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  • Direct invocation vs indirect invocation in C

    - by Mohit Deshpande
    I am new to C and I was reading about how pointers "point" to the address of another variable. So I have tried indirect invocation and direct invocation and received the same results (as any C/C++ developer could have predicted). This is what I did: int cost; int *cost_ptr; int main() { cost_ptr = &cost; //assign pointer to cost cost = 100; //intialize cost with a value printf("\nDirect Access: %d", cost); cost = 0; //reset the value *cost_ptr = 100; printf("\nIndirect Access: %d", *cost_ptr); //some code here return 0; //1 } So I am wondering if indirect invocation with pointers has any advantages over direct invocation or vice-versa. Some advantages/disadvantages could include speed, amount of memory consumed performing the operation (most likely the same but I just wanted to put that out there), safeness (like dangling pointers) , good programming practice, etc. 1Funny thing, I am using the GNU C Compiler (gcc) and it still compiles without the return statement and everything is as expected. Maybe because the C++ compiler will automatically insert the return statement if you forget.

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  • Serialize struct with pointers to NSData

    - by leolobato
    Hey guys, I need to add some kind of archiving functionality to a Objective-C Trie implementation (NDTrie on github), but I have very little experience with C and it's data structures. struct trieNode { NSUInteger key; NSUInteger count, size; id object; __strong struct trieNode ** children; __strong struct trieNode * parent; }; @interface NDTrie (Private) - (struct trieNode*)root; @end What I need is to create an NSData with the tree structure from that root - or serialize/deserialize the whole tree some other way (conforming to NSCoding?), but I have no clue how to work with NSData and a C struct containing pointers. Performance on deserializing the resulting object would be crucial, as this is an iPhone project and I will need to load it in the background every time the app starts. What would be the best way to achieve this? Thanks!

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  • WPF binding and pointers

    - by Eran
    hey guys, I have a WPF application that contains windows with few user controls and Coordinator object. the window and all its user controls pointing to an object, which instace is in the Coordinator, by thier DataContext. the problem is that I want to change this object (e.g. create new object()) in the Coordinator but I want all the dataContexts to point to the new object. I tried to send the object by ref to the window constructor but it didn't help. any idea about how can I rewrite the memory location that all pointers are pointing to? (I don't want to repalce the properties in object since its a lot of work nor to use a middle object that points to the replaced object) Thanks Eran

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  • CSS - Could use some pointers on correct positioning

    - by Kenny Bones
    Hi, I'm in need for some pointers on positioning. I've got this square which should be centered on the page. And with a logo and a logo font image kinda wrapped around the square. Now, I want this as dynamic as possible, because I use both the square and images elsewhere as well. So I can't really use stiff static positioning. This is the site: www.matkalenderen.no How should I do this? I want to logo to appear on the left side of the square. And the font to appear above the square. And the square itself should be centered. You probably get the picture :) Right now I've got a wrapper around everything, which is also centered.

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  • Grep the whole body of a function

    - by dotancohen
    Supposing I know that someFile.php contains the definition for someFunction(). How would I go about displaying the whole body of the function in stdout? If I know that the body is 10 lines long then I would use cat someFile.php | grep -A 10 "function someFunction" [1] but in reality the function could be any arbitrary length. I figured that with sed I could use Vimesque commands such as /function someFunction<Return>/{<Return>% [2] but I can't figure out exactly how to format it. Ideally, the PHPDoc before the function would be output along with the function. Any help or links to the appropriate fine manual would be appreciated. Thanks! [1] I know that the cat is redundant, but I find this format easier to read. [2] Find the function definition, go to the opening brace, go to the close brace

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  • Casting array of pointers to objects

    - by ritmbo
    If B is subclass of A. And I have in main(): B** b = new B*[10]; ... some algorithm that do b[i] = new B(..); ... So I have an array of pointers to objets B. Then I have a function: void f(A** foo); If in main, I do: f(b); I get a warning, but obviously if I do: f((A**)b);, i dont. The (A**) its a bit nasty. I was wondering if there's a more elegant way in C++ that at least do type checking as dynamic_cast.

