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  • Would a pointer to a pointer to nil match against NULL?

    - by dontWatchMyProfile
    Example: A validation method contains this check to see if an NSError object shall be created or not: - (BOOL)validateCompanyName:(NSString *)newName error:(NSError **)outError { if (outError != NULL) { // do it... Now I pass an NSError object, like this: NSError *error = nil; BOOL ok = [self validateCompanyName:@"Apple" error:&error]; I'm not sure if this matches the check for not NULL. I think it's not NULL, since I believe NULL is not nil. Maybe someone can clear this up?

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  • Delegates with explicit "this" pointer?

    - by Qwertie
    Is it possible to adapt a method like this function "F" class C { public void F(int i); } to a delegate like Action<C,int>? I have this vague recollection that Microsoft was working on supporting this kind of adaptation. But maybe I misremembered!

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  • how to make struct member pointer in assembly?

    - by sillis
    I`m trying to create a macro which would make easier to point to a structs member. Currently i am pointing to a structs member in assembly file using the STRUCT_NAME + offset method. For example if i want to point structs third member,i would have to do it like this: STRUCT_NAME + 3. This seems stupid way to do it, and if i insert more members in the struct, i have to update all the offset values in the code. Is there a way to point using STRUCT_NAME + macro(struct_name, member_name) ? I`m using texas instruments TMS320C28x hardware. Thanks!

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  • What does this pointer-heavy C code do?

    - by justRadojko
    Could someone explain to me what should two following lines do: s.httpheaderline[s.httpheaderlineptr] = *(char *)uip_appdata; ++((char *)uip_appdata); This is taken from uIP code for microcontrollers. s - structure httpheaderline - http packet presented as a string httpheadrlineptr - integer value uip_appdata - received ethernet packet (string) If some more info is needed please let me know. BTW. Eclipse is reporting an error on the second line with message Invalid lvalue in increment so i'm trying to figure out how to solve this.

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  • Cast A primitive type pointer to A structure pointer - Alignment and Padding?

    - by Seçkin Savasçi
    Just 20 minutes age when I answered a question, I come up with an interesting scenario that I'm not sure of the behavior: Let me have an integer array of size n, pointed by intPtr; int* intPtr; and let me also have a struct like this: typedef struct { int val1; int val2; //and less or more integer declarations goes on like this(not any other type) }intStruct; My question is if I do a cast intStruct* structPtr = (intStruct*) intPtr; Am I sure to get every element correctly if I traverse the elements of the struct? Is there any possibility of miss-alignment(possible because of padding) in any architecture/compiler?

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  • javascript function pointer and "this"

    - by Justin808
    I'm passing a method as a variable to be used as a callback. When its called, the "this" is not the object the method is a member of. How do I go about getting access to the method's object instance so I can get access to it variables and other member functions? I have no control over the callback call method, its a separate library. All I do is call the binding from my object init method. I would have expected this inside my _connection method to have been its object. jsPlumb.bind('connection', this._connection);

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  • Void pointer cast C++ and GTK

    - by Tarantula
    See this GTK callback function: static gboolean callback(GtkWidget *widget, GdkEventButton *event, gpointer *data) { AnyClass *obj = (AnyClass*) data; // using obj works } (please note the gpointer* on the data). And then the signal is connected using: AnyClass *obj2 = new AnyClass(); gtk_signal_connect(/*GTK params (...)*/, callback, obj2); See that the *AnyClass is going to be cast to gpointer* (void**). In fact, this is working now. The callback prototype in GTK documentation is "gpointer data" and not "gpointer *data" as shown in code, what I want to know is: how this can work ? Is this safe ?

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  • Misaligned Pointer Performance

    - by Elite Mx
    Aren't misaligned pointers (in the BEST possible case) supposed to slow down performance and in the worst case crash your program (assuming the compiler was nice enough to compile your invalid c program). Well, the following code doesn't seem to have any performance differences between the aligned and misaligned versions. Why is that? /* brutality.c */ #ifdef BRUTALITY xs = (unsigned long *) ((unsigned char *) xs + 1); #endif ... /* main.c */ #include <stdio.h> #include <stdlib.h> #define size_t_max ((size_t)-1) #define max_count(var) (size_t_max / (sizeof var)) int main(int argc, char *argv[]) { unsigned long sum, *xs, *itr, *xs_end; size_t element_count = max_count(*xs) >> 4; xs = malloc(element_count * (sizeof *xs)); if(!xs) exit(1); xs_end = xs + element_count - 1; sum = 0; for(itr = xs; itr < xs_end; itr++) *itr = 0; #include "brutality.c" itr = xs; while(itr < xs_end) sum += *itr++; printf("%lu\n", sum); /* we could free the malloc-ed memory here */ /* but we are almost done */ exit(0); } Compiled and tested on two separate machines using gcc -pedantic -Wall -O0 -std=c99 main.c for i in {0..9}; do time ./a.out; done

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  • question regarding "this" pointer in c++

    - by sil3nt
    hello there, i have been given class with int variables x and y in private, and an operator overload function, class Bag{ private: int x; int y; public: Bag(); ~Bag(); //....... //.....etc }; Bag operator+ (Bag new) const{ Bag result(*this); //what does this mean? result.x += new.x; result.y += new.y; } What is the effect of having "Bag result(*this);" there?.

