYONE group prevent domain admins from accessing a drive? ). I can't turn off UAC at the moment, so I try a "regular" group that I'm also part of. This group has no special rights assignments and is not part of any administrative groups. Still no dice: [***** This one command executed in an elevated shell *****] F:\SomeDir>icacls . /grant THEOFFICE\iteveryone:(OI)(CI)F processed file: . Successfully processed 1 files; Failed processing 0 files F:\SomeDir>net group /domain "iteveryone" The request will be processed at a domain controller for domain THEOFFICE.local. Group name ITeveryone Comment Members ------------------------------------------------------------------------------- Administrator thatguy thisisme otherguy someitguy The command completed successfully. F:\ScanningVMsForIBM>echo y > u Access is denied. As you can see, using a "regular" group didn't help. I have logged out and back in to the server to ensure my login token is up to date, and at any rate I belonged to these groups before the server was created. If I grant explicit permission to myself, it does allow me to write files: [***** This one command executed in an elevated shell *****] F:\SomeDir>icacls . /grant THEOFFICE\thisisme:(OI)(CI)F processed file: . Successfully processed 1 files; Failed processing 0 files F:\SomeDir>echo y > u F:\SomeDir>type u y My requirement is for the "Domain Admins" group to have Full Control, or if that's not possible without disabling UAC, then a second group will do, but I can't get either to work. I'm really stumped. Can someone please point out what I could be overlooking?

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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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  • 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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  • 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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  • Call the cast operator of template base class within the derived class

    - by yoni
    I have a template class, called Cell, here the definition: template <class T> class OneCell { ..... } I have a cast operator from Cell to T, here virtual operator const T() const { ..... } Now i have derived class, called DCell, here template <class T> class DCell : public Cell<T> { ..... } I need to override the Cell's cast operator (insert a little if), but after I need to call the Cell's cast operator. In other methods it's should be something like virtual operator const T() const { if (...) { return Cell<T>::operator const T; } else throw ... } but i got a compiler error error: argument of type 'const int (Cell::)()const' does not match 'const int' What can I do? Thank you, and sorry about my poor English.

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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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  • 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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  • 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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