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• Pointer to a C++ class member function as a global function's parameter?

  - by marcin1400

  I have got a problem with calling a global function, which takes a pointer to a function as a parameter. Here is the declaration of the global function: int lmdif ( minpack_func_mn fcn, void *p, int m, int n, double *x, double *fvec, double ftol) The "minpack_func_mn" symbol is a typedef for a pointer to a function, defined as: typedef int (*minpack_func_mn)(void *p, int m, int n, const double *x, double *fvec, int iflag ); I want to call the "lmdif" function with a pointer to a function which is a member of a class I created, and here is the declaration of this class function: int LT_Calibrator::fcn(void *p, int m, int n, const double *x, double *fvec,int iflag) I am calling a global function like this: info=lmdif(&LT_Calibrator::fcn, 0, m, n, x, fvec, ftol) Unfortunately, I get a compiler error, which says: "error C2664: 'lmdif' : cannot convert parameter 1 from 'int (__thiscall LT_Calibrator::* )(void *,int,int,const double *,double *,int)' to 'minpack_func_mn' 1 There is no context in which this conversion is possible" Is there any way to solve that problem?

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• How do I pass (by value) a struct in Objective-C?

  - by Striker

  This one has been driving me mad! I have a struct: typedef struct{ int a; }myStruct; Then I have: myStruct tempStruct; I am trying to pass the struct to a class method whose implementation is: - (void) myFunc:(struct myStruct)oneOfMyStructs{}; I call the method like so: [myClass myFunc:(struct myStruct)tempStruct]; The compiler complains about "Conversion to non-scalar type requested." All I want to do is pass a struct into a class method, but the syntax has me a bit confused. I'm new to Objective-C. Please let me know if you can see where I'm going wrong. I've not been able to pass by reference either, so if you could help me out with that, that would be great! Thanks!

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• LINQ .Cast() extension method fails but (type)object works.

  - by Ben Robinson

  To convert between some LINQ to SQL objects and DTOs we have created explicit cast operators on the DTOs. That way we can do the following: DTOType MyDTO = (LinqToSQLType)MyLinq2SQLObj; This works well. However when you try to cast using the LINQ .Cast() extension method it trows an invalid cast exception saying cannot cast type Linq2SQLType to type DTOType. i.e. the below does not work List<DTO.Name> Names = dbContact.tNames.Cast<DTO.Name>() .ToList(); But the below works fine: DAL.tName MyDalName = new DAL.tName(); DTO.Name MyDTOName = (DTO.Name)MyDalName; and the below also works fine List<DTO.Name> Names = dbContact.tNames.Select(name => (DTO.Name)name) .ToList(); Why does the .Cast() extension method throw an invalid cast exception? I have used the .Cast() extension method in this way many times in the past and when you are casting something like a base type to a derived type it works fine, but falls over when the object has an explicit cast operator.

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• How to store and compare time-zone sensitive times

  - by Chad Moran

  I have a data structure where an entity has times stored as an int (minutes into the day) for fast comparison. The entity also has a Foreign Key reference back to a TimeZone table which contains the .NET CLR ID Name and it's Standard Time/Daylight Time acronyms. Since this information is stored as time-zone insensitive - I was wondering how in LINQ to SQL I could convert this into a UTC DateTime for comparison against other times that will be in UTC. Just to be clear this conversion has to be done server-side so that I can execute filtering on the SQL Server and not the client. I am using .NET 3.5 SP1 and SQL Server 2008.

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• Is converting this ArrayList to a Generic List efficient?

  - by Greg

  The code I'm writing receives an ArrayList from unmanaged code, and this ArrayList will always contain one or more objects of type Grid_Heading_Blk. I've considered changing this ArrayList to a generic List, but I'm unsure if the conversion operation will be so expensive as to nullify the benefits of working with the generic list. Currently, I'm just running a foreach (Grid_Heading_Blk in myArrayList) operation to work with the ArrayList contents after passing the ArrayList to the class that will use it. Should I convert the ArrayList to a generic typed list? And if so, what is the most efficient way of doing so?

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• Is this overly clever or unsafe?

