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• Please take a stab at this VB.Net Oracle-related sample and help me with String.Format.

  - by Hamish Grubijan

  If the database is not Oracle, it is MS SQl 2008. My task: if Oracle, add two more parameters when calling a stored proc. Oracle and MSFT stored procs are generated; Oracle ones have 3 extra parameters: Vret_val out number, Vparam2 in out number, Vparam3 in out number, ... the rest (The are not actually named Vparam2 and Vparam3, but this should not matter). So, the code for a helper VB.Net class that calls a stored proc: Imports System.Data.Odbc Imports System.Configuration Dim objCon As OdbcConnection = Nothing Dim objAdapter As OdbcDataAdapter Dim cmdCommand As New OdbcCommand Dim objDataTable As DataTable Dim sconnection As String Try sconnection = mConnectionString objAdapter = New OdbcDataAdapter objCon = New OdbcConnection(sconnection) objCon.Open() objAdapter.SelectCommand = cmdCommand objAdapter.SelectCommand.Connection = objCon objAdapter.SelectCommand.CommandType = CommandType.StoredProcedure objAdapter.SelectCommand.CommandTimeout = Globals.mReportTimeOut If Not mIsOracle Then objAdapter.SelectCommand.CommandText = String.Format("{{call {0}}}", spName) Else Dim returnValue As New OdbcParameter returnValue.Direction = ParameterDirection.Output returnValue.ParameterName = "@Vret_val" returnValue.OdbcType = OdbcType.Numeric objAdapter.SelectCommand.Parameters.Add(returnValue) objAdapter.SelectCommand.CommandText = String.Format("{{call {0}(?)}}", spName) End If Try objDataTable = New DataTable(spName) objAdapter.Fill(objDataTable) Catch ex As Exception ... Question: I am puzzled as to what String.Format("{{call {0}(?)}}", spName) does, in particular the (?) part. My understanding of the String.Format is that it will simply replace {0} with spName. The {{, }}, and (?) do throw me off because { reminds me of formatting, (?) hints at some advanced regex use. Unfortunately I am getting little help from a key person who is on vacation without a leash [smart]phone. I am guessing that I simply add 5 more lines for each additional parameter, and change String.Format("{{call {0}(?)}}", spName) to String.Format("{{call {0}(?,?,?)}}", spName). I forgot to mention that I am coding this "blindly" - I have a compiler to help me, but no environment set up to test this. This will be over in a few days, but I need to do my best to try finishing it on time :) Thanks.

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• Why are virtual methods considered early bound?

  - by AspOnMyNet

  One definition of binding is that it is the act of replacing function names with memory addresses. a) Thus I assume early binding means function calls are replaced with memory addresses during compilation process, while with late binding this replacement happens during runtime? b) Why are virtual methods also considered early bound (thus the target method is found at compile time, and code is created that will call this method)? As far as I know, with virtual methods the call to actual method is resolved only during runtime and not compile time?! thanx EDIT: 1) A a=new A(); a.M(); As far as I know, it is not known at compile time where on the heap (thus at which memory address ) will instance a be created during runtime. Now, with early binding the function calls are replaced with memory addresses during compilation process. But how can compiler replace function call with memory address, if it doesn’t know where on the heap will object a be created during runtime ( here I’m assuming the address of method a.M will also be at same memory location as a )? 2) v-table calls are neither early nor late bound. Instead there's an offset into a table of function pointers. The offset is fixed at compile time, but which table the function pointer is chosen from depends on the runtime type of the object (the object contains a hidden pointer to its v-table), so the final function address is found at runtime. But assuming the object of type T is created via reflection ( thus app doesn’t even know of existence of type T ), then how can at compile time exist an entry point for that type of object?

