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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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• Design pattern: polymorphisim for list of objects

  - by ziang

  Suppose I have a class A, and A1, A2 inherits from A. There are 2 functions: List<A1> getListA1(){...} List<A2> getListA2(){...} Now I want to do something similar to both A1 and A2 in another function public void process(List<A>){...} If I want to pass the instance of either ListA1 or ListA2, of course the types doesn't match because the compiler doesn't allow the coercion from List< A1 to List< A. I can't do something like this: List<A1> listA1 = getListA1(); List<A> newList = (List<A>)listA1; //this is not allowed. So what is the best approach to the process()? Is there any way to do it in a universal way rather than write the similar code to both List and List?

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• What could possibly cause this error when declaring an object inside a class?

  - by M4design

  I'm battling with this assignment :) I've got two classes: Ocean and Grid. When I declare an object of the Grid inside the Ocean: unsigned int sharkCount; Grid grid; The compiler/complainer says: error C2146: syntax error : missing ';' before identifier 'grid' Can you possibly predict what produces this error with the limited info I provided? It seems that as if the Ocean doesn't like the Grid class. Could this be because of the poor implementation of the grid class. BTW the Grid has a default constructor. Yet the error happens in compiling time!. EDIT: They're each in separate header file, and I've included the Grid.h in the Ocean.h.

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• C++: Cannot convert from foo& to foo*

  - by Rosarch

  I have a method: odp(foo& bar); I'm trying to call it: foo baz; odp(&baz); I get a compiler error: error C2664: "odp" cannot convert parameter 1 from 'foo *' to 'foo &' What am I doing wrong? Aren't I passing in a reference to baz? UPDATE: Perhaps I have a misconception about the relationship between pointers and references. I thought that they were the same, except references couldn't be null. Is that incorrect?

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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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• Using array of asp inside javascript is not working in the loop

  - by Poomjai

  I have a problem that when i bring the array of asp and use it in the javascript, When i use the counter (i++) and print for each index of array just like "<%=app[i] %" and it is not return the value back to me. Please help me i solve this problem for a day !!!-Thanks ^_^ edit <% String[] asp = {"a","b","c"}; %> <script language="javascript"> for(var i=0;i<"<%=asp %>".length;i++){ document.write("<%=asp[i] %>") } </script> the error is = Compiler Error Message: CS0103: The name 'i' does not exist in the current context

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• How can I make this function act like an l-value?

  - by BeeBand

  Why can't I use the function ColPeekHeight() as an l-value? class View { public: int ColPeekHeight(){ return _colPeekFaceUpHeight; } void ColPeekHeight( int i ) { _colPeekFaceUpHeight = i; } private: int _colPeekFaceUpHeight; }; ... { if( v.ColPeekHeight() > 0.04*_heightTable ) v.ColPeekHeight()-=peek; } The compiler complains at v.ColPeekHeight()-=peek. How can I make ColPeekHeight() an l-value?

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• How to catch any exception (System.Exception) without a warning in F#?

  - by LLS

  I tried to catch an Exception but the compiler gives warning: This type test or downcast will always hold let testFail () = try printfn "Ready for failing..." failwith "Fails" with | :? System.ArgumentException -> () | :? System.Exception -> () The question is: how to I do it without the warning? (I believe there must be a way to do this, otherwise there should be no warning) Like C# try { Console.WriteLine("Ready for failing..."); throw new Exception("Fails"); } catch (Exception) { }

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• Linking Error: undefined reference to `MPI_Init' on Windows 7

  - by fatpipp

  I am using OpenMPI library to write a program to run on Windows 7. I compile and build with C Free 4.0, Mingw. Compiling is Ok but when the compiler links object, errors "undefined reference to ..." occurs. I have set the environment already: I added OpenMPI lib, include and bin folder into C Free Build Directories. I added them into Windows environment variables too. But the error still occurs. Can anyone tell me how to fix it? Thanks a lot.

