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• Using an embedded DB (SQLite / SQL Compact) for Message Passing within an app?

  - by wk1989

  Hello, Just out of curiosity, for applications that have a fairly complicated module tree, would something like sqlite/sql compact edition work well for message passing? So if I have modules containing data such as: \SubsystemA\SubSubSysB\ModuleB\ModuleDataC, \SubSystemB\SubSubSystemC\ModuleA\ModuleDataX Using traditional message passing/routing, you have to go through intermediate modules in order to pass a message to ModuleB to request say ModuleDataC. Instead of doing that, if we we simply store "\SubsystemA\SubSubSysB\ModuleB\ModuleDataC" in a sqlite database, getting that data is as simple as a sql query and needs no routing and passing stuff around. Has anyone done this before? Even if you haven't, do you foresee any issues & performance impact? The only concern I have right now would be the passing of custom types, e.g. if ModuleDataC is a custom data structure or a pointer, I'll need some way of storing the data structure into the DB or storing the pointer into the DB. Thanks, JW EDIT One usage case I haven't thought about is when you want to send a message from ModuleA to ModuleB to get ModuleB to do something rather than just getting/setting data. Is it possible to do this using an embedded DB? I believe callback from the DB would be needed, how feasible is this?

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• Dependency injection in C++

  - by Yorgos Pagles

  This is also a question that I asked in a comment in one of Miško Hevery's google talks that was dealing with dependency injection but it got buried in the comments. I wonder how can the factory / builder step of wiring the dependencies together can work in C++. I.e. we have a class A that depends on B. The builder will allocate B in the heap, pass a pointer to B in A's constructor while also allocating in the heap and return a pointer to A. Who cleans up afterwards? Is it good to let the builder clean up after it's done? It seems to be the correct method since in the talk it says that the builder should setup objects that are expected to have the same lifetime or at least the dependencies have longer lifetime (I also have a question on that). What I mean in code: class builder { public: builder() : m_ClassA(NULL),m_ClassB(NULL) { } ~builder() { if (m_ClassB) { delete m_ClassB; } if (m_ClassA) { delete m_ClassA; } } ClassA *build() { m_ClassB = new class B; m_ClassA = new class A(m_ClassB); return m_ClassA; } }; Now if there is a dependency that is expected to last longer than the lifetime of the object we are injecting it into (say ClassC is that dependency) I understand that we should change the build method to something like: ClassA *builder::build(ClassC *classC) { m_ClassB = new class B; m_ClassA = new class A(m_ClassB, classC); return m_ClassA; } What is your preferred approach?

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• Templates, Function Pointers and C++0x

  - by user328543

  One of my personal experiments to understand some of the C++0x features: I'm trying to pass a function pointer to a template function to execute. Eventually the execution is supposed to happen in a different thread. But with all the different types of functions, I can't get the templates to work. #include `<functional`> int foo(void) {return 2;} class bar { public: int operator() (void) {return 4;}; int something(int a) {return a;}; }; template <class C> int func(C&& c) { //typedef typename std::result_of< C() >::type result_type; typedef typename std::conditional< std::is_pointer< C >::value, std::result_of< C() >::type, std::conditional< std::is_object< C >::value, std::result_of< typename C::operator() >::type, void> >::type result_type; result_type result = c(); return result; } int main(int argc, char* argv[]) { // call with a function pointer func(foo); // call with a member function bar b; func(b); // call with a bind expression func(std::bind(&bar::something, b, 42)); // call with a lambda expression func( [](void)->int {return 12;} ); return 0; } The result_of template alone doesn't seem to be able to find the operator() in class bar and the clunky conditional I created doesn't compile. Any ideas? Will I have additional problems with const functions?