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• Closures and universal quantification

  - by Apocalisp

  I've been trying to work out how to implement Church-encoded data types in Scala. It seems that it requires rank-n types since you would need a first-class const function of type forAll a. a -> (forAll b. b -> b). However, I was able to encode pairs thusly: import scalaz._ trait Compose[F[_],G[_]] { type Apply = F[G[A]] } trait Closure[F[_],G[_]] { def apply[B](f: F[B]): G[B] } def pair[A,B](a: A, b: B) = new Closure[Compose[PartialApply1Of2[Function1,A]#Apply, PartialApply1Of2[Function1,B]#Apply]#Apply, Identity] { def apply[C](f: A => B => C) = f(a)(b) } For lists, I was able to get encode cons: def cons[A](x: A) = { type T[B] = B => (A => B => B) => B new Closure[T,T] { def apply[B](xs: T[B]) = (b: B) => (f: A => B => B) => f(x)(xs(b)(f)) } } However, the empty list is more problematic and I've not been able to get the Scala compiler to unify the types. Can you define nil, so that, given the definition above, the following compiles? cons(1)(cons(2)(cons(3)(nil)))

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• Generated LinqtoSql Sql 5x slower than SAME EXACT hand-written sql

  - by JasonM

  I have a sql statement which is hardcoded in an existing VB6 app. I'm upgrading a new version in C# and using Linq To Sql. I was able to get LinqToSql to generate the same sql (before I start refactoring), but for some reason the Sql generated by LinqToSql is 5x slower than the original sql. This is running the generated Sql Directly in LinqPad. The only real difference my meager sql eyes can spot is the WITH (NOLOCK), which if I add into the LinqToSql generated sql, makes no difference. Can someone point out what I'm doing wrong here? Thanks! Existing Hard Coded Sql (5.0 Seconds) SELECT DISTINCT CH.ClaimNum, CH.AcnProvID, CH.AcnPatID, CH.TinNum, CH.Diag1, CH.GroupNum, CH.AllowedTotal FROM Claims.dbo.T_ClaimsHeader AS CH WITH (NOLOCK) WHERE CH.ContractID IN ('123A','123B','123C','123D','123E','123F','123G','123H') AND ( ( (CH.Transmited Is Null or CH.Transmited = '') AND CH.DateTransmit Is Null AND CH.EobDate Is Null AND CH.ProcessFlag IN ('Y','E') AND CH.DataSource NOT IN ('A','EC','EU') AND CH.AllowedTotal > 0 ) ) ORDER BY CH.AcnPatID, CH.ClaimNum Generated Sql from LinqToSql (27.6 Seconds) -- Region Parameters DECLARE @p0 NVarChar(4) SET @p0 = '123A' DECLARE @p1 NVarChar(4) SET @p1 = '123B' DECLARE @p2 NVarChar(4) SET @p2 = '123C' DECLARE @p3 NVarChar(4) SET @p3 = '123D' DECLARE @p4 NVarChar(4) SET @p4 = '123E' DECLARE @p5 NVarChar(4) SET @p5 = '123F' DECLARE @p6 NVarChar(4) SET @p6 = '123G' DECLARE @p7 NVarChar(4) SET @p7 = '123H' DECLARE @p8 VarChar(1) SET @p8 = '' DECLARE @p9 NVarChar(1) SET @p9 = 'Y' DECLARE @p10 NVarChar(1) SET @p10 = 'E' DECLARE @p11 NVarChar(1) SET @p11 = 'A' DECLARE @p12 NVarChar(2) SET @p12 = 'EC' DECLARE @p13 NVarChar(2) SET @p13 = 'EU' DECLARE @p14 Decimal(5,4) SET @p14 = 0 -- EndRegion SELECT DISTINCT [t0].[ClaimNum], [t0].[acnprovid] AS [AcnProvID], [t0].[acnpatid] AS [AcnPatID], [t0].[tinnum] AS [TinNum], [t0].[diag1] AS [Diag1], [t0].[GroupNum], [t0].[allowedtotal] AS [AllowedTotal] FROM [Claims].[dbo].[T_ClaimsHeader] AS [t0] WHERE ([t0].[contractid] IN (@p0, @p1, @p2, @p3, @p4, @p5, @p6, @p7)) AND (([t0].[Transmited] IS NULL) OR ([t0].[Transmited] = @p8)) AND ([t0].[DATETRANSMIT] IS NULL) AND ([t0].[EOBDATE] IS NULL) AND ([t0].[PROCESSFLAG] IN (@p9, @p10)) AND (NOT ([t0].[DataSource] IN (@p11, @p12, @p13))) AND ([t0].[allowedtotal] > @p14) ORDER BY [t0].[acnpatid], [t0].[ClaimNum] New LinqToSql Code (30+ seconds... Times out ) var contractIds = T_ContractDatas.Where(x => x.EdiSubmissionGroupID == "123-01").Select(x => x.CONTRACTID).ToList(); var processFlags = new List<string> {"Y","E"}; var dataSource = new List<string> {"A","EC","EU"}; var results = (from claims in T_ClaimsHeaders where contractIds.Contains(claims.contractid) && (claims.Transmited == null || claims.Transmited == string.Empty ) && claims.DATETRANSMIT == null && claims.EOBDATE == null && processFlags.Contains(claims.PROCESSFLAG) && !dataSource.Contains(claims.DataSource) && claims.allowedtotal > 0 select new { ClaimNum = claims.ClaimNum, AcnProvID = claims.acnprovid, AcnPatID = claims.acnpatid, TinNum = claims.tinnum, Diag1 = claims.diag1, GroupNum = claims.GroupNum, AllowedTotal = claims.allowedtotal }).OrderBy(x => x.ClaimNum).OrderBy(x => x.AcnPatID).Distinct(); I'm using the list of constants above to make LinqToSql Generate IN ('xxx','xxx',etc) Otherwise it uses subqueries which are just as slow...

