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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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• 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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• 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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• 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 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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• Porting - Shared Memory x32 & x64 processes

  - by dpb

  A 32 bit host Windows application setups shared memory (using memory mapped file / CreateFileMapping() API), and then other 32 bit client processes use this shared memory to communicate with each other. I am planning to port the host application to 64 bit platform and once it is ready, I intend that both 32 bit and 64 bit client processes should be able to use the shared memory setup by the main 64 bit host application. The original code written for host x32 application uses "size_t" almost everywhere, since this differs from 4 bytes to 8 bytes as we move from x32 to x64, I am looking for replacing it. I intend to replace "size_t" by "unsigned long long", so that its size will be same on 32 bit & 64 bit. Can you please suggest me better alternative? Also, will the use of "unsigned long long" have performance impact on x32 app .. i guess yes? Research Done - Found very useful articles - a) 20 issue in porting from 32 bit to 64 bit (www.viva64.com) b) No way to restrict/change "size_t" on x64 platform to 4 bytes using compiler flags or any hooks/crooks since it is typedef

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• Destructors not called when native (C++) exception propagates to CLR component

  - by Phil Nash

  We have a large body of native C++ code, compliled into DLLs. Then we have a couple of dlls containing C++/CLI proxy code to wrap the C++ interfaces. On top of that we have C# code calling into the C++/CLI wrappers. Standard stuff, so far. But we have a lot of cases where native C++ exceptions are allowed to propagate to the .Net world and we rely on .Net's ability to wrap these as System.Exception objects and for the most part this works fine. However we have been finding that destructors of objects in scope at the point of the throw are not being invoked when the exception propagates! After some research we found that this is a fairly well known issue. However the solutions/ workarounds seem less consistent. We did find that if the native code is compiled with /EHa instead of /EHsc the issue disappears (at least in our test case it did). However we would much prefer to use /EHsc as we translate SEH exceptions to C++ exceptions ourselves and we would rather allow the compiler more scope for optimisation. Are there any other workarounds for this issue - other than wrapping every call across the native-managed boundary in a (native) try-catch-throw (in addition to the C++/CLI layer)?

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• can not override showDialog in Activity tab

  - by hornetbzz

  Trying to downgrade my appl from android 2.2 (API 8) down to android 2.1 (API7), I'm facing some issues with dialog boxes. Based on this thread, I'm trying to catch these exceptions but can't override the showDialog method. I turned the Java compiler from 1.5 to 1.6 according to this answer to a similar issue, but no changes, Eclipse still returns : Cannot override the final method from Activity public class MyActivity extends Activity implements SeekBar.OnSeekBarChangeListener { // ... some stuffs @Override // here is the issue public void showDialog(int dialogId) { try { super.showDialog(dialogId); } catch (IllegalArgumentException e) { Log.e(ACTIVITY_TAG, "Error dialog"); } } @Override protected Dialog onCreateDialog(int id) { switch (id) { case DIALOG_ALERT: // Create out AlertDialog Builder builder = new AlertDialog.Builder(this); builder.setMessage(msg); builder.setCancelable(false); builder.setPositiveButton(GOTO_BOOK, new OkOnClickListener()); builder.setNegativeButton(STAY_HERE, new CancelOnClickListener()); AlertDialog dialog = builder.create(); dialog.show(); break; case DIALOG_ONCREATE: // Create out AlertDialog during the "onCreate" method (only "Ok" // button) Builder builder2 = new AlertDialog.Builder(getParent()); builder2.setMessage(msg); builder2.setCancelable(false); builder2.setPositiveButton(GO_BACK, new OkOnClickListener()); AlertDialog dialog2 = builder2.create(); dialog2.show(); break; } return super.onCreateDialog(id); } // ... some stuffs }

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• Compile time float packing/punning