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  • Only compiles as an array of pointers, not array of arrays

    - by Dustin
    Suppose I define two arrays, each of which have 2 elements (for theoretical purposes): char const *arr1[] = { "i", "j" }; char const *arr2[] = { "m", "n" }; Is there a way to define a multidimensional array that contains these two arrays as elements? I was thinking of something like the following, but my compiler displays warnings about incompatible types: char const *combine[][2] = { arr1, arr2 }; The only way it would compile was to make the compiler treat the arrays as pointers: char const *const *combine[] = { arr1, arr2 }; Is that really the only way to do it or can I preserve the type somehow (in C++, the runtime type information would know it is an array) and treat combine as a multidimensional array? I realise it works because an array name is a const pointer, but I'm just wondering if there is a way to do what I'm asking in standard C/C++ rather than relying on compiler extensions. Perhaps I've gotten a bit too used to Python's lists where I could just throw anything in them...

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  • Quick question about pointers

    - by xbonez
    So, I have this code fragment: int * iPtr ; int * jPtr ; int i = 5, k = 7; iPtr = &i; jPtr = iPtr ; I have just started learning about pointers, and need to get some doubts cleared. is jPtr now essentially also pointing at i? I know I can change the value of i by using *iPtr, but how can I change the value of the object being pointed to by jPtr? How will changing the object being pointed to by jPtr affect the value of the object pointed to by iPtr, and i ?

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  • Swapping values using pointers

    - by xbonez
    I have this code fragment int i = 5; int k = 7; int * iPtr; int * jPtr; int * kPtr; iPtr = &i; kPtr = &k; I am required to swap i and k using the pointers. This is how I'm doing it: *jPtr = *kPtr ; *kPtr = *iPtr ; *iPtr = *jPtr ; Is this the best way to do it, or is there a better way?

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  • Can I use memcpy in C++ to copy classes that have no pointers or virtual functions

    - by Shane MacLaughlin
    Say I have a class, something like the following; class MyClass { public: MyClass(); int a,b,c; double x,y,z; }; #define PageSize 1000000 MyClass Array1[PageSize],Array2[PageSize]; If my class has not pointers or virtual methods, is it safe to use the following? memcpy(Array1,Array2,PageSize*sizeof(MyClass)); The reason I ask, is that I'm dealing with very large collections of paged data, as decribed here, where performance is critical, and memcpy offers significant performance advantages over iterative assignment. I suspect it should be ok, as the 'this' pointer is an implicit parameter rather than anything stored, but are there any other hidden nasties I should be aware of?

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  • Basic help needed with pointers

    - by sbsp
    Hi, i asked some time ago on an account i cant remember how to manipulate basic pointers and someone gave me a really good demo for example char *ptr = hello (hello = a char array) so now *ptr is pointing at h ptr++ = moves the ptr to point at the next element, to get its value i do *ptr and that gives me e ok so far i hope :D but now i need to manipulate a char **ptr and was wondering how i do this in a way that mimmicks the effects of a 2d array? some basic tips would be much appreciated as i need to do an assignment that has a **ptr to immitate a 2d array and without knowing how it does this first means i cant even solve it on paper (for example, how do you dereference a **ptr, how do you get [x][y] values etc) thanks

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  • Basic help needed with pointers (double indirection)

    - by sbsp
    Hi, i asked some time ago on an account i cant remember how to manipulate basic pointers and someone gave me a really good demo for example char *ptr = "hello" (hello = a char array) so now *ptr is pointing at h ptr++ = moves the ptr to point at the next element, to get its value i do *ptr and that gives me e ok so far i hope :D but now i need to manipulate a char **ptr and was wondering how I do this in a way that mimmicks the effects of a 2d array? some basic tips would be much appreciated as I need to do an assignment that has a **ptr to imitate a 2d array and without knowing how it does this first means I cant even solve it on paper (for example, how do you dereference a **ptr, how do you get [x][y] values etc) thanks

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  • c++ signatures, pointers

    - by coubeatczech
    Hello, what's the difference between these signatures? T * f(T & identifier); T & f(T & identifier); T f(T & identifier); void f(T * identifier); void f(T & identifier); void f(T identifier); I met pointers in c, but the amperstand in function signature is new for me. Can Anyone explain this?

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  • Why do they initialize pointers this way?

    - by Rob
    In almost all of the books I read and examples I go through I see pointers initialized this way. Say that I have a class variable NSString *myString that I want to initialize. I will almost always see that done this way: -(id)init { if (self = [super init]) { NSString *tempString = [[NSString alloc] init]; myString = tempString; [tempString release]; } return self; } Why can't I just do the following? -(id)init { if (self = [super init]) { myString = [[NSString alloc] init]; } return self; } I don't see why the extra tempString is ever needed in the first place, but I could be missing something here with memory management. Is the way I want to do things acceptable or will it cause some kind of leak? I have read the Memory Management Guide on developer.apple.com and unless I am just missing something, I don't see the difference.