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• ASP.NET web setup class is not defined

  - by Wayne Werner

  Hi, I've got an ASP.NET application that I installed by creating a web setup. I ran into a problem where ASP.NET wasn't registered with IIS so it gave me a "installation was interrupted" message that told me exactly nothing. Anyhow, I finally got it installed, and I can access the main page, but it's telling me that my class isn't defined. The dll is in the same directory as the Default.aspx page Here's the main error information Compiler Error Message: BC30002: Type 'SIValidator.SIValidator' is not defined. Source Error: Line 4: Line 5: <script runat="server"> Line 6: Dim validator As New SIValidator.SIValidator() Line 7: Protected table As New arrayList() Line 8: Protected countyByDistrict As New Hashtable() Version Information: Microsoft .NET Framework Version:2.0.50727.1873; ASP.NET Version:2.0.50727.1433 Am I doing it wrong? Is there some obscure setting that may not be set? I'm completely new to this VS deployment deal, so I'm trying to learn the right terms to ask the right questions... Thanks for any help edit: As an aside, when I searched google 5 minutes later, this entry came up as the first result. Would have been awesome if there was an answer for me then :P

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• Function parameters evaluation order: is undefined behaviour if we pass reference?

  - by bolov

  This is undefined behaviour: void feedMeValue(int x, int a) { cout << x << " " << a << endl; } int main() { int a = 2; int &ra = a; feedMeValue(ra = 3, a); return 0; } because depending on what parameter gets evaluated first we could call (3, 2) or (3, 3). However this: void feedMeReference(int x, int const &ref) { cout << x << " " << ref << endl; } int main() { int a = 2; int &ra = a; feedMeReference(ra = 3, a); return 0; } will always output 3 3 since the second parameter is a reference and all parameters have been evaluated before the function call, so even if the second parameter is evaluated before of after ra = 3, the function received a reference to a wich will have a value of 2 or 3 at the time of the evaluation, but will always have the value 3 at the time of the function call. Is the second example UB? It is important to know because the compiler is free to do anything if he detects undefined behaviour, even if I know it would always yield the same results. *Note: I think that feedMeReference(a = 3, a) is the exact same situation as feedMeReference(ra = 3, a). However it seems not everybody agrees, in the addition to having 2 completely different answers.

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• Compiling Objective-C project on Linux (Ubuntu)