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• Read in double type from txt file - C++

  - by Greenhouse Gases

  Hi there I'm in the midst of a university project and have decided to implement a method that can accept information from a text file (in this instance called "locations.txt"). input from the text file will look like this: London 345 456 Madrid 234 345 Beinjing 345 456 Frankfurt 456 567 The function looks like this currently (and you will notice I am missing the While condition to finish adding input when reaches end of text in locations.txt, i tried using eof but this didnt work?!). Also get function expects a char and so cant accept input thats a double which is what the latitude and longitude are defined as... void populateList(){ ifstream inputFile; inputFile.open ("locations.txt"); temp = new locationNode; // declare the space for a pointer item and assign a temporary pointer to it while(HASNT REACHED END OF TEXT FILE!!) { inputFile.getline(temp-nodeCityName, MAX_LENGTH); // inputFile.get(temp-nodeLati, MAX_LENGTH); // inputFile.get(temp-nodeLongi, MAX_LENGTH); temp-Next = NULL; //set to NULL as when one is added it is currently the last in the list and so can not point to the next if(start_ptr == NULL){ // if list is currently empty, start_ptr will point to this node start_ptr = temp; } else { temp2 = start_ptr; // We know this is not NULL - list not empty! while (temp2-Next != NULL) { temp2 = temp2-Next; // Move to next link in chain until reach end of list } temp2->Next = temp; } } inputFile.close(); } Any help you can provide would be most useful. If I need to provide anymore detail I will do, I'm in a bustling canteen atm and concentrating is hard!!

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• C++, using one byte to store two variables

  - by 2di

  Hi All I am working on representation of the chess board, and I am planning to store it in 32 bytes array, where each byte will be used to store two pieces. (That way only 4 bits are needed per piece) Doing it in that way, results in a overhead for accessing particular index of the board. Do you think that, this code can be optimised or completely different method of accessing indexes can be used? c++ char getPosition(unsigned char* c, int index){ //moving pointer c+=(index>>1); //odd number if (index & 1){ //taking right part return *c & 0xF; }else { //taking left part return *c>>4; } } void setValue(unsigned char* board, char value, int index){ //moving pointer board+=(index>>1); //odd number if (index & 1){ //replace right part //save left value only 4 bits *board = (*board & 0xF0) + value; }else { //replacing left part *board = (*board & 0xF) + (value<<4); } } int main() { char* c = (char*)malloc(32); for (int i = 0; i < 64 ; i++){ setValue((unsigned char*)c, i % 8,i); } for (int i = 0; i < 64 ; i++){ cout<<(int)getPosition((unsigned char*)c, i)<<" "; if (((i+1) % 8 == 0) && (i > 0)){ cout<<endl; } } return 0; } I am equally interested in your opinions regarding chess representations, and optimisation of the method above, as a stand alone problem. Thanks a lot

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• C++ private inheritance and static members/types

  - by WearyMonkey

  I am trying to stop a class from being able to convert its 'this' pointer into a pointer of one of its interfaces. I do this by using private inheritance via a middle proxy class. The problem is that I find private inheritance makes all public static members and types of the base class inaccessible to all classes under the inheriting class in the hierarchy. class Base { public: enum Enum { value }; }; class Middle : private Base { }; class Child : public Middle { public: void Method() { Base::Enum e = Base::value; // doesn't compile BAD! Base* base = this; // doesn't compile GOOD! } }; I've tried this in both VS2008 (the required version) and VS2010, neither work. Can anyone think of a workaround? Or a different approach to stopping the conversion? Also I am curios of the behavior, is it just a side effect of the compiler implementation, or is it by design? If by design, then why? I always thought of private inheritance to mean that nobody knows Middle inherits from Base. However, the exhibited behavior implies private inheritance means a lot more than that, in-fact Child has less access to Base than any namespace not in the class hierarchy!

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• sIFR multiple calls don't work :(

  - by roxane

  Hello ! I'm trying to use sIFR on my menu and on my headers... but only one call works... the others that I put after never appear :(... Can somebody help me ? Note : I'm using the r436 and below is my code ... var segoe = { src: 'pathto/segoe.swf', ratios: [7, 1.58, 8, 1.49, 10, 1.5, 11, 1.45, 16, 1.46, 21, 1.44, 22, 1.41, 27, 1.42, 30, 1.41, 32, 1.4, 35, 1.41, 36, 1.4, 38, 1.39, 41, 1.4, 58, 1.39, 65, 1.38, 66, 1.39, 102, 1.38, 104, 1.37, 106, 1.38, 107, 1.37, 108, 1.38, 109, 1.37, 110, 1.38, 112, 1.37, 114, 1.38, 120, 1.37, 121, 1.38, 1.37] }; sIFR.activate(segoe); sIFR.replace(segoe, { selector: '#header ul li a span.title', css: ['.sIFR-root { text-align: center; font-size:13px; letter-spacing:2; font-weight: bold; text-transform:uppercase; cursor: pointer; color:#FFFFFF; background-color:#0C2C39; margin:0 3px; }'], wmode: 'transparent' }); sIFR.replace(segoe, { selector: 'h1', css: ['.sIFR-root { text-align: center; font-size:13px; letter-spacing:2; font-weight: bold; text-transform:uppercase; cursor: pointer; color:#000; background-color:#fff; margin:0 3px; }'] });

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• Stretch ListBox Items hit area to full width if the ListBox?

