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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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  • Potential g++ template bug?

    - by Evan Teran
    I've encountered some code which I think should compile, but doesn't. So I'm hoping some of the local standards experts here at SO can help :-). I basically have some code which resembles this: #include <iostream> template <class T = int> class A { public: class U { }; public: U f() const { return U(); } }; // test either the work around or the code I want... #ifndef USE_FIX template <class T> bool operator==(const typename A<T>::U &x, int y) { return true; } #else typedef A<int> AI; bool operator==(const AI::U &x, int y) { return true; } #endif int main() { A<int> a; std::cout << (a.f() == 1) << std::endl; } So, to describe what is going on here. I have a class template (A) which has an internal class (U) and at least one member function which can return an instance of that internal class (f()). Then I am attempting to create an operator== function which compares this internal type to some other type (in this case an int, but it doesn't seem to matter). When USE_FIX is not defined I get the following error: test.cc: In function 'int main()': test.cc:27:25: error: no match for 'operator==' in 'a.A<T>::f [with T = int]() == 1' Which seems odd, because I am clearly (I think) defining a templated operator== which should cover this, in fact if I just do a little of the work for the compiler (enable USE_FIX), then I no longer get an error. Unfortunately, the "fix" doesn't work generically, only for a specific instantiation of the template. Is this supposed to work as I expected? Or is this simply not allowed? BTW: if it matters I am using gcc 4.5.2.

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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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  • Adding items to a combo box's internal list programatically.

    - by Andrew
    So, despite Matt's generous explanation in my last question, I still didn't understand and decided to start a new project and use an internal list. - (void)applicationDidFinishLaunching:(NSNotification *)aNotification { codesList = [[NSString alloc] initWithContentsOfFile: @".../.../codelist.txt"]; namesList = [[NSString alloc] initWithContentsOfFile: @".../.../namelist.txt"]; codesListArray = [[NSMutableArray alloc]initWithArray:[codesList componentsSeparatedByString:@"\n"]]; namesListArray = [[NSMutableArray alloc]initWithArray:[namesList componentsSeparatedByString:@"\n"]]; addTheDash = [[NSString alloc]initWithString:@" - "]; flossNames = [[NSMutableArray alloc]init]; [flossNames removeAllObjects]; for (int n=0; n<=[codesListArray count]; n++){ NSMutableString *nameBuilder = [[NSMutableString alloc]initWithFormat:@"%@", [codesListArray objectAtIndex:n]]; [nameBuilder appendString:addTheDash]; [nameBuilder appendString:[namesListArray objectAtIndex:n]]; [comboBoz addItemWithObjectValue:[NSMutableString stringWithString:nameBuilder]]; [nameBuilder release]; } } So this is my latest attempt at this and the list still isn't showing in my combo box. I've tried using the addItemsWithObjectValues outside the for loop along with the suggestions at this question: Is this the right way to add items to NSCombobox in Cocoa ? But still no luck. If you can't tell, I'm trying to combine two strings from the files with a hyphen in between them and then put that new string into the combo box. There are over 400 codes and matching names in the two files, so manually putting them in would be a huge chore, not to mention, I don't see what would be causing this problem. The compiler shows no warnings or errors, and in the IB, I have it set to use the internal list, but when I run it, the list is not populated unless I do it manually. Some things I thought might be causing it: Being in the applicationDidFinishLaunching: method Having the string and array variables declared as instance variables in the header (along with @property and @synth done to them) Messing around with using appendString multiple times with NSMutableArrays Nothing seems to be causing this to me, but maybe someone else will know something I don't. Thanks for the help.

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • Writing a VM - well formed bytecode?

    - by David Titarenco
    Hi, I'm writing a virtual machine in C just for fun. Lame, I know, but luckily I'm on SO so hopefully no one will make fun :) I wrote a really quick'n'dirty VM that reads lines of (my own) ASM and does stuff. Right now, I only have 3 instructions: add, jmp, end. All is well and it's actually pretty cool being able to feed lines (doing it something like write_line(&prog[1], "jmp", regA, regB, 0); and then running the program: while (machine.code_pointer <= BOUNDS && DONE != true) { run_line(&prog[machine.cp]); } I'm using an opcode lookup table (which may not be efficient but it's elegant) in C and everything seems to be working OK. My question is more of a "best practices" question but I do think there's a correct answer to it. I'm making the VM able to read binary files (storing bytes in unsigned char[]) and execute bytecode. My question is: is it the VM's job to make sure the bytecode is well formed or is it just the compiler's job to make sure the binary file it spits out is well formed? I only ask this because what would happen if someone would edit a binary file and screw stuff up (delete arbitrary parts of it, etc). Clearly, the program would be buggy and probably not functional. Is this even the VM's problem? I'm sure that people much smarter than me have figured out solutions to these problems, I'm just curious what they are!