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  • Call random function on percents?

    - by Angelena Godkin
    I cannot figure this out. I need a solution to call a random function for it's percent. Ex. there is 10% chances that the script calls subscriptions() and 3% chance that the system call the function "specialitems()". I am stuck in this, so i hope someone can help me with this brainkiller. <?php class RandomGifts { public $chances = ''; public function __construct($user) { $this->user = $user; //Find percent for each function $this->chances = array( 'subscriptions' => 10, // 10% 'specialitems' => 3, // 5% 'normalitems' => 30, // 40% 'fuser' => 50, // 70% 'giftcards' => 7, // 7% ); //This should call the function which has been calculated. self::callFunction(?); } public function subscriptions(){} public function specialitems(){} public function normalitems(){} public function fuser(){} public function giftcards(){} } ?>

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  • Array-size macro that rejects pointers

    - by nneonneo
    The standard array-size macro that is often taught is #define ARRAYSIZE(arr) (sizeof(arr) / sizeof(arr[0])) or some equivalent formation. However, this kind of thing silently succeeds when a pointer is passed in, and gives results that can seem plausible at runtime until things mysteriously fall apart. It's all-too-easy to make this mistake: a function that has a local array variable is refactored, moving a bit of array manipulation into a new function called with the array as a parameter. So, the question is: is there a "sanitary" macro to detect misuse of the ARRAYSIZE macro in C, preferably at compile-time? In C++ we'd just use a template specialized for array arguments only; in C, it seems we'll need some way to distinguish arrays and pointers. (If I wanted to reject arrays, for instance, I'd just do e.g. (arr=arr, ...) because array assignment is illegal).

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  • Is it possible to create a link that acts like a button and can carry out a function when clicked?

    - by Tim
    In PHP, I want to execute a function when a hyperlink is clicked. The only way I can think of doing this is by having the link attach a get parameter to the url when clicked and by doing an if statement that checks to see if that parameter exists and if so then have the function executed. But is there a way to do this like: <a href='#' onclick='<?php functionName(); ?>'> Obviously there are a million things wrong with this example but is it possible in any other way?

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  • Extending the InputBox function for MS Access Forms

    While it's not possible to change the behavior of the InputBox function, this article illustrates how to create your own Access form that includes a text box with its InputMask property set to Password, and then use that form instead of the one generated by the VBA InputBox function.

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  • Boost bind with asio::placeholders::error

    - by Leandro
    Why it doesn't work? --- boost_bind.cc --- #include #include #include void func1 (const int& i) { } void func2 (const ::asio::error_code& e) { } int main () { ::boost::function f1 = ::boost::bind (&func1, 1); // it doesn't work! ::boost::function f2 = ::boost::bind (&func2, ::asio::placeholders::error); return 0; } This is the error: while_true@localhost:~ g++ -lpthread boost_bind.cc -o boost_bind In file included from boost_bind.cc:2: /usr/include/boost/bind.hpp: In member function ‘void boost::_bi::list1::operator()(boost::_bi::type, F&, A&, int) [with F = void (*)(const asio::error_code&), A = boost::_bi::list0, A1 = boost::arg (*)()]’: /usr/include/boost/bind/bind_template.hpp:20: instantiated from ‘typename boost::_bi::result_traits::type boost::_bi::bind_t::operator()() [with R = void, F = void (*)(const asio::error_code&), L = boost::_bi::list1 (*)()]’ /usr/include/boost/function/function_template.hpp:152: instantiated from ‘static void boost::detail::function::void_function_obj_invoker0::invoke(boost::detail::function::function_buffer&) [with FunctionObj = boost::_bi::bind_t (*)() , R = void]’ /usr/include/boost/function/function_template.hpp:904: instantiated from ‘void boost::function0::assign_to(Functor) [with Functor = boost::_bi::bind_t (*)() , R = void]’ /usr/include/boost/function/function_template.hpp:720: instantiated from ‘boost::function0::function0(Functor, typename boost::enable_if_c::type) [with Functor = boost::_bi::bind_t (*)() , R = void]’ /usr/include/boost/function/function_template.hpp:1040: instantiated from ‘boost::function::function(Functor, typename boost::enable_if_c::type) [with Functor = boost::_bi::bind_t (*)() , R = void]’ boost_bind.cc:14: instantiated from here /usr/include/boost/bind.hpp:232: error: no match for ‘operator[]’ in ‘a[boost::_bi::storage1 (*)()::a1_ [with int I = 1]]’ while_true@localhost:~