  - by Nicholas

  I've looked around for an answer on this, but the potential duplicates are more concerned with presentation than interaction. I have a basic list box, and each item's content is a simple string. The ListBox itself is stretched to fill it's grid container, but each ListBoxItem's hitarea does not mirror the ListBox width. It looks as if the hitarea (pointer contact area) for each item is only the width of the text content. How do I make this stretch all the way across, regardless of the text size. I've set HorizontalContentAlignment to Stretch, but this doesn't solve my problem. My only other guess is that the content is actually stretching, but the background is invisible and so not capturing the mouse pointer. <ListBox Grid.Row="1" x:Name="ProjectsListBox" DisplayMemberPath="Name" ItemsSource="{Binding Path=Projects}" SelectedItem="{Binding Path=SelectedProject}" HorizontalContentAlignment="Stretch"/> The XAML is pretty straight forward on this. If I mouse over the text in one of the items, then the entire width of the item becomes active. I guess I just need to know how to create an interactive background that is invisible.

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• casting char[][] to char** causes segfault?

  - by Earlz

  Ok my C is a bit rusty but I figured I'd make my next(small) project in C so I could polish back up on it and less than 20 lines in I already have a seg fault. This is my complete code: #define ROWS 4 #define COLS 4 char main_map[ROWS][COLS+1]={ "a.bb", "a.c.", "adc.", ".dc."}; void print_map(char** map){ int i; for(i=0;i<ROWS;i++){ puts(map[i]); //segfault here } } int main(){ print_map(main_map); //if I comment out this line it will work. puts(main_map[3]); return 0; } I am completely confused as to how this is causing a segfault. What is happening when casting from [][] to **!? That is the only warning I get. rushhour.c:23:3: warning: passing argument 1 of ‘print_map’ from incompatible pointer type rushhour.c:13:7: note: expected ‘char **’ but argument is of type ‘char (*)[5]’ Are [][] and ** really not compatible pointer types? They seem like they are just syntax to me.

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• Passing C++ object to C++ code through Python?

  - by cornail

  Hi all, I have written some physics simulation code in C++ and parsing the input text files is a bottleneck of it. As one of the input parameters, the user has to specify a math function which will be evaluated many times at run-time. The C++ code has some pre-defined function classes for this (they are actually quite complex on the math side) and some limited parsing capability but I am not satisfied with this construction at all. What I need is that both the algorithm and the function evaluation remain speedy, so it is advantageous to keep them both as compiled code (and preferrably, the math functions as C++ function objects). However I thought of glueing the whole simulation together with Python: the user could specify the input parameters in a Python script, while also implementing storage, visualization of the results (matplotlib) and GUI, too, in Python. I know that most of the time, exposing C++ classes can be done, e.g. with SWIG but I still have a question concerning the parsing of the user defined math function in Python: Is it possible to somehow to construct a C++ function object in Python and pass it to the C++ algorithm? E.g. when I call f = WrappedCPPGaussianFunctionClass(sigma=0.5) WrappedCPPAlgorithm(f) in Python, it would return a pointer to a C++ object which would then be passed to a C++ routine requiring such a pointer, or something similar... (don't ask me about memory management in this case, though :S) The point is that no callback should be made to Python code in the algorithm. Later I would like to extend this example to also do some simple expression parsing on the Python side, such as sum or product of functions, and return some compound, parse-tree like C++ object but let's stay at the basics for now. Sorry for the long post and thx for the suggestions in advance.

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• template specialization for static member functions; howto?