  - by detly

  I'm writing C for the PIC32MX, compiled with Microchip's PIC32 C compiler (based on GCC 3.4). My problem is this: I have some reprogrammable numeric data that is stored either on EEPROM or in the program flash of the chip. This means that when I want to store a float, I have to do some type punning: typedef union { int intval; float floatval; } IntFloat; unsigned int float_as_int(float fval) { IntFloat intf; intf.floatval = fval; return intf.intval; } // Stores an int of data in whatever storage we're using void StoreInt(unsigned int data, unsigned int address); void StoreFPVal(float data, unsigned int address) { StoreInt(float_as_int(data), address); } I also include default values as an array of compile time constants. For (unsigned) integer values this is trivial, I just use the integer literal. For floats, though, I have to use this Python snippet to convert them to their word representation to include them in the array: import struct hex(struct.unpack("I", struct.pack("f", float_value))[0]) ...and so my array of defaults has these indecipherable values like: const unsigned int DEFAULTS[] = { 0x00000001, // Some default integer value, 1 0x3C83126F, // Some default float value, 0.005 } (These actually take the form of X macro constructs, but that doesn't make a difference here.) Commenting is nice, but is there a better way? It's be great to be able to do something like: const unsigned int DEFAULTS[] = { 0x00000001, // Some default integer value, 1 COMPILE_TIME_CONVERT(0.005), // Some default float value, 0.005 } ...but I'm completely at a loss, and I don't even know if such a thing is possible. Notes Obviously "no, it isn't possible" is an acceptable answer if true. I'm not overly concerned about portability, so implementation defined behaviour is fine, undefined behaviour is not (I have the IDB appendix sitting in front of me). As fas as I'm aware, this needs to be a compile time conversion, since DEFAULTS is in the global scope. Please correct me if I'm wrong about this.

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• A monkey could do this better - Access to and availability of private member functions in C++

  - by David

  I am wandering the desert of my brain. I'm trying to write something like the following: class MyClass { // Peripherally Related Stuff public: void TakeAnAction(int oneThing, int anotherThing) { switch(oneThing){ case THING_A: TakeThisActionWith(anotherThing); break; //cases THINGS_NOT_A: }; private: void TakeThisActionWith(int thing) { string outcome = new string; outcome = LookUpOutcome(thing); // Do some stuff based on outcome return; } string LookUpOutcome(int key) { string oc = new string; oc = MyPrivateMap[key]; return oc; } map<int, string> MyPrivateMap; Then in the .cc file where I am actually using these things, while compiling the TakeAnAction section, it [CC, the solaris compiler] throws an an error: 'The function LookUpOutcome must have a prototype' and bombs out. In my header file, I have declared 'string LookUpOutcome(int key);' in the private section of the class. I have tried all sorts of variations. I tried to use 'this' for a little while, and it gave me 'Can only use this in non-static member function.' Sadly, I haven't declared anything static and these are all, putatively, member functions. I tried it [on TakeAnAction and LookUp] when I got the error, but I got something like, 'Can't access MyPrivateMap from LookUp'. MyPrivateMap could be made public and I could refer to it directly, I guess, but my sensibility says that is not the right way to go about this [that means that namespace scoped helper functions are out, I think]. I also guess I could just inline the lookup and subsequent other stuff, but my line-o-meter goes on tilt. I'm trying desperately not to kludge it.

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• TypeScript - separating code output

  - by Andrea Baccega

  i'm trying typescript and I find it very useful. I've a quite large project and i was considering rewriting it using typescript. The main problem here is the following: file A.ts: class A extends B { // A stuff } file B.ts: class B { // B stuff } If I compile A.ts with this command: tsc --out compiledA.js A.ts I'll get error from the compiler cause he doesn't know how to threat the "B" after extends. So, a "solution" would be including in A.ts (as first line of code): /// <reference path="./B.ts" /> Compiling again A.ts with the same command tsc --out compiledA.js A.ts Will result in compiledA.js containing both B.ts and A.ts code. ( which could be very nice ) In my case, I only need to compile the A.ts code in the compiledA.js file and I don't want the B.ts stuff to be in there. Indeed, what I want is: tsc --out A.js A.ts = compile only the A.ts stuff tsc --out B.js B.ts = compile only the B.ts stuff I can do it by removing the "extends" keyword but doing that I'll loose most of the typescript goodness. Can someone telll me if there's a way to do this ?

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• help understanding differences between #define, const and enum in C and C++ on assembly level.

  - by martin

  recently, i am looking into assembly codes for #define, const and enum: C codes(#define): 3 #define pi 3 4 int main(void) 5 { 6 int a,r=1; 7 a=2*pi*r; 8 return 0; 9 } assembly codes(for line 6 and 7 in c codes) generated by GCC: 6 mov $0x1, -0x4(%ebp) 7 mov -0x4(%ebp), %edx 7 mov %edx, %eax 7 add %eax, %eax 7 add %edx, %eax 7 add %eax, %eax 7 mov %eax, -0x8(%ebp) C codes(enum): 2 int main(void) 3 { 4 int a,r=1; 5 enum{pi=3}; 6 a=2*pi*r; 7 return 0; 8 } assembly codes(for line 4 and 6 in c codes) generated by GCC: 6 mov $0x1, -0x4(%ebp) 7 mov -0x4(%ebp), %edx 7 mov %edx, %eax 7 add %eax, %eax 7 add %edx, %eax 7 add %eax, %eax 7 mov %eax, -0x8(%ebp) C codes(const): 4 int main(void) 5 { 6 int a,r=1; 7 const int pi=3; 8 a=2*pi*r; 9 return 0; 10 } assembly codes(for line 7 and 8 in c codes) generated by GCC: 6 movl $0x3, -0x8(%ebp) 7 movl $0x3, -0x4(%ebp) 8 mov -0x4(%ebp), %eax 8 add %eax, %eax 8 imul -0x8(%ebp), %eax 8 mov %eax, 0xc(%ebp) i found that use #define and enum, the assembly codes are the same. The compiler use 3 add instructions to perform multiplication. However, when use const, imul instruction is used. Anyone knows the reason behind that?