  - by Alex

  How to make an Objective-C project work on Ubuntu? My files are: Fraction.h #import <Foundation/NSObject.h> @interface Fraction: NSObject { int numerator; int denominator; } -(void) print; -(void) setNumerator: (int) n; -(void) setDenominator: (int) d; -(int) numerator; -(int) denominator; @end Fraction.m #import "Fraction.h" #import <stdio.h> @implementation Fraction -(void) print { printf( "%i/%i", numerator, denominator ); } -(void) setNumerator: (int) n { numerator = n; } -(void) setDenominator: (int) d { denominator = d; } -(int) denominator { return denominator; } -(int) numerator { return numerator; } @end main.m #import <stdio.h> #import "Fraction.h" int main( int argc, const char *argv[] ) { // create a new instance Fraction *frac = [[Fraction alloc] init]; // set the values [frac setNumerator: 1]; [frac setDenominator: 3]; // print it printf( "The fraction is: " ); [frac print]; printf( "\n" ); // free memory [frac release]; return 0; } I've tried two approaches to compile it: Pure gcc: $ sudo apt-get install gobjc gnustep gnustep-devel $ gcc `gnustep-config --objc-flags` -o main main.m -lobjc -lgnustep-base /tmp/ccIQKhfH.o:(.data.rel+0x0): undefined reference to `__objc_class_name_Fraction' I created a GNUmakefile Makefile: include ${GNUSTEP_MAKEFILES}/common.make TOOL_NAME = main main_OBJC_FILES = main.m include ${GNUSTEP_MAKEFILES}/tool.make ... and ran: $ source /usr/share/GNUstep/Makefiles/GNUstep.sh $ make Making all for tool main... Linking tool main ... ./obj/main.o:(.data.rel+0x0): undefined reference to `__objc_class_name_Fraction' So in both cases compiler gets stuck at undefined reference to `__objc_class_name_Fraction' Do you have and idea how to resolve this issue?

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• Constructor or Assignment Operator

  - by ju

  Can you help me is there definition in C++ standard that describes which one will be called constructor or assignment operator in this case: #include <iostream> using namespace std; class CTest { public: CTest() : m_nTest(0) { cout << "Default constructor" << endl; } CTest(int a) : m_nTest(a) { cout << "Int constructor" << endl; } CTest(const CTest& obj) { m_nTest = obj.m_nTest; cout << "Copy constructor" << endl; } CTest& operatorint rhs) { m_nTest = rhs; cout << "Assignment" << endl; return *this; } protected: int m_nTest; }; int _tmain(int argc, _TCHAR* argv[]) { CTest b = 5; return 0; } Or is it just a matter of compiler optimization?

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• Why do case class companion objects extend FunctionN?

  - by retronym

  When you create a case class, the compiler creates a corresponding companion object with a few of the case class goodies: an apply factory method matching the primary constructor, equals, hashCode, and copy. Somewhat oddly, this generated object extends FunctionN. scala> case class A(a: Int) defined class A scala> A: (Int => A) res0: (Int) => A = <function1> This is only the case if: There is no manually defined companion object There is exactly one parameter list There are no type arguments The case class isn't abstract. Seems like this was added about two years ago. The latest incarnation is here. Does anyone use this, or know why it was added? It increases the size of the generated bytecode a little with static forwarder methods, and shows up in the #toString() method of the companion objects: scala> case class A() defined class A scala> A.toString res12: java.lang.String = <function0>

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• Is it possible to declare multiple static variable with same name in a single C file?

  - by Mohammed Khalid Kherani

  Hi Experts, Is it possible to declare multiple static variables of same name in a single C file with different scopes? I wrote a simple programme to check this and in gcc it got compiled and worked fine. code: static int sVar = 44; void myPrint2() { printf("sVar = %d\n", sVar++); } void myPrint() { static int sVar =88; printf("sVar = %d\n", sVar++); } int main(void) { static int sVar = 55; int i = 0; for (i = 0; i < 5; i++) myPrint(); printf("sVar = %d\n", sVar); myPrint2(); return(0); } Now my question is since all "static" variable will reside in same section (.data) then how we can have multiple variable with same name in one section? I used objdump to check the different section and found that all Static variables (sVar) were in .data section but with different names 0804960c l O .data 00000004 sVar 08049610 l O .data 00000004 sVar.1785 08049614 l O .data 00000004 sVar.1792 Why compiler is changing the name of variables (since C doesnt support name mangling)? Thanks in advance.

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• c++ callback syntax in a class