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• C/C++ usage of special CPU features

  - by b-gen-jack-o-neill

  Hi, I am curious, do new compilers use some extra features built into new CPUs such as MMX SSE,3DNow! and so? I mean, in original 8086 there was even no FPU, so compiler that old cannot even use it, but new compilers can, since FPU is part of every new CPU. So, does new compilers use new features of CPU? Or, it should be more right to ask, does new C/C++ standart library functions use new features? Thanks for answer.

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• Version resource in DLL not visible with right-click

  - by abunetta

  I'm trying to do something which is very easy to do in the regular MSVC, but not supported easily in VC++ Express. There is no resource editor in VC++ Express. So I added a file named version.rc into my DLL project. The file has the below content, which is compiled by the resource compiler and added to the final DLL. This resource is viewable in the DLL using reshacker, though not when right-clicking the DLL in Windows Explorer. What is missing from my RC file to make it appear when right-clicking? VS_VERSION_INFO VERSIONINFO FILEVERSION 1,0,0,1 PRODUCTVERSION 1,0,0,1 FILEFLAGSMASK 0x17L #ifdef _DEBUG FILEFLAGS 0x1L #else FILEFLAGS 0x0L #endif FILEOS 0x4L FILETYPE 0x1L FILESUBTYPE 0x0L BEGIN BLOCK "StringFileInfo" BEGIN BLOCK "040904b0" BEGIN VALUE "FileDescription", "something Application" VALUE "FileVersion", "1, 0, 0, 1" VALUE "InternalName", "something" VALUE "LegalCopyright", "Copyright (C) 2008 Somebody" VALUE "OriginalFilename", "something.exe" VALUE "ProductName", "something Application" VALUE "ProductVersion", "1, 0, 0, 1" END END BLOCK "VarFileInfo" BEGIN VALUE "Translation", 0x409, 1200 END END

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• How does cast in C#/.NET 3.5 work for types with '?'

  - by Inez

  This is my code which works public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : (decimal?) null; } and this one doesn't work public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : null; } giving the compiler error: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'decimal' and '<null>' I wonder why? any ideas?

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• Breakpoint when variable takes on a certain value.

  - by Mick

  I have something analogous to the following code... void function(int x) { // complicated operation on x blah blah } It all appears to be working fine except when x happens to be a particular value, say "273". But x being 273 is a rare event, 99.999% of the time it is some other value. Now I wish to observe the events when this function is called with x=273, so I would like to insert a breakpoint that gets hit only with x is that value. Perhaps I could do it like this: void function(int x) { if (x == 273) { // put breakpoint on this line. } // complicated operation on x blah blah } The problem is that presumably the compiler will optimise away this "if" statement because it doesn't do anything. So my question is what should I put within the "if" statement to to make sure it gets compiled in to something... or should I be tracing the x==273 case in some completely different way.

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• Running ASP.NET MVC 1.0 application

  - by Jack Daniels

  Hello I'm trying to build an app with ASP.NET MVC 1.0. I already have installed MVC 1.0 but after running the application It trows an exception: Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. Compiler Error Message: CS1705: Assembly 'MVC_CustomControls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' uses 'System.Web.Routing, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' which has a higher version than referenced assembly 'System.Web.Routing, Version=0.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' Any help is greatly appreciated.

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• Visual Studio 2008 awful performance

  - by Nima

  Hi, I have ported a piece of C++ code, that works out of core, from Linux(Ubuntu) to Windows(Vista) and I realized that it works about 50times slower on VS2008! I removed all the out of core parts and now I just have a piece of code that has nothing to do with the hard disk. I set compiler parameters to O2 in Project Properties but still get about 10times slower than g++ in linux! Does anybody have an idea why it is this much slower under VS? I really appreciate any kind of hint! Thanks,

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• Casting a container of shared_ptr