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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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• 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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• 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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• 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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• Is a call to the following method considered late binding?

  - by AspOnMyNet

  1) Assume: • B1 defines methods virtualM() and nonvirtualM(), where former method is virtual while the latter is non-virtual • B2 derives from B1 • B2 overrides virtualM() • B2 is defined inside assembly A • Application app doesn’t have a reference to assembly A In the following code application app dynamically loads an assembly A, creates an instance of a type B2 and calls methods virtualM() and nonvirtualM(): Assembly a=Assembly.Load(“A”); Type t= a.GetType(“B2”); B1 a = ( B1 ) Activator.CreateInstance ( “t” ); a.virtualM(); a.nonvirtualM(); a) Is call to a.virtualM() considered early binding or late binding? b) I assume a call to a.nonvirtualM() is resolved during compilation time? 2) Does the term late binding refer only to looking up the target method at run time or does it also refer to creating an instance of given type at runtime? 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) The method slot is determined at compile time I assume that by method slot you’re referring to the entry point in V-table?

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• Casting to specify unknown object type?

  - by fuzzygoat

  In the following code I have a view object that is an instance of UIScrollView, if I run the code below I get warnings saying that "UIView might not respond to -setContentSize etc." UIImage *image = [UIImage imageNamed:@"Snowy_UK.jpg"]; imageView = [[UIImageView alloc] initWithImage:image]; [[self view] addSubview:imageView]; [[self view] setContentSize:[image size]]; [[self view] setMaximumZoomScale:2.0]; [[self view] setMinimumZoomScale: [[self view] bounds].size.width / [image size].width]; I have checked the type of the object and [self view] is indeed a UIScrollView. I am guessing that this is just the compiler making a bad guess as to the type and the solution is simply to cast the object to the correct type manually, am I getting this right? UIScrollView *scrollView = (UIScrollView *)[self view]; UIImage *image = [UIImage imageNamed:@"Snowy_UK.jpg"]; imageView = [[UIImageView alloc] initWithImage:image]; [[self view] addSubview:imageView]; [scrollView setContentSize:[image size]]; [scrollView setMaximumZoomScale:2.0]; [scrollView setMinimumZoomScale: [scrollView bounds].size.width / [image size].width]; cheers Gary.

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• Strange inheritance behaviour in Objective-C

  - by Smikey

  Hi all, I've created a class called SelectableObject like so: #define kNumberKey @"Object" #define kNameKey @"Name" #define kThumbStringKey @"Thumb" #define kMainStringKey @"Main" #import <Foundation/Foundation.h> @interface SelectableObject : NSObject <NSCoding> { int number; NSString *name; NSString *thumbString; NSString *mainString; } @property (nonatomic, assign) int number; @property (nonatomic, retain) NSString *name; @property (nonatomic, retain) NSString *thumbString; @property (nonatomic, retain) NSString *mainString; @end So far so good. And the implementation section conforms to the NSCoding protocol as expected. HOWEVER, when I add a new class which inherits from this class, i.e. #import <Foundation/Foundation.h> #import "SelectableObject.h" @interface Pet : SelectableObject <NSCoding> { } @end I suddenly get the following compiler error in the Selectable object class! SelectableObject.h:16: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'interface' This makes no sense to me. Why is the interface declaration for the SelectableObject class suddenly broken? I also import it in a couple of other classes I've written... Any help would be very much appreciated. Thanks! Michael

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• Visibility of reintroduced constructor