  - by Mr Bell

  I am trying to figure out the syntax to register a callback with this 3rd party software. I think it is probably a basic question, I just am not too familiar with c++. They have a method for registering a callback function so their code can call a function in my code when an event happens. They provided a working example that registers the callback from the main file, but I want to know how to do it when working inside a class Their method signature: smHTRegisterHeadPoseCallback(smEngineHandle engine_handle, void *user_data, smHTHeadPoseCallback callback_fun); Working example from the main file: void STDCALL receiveHeadPose(void *,smEngineHeadPoseData head_pose, smCameraVideoFrame video_frame) { ... } void main() { ... smHTRegisterHeadPoseCallback(engine_handle,0,receiveHeadPose) ... } But I want to use this from my class MyClass.h class FaceEngine { public: void STDCALL receiveFaceData(void *, smEngineFaceData face_data, smCameraVideoFrame video_frame); ... MyClass.cpp void FaceEngine::Start(void) { rc = smHTRegisterFaceDataCallback(hFaceAPIEngine,0,&FaceEngine::receiveFaceData); ... Results in this compiler error: Error 1 error C2664: 'smHTRegisterFaceDataCallback' : cannot convert parameter 3 from 'void (__stdcall FaceEngine::* )(void *,smEngineFaceData,smCameraVideoFrame)' to 'smHTFaceDataCallback' d:\stuff\programming\visual studio 2008\projects\tut02_vertices\faceengine.cpp 43 Beard If my question isn't clear please let me know how I can clarify.

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• How to access hidden template in unnamed namespace?

  - by Johannes Schaub - litb

  Here is a tricky situation, and i wonder what ways there are to solve it namespace { template <class T> struct Template { /* ... */ }; } typedef Template<int> Template; Sadly, the Template typedef interferes with the Template template in the unnamed namespace. When you try to do Template<float> in the global scope, the compiler raises an ambiguity error between the template name and the typedef name. You don't have control over either the template name or the typedef-name. Now I want to know whether it is possible to: Create an object of the typedefed type Template (i.e Template<int>) in the global namespace. Create an object of the type Template<float> in the global namespace. You are not allowed to add anything to the unnamed namespace. Everything should be done in the global namespace. This is out of curiosity because i was wondering what tricks there are for solving such an ambiguity. It's not a practical problem i hit during daily programming.

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• C++0x rvalue references and temporaries

  - by Doug

  (I asked a variation of this question on comp.std.c++ but didn't get an answer.) Why does the call to f(arg) in this code call the const ref overload of f? void f(const std::string &); //less efficient void f(std::string &&); //more efficient void g(const char * arg) { f(arg); } My intuition says that the f(string &&) overload should be chosen, because arg needs to be converted to a temporary no matter what, and the temporary matches the rvalue reference better than the lvalue reference. This is not what happens in GCC and MSVC. In at least G++ and MSVC, any lvalue does not bind to an rvalue reference argument, even if there is an intermediate temporary created. Indeed, if the const ref overload isn't present, the compilers diagnose an error. However, writing f(arg + 0) or f(std::string(arg)) does choose the rvalue reference overload as you would expect. From my reading of the C++0x standard, it seems like the implicit conversion of a const char * to a string should be considered when considering if f(string &&) is viable, just as when passing a const lvalue ref arguments. Section 13.3 (overload resolution) doesn't differentiate between rvalue refs and const references in too many places. Also, it seems that the rule that prevents lvalues from binding to rvalue references (13.3.3.1.4/3) shouldn't apply if there's an intermediate temporary - after all, it's perfectly safe to move from the temporary. Is this: Me misreading/misunderstand the standard, where the implemented behavior is the intended behavior, and there's some good reason why my example should behave the way it does? A mistake that the compiler vendors have somehow all made? Or a mistake based on common implementation strategies? Or a mistake in e.g. GCC (where this lvalue/rvalue reference binding rule was first implemented), that was copied by other vendors? A defect in the standard, or an unintended consequence, or something that should be clarified?

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• C Nested Structure Pointer Problem

  - by Halo

  I have a shared structure, and inside it a request structure: struct shared_data { pthread_mutex_t th_mutex_queue; struct request_queue { int min; int max; char d_name[DIR_SIZE]; pid_t pid; int t_index; } request_queue[BUFSIZE]; int count; int data_buffer_allocation[BUFSIZE]; int data_buffers[BUFSIZE][100]; }; Then I prepare a request; struct shared_data *sdata_ptr; ... ... sdata_ptr->request_queue[index].pid = pid; strcpy(sdata_ptr->request_queue[index].d_name, dir_path_name); sdata_ptr->request_queue[index].min = min; sdata_ptr->request_queue[index].max = max; And the compiler warns me that I'm doing an incompatible implicit declaration in the strcpy function. I guess that's a problem with the pointers, but isn't what I wrote above supposed to be true?

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• Should i enforce realloc check if the new block size is smaller than the initial ?