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  • Set Covering : Runtime hang\error at function call in c

    - by EnthuCrazy
    I am implementing a set covering application which uses cover function int cover(set *skill_list,set *player_list,set *covering) Suppose skill_set={a,b,c,d,e}, player_list={s1,s2,s3} then output coverin ={s1,s3} where say s1={a,b,c}, s3={d,e} and s2={b,d}. Now when I am calling this function it's hanging at run (set_cover.exe stopped working). Here is my cover function: typedef struct Spst_{ void *key; set *st; }Spst; int cover(set *skill_list,set *player_list,set *covering) { Liste *member,*max_member; Spst *subset; set *intersection; void **data; int max_size; set_init(covering); //to initialize set covering initially while(skill_list->size>0&&player_list->size>0) { max_size=0; for(member=player_list->head;member!=NULL;member=member->next) { if(set_intersection(intersection,((Spst *)(member->data))->st,skill_list)!=0) return -1; if(intersection->size>max_size) { max_member=member; max_size=intersection->size; } set_destroy(intersection); //at the end of iteration } if(max_size==0) //to check for no covering return -1; subset=(Spst *)max_member->data; //to insert max subset from play list to covering set set_inselem(covering,subset); for(member=(((Spst *)max_member->data)->st->head);member!=NULL;member=member->next) //to rem elem from skill list { data=(void **)member->data; set_remelem(skill_list,data); } set_remelem(player_list,(void **)subset); //to rem subset from set of subsets play list } if(skill_list->size>0) return -1; return 0; } Now assuming I have defined three set type sets(as stated above) and calling from main as cover(skills,subsets,covering);=> runtime hang Here Please give inputs on the missing link in this or the prerequisites for a proper call to this function type required. EDIT: Assume other functions used in cover are tested and working fine.

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  • How can I clear explosions in my function?

    - by hustlerinc
    Hi I have a function to place bombs, and a for loop that places explosions on the tiles where possible. My problem is that I can't remove the explosions after a while. I've tried everything I can come up with so now I turn here as a last resort. The function looks like this: function Bomb(){ var placebomb = false; if(placeBomb && player.bombs != 0){ map[player.Y][player.X].object = 2; var bombX = player.X; var bombY = player.Y; placeBomb = false; player.bombs--; setTimeout(explode, 3000); } function explode(){ var explodeNorth = true; var explodeEast = true; var explodeSouth = true; var explodeWest = true; map[bombY][bombX].explosion = 1; delete map[bombY][bombX].object; for(i=0;i<=player.bombRadius;i++){ if(explodeNorth && map[bombY-i][bombX]){ if(!map[bombY-i][bombX].wall){ if(!map[bombY-i][bombX].object){ map[bombY-i][bombX].explosion = 1; } else var explodeNorth = false; delete map[bombY-i][bombX].object; map[bombY-i][bombX].explosion = 1; } else var explodeNorth = false; } if(explodeEast && map[bombY][bombX+i]){ if(!map[bombY][bombX+i].wall){ if(!map[bombY][bombX+i].object){ map[bombY][bombX+i].explosion = 1; } else var explodeEast = false; delete map[bombY][bombX+i].object; map[bombY][bombX+i].explosion = 1; } else var explodeEast = false; } if(explodeSouth && map[bombY+i][bombX]){ if(!map[bombY+i][bombX].wall){ if(!map[bombY+i][bombX].object){ map[bombY+i][bombX].explosion = 1; } else var explodeSouth = false; delete map[bombY+i][bombX].object; map[bombY+i][bombX].explosion = 1; } else var explodeSouth = false; } if(explodeWest && map[bombY][bombX-i]){ if(!map[bombY][bombX-i].wall){ if(!map[bombY][bombX-i].object){ map[bombY][bombX-i].explosion = 1; } else var explodeWest = false; delete map[bombY][bombX-i].object; map[bombY][bombX-i].explosion = 1; } else var explodeWest = false; } } player.bombs++; } } If anyone can think of a good way to remove the explosion after a delay please help.

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  • Work around for calculating age using the SQL Server DateDiff function

    Have you ever wanted to compute age, but the results from the DATEDIFF function seemed to be wrong some of the time? This tip covers why the DATEDIFF function does not always reliably compute age. New! SQL Monitor 3.0 Red Gate's multi-server performance monitoring and alerting tool gets results from Day One.Simple to install and easy to use – download a free trial today.

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