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  • C/C++ opaque pointer library

    - by aaa
    hello Is there library/header already written to manage C++ objects from C using opaque pointers/handles? I can write one myself, but I would rather use already made solution, especially if it has fortran bindings. Thanks

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  • Why do I get a Null Pointer Exception?

    - by Roman
    I have this code: Manager manager = new Manager("Name"); MyWindowListener windowListener = new MyWindowListener(); manager.addWindowListener(windowListener); Eclipse writes that I have a NullPointerException in the last line. What can be the reason for that. I do have constructors in the Manager and MyWindowListener. If it's important MyWindowListener implements WindowListener.

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  • Doubt regarding usage of array as a pointer in C

    - by Som
    For eg. I have an array of structs 'a' as below: struct mystruct{ int b int num; }; struct bigger_struct { struct my_struct a[10]; } struct bigger_struct *some_var; i know that the name of an array when used as a value implicitly refers to the address of the first element of the array.(Which is how the array subscript operator works at-least) Can i know do the other way around i.e if i do: some_var->a->b, it should be equivalent to some_var->a[0]->b, am i right? I have tested this and it seems to work , but is this semantically 100% correct?

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  • Extract inputs from a pointer to array of characters in C / C++

    - by user2066884
    I am writing a command line utility but I cannot find a way to store the commands and arguments. so far I have the following but I get a Segmentation fault: int main(void) { char *command; char *args[MAX_LINE/2 + 1]; int should_run = 1; do{ cout << "cmd> "; int counter = 0; while(cin >> command) { strcpy(args[counter],command); counter++; } cout << args[0] << "\n"; } }

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  • Obtaining frame pointer in C

    - by assketchum
    I'm trying to get the FP in my C program, I tried two different ways, but they both differ from what I get when I run GDB. The first way I tried, I made a protocol function in C for the Assembly function: int* getEbp(); and my code looks like this: int* ebp = getEbp(); printf("ebp: %08x\n", ebp); // value i get here is 0xbfe2db58 while( esp <= ebp ) esp -= 4; printf( "ebp: %08x, esp" ); //value i get here is 0xbfe2daec My assembly code getEbp: movl %ebp, %eax ret I tried making the prototype function to just return an int, but that also doesn't match up with my GDB output. We are using x86 assembly. EDIT: typos, and my getEsp function looks exactly like the other one: getEsp: movl %esp, %eax ret

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  • Changing Value of Array Pointer When Passed to a Function

    - by ZAX
    I have a function which receives both the array, and a specific instance of the array. I try to change the specific instance of the array by accessing one of its members "color", but it does not actually change it, as can be seen by debugging (checking the value of color after function runs in the main program). I am hoping someone can help me to access this member and change it. Essentially I need the instance of the array I'm specifying to be passed by reference if nothing else, but I'm hoping there is an easier way to accomplish what I'm trying to do. Here's the structures: typedef struct adjEdge{ int vertex; struct adjEdge *next; } adjEdge; typedef struct vertex{ int sink; int source; int color; //0 will be white, 1 will be grey, 5 will be black int number; adjEdge *nextVertex; } vertex; And here is the function: void walk(vertex *vertexArray, vertex v, int source, maxPairing *head) { int i; adjEdge *traverse; int moveVertex; int sink; traverse = vertexArray[v.number-1].nextVertex; if(v.color != 5 && v.sink == 5) { sink = v.number; v.color = 5; addMaxPair(head, source, sink); } else { walk(vertexArray, vertexArray[traverse->vertex-1], source, head); } } In particular, v.color needs to be changed to a 5, that way later after recursion the if condition blocks it.

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  • cant figure out pointer assignment in c

    - by vadiklk
    int add(char *var1, char *var2, char **var3) { int num1, num2, length1 = strlen(var1), length2 = strlen(var2), length = max(length1, length2) + 1; char *result = (char*) calloc(length, sizeof(char)); ... free(*var3); *var3 = result; return 0; } out side of the function i get its still nothing(var3); more detail: int addSubCommand(char **vars, int isAdd) { ... return add(vars[index1], var2, &(vars[index3])); } that's where i call add. the char** vars goes from every function to the other.