  - by nomemory

  Can realloc fail in this case ? int *a = NULL; a = calloc(100, sizeof(*a)); printf("1.ptr: %d \n", a); a = realloc(a, 50 * sizeof(*a)); printf("2.ptr: %d \n", a); if(a == NULL){ printf("Is it possible?"); } return (0); } The output in my case is: 1.ptr: 4072560 2.ptr: 4072560 So 'a' points to the same adress. So should i enforce realloc check ? Later edit: Using MinGW compiler under Windows XP. Is the behaviour similar with gcc on Linux ? Later edit 2: Is it OK to check this way ? int *a = NULL, *b = NULL; a = calloc(100, sizeof(*a)); b = realloc(a, 50 * sizeof(*a)); if(b == NULL){ return a; } a = b; return a;

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• Is there any reason to use C instead of C++ for embedded development?

  - by Piotr Czapla

  Question I have two compilers on my hardware C++ and C89 I'm thinking about using C++ with classes but without polymorphism (to avoid vtables). The main reasons I’d like to use C++ are: I prefer to use “inline” functions instead of macro definitions. I’d like to use namespaces as I prefixes clutter the code. I see C++ a bit type safer mainly because of templates, and verbose casting. I really like overloaded functions and constructors (used for automatic casting). Do you see any reason to stick with C89 when developing for very limited hardware (4kb of RAM)? Conclusion Thank you for your answers, they were really helpful! I though the subject through and I will stick with C mainly because: It is easier to predict actual code in C and this is really important if you have only 4kb of ram. My team consists of C developers mainly so advance features of C++ won't be frequently used. I've found a way to inline functions in my C compiler (C89). It is hard to accept one answer as you provided so many good answers. Unfortunately I can't create a wiki and accept it so I will choose one answer that made me think most.

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• gcc compilation without using system defined header locations

  - by bogertron

  I am attempting to compile a c++ class using gcc. Due to the nature of the build, I need to invoke gcc from a non-standard location and include non-system defined headers, only to add a set from a different location. However, when I do this, I run into an issue where I cannot find some base symbols (suprise suprise). So i am basically running this command to compile my code: -->(PARENT_DIR)/usr/bin/gcc # invoke compiler -B$(PARENT_DIR)/usr/lib64/gcc/suselinux-x8664 -B$(PARENT_DIR)/usr/lib64 #C/C++ flags -fPIC -fvisibility=default -g -c -Wall -m64 -nostdinc # source files -I$(SRC_DIR_ONE)/ -I$(SRC_DIR_TWO) -I../include # 'Mock' include the system header files -I$(PARENT_DIR)/usr/include/c++/$(GCC_VERSION) -I$(PARENT_DIR)/usr/include/c++/$(GCC_VERSION)/backward -I$(PARENT_DIR)/usr/include/c++/$(GCC_VERSION)/x86_64-suse-linux -I$(PARENT_DIR)/usr/lib64/x86_64-suse-linux/$(GCC_VERSION)/include -I$(PARENT_DIR)/usr/lib64/gcc/x86_64-suse-linux/$(GCC_VERSION)/include -I$(PARENT_DIR)/usr/lib64/gcc/x86_64-suse-linux/$(GCC_VERSION)/include-fixed -I$(PARENT_DIR)/usr/src/linux/include -I$(PARENT_DIR)/usr/x86_64-suse-linux/include -I$(PARENT_DIR)/usr/include/suselinux-x8664 -I$(PARENT_DIR)/usr/suselinux-x8664/include -I$(PARENT_DIR)/usr/include -I$(PARENT_DIR)/usr/include/linux file.cpp I am getting several errors which indicate that the base headers are not being included: such as: $(PARENT_DIR)/usr/include/c++/$(GCC_VERSION)/cstddef ::prtdiff_t has not been declared $(PARENT_DIR)/usr/include/c++/$(GCC_VERSION)/cstddef ::size_t has not bee declared. Is there something that I am doing wrong when I include the header file directories? Or am I looking in the wrong place?

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• Case class copy() method abstraction.