  - by Rolle

  I am trying to implement a template function with handles void differently using template specialization. The following code gives me an "Explicit specialization in non-namespace scope" in gcc: template <typename T> static T safeGuiCall(boost::function<T ()> _f) { if (_f.empty()) throw GuiException("Function pointer empty"); { ThreadGuard g; T ret = _f(); return ret; } } // template specialization for functions wit no return value template <> static void safeGuiCall<void>(boost::function<void ()> _f) { if (_f.empty()) throw GuiException("Function pointer empty"); { ThreadGuard g; _f(); } } I have tried moving it out of the class (the class is not templated) and into the namespace but then I get the error "Explicit specialization cannot have a storage class". I have read many discussions about this, but people don't seem to agree how to specialize function templates. Any ideas?

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• Why do I get "request for member in something not a struct or union" from this code?

  - by pyroxene

  I'm trying to teach myself C by coding up a linked list. I'm new to pointers and memory management and I'm getting a bit confused. I have this code: /* Remove a node from the list and rejiggle the pointers */ void rm_node(struct node **listP, int index) { struct node *prev; struct node *n = *listP; if (index == 0) { *listP = *listP->next; free(n); return; } for (index; index > 0; index--) { n = n->next; if (index == 2) { prev = n; } } prev->next = n->next; free(n); } to remove an element from the list. If I want to remove the first node, I still need some way of referring to the list, which is why the listP arg is a double pointer, so it can point to the first element of the list and allow me to free the node that used to be the head. However, when I try to dereference listP to access the pointer to the next node, the compiler tells me error: request for member ‘next’ in something not a structure or union . What am I doing wrong here? I think I might be hopelessly mixed up..?

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• "Address of" (&) an array / address of being ignored be gcc?

  - by dbarbosa

  Hi, I am a teaching assistant of a introductory programming course, and some students made this type of error: char name[20]; scanf("%s",&name); which is not surprising as they are learning... What is surprising is that, besides gcc warning, the code works (at least this part). I have been trying to understand and I wrote the following code: void foo(int *str1, int *str2) { if (str1 == str2) printf("Both pointers are the same\n"); else printf("They are not the same\n"); } int main() { int test[50]; foo(&test, test); if (&test == test) printf("Both pointers are the same\n"); else printf("They are not the same\n"); } Compiling and executing: $ gcc test.c -g test.c: In function ‘main’: test.c:12: warning: passing argument 1 of ‘foo’ from incompatible pointer type test.c:13: warning: comparison of distinct pointer types lacks a cast $ ./a.out Both pointers are the same Both pointers are the same Can anyone explain why they are not different? I suspect it is because I cannot get the address of an array (as I cannot have & &x), but in this case the code should not compile.

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• Does ReleaseStringUTF do more than free memory?

  - by Bayou Bob

  Consider the following C code segments. Segment 1: char * getSomeString(JNIEnv *env, jstring jstr) { char * retString; retString = (*env)->GetStringUTFChars(env, jstr, NULL); return retString; } void useSomeString(JNIEnv *env, jobject jobj, char *mName) { jclass cl = (*env)->GetObjectClass(env, jobj); jmethodId mId = (*env)->GetMethodID(env, cl, mName, "()Ljava/lang/String;"); jstring jstr = (*env)->CallObjectMethod(env, obj, id, NULL); char * myString = getSomeString(env, jstr); /* ... use myString without modifing it */ free(myString); } Because myString is freed in useSomeString, I do not think I am creating a memory leak; however, I am not sure. The JNI spec specifically requires the use of ReleaseStringUTFChars. Since I am getting a C style 'char *' pointer from GetStringUTFChars, I believe the memory reference exists on the C stack and not in the JAVA heap so it is not in danger of being Garbage Collected; however, I am not sure. I know that changing getSomeString as follows would be safer (and probably preferable). Segment 2: char * getSomeString(JNIEnv *env, jstring jstr) { char * retString; char * intermedString; intermedString = (*env)->GetStringUTFChars(env, jstr, NULL); retString = strdup(intermedString); (*env)->ReleaseStringUTFChars(env, jstr, intermedString); return retString; } Because of our 'process' I need to build an argument on why getSomeString in Segment 2 is preferable to Segment 1. Is anyone aware of any documentation or references which detail the behavior of GetStringUTFChars and ReleaseStringUTFChars in relation to where memory is allocated or what (if any) additional bookkeeping is done (i.e. local Reference Pointer to the Java Heap being created, etc). What are the specific consequences of ignoring that bookkeeping. Thanks in advance.