  - by Liberalkid

  I was working on some code recently and decided to work on my operator overloading in c++, because I've never really implemented it before. So I overloaded the comparison operators for my matrix class using a compare function that returned 0 if LHS was less than RHS, 1 if LHS was greater than RHS and 2 if they were equal. Then I exploited the properties of logical not in c++ on integers, to get all of my compares in one line: inline bool Matrix::operator<(Matrix &RHS){ return ! (compare(*this,RHS)); } inline bool Matrix::operator>(Matrix &RHS){ return ! (compare((*this),RHS)-1); } inline bool Matrix::operator>=(Matrix &RHS){ return compare((*this),RHS); } inline bool Matrix::operator<=(Matrix &RHS){ return compare((*this),RHS)-1; } inline bool Matrix::operator!=(Matrix &RHS){ return compare((*this),RHS)-2; } inline bool Matrix::operator==(Matrix &RHS){ return !(compare((*this),RHS)-2); } Obviously I should be passing RHS as a const, I'm just probably not going to use this matrix class again and I didn't feel like writing another function that wasn't a reference to get the array index values solely for the comparator operation.

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• Simple Scala syntax - trying to define "==" operator - what am I missing?

  - by Alex R

  While experimenting with some stuff on the REPL, I got to a point where I needed something like this: scala class A(x:Int) { println(x); def ==(a:A) : Boolean = { this.x == a.x; } } Just a simple class with an "==" operator. Why doesn't it work??? Here's the result: :10: error: type mismatch; found : A required: ?{val x: ?} Note that implicit conversions are not applicable because they are ambiguous: both method any2ArrowAssoc in object Predef of type [A](x: A)ArrowAssoc[A] and method any2Ensuring in object Predef of type [A](x: A)Ensuring[A] are possible conversion functions from A to ?{val x: ?} class A(x:Int) { println(x); def ==(a:A) : Boolean = { this.x == a.x; } } ^ This is scala 2.8 RC1. Thanks

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• How to get this to compile?

  - by ShaChris23

  I have this code which compiles and works as expected: class Right {}; class Left { public: Left& operator = (Right const&) { //... Do something ... return *this; } }; int main() { Right right; Left left; // Assign individual object -- this works left = right; } But now, this one surprises me, I thought the template would work itself out since I already provided the = operator() to the Left class. int main() { ... std::list<Right> rightLst; std::list<Left> leftLst; // Assign a list of objects -- this doesn't compile leftLst = rightLst; } What can I do so that I could convert the rightLst to leftLst conversion in a single line?

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• Dynamic order by without using dynamic sql ?

  - by Rohit

  I have the following stored procedure which can be sorted ascending and descending on TemplateName,CreatedOn and UploadedBy. The following SP when runs doesnot sort records.if i replace 2,3,4 by columnname, i got an error message "Conversion failed when converting the nvarchar value 'Test Template' to data type int.".Please suggest how to achieve sorting. CREATE PROCEDURE [dbo].[usp_SEL_GetRenderingTemplate] ( @facilityID INT, @sortOrder VARCHAR(5), @sortExpression VARCHAR(100), @errorCode INT OUTPUT ) AS BEGIN SET NOCOUNT ON ; BEGIN TRY SET @sortOrder = CASE @sortOrder WHEN 'Ascending' THEN 'ASC' WHEN 'Descending' THEN 'DESC' ELSE 'ASC' END SELECT TemplateID, TemplateName, CreatedOn, ( [user].LastName + ' ' + [user].FirstName ) AS UploadedBy FROM Templates INNER JOIN [user] ON [user].UserID = Templates.CreatedBy WHERE facilityid = @facilityID ORDER BY CASE WHEN @sortExpression = 'TemplateName' AND @sortOrder = 'ASC' THEN 2 WHEN @sortExpression = 'CreatedOn' AND @sortOrder = 'ASC' THEN 3 WHEN @sortExpression = 'UploadedBy' AND @sortOrder = 'ASC' THEN 4 END ASC, CASE WHEN @sortExpression = 'TemplateName' AND @sortOrder = 'DESC' THEN 2 WHEN @sortExpression = 'CreatedOn' AND @sortOrder = 'DESC' THEN 3 WHEN @sortExpression = 'UploadedBy' AND @sortOrder = 'DESC' THEN 4 END DESC SET @errorCode = 0 END TRY BEGIN CATCH SET @errorCode = -1 DECLARE @errorMsg AS VARCHAR(MAX) DECLARE @utcDate AS DATETIME SET @errorMsg = CAST(ERROR_MESSAGE() AS VARCHAR(MAX)) SET @utcDate = CAST(GETUTCDATE() AS DATETIME) EXEC usp_INS_LogException 'usp_SEL_GetFacilityWorkTypeList', @errorMsg, @utcDate END CATCH END

