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  • Alternates to C++ Reference/Pointer Syntax

    - by Jon Purdy
    What languages other than C and C++ have explicit reference and pointer type qualifiers? People seem to be easily confused by the right-to-left reading order of types, where char*& is "a reference to a pointer to a character", or a "character-pointer reference"; do any languages with explicit references make use of a left-to-right reading order, such as &*char/ref ptr char? I'm working on a little language project, and legibility is one of my key concerns. It seems to me that this is one of those questions to which it's easy for a person but hard for a search engine to provide an answer. Thanks in advance!

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  • Alternatives to C++ Reference/Pointer Syntax

    - by Jon Purdy
    What languages other than C and C++ have explicit reference and pointer type qualifiers? People seem to be easily confused by the right-to-left reading order of types, where char*& is "a reference to a pointer to a character", or a "character-pointer reference"; do any languages with explicit references make use of a left-to-right reading order, such as &*char/ref ptr char? I'm working on a little language project, and legibility is one of my key concerns. It seems to me that this is one of those questions to which it's easy for a person but hard for a search engine to provide an answer. Thanks in advance!

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  • C++ deleting a pointer

    - by eSKay
    On this page, its written that One reason is that the operand of delete need not be an lvalue. Consider: delete p+1; delete f(x); Here, the implementation of delete does not have a pointer to which it can assign zero. Adding a number to a pointer shifts it forward in memory by those many number of sizeof(*p) units. So, what is the difference between delete p and delete p+1, and why would making the pointer 0 only be a problem with delete p+1?

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  • Size of a class with 'this' pointer

    - by psvaibhav
    The size of a class with no data members is returned as 1 byte, even though there is an implicit 'this' pointer declared. Shouldn't the size returned be 4 bytes(on a 32 bit machine)? I came across articles which indicated that 'this' pointer is not counted for calculating the size of the object. But I am unable to understand the reason for this. Also, if any member function is declared virtual, the size of the class is now returned as 4 bytes. This means that the vptr is counted for calculating the size of the object. Why is the vptr considered and 'this' pointer ignored for calculating the size of object?

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  • Boost Shared Pointer: Simultaneous Read Access Across Multiple Threads

    - by Nikhil
    I have a thread A which allocates memory and assigns it to a shared pointer. Then this thread spawns 3 other threads X, Y and Z and passes a copy of the shared pointer to each. When X, Y and Z go out of scope, the memory is freed. But is there a possibility that 2 threads X, Y go out of scope at the exact same point in time and there is a race condition on reference count so instead of decrementing it by 2, it only gets decremented once. So, now the reference count newer drops to 0, so there is a memory leak. Note that, X, Y and Z are only reading the memory. Not writing or resetting the shared pointer. To cut a long story short, can there be a race condition on the reference count and can that lead to memory leaks?

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  • Call function by pointer and set parametrs in memory block

    - by Ellesmess Glain
    Hi, I've little problem : I'm solving problem with calling function by pointer and passing to it parameters in continuous memory block. My goal is to have function named e.g CallFunc(void * func,void *params, unsigned int param_length); that I'll send function pointer, pointer to function's parameters and eventually parameters length and this calling function will call passed function with it's parameters. I will like write this in C/C++, but if somebody has idea, how this resolve in other language, that supports DLL generation and exportet functions, it will be fine too. Thanks for answers, Ellesmess P.S. I'm sorry about my English, but I'm Czech, thanks :o)

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  • Add 64 bit offset to a pointer

    - by Novox
    In F#, there's the NativePtr module, but it seems to only support 32 bit offsets for its’ add/get/set functions, just like System.IntPtr does. Is there a way to add a 64 bit offset to a native pointer (nativeptr<'a) in F#? Of course I could convert all addresses to 64 bit integers, do normal integer operations and then convert the result again to nativeptr<'a, but this would cost additional add and imul instructions. I really want the AGUs to perform the address calculations. For instance, using unsafe in C# you could do something like void* ptr = Marshal.AllocHGlobal(...).ToPointer(); int64 offset = ...; T* newAddr = (T*)ptr + offset; // T has to be an unmanaged type Well actually you can't, because there is no "unmanaged" constraint for type parameters, but at least you can do general pointer arithmetic in a non-generic way. In F# we finally got the unmanaged constraint; but how do I do the pointer arithmetic?

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  • Objective-C classes, pointers to primitive types, etc.