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• How to detect iPhone movement in space using accelerometer ?

  - by super_tomtom

  Hi ! I am trying to make an application that would detect what kind of shape you made with your iPhone using accelerometer. As an example, if you draw a circle with your hand holding the iPhone, the app would be able to redraw it on the screen. This could also work with squares, or even more complicated shapes. The only example of application I've seen doing such a thing is AirPaint (http://vimeo.com/2276713), but it doesn't seems to be able to do it in real time. My first try is to apply a low-pass filter on the X and Y parameters from the accelerometer, and to make a pointer move toward these values, proportionally to the size of the screen. But this is clearly not enought, I have a very low accuracy, and if I shake the device it also makes the pointer move... Any ideas about that ? Do you think accelerometer data is enought to do it ? Or should I consider using other data, such as the compass ? Thanks in advance !

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• Aliasing `T*` with `char*` is allowed. Is it also allowed the other way around?

  - by StackedCrooked

  Note: This question has been renamed and reduced to make it more focused and readable. Most of the comments refer to the old text. According to the standard objects of different type may not share the same memory location. So this would not be legal: int i = 0; short * s = reinterpret_cast<short*>(&i); // BAD! The standard however allows an exception to this rule: any object may be accessed through a pointer to char or unsigned char: int i = 0; char * c = reinterpret_cast<char*>(&i); // OK However, it is not clear to me if this is also allowed the other way around. For example: char * c = read_socket(...); unsigned * u = reinterpret_cast<unsigned*>(c); // huh? Summary of the answers The answer is NO for two reasons: You an only access an existing object as char*. There is no object in my sample code, only a byte buffer. The pointer address may not have the right alignment for the target object. In that case dereferencing it would result in undefined behavior. On the Intel and AMD platforms it will result performance overhead. On ARM it will trigger a CPU trap and your program will be terminated! This is a simplified explanation. For more detailed information see answers by @Luc Danton, @Cheers and hth. - Alf and @David Rodríguez.

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• ARC and __unsafe_unretained

  - by J Shapiro

  I think I have a pretty good understanding of ARC and the proper use cases for selecting an appropriate lifetime qualifiers (__strong, __weak, __unsafe_unretained, and __autoreleasing). However, in my testing, I've found one example that doesn't make sense to me. As I understand it, both __weak and __unsafe_unretained do not add a retain count. Therefore, if there are no other __strong pointers to the object, it is instantly deallocated. The only difference in this process is that __weak pointers are set to nil, and __unsafe_unretained pointers are left alone. If I create a __weak pointer to a simple, custom object (composed of one NSString property), I see the expected (null) value when trying to access a property: Test * __weak myTest = [[Test alloc] init]; myTest.myVal = @"Hi!"; NSLog(@"Value: %@", myTest.myVal); // Prints Value: (null) Similarly, I would expect the __unsafe_unretained lifetime qualifier to cause a crash, due to the resulting dangling pointer. However, it doesn't. In this next test, I see the actual value: Test * __unsafe_unretained myTest = [[Test alloc] init]; myTest.myVal = @"Hi!"; NSLog(@"Value: %@", myTest.myVal); // Prints Value: Hi! Why doesn't the __unsafe_unretained object become deallocated?

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• Passing Data to Multi Threads

  - by alaamh

  I study this code from some book: #include <pthread.h> #include <stdio.h> /* Parameters to print_function. */ struct char_print_parms { /* The character to print. */ char character; /* The number of times to print it. */ int count; }; /* Prints a number of characters to stderr, as given by PARAMETERS, which is a pointer to a struct char_print_parms. */ void* char_print(void* parameters) { /* Cast the cookie pointer to the right type. */ struct char_print_parms* p = (struct char_print_parms*) parameters; int i; for (i = 0; i < p->count; ++i) fputc(p->character, stderr); return NULL; } /* The main program. */ int main() { pthread_t thread1_id; pthread_t thread2_id; struct char_print_parms thread1_args; struct char_print_parms thread2_args; /* Create a new thread to print 30,000 ’x’s. */ thread1_args.character = 'x'; thread1_args.count = 30000; pthread_create(&thread1_id, NULL, &char_print, &thread1_args); /* Create a new thread to print 20,000 o’s. */ thread2_args.character = 'o'; thread2_args.count = 20000; pthread_create(&thread2_id, NULL, &char_print, &thread2_args); usleep(20); return 0; } after running this code, I see different result each time. and some time corrupted result. what is wrong and what the correct way to do that?