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  • Is there performance to be gained by moving storage allocation local to a member function to its cla

    - by neuviemeporte
    Suppose I have the following C++ class: class Foo { double bar(double sth); }; double Foo::bar(double sth) { double a,b,c,d,e,f a = b = c = d = e = f = 0; /* do stuff with a..f and sth */ } The function bar() will be called millions of times in a loop. Obviously, each time it's called, the variables a..f have to be allocated. Will I gain any performance by making the variables a..f members of the Foo class and just initializing them at the function's point of entry? On the other hand, the values of a..f will be dereferenced through this-, so I'm wondering if it isn't actually a possible performance degradation. Is there any overhead to accessing a value through a pointer? Thanks!

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  • How do I output an individual character when using char *[] = "something"

    - by Matt
    I've been playing with pointers to better understand them and I came across something I think I should be able to do, but can't sort out how. The code below works fine - I can output "a", "dog", "socks", and "pants" - but what if I wanted to just output the 'o' from "socks"? How would I do that? char *mars[4] = { "a", "dog", "sock", "pants" }; for ( int counter = 0; counter < 4; counter++ ) { cout << mars[ counter ]; } Please forgive me if the question is answered somewhere - there are 30+ pages of C++ pointer related question, and I spent about 90 minutes looking through them, as well as reading various (very informative) articles, before deciding to ask.

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  • C++ object in memory

    - by Neo_b
    Hello. Is there a standard in storing a C++ objects in memory? I wish to set a char* pointer to a certain address in memory, so that I can read certain objects' variables directly from the memory byte by byte. When I am using Dev C++, the variables are stored one by one right in the memory address of an object in the order that they were defined. Now, can it be different while using a different compiler (like the variables being in a different order, or somewhere else)? Thank you in advance. :-)

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  • fill a buffer successively

    - by mkind
    i intend to fill a char-pointer array successively in a for-loop. the content to fill in is a integer so i need to cast. but i didn't get the result i want to.. for (i=0;i<max0;i++){ sprintf(buf, "%d", content[i]); } sprintf replaces the hole buf, but i want to append. for (i=0;i<max0;i++){ buf[i]=(char) contint[i] } but this isn't working too. it seems to me, i get ascii-code of the content[i].

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  • C++ How do you set an array of pointers to null in an initialiser list like way?

    - by boredjoe
    I am aware you cannot use an initialiser list for an array. However I have heard of ways that you can set an array of pointers to NULL in a way that is similar to an initialiser list. I am not certain how this is done. I have heard that a pointer is set to NULL by default, though I do not know if this is guaranteed/ in the C++ standard. I am also not sure if initialising through the new operator compared to normal allocation can make a difference too.

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  • Cannot determine why pointer variable will not address elements in a string in this program?

    - by Smith Will Suffice
    I am attempting to utilize a pointer variable to access elements of a string and there are issues with my code generating a compilation error: #include <stdio.h> #define MAX 29 char arrayI[250]; char *ptr; int main(void) { ptr = arrayI; puts("Enter string to arrayI: up to 29 chars:\n"); fgets(arrayI, MAX, stdin); printf("\n Now printing array by pointer:\n"); printf("%s", *ptr); ptr = arrayI[1]; //(I set the pointer to the second array char element) printf("%c", *ptr); //Here is where I was wanting to use my pointer to //point to individual array elements. return 0; } My compiler crieth: [Warning] assignment makes pointer from integer without a cast [enabled by default] I do not see where my pointer was ever assigned to the integer data type? Could someone please explain why my attempt to implement a pointer variable is failing? Thanks all!

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  • Objective C ASIHTTPRequest nested GCD block in complete block

    - by T.Leavy
    I was wondering if this is the correct way to have nested blocks working on the same variable in Objective C without causing any memory problems or crashes with ARC. It starts with a ASIHttpRequest complete block. MyObject *object = [dataSet objectAtIndex:i]; ASIHTTPRequest *request = [[ASIHTTPRequest alloc]initWithURL:@"FOO"]; __block MyObject *mutableObject = object; [request setCompleteBlock:^{ mutableObject.data = request.responseData; __block MyObject *gcdMutableObject = mutableObject; dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0),^{ [gcdMutableObject doLongComputation]; dispatch_async(dispatch_get_main_queue(),^{ [self updateGUIWithObject:gcdMutableObject]; }); }); [request startAsynchronous]; My main concern is nesting the dispatch queues and using the __block version of the previous queue to access data. Is what I am doing safe?