  - by Jamie Cook

  Hi all, I have a method void foo(list<shared_ptr<Base>>& myList); Which I'm trying to call with a two different types of lists, one of DerivedClass1 and one of DerivedClass2 list<shared_ptr<DerivedClass1>> myList1; foo(myList1); list<shared_ptr<DerivedClass2>> myList2; foo(myList2); However this obviously generates a compiler error error: a reference of type "std::list<boost::shared_ptr<Base>, std::allocator<boost::shared_ptr<Base>>> &" (not const-qualified) cannot be initialized with a value of type "std::list<boost::shared_ptr<DerivedClass1>, std::allocator<boost::shared_ptr<DerivedClass1>>>" Is there any easy way to cast a container of shared_ptr? Of alternate containers that can accomplish this?

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• Is there a good collection library for C-language?

  - by matti

  We have to maintain and even develop C-code of our legacy system. Is there good collection library that would support Java/C# (new versions) style collections. Hashtable, HashSet, etc. Of course without objects, but with structs. The HashTable key limitations to "strings" and ints is not a problem. It wouldn't be bad if it's free even for commercial use. I'm back to C from C# and I must say i'm depressed using our own libraries and the language in general. We're using VS2005 and MS C-compiler if that has nothing to do with anything. Thanks & BR -Matti

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• Why "constructor-way" of declaring variable in "for-loop" allowed but in "if-statement" not allowed?

  - by PiotrNycz

  Consider this simple example: /*1*/ int main() { /*2*/ for (int i(7); i;){break;} /*3*/ if (int i(7)) {} /*4*/ } Why line-2 compiles just fine, whilst line-3 gives the error? This is little strange to me why if-statement is in this aspect treated worse than for-loop? If this is compiler specific - I tested with gcc-4.5.1: prog.cpp: In function 'int main()': prog.cpp:3:7: error: expected primary-expression before 'int' prog.cpp:3:7: error: expected ')' before 'int' I was inspired by this question [UPDATE] I know this compiles just fine: /*1*/ int main() { /*2*/ for (int i = 7; i;){break;} /*3*/ if (int i = 7) {} /*4*/ }

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• In C#: How to declare a generic Dictionary with a type as key and an enumeration of that type as val

  - by Marcel

  Hi all, I want to declare a dictionary that stores typed IEnumerable's of a specific type, with that exact type as key, like so: (Edited to follow johny g's comment) private IDictionary<Type, IEnumerable<T>> _dataOfType where T: BaseClass; //does not compile! The concrete classes I want to store, all derive from BaseClass, therefore the idea to use it as constraint. The compiler complains that it expects a semicolon after the member name. If it would work, I would expect this would make the later retrieval from the dictionary simple like: IEnumerable<ConcreteData> concreteData; _sitesOfType.TryGetValue(typeof(ConcreteType), out concreteData); How to define such a dictionary?

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• hiding inner class implementation using namespace

  - by Abruzzo Forte e Gentile

  Hi all I am developing a library and a would like to provide my users a public interface separate from the real implementatino that is hidden in a namespace. This way, I could change only the class HiddenQueue without changing myQueue that will be exposed to users only. If I put the C++ code of HiddenQueue in the myQueue.cpp file the compiler complains saying _innerQueue has incomplete type. I thought that the linker was able to resolve this. What I am doing wrong here? Thanks Afg // myQueue.h namespace inner{ class HiddenQueue; }; class myQueue{ public: myQueue(); ); private: inner::HiddenQueue _innerQueue; }; /////////////////////////// // myQueue.cpp namespace inner{ class HiddenQueue{}; };

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• How does windows differentiate between regular exe and a .Net exe?

  - by Yogendra

  Hi All, This might be a duplicate entry. Excuse me if it is. I was asked in an interview as to how does Windows OS differentiate between regular exe and .Net exe. My reply was, when .Net exe is build, the compiler emits some information into the header. The information is PE32 or PE32+. windows verifies the header to determine if it needs to load the MSCOREE.dll which loads the CLR and executes the exe. I am not sure if my answer is correct ? Your inputs is appreciated.