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  • Strange Behaviour in Swift: constant defined with LET but behaving like a variable defined with VAR

    - by Sam
    Stuck on the below for a day! Any insight would be greatly appreciated. The constant in the first block match0 behaves as expected. The constant defined in the second block does not behave as nicely in the face of a change to its "source": var str = "+y+z*1.0*sum(A1:A3)" if let range0 = str.rangeOfString("^\\+|^\\-|^\\*|^\\/", options: NSStringCompareOptions.RegularExpressionSearch){ let match0 = str[range0] println(match0) //yields "+" - as expexted str.removeRange(range0) println(match0) //yields "+" - as expected str.removeRange(range0) println(match0) //yields "+" - as expected } if let range1 = str.rangeOfString("^\\+|^\\-|^\\*|^\\/", options: NSStringCompareOptions.RegularExpressionSearch){ let match1 = str[range1] println(match1) //yields "+" as expected str.removeRange(range1) println(match1) //!@#$ OMG!!!!!!!!!!! a constant variable has changed! This prints "z" } The following are the options I can see: match1 has somehow obtained a reference to its source instead of being copied by value [Problem: Strings are value types in Swift] match1 has somehow obtained a closure to its source instead of just being a normal constant/variable? [Problem: sounds like science fiction & then why does match0 behave so well?] Could there be a bug in the Swift compiler? [Problem: Experience has taught me that this is very very very rarely the solution to your problem...but it is still in beta]

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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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  • Why Does Private Access Remain Non-Private in .NET Within a Class?

    - by AMissico
    While cleaning some code today written by someone else, I changed the access modifier from Public to Private on a class variable/member/field. I expected a long list of compiler errors that I use to "refactor/rework/review" the code that used this variable. Imagine my surprise when I didn't get any errors. After reviewing, it turns out that another instance of the Class can access the private members of another instance declared within the Class. Totally unexcepted. Is this normal? I been coding in .NET since the beginning and never ran into this issue, nor read about it. I may have stumbled onto it before, but only "vaguely noticed" and move on. Can anyone explain this behavoir to me? Am I doing something wrong? I found this behavior in both C# and VB.NET. The code seems to take advantage of the ability to access private variables. Sincerely, Totally Confused Class Foo Private _int As Integer Private _foo As Foo Private _jack As Jack Private _fred As Fred Public Sub SetPrivate() _foo = New Foo _foo._int = 3 'TOTALLY UNEXPECTED _jack = New Jack '_jack._int = 3 'expected compile error because Foo doesn't know Jack _fred = New Fred '_fred._int = 3 'expected compile error because Fred hides from Foo End Sub Private Class Fred Private _int As Integer End Class End Class Class Jack Private _int As Integer End Class

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  • Is it possible to defer member initialization to the constructor body?

    - by Kjir
    I have a class with an object as a member which doesn't have a default constructor. I'd like to initialize this member in the constructor, but it seems that in C++ I can't do that. Here is the class: #include <boost/asio.hpp> #include <boost/array.hpp> using boost::asio::ip::udp; template<class T> class udp_sock { public: udp_sock(std::string host, unsigned short port); private: boost::asio::io_service _io_service; udp::socket _sock; boost::array<T,256> _buf; }; template<class T> udp_sock<T>::udp_sock(std::string host = "localhost", unsigned short port = 50000) { udp::resolver res(_io_service); udp::resolver::query query(udp::v4(), host, "spec"); udp::endpoint ep = *res.resolve(query); ep.port(port); _sock(_io_service, ep); } The compiler tells me basically that it can't find a default constructor for udp::socket and by my research I understood that C++ implicitly initializes every member before calling the constructor. Is there any way to do it the way I wanted to do it, or is it too "Java-oriented" and not feasible in C++? I worked around the problem by defining my constructor like this: template<class T> udp_sock<T>::udp_sock(std::string host = "localhost", unsigned short port = 50000) : _sock(_io_service) { udp::resolver res(_io_service); udp::resolver::query query(udp::v4(), host, "spec"); udp::endpoint ep = *res.resolve(query); ep.port(port); _sock.bind(ep); } So my question is more out of curiosity and to better understand OOP in C++

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  • Why my object sees variables which were not given to it in the constructor?

    - by Roman
    I have the following code. Which is "correct" and which I do not understand: private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater( new Runnable() { public void run() { label.setText("You have " + i + " seconds."); } } ); } I create a new instance of the Runnable class and then in the run method of this instance I use variables label and i. It works, but I do not understand why it work. Why the considered object sees values of these variables. According to my understanding the code should look like that (and its wrong): private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater(new Runnable(i,label) { public Runnable(int i, JLabel label) { this.i = i; this.label = label; } public void run() { label.setText("You have " + i + " seconds."); } }); } So, I would give the i and label variables to the constructor so the object can access them... By the way, in the updateGUI I use final before the i and label. I think I used final because compiler wanted that. But I do not understand why.

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