    - by Toby Wilson
    I'll cut a really long story short and give an example of my problem. Given a class that has a pointer to a primitive type as a property: @interface ClassOne : NSObject { int* aNumber } @property int* aNumber; The class is instantiated, and aNumber is allocated and assigned a value, accordingly: ClassOne* bob = [[ClassOne alloc] init]; bob.aNumber = malloc(sizeof(int)); *bob.aNumber = 5; It is then passed, by reference, to assign the aNumber value of a seperate instance of this type of class, accordingly: ClassOne* fred = [[ClassOne alloc] init]; fred.aNumber = bob.aNumber; Fred's aNumber pointer is then freed, reallocated, and assigned a new value, for example 7. Now, the problem I'm having; Since Fred has been assigned the same pointer that Bob had, I would expect that Bob's aNumber will now have a value of 7. It doesn't, because for some reason it's pointer was freed, but not reassigned (it is still pointing to the same address it was first allocated which is now freed). Fred's pointer, however, has the allocated value 7 in a different memory location. Why is it behaving like this? What am I minsunderstanding? How can I make it work like C++ does?

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  • JSlider jump on mouse click

    - by Aly
    Hi, I have a JSlider which shows bet sizes (for a poker game) I am trying to achieve the effect that when a mouse click occurs the slider jumps forward by a bet amount (i.e. a big blind amount) rather than just incrementing by one. If the mouse click happens to the left of the bar i want it to decrement by a fixed amount else increment. I looked into attaching a mouse listener, but do not know how I can use the event to find out on what side of the bar the mouse was clicked. Any ideas?

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  • When does invoking a member function on a null instance result in undefined behavior?

    - by GMan
    This question arose in the comments of a now-deleted answer to this other question. Our question was asked in the comments by STingRaySC as: Where exactly do we invoke UB? Is it calling a member function through an invalid pointer? Or is it calling a member function that accesses member data through an invalid pointer? With the answer deleted I figured we might as well make it it's own question. Consider the following code: #include <iostream> struct foo { void bar(void) { std::cout << "gman was here" << std::endl; } void baz(void) { x = 5; } int x; }; int main(void) { foo* f = 0; f->bar(); // (a) f->baz(); // (b) } We expect (b) to crash, because there is no corresponding member x for the null pointer. In practice, (a) doesn't crash because the this pointer is never used. Because (b) dereferences the this pointer (this->x = 5;), and this is null, the program enters undefined behavior. Does (a) result in undefined behavior? What about if both functions are static?

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  • Set focus and carret position in textarea according to mouse position, as if user had clicked

    - by JeanHuguesRobert
    Once a page with a textarea is loaded, I want some textarea to have the focus immediatly if the mouse cursor is inside that textarea. This is the easy part because a onmousehover handler can set the focus. Now, how to I also set the position of the caret? I would like the caret to be where it would be if the user had clicked using the mouse to set the focus/caret. The basic use case is : User clicks on a link and waits (mouse barely moves) A page is delivered, it contains a big textarea only, full of text User types using keyboard Characters are inserted right below the mouse cursor Today the user has to wait until the caret is visible (at the top left of the textarea) and then click to move the caret before typing. Thanks!

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  • getting JSlider bar to move on mouse click event

    - by Aly
    Hi, I have a JSlider which shows bet sizes (for a poker game) I am trying to achieve the effect that when a mouse click occurs the slider jumps forward by a bet amount (i.e. a big blind amount) rather than just incrementing by one. If the mouse click happens to the left of the bar i want it to decrement by a fixed amount else increment. I looked into attaching a mouse listener, but do not know how I can use the event to find out on what side of the bar the mouse was clicked. Any ideas?

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  • change background color with change in mouse position

    - by Ashish Rajan
    I was wondering if it is possible to set background-color with help of mouse coordinates. What is have is: I have a DIV-A which is draggable and some other divs which are droppable. What is need is : I need to highlight other divs on my page which are droppable, whenever my DIV-A passes over them. What i have is mouse coordinates, is it possible to apply css on the bases of mouse coordinates using jquery.

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  • how to make tooltip move along with mouse?