  - by Joa Ebert

  I would like to know if it is possible to abstract the copy method of case classes. Basically I have something like sealed trait Op and then something like case class Push(value: Int) extends Op and case class Pop() extends Op. The first problem: A case class without arguments/members does not define a copy method. You can try this in the REPL. scala> case class Foo() defined class Foo scala> Foo().copy() <console>:8: error: value copy is not a member of Foo Foo().copy() ^ scala> case class Foo(x: Int) defined class Foo scala> Foo(0).copy() res1: Foo = Foo(0) Is there a reason why the compiler makes this exception? I think it is rather unituitive and I would expect every case class to define a copy method. The second problem: I have a method def ops: List[Op] and I would like to copy all ops like ops map { _.copy() }. How would I define the copy method in the Op trait? I get a "too many arguments" error if I say def copy(): this.type. However, since all copy() methods have only optional arguments: why is this incorrect? And, how do I do that correct? By making another method named def clone(): this.type and write everywhere def clone() = copy() for all the case classes? I hope not.

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• How can I marshal JSON to/from a POJO for BlackBerry Java?

  - by sowbug

  I'm writing a RIM BlackBerry client app. BlackBerry uses a simplified version of Java (no generics, no annotations, limited collections support, etc.; roughly a Java 1.3 dialect). My client will be speaking JSON to a server. We have a bunch of JAXB-generated POJOs, but they're heavily annotated, and they use various classes that aren't available on this platform (ArrayList, BigDecimal, XMLGregorianCalendar). We also have the XSD used by the JAXB-XJC compiler to generate those source files. Being the lazy programmer that I am, I'd really rather not manually translate the existing source files to Java 1.3-compatible JSON-marshalling classes. I already tried JAXB 1.0.6 xjc. Unfortunately, it doesn't understand the XSD file well enough to emit proper classes. Do you know of a tool that will take JAXB 2.0 XSD files and emit Java 1.3 classes? And do you know of a JSON marshalling library that works with old Java? I think I am doomed because JSON arrived around 2006, and Java 5 was released in late 2004, meaning that people probably wouldn't be writing JSON-parsing code for old versions of Java. However, it seems that there must be good JSON libraries for J2ME, which is why I'm holding out hope.

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• C# - Referencing a type in a dynamically generated assembly

  - by Ashley

  I'm trying to figure out if it's possible when you are dynamically generating assemblies, to reference a type in a previously dynamically generated assembly. For example: using System; using System.CodeDom.Compiler; using System.Reflection; using Microsoft.CSharp; CodeDomProvider provider = new CSharpCodeProvider(); CompilerParameters parameters = new CompilerParameters(); parameters.GenerateInMemory = true; CompilerResults results = provider.CompileAssemblyFromSource(parameters, @" namespace Dynamic { public class A { } } "); Assembly assem = results.CompiledAssembly; CodeDomProvider provider2 = new CSharpCodeProvider(); CompilerParameters parameters2 = new CompilerParameters(); parameters2.ReferencedAssemblies.Add(assem.FullName); parameters2.GenerateInMemory = true; CompilerResults results2 = provider2.CompileAssemblyFromSource(parameters, @" namespace Dynamic { public class B : A { } } "); if (results2.Errors.HasErrors) { foreach (CompilerError error in results2.Errors) { Console.WriteLine(error.ErrorText); } } else { Assembly assem2 = results2.CompiledAssembly; } This code prints the following on the console: The type or namespace name 'A' could not be found (are you missing a using directive or an assembly reference?) I've tried it lots of different ways, but nothing seems to be working. Am I missing something? Is this even possible?

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• Dynamic stack allocation in C++

  - by Poni

  I want to allocate memory on the stack. Heard of _alloca / alloca and I understand that these are compiler-specific stuff, which I don't like. So, I came-up with my own solution (which might have it's own flaws) and I want you to review/improve it so for once and for all we'll have this code working: /*#define allocate_on_stack(pointer, size) \ __asm \ { \ mov [pointer], esp; \ sub esp, [size]; \ }*/ /*#define deallocate_from_stack(size) \ __asm \ { \ add esp, [size]; \ }*/ void test() { int buff_size = 4 * 2; char *buff = 0; __asm { // allocate mov [buff], esp; sub esp, [buff_size]; } // playing with the stack-allocated memory for(int i = 0; i < buff_size; i++) buff[i] = 0x11; __asm { // deallocate add esp, [buff_size]; } } void main() { __asm int 3h; test(); } Compiled with VC9. What flaws do you see in it? Me for example, not sure that subtracting from ESP is the solution for "any kind of CPU". Also, I'd like to make the commented-out macros work but for some reason I can't.