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• python dictionary with constant value-type

  - by s.kap

  hi there, I bumped into a case where I need a big (=huge) python dictionary, which turned to be quite memory-consuming. However, since all of the values are of a single type (long) - as well as the keys, I figured I can use python (or numpy, doesn't really matter) array for the values ; and wrap the needed interface (in: x ; out: d[x]) with an object which actually uses these arrays for the keys and values storage. I can use a index-conversion object (input -- index, of 1..n, where n is the different-values counter), and return array[index]. I can elaborate on some techniques of how to implement such an indexing-methods with reasonable memory requirement, it works and even pretty good. However, I wonder if there is such a data-structure-object already exists (in python, or wrapped to python from C/++), in any package (I checked collections, and some Google searches). Any comment will be welcome, thanks.

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• Why is 'volatile' parasitic in C++?

  - by Steve

  Consider the following code: int main() { int i; volatile int* p = &i; int *v = p; return 0; } This gives an error in g++: $ g++ -o volatile volatile.cpp volatile.cpp: In function ‘int main()’: volatile.cpp:6: error: invalid conversion from ‘volatile int*’ to ‘int*’ My intention was that I want to make p volatile. However, once I've read the value of p, I don't care if accessing v is volatile. Why is it required that v be declared volatile? This is hypothetical code of course. In a real situation you could imagine that p points to a memory location, but is modified externally and I want v to point to the location that p pointed to at the time of v = p, even if later p is externally modified. Therefore p is volatile, but v is not. By the way I am interested in the behaviour both when this is considered C and C++, but in C this only generates a warning, not an error.

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• C++ enumeration

  - by asli

  Hi,my question is about enumeration,my codes are : #include<iostream> using namespace std; int main() { enum bolumler {programcilik,donanim,muhasebe,motor,buro} bolum; bolum = donanim; cout << bolum << endl; bolum += 2; // bolum=motor cout << bolum; return 0; } The output should be 1 3 but according to these codes the error is: error C2676: binary '+=' : 'enum main::bolumler' does not define this operator or a conversion to a type acceptable to the predefined operator Error executing cl.exe. 111.obj - 1 error(s), 0 warning(s) Can you help me ?The other question is what can I do if I want to see the output like that "muhasebe"?

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• Haskel dot (.) and dollar ($) composition: correct use.

  - by Robert Massaioli

  I have been reading Real World Haskell and I am nearing the end but a matter of style has been niggling at me to do with the (.) and ($) operators. When you write a function that is a composition of other functions you write it like: f = g . h But when you apply something to the end of those functions I write it like this: k = a $ b $ c $ value But the book would write it like this: k = a . b . c $ value Now to me they look functionally equivalent, they do the exact same thing in my eyes. However, the more I look, the more I see people writing their functions in the manner that the book does: compose with (.) first and then only at the end use ($) to append a value to evaluate the lot (nobody does it with many dollar compositions). Is there a reason for using the books way that is much better than using all ($) symbols? Or is there some best practice here that I am not getting? Or is it superfluous and I shouldn't be worrying about it at all? Thanks.

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• Sql server management studio reporting "The semaphore timeout period has expired."

  - by nis-simonsen

  On our development sql server, executing any query containing more than approximately 700 characters stalls for about 10 seconds and then reports the following error: Msg 121, Level 20, State 0, Line 0 A transport-level error has occurred when receiving results from the server. (provider: TCP Provider, error: 0 - The semaphore timeout period has expired.) for example, this query select * from FooTable where id = ' (.. and then 700 spaces ..) ' fails fails with the timeout error while this one select * from FooTable where id = ' (.. and then 600 spaces ..) ' fails with the expected Msg 8169, Level 16, State 2, Line 1 Conversion failed when converting from a character string to uniqueidentifier. - immediately. Indeed, throwing any query, including random garbage at our dev sql server exhibits this behaviour, while any other sql server I have available acts as expected, so I would think that the query never actually gets to parsing on the server. I'm at a loss here - any hints?

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• Fastest way to convert file from latin1 to utf-8 in python.

  - by xsaero00

  I need fastest way to convert files from latin1 to utf-8 in python. The files are large ~ 2G. ( I am moving DB data ). So far I have import codecs infile = codecs.open(tmpfile, 'r', encoding='latin1') outfile = codecs.open(tmpfile1, 'w', encoding='utf-8') for line in infile: outfile.write(line) infile.close() outfile.close() but it is still slow. The conversion takes one fourth of the whole migration time. I could also use a linux command line utility if it is faster than native python code.