    - by George2
    Hello everyone, I am using Silverlight 3 + VSTS 2008. I have a image (Multiscale image control) and I place tooltip on this image. The function of Tooltip works fine. Since the image is big (about 500 * 500 size), and since end user could move mouse on the picture, and I want to display tooltip position along with the mouse (i.e. when mouse moves, I want to tooltip move along with the mouse). Currently, the tooltip displays at a fixed position. Here is my current XAML code, any ideas how to solve this issue? <MultiScaleImage x:Name="msi" Height="500" Width="500"> <ToolTipService.ToolTip> <ToolTip Content="Here is a tool tip" Name="DeepZoomToolTip"></ToolTip> </ToolTipService.ToolTip> </MultiScaleImage> thanks in advance, George

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  • Tracking Mouse Stop

    - by Hallik
    I am trying to track mouse movements in the browser, and if a user stops their mouse for 0.5 seconds, to execute some code. I have put a breakpoint in the code below in firebug, and it breaks on the var mousestop = function(evt) line, but then jumps to the return statement. Am I missing something simple? Why isn't it executing the POST statement? I am tracking mouse clicks in a similar way, and it posts to the server just fine. Just not mouse stops. $.fn.saveStops = function() { $(this).bind('mousemove.clickmap', function(evt) { var mousestop = function(evt) { $.post('/heat-save.php', { x:evt.pageX, y:evt.pageY, click:"false", w:window.innerWidth, h:window.innerHeight, l:escape(document.location.pathname) }); }, thread; return function() { clearTimeout(thread); thread = setTimeout(mousestop, 500); }; }); };

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  • Disable the mouse click event of a button placed inside a listbox item

    - by Malcolm
    I have a button placed inside a listbox item and i have style defined fro that button where i have two images and on mouse hover i change the image. Now the problem is I am handling the listbox mouse event and when click the button the listbox mouse event doesn't fires. I tried to make the property of button ishittestvisisble=false And now if i click on button the listbox mouse event fires but the problem is the two images placed inside the styling of button don't apply as they are the child of button and by default their ishittestvisible also turn out to be false. So any suggestion or idea will be helpfull ....tx in advance...

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  • C++ this as thread parameter, variables unavailable

    - by brecht
    I have three classes: class Rtss_Generator { int mv_transfersize; } class Rtss_GenSine : Rtss_Generator class Rtss_GenSineRpm : Rtss_GenSine Rtss_GenSine creates a thread in his constructer, it is started immediatly and the threadfunction is off-course declared static, waiting for an event to start calculating. the problem: all the variables that are accessed through the gen-pointer are 0, but it does not fail. Also, this-address in the constructer and the gen-pointer-address in the thread are the same, so the pointer is ok. this code is created and compile in visual studio 6.0 service pack 2003 ORIGINAL CODE no thread Rtss_GenSine::getNextData() { //[CALCULATION] //mv_transferSize is accessible and has ALWAYS value 1600 which is ok } NEW CODE Rtss_GenSine::Rtss_GenSine() { createThread(NULL, threadFunction, (LPVOID) this,0,0); } Rtss_GenSine::getNextData() { SetEvent(startCalculating); WaitForSingleObject(stoppedCalculaing, INFINITE); } DWORD Rtss_GenSine::threadFunction(LPVOID pParam) { Rtss_GenSine* gen = (Rtss_GenSine*) pParam; while(runThread) { WaitForSingleObject(startCalculating, INFINITE); ResetEvent(startCalculating) //[CALCULATION] //gen->mv_transferSize ---> it does not fail, but is always zero //all variables accessed via the gen-pointer are 0 setEvent(stoppedCalculaing) } }

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  • Standard and reliable mouse-reporting with GLUT

    - by Victor
    Hello! I'm trying to use GLUT (freeglut) in my OpenGL application, and I need to register some callbacks for mouse wheel events. I managed to dig out a fairly undocumented function: api documentation But the man page and the API entry for this function both state the same thing: Note: Due to lack of information about the mouse, it is impossible to implement this correctly on X at this time. Use of this function limits the portability of your application. (This feature does work on X, just not reliably.) You are encouraged to use the standard, reliable mouse-button reporting, rather than wheel events. Fair enough, but how do I use this standard, reliable mouse-reporting? And how do I know which is the standard? Do I just use glutMouseFunc() and use button values like 4 and 5 for the scroll up and down values respectively, say if 1, 2 and 3 are the left, middle and right buttons? Is this the reliable method? Bonus question: it seems the `xev' tool is reporting different values for my buttons. My mouse buttons are numbered from 1 to 5 with xev, but glut is reporting buttons from 0 to 4, i.e. an off-by-one. Is this common?

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  • Using a Function returning apointer as LValue

    - by Amrish
    Why cant I used a function returning a pointer as a lvalue? For example this one works int* function() { int* x; return x; } int main() { int* x = function(); x = new int(9); } but not this int* function() { int* x; return x; } int main() { int* x; function() = x; } While I can use a pointer variable as a lvalue, why can't I use a function returning a pointer as a lvalue? Also, when the function returns a refernce, instead of a pointer, then it becomes a valid lvalue.

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