  - by avenmore

  I have reintroduced the form constructor in a base form, but if I override the original constructor in a descendant form, the reintroduced constructor is no longer visible. type TfrmA = class(TForm) private FWndParent: HWnd; public constructor Create(AOwner: TComponent; const AWndParent: Hwnd); reintroduce; overload; virtual; end; constructor TfrmA.Create(AOwner: TComponent; const AWndParent: Hwnd); begin FWndParent := AWndParent; inherited Create(AOwner); end; type TfrmB = class(TfrmA) private public end; type TfrmC = class(TfrmB) private public constructor Create(AOwner: TComponent); override; end; constructor TfrmC.Create(AOwner: TComponent); begin inherited Create(AOwner); end; When creating: frmA := TfrmA.Create(nil, 0); frmB := TfrmB.Create(nil, 0); frmC := TfrmC.Create(nil, 0); // Compiler error My work-around is to override the reintroduced constructor or to declare the original constructor overloaded, but I'd like to understand the reason for this behavior. type TfrmA = class(TForm) private FWndParent: HWnd; public constructor Create(AOwner: TComponent); overload; override; constructor Create(AOwner: TComponent; const AWndParent: Hwnd); reintroduce; overload; virtual; end; type TfrmC = class(TfrmB) private public constructor Create(AOwner: TComponent; const AWndParent: Hwnd); override; end;

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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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• Stack usage with MMX intrinsics and Microsoft C++

  - by arik-funke

  I have an inline assembler loop that cumulatively adds elements from an int32 data array with MMX instructions. In particular, it uses the fact that the MMX registers can accommodate 16 int32s to calculate 16 different cumulative sums in parallel. I would now like to convert this piece of code to MMX intrinsics but I am afraid that I will suffer a performance penalty because one cannot explicitly intruct the compiler to use the 8 MMX registers to accomulate 16 independent sums. Can anybody comment on this and maybe propose a solution on how to convert the piece of code below to use intrinsics? == inline assembler (only part within the loop) == paddd mm0, [esi+edx+8*0] ; add first & second pair of int32 elements paddd mm1, [esi+edx+8*1] ; add third & fourth pair of int32 elements ... paddd mm2, [esi+edx+8*2] paddd mm3, [esi+edx+8*3] paddd mm4, [esi+edx+8*4] paddd mm5, [esi+edx+8*5] paddd mm6, [esi+edx+8*6] paddd mm7, [esi+edx+8*7] ; add 15th & 16th pair of int32 elements esi points to the beginning of the data array edx provides the offset in the data array for the current loop iteration the data array is arranged such that the elements for the 16 independent sums are interleaved.

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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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• C++ Beginner Delete Question

  - by Pooch

  Hi all, This is my first year learning C++ so bear with me. I am attempting to dynamically allocate memory to the heap and then delete the allocated memory. Below is the code that is giving me a hard time: // String.cpp #include "String.h" String::String() {} String::String(char* source) { this->Size = this->GetSize(source); this->CharArray = new char[this->Size + 1]; int i = 0; for (; i < this->Size; i++) this->CharArray[i] = source[i]; this->CharArray[i] = '\0'; } int String::GetSize(const char * source) { int i = 0; for (; source[i] != '\0'; i++); return i; } String::~String() { delete[] this->CharArray; } Here is the error I get when the compiler tries to delete the CharArray: 0xC0000005: Access violation reading location 0xccccccc0. And here is the last call on the stack: msvcr100d.dll!operator delete(void * pUserData) Line 52 + 0x3 bytes C++ I am fairly certain the error exists within this piece of code but will provide you with any other information needed. Oh yeah, using VS 2010 for XP. Thanks for any and all help!

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• Safe and polymorphic toEnum

  - by jetxee

  I'd like to write a safe version of toEnum: safeToEnum :: (Enum t, Bounded t) => Int -> Maybe t A naive implementation: safeToEnum :: (Enum t, Bounded t) => Int -> Maybe t safeToEnum i = if (i >= fromEnum (minBound :: t)) && (i <= fromEnum (maxBound :: t)) then Just . toEnum $ i else Nothing main = do print $ (safeToEnum 1 :: Maybe Bool) print $ (safeToEnum 2 :: Maybe Bool) And it doesn't work: safeToEnum.hs:3:21: Could not deduce (Bounded t1) from the context () arising from a use of `minBound' at safeToEnum.hs:3:21-28 Possible fix: add (Bounded t1) to the context of an expression type signature In the first argument of `fromEnum', namely `(minBound :: t)' In the second argument of `(>=)', namely `fromEnum (minBound :: t)' In the first argument of `(&&)', namely `(i >= fromEnum (minBound :: t))' safeToEnum.hs:3:56: Could not deduce (Bounded t1) from the context () arising from a use of `maxBound' at safeToEnum.hs:3:56-63 Possible fix: add (Bounded t1) to the context of an expression type signature In the first argument of `fromEnum', namely `(maxBound :: t)' In the second argument of `(<=)', namely `fromEnum (maxBound :: t)' In the second argument of `(&&)', namely `(i <= fromEnum (maxBound :: t))' As well as I understand the message, the compiler does not recognize that minBound and maxBound should produce exactly the same type as in the result type of safeToEnum inspite of the explicit type declaration (:: t). Any idea how to fix it?

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