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• Using an IN clause in Vb.net to save something to the database using SQL

  - by Rob

  I have a textbox and a button on a form. I wish to run a query (in Vb.Net) that will produce a query with the IN Values. Below is an example of my code myConnection = New SqlConnection("Data Source=sqldb\;Initial Catalog=Rec;Integrated Security=True") myConnection.Open() myCommand = New SqlCommand("UPDATE dbo.Recordings SET Status = 0 where RecID in ('" & txtRecID.Text & "') ", myConnection) ra = myCommand.ExecuteNonQuery() myConnection.Close() MsgBox("Done!", _ MsgBoxStyle.Information, "Done") When I enter a single value it works but when I enter values with commas it throws an error: "Conversion failed when converting the varchar value '1234,4567' to data type int." Could someone please help me to solve this or if there is an alternative way? Many Thanks

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• Delegates doesnot work properly

  - by Warrior

  I am new to iphone development.I am covering the date to the desired format and set it to the delegates and get its value in the another view.The session restarts when i tried to get the value from delegates.If i set the original date and not the formatted date in the set delegate ,then i able to get the value in the another view.If i also give any static string value,then also i am able to the static string value back.Only the formatted date which is string is set then the session restarts.If i print and check the value of the formatted date it prints the correct formatted date only.Please help me out.Here is my code for date conversion NSString *dateval=[[stories objectAtIndex: storyIndex] objectForKey:@"date"]; NSDateFormatter *inputFormatter = [[NSDateFormatter alloc] init]; [inputFormatter setDateFormat:@"EEE, MMM dd, yyyy"]; NSDate *inputDate = [inputFormatter dateFromString:dateval]; NSDateFormatter *outputFormatter = [[NSDateFormatter alloc] init]; [outputFormatter setDateFormat:@"MMMM dd"]; NSString *outputDate = [outputFormatter stringFromDate:inputDate]; AppDelegate *delegate=(AppDelegate *)[[UIApplication sharedApplication]delegate]; [delegate setCurrentDates:outputDate]; Thanks.

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• Export MySQL Data as Insert Statements

  - by gav

  Hi All, I'm working in Ubuntu with MySql and I also have Query Browser and Administrator installed, I'm not afraid of the command line either if it helps. I want simply to be able to run a query and see a result set but then convert that result set into a series of commands that could be used to create the same rows in a table of an identical schema. I hope the question makes sense, it's quite a simple problem and one that must have been solved but I can't for the life of me work out where this kind of conversion is made available. Thanks in advance, Gav

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• varchar data type to datetime data type resulted in an out-of-range??

  - by leen3o

  Very weird problem occurred, I have moved a site from one server to another - All is working, but any query involving a date is playing up. I get the following: DELETE FROM MYTABLE WHERE categoryId = -2 AND datecreated < '3/23/2010'; The conversion of a varchar data type to a datetime data type resulted in an out-of-range value Now what's strange is I have changed the LCID to 1033 on the new server as the date is showing as US format and its still throwing an error! I then tried 2057 and again the same error? Made no difference. I'm a little confused, as this is a working site from a server with IIS6 - The locale is 1033 on that server and it works perfectly!! :S I have just tried thrown a Cdate() around the date too and yet again the same error??? Any ideas??

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• Haskell function composition (.) and function application ($) idioms: correct use.

  - by Robert Massaioli

  I have been reading Real World Haskell and I am nearing the end but a matter of style has been niggling at me to do with the (.) and ($) operators. When you write a function that is a composition of other functions you write it like: f = g . h But when you apply something to the end of those functions I write it like this: k = a $ b $ c $ value But the book would write it like this: k = a . b . c $ value Now to me they look functionally equivalent, they do the exact same thing in my eyes. However, the more I look, the more I see people writing their functions in the manner that the book does: compose with (.) first and then only at the end use ($) to append a value to evaluate the lot (nobody does it with many dollar compositions). Is there a reason for using the books way that is much better than using all ($) symbols? Or is there some best practice here that I am not getting? Or is it superfluous and I shouldn't be worrying about it at all? Thanks.

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• floating constants in C

  - by Daziplqa

  Hi floks, I have a question concerning floating constants in C. In Java, the default type of floating point constants in double, so the following will causes a compilation error in java: float f = 100.0; // we either need to uses type case operator or put f at the end of the number constant. This is because the default floating-point constants are of type double and casting from double to float without type cast operator is an error, so we need either add a type case operator or put f at the end of the number. So, Why in C this doesn't produce an error, Is it because the default floating-point constants are of type float, or because the compiler do an implicit down-cast conversion (that doesn't requires type case operator in C)????