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• Connect to a website via HTTP in C

  - by sfactor

  i have a C code that parses a file and generates another file for the processed data. i now need to send these files to a web server (website). i guess there way is to do a HTTP POST. but i have never done this in c (Linux gcc compiler in ubuntu). Does anyone know how to do this. i need to a starting point as i have no clue of doing this in C. i also need to be able to authenticate with the website.

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• C++ app fails to initialize (0xc0000005), when using C# dll

  - by Simon

  Hi, I have a C# DLL, which I call from a native C++ programm. As I use Qt and /clr compiler option did not work I followed this tutorial for a bridge. So I have a VS2008 project (compiled with /clr), which links to the C# DLL and contains the bridge class and the native class, which exposes interfaces to my C++ programm. Another VS2008 project (no .net stuff) calls the native class (statically linked). I had some issues, but now the programm at least compiles. However, if I try to run this programm, I get a (0xc0000005) error on initialization, when I try to use the native class. As this happens on initialization, I don't even see, which DLLs fail to initialize. All DLLs should be in the right place. Any hints? Thank you.

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• How do you make your Java application memory efficient?

  - by Boune

  How do you optimize the heap size usage of an application that has a lot (millions) of long-lived objects? (big cache, loading lots of records from a db) Use the right data type Avoid java.lang.String to represent other data types Avoid duplicated objects Use enums if the values are known in advance Use object pools String.intern() (good idea?) Load/keep only the objects you need I am looking for general programming or Java specific answers. No funky compiler switch. Edit: Optimize the memory representation of a POJO that can appear millions of times in the heap. Use cases Load a huge csv file in memory (converted into POJOs) Use hibernate to retrieve million of records from a database Resume of answers: Use flyweight pattern Copy on write Instead of loading 10M objects with 3 properties, is it more efficient to have 3 arrays (or other data structure) of size 10M? (Could be a pain to manipulate data but if you are really short on memory...)

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• Option Value Changed - ODBC Error 2169

  - by fredrick-ughimi

  Hello Edgar, Thank you for your response. I am using Powerbasic (www.powerbasic.com) as my compiler and SQLTools as a third party tool to access ADS through ODBC. I must stat that this error also appers when I take other actions like Update, Delete, Find, etc. But I don't get this error when I am using MS Access. Here is my save routine: [Code] Local sUsername As String Local sPassword As String Local sStatus As String Local sSQLStatement1 As String sUsername = VD_GetText (nCbHndl, %ID_FRMUPDATEUSERS_TXTUSERNAME) If Trim$(sUsername) = "" Then MsgBox "Please, enter Username", %MB_ICONINFORMATION Or %MB_TASKMODAL, VD_App.Title Control Set Focus nCbHndl, %ID_FRMUPDATEUSERS_TXTUSERNAME Exit Function End If sPassword = VD_GetText (nCbHndl, %ID_FRMUPDATEUSERS_TXTPASSWORD) If Trim$(sPassword) = "" Then MsgBox "Please, enter Password", %MB_ICONINFORMATION Or %MB_TASKMODAL, VD_App.Title Control Set Focus nCbHndl, %ID_FRMUPDATEUSERS_TXTPASSWORD Exit Function End If sStatus = VD_GetText (nCbHndl, %ID_FRMUPDATEUSERS_CBOSTATUS) sSQLStatement1 = "INSERT INTO [tblUsers] (Username, Password, Status) " + _ "VALUES ('" + sUsername + "','" + sPassword + "','" + sStatus +"')" 'Submit the SQL Statement to the database SQL_Stmt %SQL_STMT_IMMEDIATE, sSQLStatement1 'Check for errors If SQL_ErrorPending Then SQL_MsgBox SQL_ErrorQuickAll, %MSGBOX_OK End If [/code] Best regards,

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