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• C++ Function pointers vs Switch

  - by Perfix

  What is faster: Function pointers or switch? The switch statement would have around 30 cases, consisting of enumarated unsigned ints from 0 to 30. I could do the following: class myType { FunctionEnum func; string argv[123]; int someOtherValue; }; // In another file: myType current; // Iterate through a vector containing lots of myTypes // ... for ( i=0; i < myVecSize; i ++ ) switch ( current.func ) { case 1: //... break; // ........ case 30: // blah break; } And go trough the switch with func every time. The good thing about switch would also be that my code is more organized than with 30 functions. Or I could do that (not so sure with that): class myType { myReturnType (*func); string argv[123]; int someOtherValue; }; I'd have 30 different functions then, at the beginning a pointer to one of them is assigned to myType. What is probably faster: Switch statement or function pointer? Calls per second: Around 10 million. I can't just test it out - that would require me to rewrite the whole thing. Currently using switch. I'm building an interpreter which I want to be faster than Python & Ruby - every clock cycle matters!

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• How to know the type of an object in a list?

  - by nacho4d

  Hi, I want to know the type of object (or type) I have in my list so I wrote this: void **list; //list of references list = new void * [2]; Foo foo = Foo(); const char *not_table [] = {"tf", "ft", 0 }; list[0] = &foo; list[1] = not_table; if (dynamic_cast<LogicProcessor*>(list[0])) { //ERROR here ;( printf("Foo was found\n"); } if (dynamic_cast<char*> (list[0])) { //ERROR here ;( printf("char was found\n"); } but I get : error: cannot dynamic_cast '* list' (of type 'void*') to type 'class Foo*' (source is not a pointer to class) error: cannot dynamic_cast '* list' (of type 'void*') to type 'char*' (target is not pointer or reference to class) Why is this? what I am doing wrong here? Is dynamic_cast what I should use here? Thanks in advance EDIT: I know above code is much like plain C and surely sucks from the C++ point of view but is just I have the following situation and I was trying something before really implementing it: I have two arrays of length n but both arrays will never have an object at the same index. Hence, or I have array1[i]!=NULL or array2[i]!=NULL. This is obviously a waste of memory so I thought everything would be solved if I could have both kind of objects in a single array of length n. I am looking something like Cocoa's (Objective-C) NSArray where you don't care about the type of the object to be put in. Not knowing the type of the object is not a problem since you can use other method to get the class of a certain later. Is there something like it in c++ (preferably not third party C++ libraries) ? Thanks in advance ;)

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• How to debug properly and find causes for crashes?

  - by Newbie

  I dont know what to do anymore... its hopeless. I'm getting tired of guessing whats causing the crashes. Recently i noticed some opengl calls crashes programs randomly on some gfx cards. so i am getting really paranoid what can cause crashes now. The bad thing on this crash is that it crashes only after a long time of using the program, so i can only guess what is the problem. I cant remember what changes i made to the program that may cause the crashes, its been so long time. But luckily the previous version doesnt crash, so i could just copypaste some code and waste 10 hours to see at which point it starts crashing... i dont think i want to do that yet. The program crashes after i make it to process the same files about 5 times in a row, each time it uses about 200 megabytes of memory in the process. It crashes at random times while and after the reading process. I have createn a "safe" free() function, it checks the pointer if its not NULL, and then frees the memory, and then sets the pointer to NULL. Isn't this how it should be done? I watched the task manager memory usage, and just before it crashed it started to eat 2 times more memory than usual. Also the program loading became exponentially slower every time i loaded the files; first few loads didnt seem much slower from each other, but then it started rapidly doubling the load speeds. What should this tell me about the crash? Also, do i have to manually free the c++ vectors by using clear() ? Or are they freed after usage automatically, for example if i allocate vector inside a function, will it be freed every time the function has ended ? I am not storing pointers in the vector. -- Shortly: i want to learn to catch the damn bugs as fast as possible, how do i do that? Using Visual Studio 2008.