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• C89, Mixing Variable Declarations and Code

  - by rutski

  I'm very curious to know why exactly C89 compilers will dump on you when you try to mix variable declarations and code, like this for example: rutski@imac:~$ cat test.c #include <stdio.h> int main(void) { printf("Hello World!\n"); int x = 7; printf("%d!\n", x); return 0; } rutski@imac:~$ gcc -std=c89 -pedantic test.c test.c: In function ‘main’: test.c:7: warning: ISO C90 forbids mixed declarations and code rutski@imac:~$ Yes, you can avoid this sort of thing by staying away from -pedantic. But then your code is no longer standards compliant. And as anybody capable of answering this post probably already knows, this is not just a theoretical concern. Platforms like Microsoft's C compiler enforce this quick in the standard under any and all circumstances. Given how ancient C is, I would imagine that this feature is due to some historical issue dating back to the extraordinary hardware limitations of the 70's, but I don't know the details. Or am I totally wrong there?

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• Float addition promoted to double?

  - by Andreas Brinck

  I had a small WTF moment this morning. Ths WTF can be summarized with this: float x = 0.2f; float y = 0.1f; float z = x + y; assert(z == x + y); //This assert is triggered! (Atleast with visual studio 2008) The reason seems to be that the expression x + y is promoted to double and compared with the truncated version in z. (If i change z to double the assert isn't triggered). I can see that for precision reasons it would make sense to perform all floating point arithmetics in double precision before converting the result to single precision. I found the following paragraph in the standard (which I guess I sort of already knew, but not in this context): 4.6.1. "An rvalue of type float can be converted to an rvalue of type double. The value is unchanged" My question is, is x + y guaranteed to be promoted to double or is at the compiler's discretion? UPDATE: Since many people has claimed that one shouldn't use == for floating point, I just wanted to state that in the specific case I'm working with, an exact comparison is justified. Floating point comparision is tricky, here's an interesting link on the subject which I think hasn't been mentioned.

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• Getting zeros between data while reading a binary file in C

  - by indiajoe

  I have a binary data which I am reading into an array of long integers using a C programme. hexdump of the binary data shows, that after first few data points , it starts again at a location 20000 hexa adresses away. hexdump output is as shown below. 0000000 0000 0000 0000 0000 0000 0000 0000 0000 * 0020000 0000 0000 0053 0000 0064 0000 006b 0000 0020010 0066 0000 0068 0000 0066 0000 005d 0000 0020020 0087 0000 0059 0000 0062 0000 0066 0000 ........ and so on... But when I read it into an array 'data' of long integers. by the typical fread command fread(data,sizeof(*data),filelength/sizeof(*data),fd); It is filling up with all zeros in my data array till it reaches the 20000 location. After that it reads in data correctly. Why is it reading regions where my file is not there? Or how will I make it read only my file, not anything inbetween which are not in file? I know it looks like a trivial problem, but I cannot figure it out even after googling one night.. Can anyone suggest me where I am doing it wrong? Other Info : I am working on a gnu/linux machine. (slax-atma distro to be specific) My C compiler is gcc.

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• Converting Generic Type into reference type after checking its type using GetType(). How ?

  - by Shantanu Gupta

  i am trying to call a function that is defined in a class RFIDeas_Wrapper(dll being used). But when i checked for type of reader and after that i used it to call function it shows me error Cannot convert type T to RFIDeas_Wrapper. EDIT private List<string> GetTagCollection<T>(T Reader) { TagCollection = new List<string>(); if (Reader.GetType() == typeof(RFIDeas_Wrapper)) { ((RFIDeas_Wrapper)Reader).OpenDevice(); // here Reader is of type RFIDeas_Wrapper //, but i m not able to convert Reader into its datatype. string Tag_Id = ((RFIDeas_Wrapper)Reader).TagID(); //Adds Valid Tag Ids into the collection if(Tag_Id!="0") TagCollection.Add(Tag_Id); } else if (Reader.GetType() == typeof(AlienReader)) TagCollection = ((AlienReader)Reader).TagCollection; return TagCollection; } ((RFIDeas_Wrapper)Reader).OpenDevice(); , ((AlienReader)Reader).TagCollection; I want this line to be executed without any issue. As Reader will always be of the type i m specifying. How to make compiler understand the same thing.

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