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  • EXC_BAD_ACCESS error on a UITableView with ARC?

    - by Arnaud Drizard
    I am building a simple app with a custom bar tab which loads the content of the ViewController from a UITableView located in another ViewController. However, every time I try to scroll on the tableview, I get an exc_bad_access error. I enabled NSzombies and guard malloc to get more info on the issue. In the console I get: "message sent to deallocated instance 0x19182f20" and after profiling I get: # Address Category Event Type RefCt Timestamp Size Responsible Library Responsible Caller 56 0x19182f20 FirstTabBarViewController Zombie -1 00:16.613.309 0 UIKit -[UIScrollView(UIScrollViewInternal) _scrollViewWillBeginDragging] Here is a bit of the code of the ViewController in which the error occurs: .h file: #import <UIKit/UIKit.h> #import "DataController.h" @interface FirstTabBarViewController : UIViewController <UITableViewDelegate, UITableViewDataSource> { IBOutlet UITableView* tabBarTable; } @property (strong, nonatomic) IBOutlet UIView *mainView; @property (strong, nonatomic) IBOutlet UITableView *tabBarTable; @property (nonatomic, strong) DataController *messageDataController; @end .m file: #import "FirstTabBarViewController.h" #import "DataController.h" @interface FirstTabBarViewController () @end @implementation FirstTabBarViewController @synthesize tabBarTable=_tabBarTable; - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; if (self) { // Custom initialization } return self; } - (void)viewDidLoad { [super viewDidLoad]; } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. } - (void)awakeFromNib { [super awakeFromNib]; self.messageDataController=[[DataController alloc] init]; } - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return 1; } - (NSInteger) tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{ return [self.messageDataController countOfList]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"mainCell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil){ cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier]; }; NSString *expenseAtIndex = [self.messageDataController objectInListAtIndex:indexPath.row]; [[cell textLabel] setText:expenseAtIndex]; return cell; } - (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath { // Return NO if you do not want the specified item to be editable. return NO; } @end This FirstTabBarViewController is loaded in the MainViewController with the following custom segue: #import "customTabBarSegue.h" #import "MainViewController.h" @implementation customTabBarSegue -(void) perform { MainViewController *src= (MainViewController *) [self sourceViewController]; UIViewController *dst=(UIViewController *)[self destinationViewController]; for (UIView *view in src.placeholderView.subviews){ [view removeFromSuperview]; } src.currentViewController =dst; [src.placeholderView addSubview:dst.view]; } @end The Datacontroller class is just a simple NSMutableArray containing strings. I am using ARC so I don't understand where the memory management error comes from. Does anybody have a clue? Any help much appreciated ;) Thanks!!

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  • Using mem_fun_ref with boost::shared_ptr

    - by BlueRaja
    Following the advice of this page, I'm trying to get shared_ptr to call IUnknown::Release() instead of delete: IDirectDrawSurface* dds; ... //Allocate dds return shared_ptr<IDirectDrawSurface>(dds, mem_fun_ref(&IUnknown::Release)); error C2784: 'std::const_mem_fun1_ref_t<_Result,_Ty,_Arg std::mem_fun_ref(Result (_thiscall _Ty::* )(_Arg) const)' : could not deduce template argument for 'Result (_thiscall _Ty::* )(Arg) const' from 'ULONG (_cdecl IUnknown::* )(void)' error C2784: 'std::const_mem_fun_ref_t<_Result,_Ty std::mem_fun_ref(Result (_thiscall _Ty::* )(void) const)' : could not deduce template argument for 'Result (_thiscall _Ty::* )(void) const' from 'ULONG (__cdecl IUnknown::* )(void)' error C2784: 'std::mem_fun1_ref_t<_Result,_Ty,_Arg std::mem_fun_ref(Result (_thiscall _Ty::* )(_Arg))' : could not deduce template argument for 'Result (_thiscall _Ty::* )(Arg)' from 'ULONG (_cdecl IUnknown::* )(void)' error C2784: 'std::mem_fun_ref_t<_Result,_Ty std::mem_fun_ref(Result (_thiscall _Ty::* )(void))' : could not deduce template argument for 'Result (_thiscall _Ty::* )(void)' from 'ULONG (__cdecl IUnknown::* )(void)' error C2661: 'boost::shared_ptr::shared_ptr' : no overloaded function takes 2 arguments I have no idea what to make of this. My limited template/functor knowledge led me to try typedef ULONG (IUnknown::*releaseSignature)(void); shared_ptr<IDirectDrawSurface>(dds, mem_fun_ref(static_cast<releaseSignature>(&IUnknown::Release))); But to no avail. Any ideas?

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