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• Using an iterator without its container

  - by User1

  I am mixing some C and C++ libraries and have only a single pointer available to do some work in a callback function. All I need to do is iterate through a vector. Here's a simplified, untested example: bool call_back(void* data){ done=... if (!done) cout << *data++ << endl; return done; } Note that this function is in an extern "C" block in C++. call_back will be called until true is returned. I want it to cout the next element each time it's called. data is a pointer to something that I can pass from elsewhere in the code (an iterator in the above example, but can be anything). Something from data will likely be used to calculate done. I see two obvious options to give to data: Have data point to my vector. Have data point to an iterator of my vector. I can't use an iterator without having the .end() method available, right? I can't use a vector alone (unless maybe I start removing its data). I could make a struct with both vector and iterator, but is there a better way? What would you do?

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• on click submit button move itsplace

  - by Mayur

  Hi All, I m Using submit button for my form its work fine in all browser except ie7 when an user click on it it moved please suggest me what to do .confirm-button-submit { width : 79px; font : bold 12px sans-serif;; color : #000; background : url("../images/confirm-btn.png") 0 -33px no-repeat; text-decoration : none; margin-top :0px; text-align:center; border:0px; cursor : pointer; height:32px; padding : 8px 0px 12px 0px; } .confirm-button-submit:hover { width : 79px; font : bold 12px sans-serif;; color : #fff; background : url("../images/confirm-btn.png") 0 0 no-repeat; text-decoration : none; margin-top :0px; text-align:center; border:0px; cursor : pointer; height:32px; padding : 8px 0px 12px 0px; } i used this css please tell me what to do code: <input type="button" value="Show" name="commit" onclick="range_validation(this)" class="confirm-button-submit"/>`

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• Accessing Application Scoped Bean Causes NullPointerException

  - by user2946861

  What is an Application Scoped Bean? I understand it to be a bean which will exist for the life of the application, but that doesn't appear to be the correct interpretation. I have an application which creates an application scoped bean on startup (eager=true) and then a session bean that tries to access the application scoped bean's objects (which are also application scoped). But when I try to access the application scoped bean from the session scoped bean, I get a null pointer exception. Here's excerpts from my code: Application Scoped Bean: @ManagedBean(eager=true) @ApplicationScoped public class Bean1 implements Serializable{ private static final long serialVersionUID = 12345L; protected ArrayList<App> apps; // construct apps so they are available for the session scoped bean // do time consuming stuff... // getters + setters Session Scoped Bean: @ManagedBean @SessionScoped public class Bean2 implements Serializable{ private static final long serialVersionUID = 123L; @Inject private Bean1 bean1; private ArrayList<App> apps = bean1.getApps(); // null pointer exception What appears to be happening is, Bean1 is created, does it's stuff, then is destroyed before Bean2 can access it. I was hoping using application scoped would keep Bean1 around until the container was shutdown, or the application was killed, but this doesn't appear to be the case.

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• The cross-thread usage of "HttpContext.Current" property and related things

  - by smwikipedia

  I read from < Essential ASP.NET with Examples in C# the following statement: Another useful property to know about is the static Current property of the HttpContext class. This property always points to the current instance of the HttpContext class for the request being serviced. This can be convenient if you are writing helper classes that will be used from pages or other pipeline classes and may need to access the context for whatever reason. By using the static Current property to retrieve the context, you can avoid passing a reference to it to helper classes. For example, the class shown in Listing 4-1 uses the Current property of the context to access the QueryString and print something to the current response buffer. Note that for this static property to be correctly initialized, the caller must be executing on the original request thread, so if you have spawned additional threads to perform work during a request, you must take care to provide access to the context class yourself. I am wondering about the root cause of the bold part, and one thing leads to another, here is my thoughts: We know that a process can have multiple threads. Each of these threads have their own stacks, respectively. These threads also have access to a shared memory area, the heap. The stack then, as I understand it, is kind of where all the context for that thread is stored. For a thread to access something in the heap it must use a pointer, and the pointer is stored on its stack. So when we make some cross-thread calls, we must make sure that all the necessary context info is passed from the caller thread's stack to the callee thread's stack. But I am not quite sure if I made any mistake. Any comments will be deeply appreciated. Thanks. ADD Here the stack is limited to user stack.

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