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• Fastest way to clamp a real (fixed/floating point) value?

  - by Niklas

  Hi, Is there a more efficient way to clamp real numbers than using if statements or ternary operators? I want to do this both for doubles and for a 32-bit fixpoint implementation (16.16). I'm not asking for code that can handle both cases; they will be handled in separate functions. Obviously, I can do something like: double clampedA; double a = calculate(); clampedA = a > MY_MAX ? MY_MAX : a; clampedA = a < MY_MIN ? MY_MIN : a; or double a = calculate(); double clampedA = a; if(clampedA > MY_MAX) clampedA = MY_MAX; else if(clampedA < MY_MIN) clampedA = MY_MIN; The fixpoint version would use functions/macros for comparisons. This is done in a performance-critical part of the code, so I'm looking for an as efficient way to do it as possible (which I suspect would involve bit-manipulation) EDIT: It has to be standard/portable C, platform-specific functionality is not of any interest here. Also, MY_MIN and MY_MAX are the same type as the value I want clamped (doubles in the examples above).

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• How to extract data from F# list

  - by David White

  Following up my previous question, I'm slowly getting the hang of FParsec (though I do find it particularly hard to grok). My next newbie F# question is, how do I extract data from the list the parser creates? For example, I loaded the sample code from the previous question into a module called Parser.fs, and added a very simple unit test in a separate module (with the appropriate references). I'm using XUnit: open Xunit [<Fact>] let Parse_1_ShouldReturnListContaining1 () = let interim = Parser.parse("1") Assert.False(List.isEmpty(interim)) let head = interim.Head // I realise that I have only one item in the list this time Assert.Equal("1", ???) Interactively, when I execute parse "1" the response is: val it : Element list = [Number "1"] and by tweaking the list of valid operators, I can run parse "1+1" to get: val it : Element list = [Number "1"; Operator "+"; Number "1"] What do I need to put in place of my ??? in the snippet above? And how do I check that it is a Number, rather than an Operator, etc.?

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• Linq-to-XML explicit casting in a generic method

  - by vlad

  I've looked for a similar question, but the only one that was close didn't help me in the end. I have an XML file that looks like this: <Fields> <Field name="abc" value="2011-01-01" /> <Field name="xyz" value="" /> <Field name="tuv" value="123.456" /> </Fields> I'm trying to use Linq-to-XML to get the values from these fields. The values can be of type Decimal, DateTime, String and Int32. I was able to get the fields one by one using a relatively simple query. For example, I'm getting the 'value' from the field with the name 'abc' using the following: private DateTime GetValueFromAttribute(IEnumerable<XElement> fields, String attName) { return (from field in fields where field.Attribute("name").Value == "abc" select (DateTime)field.Attribute("value")).FirstOrDefault() } this is placed in a separate function that simply returns this value, and everything works fine (since I know that there is only one element with the name attribute set to 'abc'). however, since I have to do this for decimals and integers and dates, I was wondering if I can make a generic function that works in all cases. this is where I got stuck. here's what I have so far: private T GetValueFromAttribute<T>(IEnumerable<XElement> fields, String attName) { return (from field in fields where field.Attribute("name").Value == attName select (T)field.Attribute("value").Value).FirstOrDefault(); } this doesn't compile because it doesn't know how to convert from String to T. I tried boxing and unboxing (i.e. select (T) (Object) field.Attribute("value").Value but that throws a runtime Specified cast is not valid exception as it's trying to convert the String to a DateTime, for instance. Is this possible in a generic function? can I put a constraint on the generic function to make it work? or do I have to have separate functions to take advantage of Linq-to-XML's explicit cast operators?

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• What are the effects of using VS2005 to migrate from .NET 1.1

  - by andy

  Hey guys, I'm working on some legacy code for a client, involving Microsoft Content Management System (MCMS). Currently, everything is local, the code, MCMS, SQLServer, and IIS (5.x). I copied the project folder, and then opened the new copied solution in VS2005, and let it do it's conversion thing. But now nothing works. I've nnotice there have been some changes to IIS profile. What are the extent of these changes...?? Also, my VS2003 fails to recognize the Web Project?? Anyone have any idea what's going on? cheers!

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